Search

We examined the relationship between the work of breathing (W b ) during exercise and in vivo measures of airway size in healthy females and males. We hypothesized that sex differences in airway luminal area would explain the larger resistive W b during exercise in females. Healthy participants ( n = 11 females and n = 11 males; 19-30 yr) completed a cycle exercise test to exhaustion where W b was assessed using an esophageal balloon catheter. On a separate day, each participant underwent a bronchoscopy procedure for optical coherence tomography measures of seven airways. In vivo measures of luminal area were made for the fourth to eighth airway generations. A composite index of airway size was calculated as the sum of the luminal area for each generation, and the total area was calculated based on Weibel's model. We found that index of airway size (males: 37.4 ± 6.3 mm 2 vs. females: 27.5 ± 7.4 mm 2 ) and airway area calculated based on Weibel's model (males: 2,274 ± 557 mm 2 vs. females: 1,594 ± 389 mm 2 ) were significantly larger in males (both P = 0.003). When minute ventilation was greater than ∼60 L·min -1 , the resistive W b was higher in females. At the highest equivalent flow achieved by all subjects, resistance to inspired flow was larger in females and significantly associated with two measures of airway size in all subjects: index of airway size ( r = 0.524, P = 0.012) and Weibel area ( r = 0.525, P = 0.012). Our findings suggest that innate sex differences in luminal area result in a greater resistive W b during exercise in females compared with males. NEW & NOTEWORTHY We hypothesized that the higher resistive work of breathing in females compared with males during high-intensity exercise is due to smaller airways. In vivo measures of the fourth to eighth airway generations made using optical coherence tomography show that females tend to have smaller airway luminal areas of the fourth to sixth airway generations. Sex differences in airway luminal area result in a greater resistive work of breathing during exercise in females compared with males.

This case report characterizes the physiological responses to incremental cycling and determines the effects of 12 wk of inspiratory muscle training (IMT) on respiratory muscle strength, exercise capacity, and dyspnea in a physically active 59-yr-old female, 4 years after a left-sided extrapleural pneumonectomy (EPP). On separate days, a symptom-limited incremental exercise test and a constant work rate (CWR) test at 75% of peak work rate (WR) were completed, followed by 12 wk of IMT and another CWR test. IMT consisted of two sessions of 30 repetitions twice daily for 5 days per week. Physiological and perceptual variables were measured throughout each exercise test. The participant had a total lung capacity that was 43% predicted post-EPP. A rapid and shallow breathing pattern was adopted throughout exercise, and the ratio of minute ventilation to carbon dioxide output was elevated for a given work rate. Oxygen uptake was 71% predicted and WR was 88% predicted. Following IMT, maximal inspiratory pressure improved by 36% (-27.1 cmH 2 O) and endurance time by 31 s, with no observable changes in any submaximal or peak cardiorespiratory variables during exercise. The intensity and unpleasantness of dyspnea increased by 2 and 3 Borg 0-10 units, respectively, at the highest equivalent submaximal exercise time achieved on both tests. Despite having undergone a significant reduction in lung volume post-EPP, the participant achieved a relatively normal peak incremental WR, which may reflect a high level of physical conditioning. This case report also demonstrates that IMT can effectively increase respiratory muscle strength several years following EPP. NEW & NOTEWORTHY Constraints on tidal volume expansion and the adoption of a rapid and shallow breathing pattern result in a ventilatory limitation and increased ventilatory inefficiency during exercise in a patient several years after extrapleural pneumonectomy (EPP). Inspiratory muscle training can effectively increase respiratory muscle strength after EPP.

We compared cardiopulmonary responses to arm-ergometry in individuals with cervical spinal cord injury (C-SCI) and able-bodied controls. We hypothesized that individuals with C-SCI would have higher respiratory frequency (f b ) but lower tidal volume (VT) at a given work rate and dynamically hyperinflate during exercise, whereas able-bodied individuals would not. Participants completed pulmonary function testing, an arm-ergometry test to exhaustion, and a sub-maximal exercise test consisting of four-minute stages at 20, 40, 60, and 80% peak work rate. Able-bodied individuals completed a further sub-maximal test with absolute work rate matched to C-SCI. During work rate matched sub-maximal exercise, C-SCI had smaller VT (main effect p < 0.001) compensated by an increased f b (main effect p = 0.009). C-SCI had increased end-expiratory lung volume at 80% peak work rate vs. rest (p < 0.003), whereas able-bodied did not. In conclusion, during arm-ergometry, individuals with C-SCI exhibit altered ventilatory patterns characterized by reduced VT, higher f b , and dynamic hyperinflation that may contribute to the observed reduced aerobic exercise capacity., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Historically, many studies investigating the pulmonary physiology of exercise (and biomedical research in general) were performed exclusively or predominantly with male research participants. This has led to an incomplete understanding of the pulmonary response to exercise. More recently, important sex-based differences with respect to the human respiratory system have been identified. The purpose of this review is to summarize current findings related to sex-based differences in the pulmonary physiology of exercise. To that end, we will discuss how morphological sex-based differences of the respiratory system affect the respiratory response to exercise. Moreover, we will discuss sex-based differences of the physiological integrative responses to exercise, and how all these differences can influence the regulation of breathing. We end with a brief discussion of pregnancy and menopause and the accompanying ventilatory changes observed during exercise., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Respiratory modulation of sympathetic vasomotor outflow to skeletal muscles (muscle sympathetic nerve activity; MSNA) occurs in resting humans. Specifically, MSNA is highest at end-expiration and lowest at end-inspiration during quiet, resting breathing. We tested the hypothesis that within-breath modulation of MSNA would be amplified during graded leg cycling. Thirteen ( n = 3 females) healthy young (age: 25.2 ± 4.7 yr) individuals completed all testing. MSNA (right median nerve) was measured at rest (baseline) and during semirecumbent cycle exercise at 40%, 60%, and 80% of maximal workload (W max ). MSNA burst frequency (BF) was 20.0 ± 4.0 bursts/min at baseline and was not different during exercise at 40%W max (21.3 ± 3.7 bursts/min; P = 0.292). Thereafter, MSNA BF increased significantly compared with baseline (60%W max : 31.6 ± 5.8 bursts/min; P < 0.001, 80%W max : 44.7 ± 5.3 bursts/min; P < 0.001). At baseline and all exercise intensities, MSNA BF was lowest at end-inspiration and greatest at mid-to-end expiration. The within-breath change in MSNA BF (ΔMSNA BF; end-expiration minus end-inspiration) gradually increased from baseline to 60%W max leg cycling, but no further increase appeared at 80%W max exercise. Our results indicate that within-breath modulation of MSNA is amplified from baseline to moderate intensity during dynamic exercise in young healthy individuals, and that no further potentiation occurs at higher exercise intensities. Our findings provide an important extension of our understanding of respiratory influences on sympathetic vasomotor control. NEW & NOTEWORTHY Within-breath modulation of sympathetic vasomotor outflow to skeletal muscle (muscle sympathetic nerve activity; MSNA) occurs in spontaneously breathing humans at rest. It is unknown if respiratory modulation persists during dynamic whole body exercise. We found that MSNA burst frequency was lowest at end-inspiration and highest at mid-to-end expiration during rest and graded leg cycling. Respiratory modulation of sympathetic vasomotor outflow remains intact and is amplified during dynamic whole body exercise.

Work of breathing ([Formula: see text]) derived from a single lung volume and pleural pressure is limited and does not fully characterize the mechanical work done by the respiratory musculature. It has long been known that abdominal activation increases with increasing exercise intensity, yet the mechanical work done by these muscles is not reflected in [Formula: see text]. Using optoelectronic plethysmography (OEP), we sought to show first that the volumes obtained from OEP (V CW ) were comparable to volumes obtained from flow integration (V t ) during cycling and running, and second, to show that partitioned volume from OEP could be utilized to quantify the mechanical work done by the rib cage ([Formula: see text] RC ) and abdomen ([Formula: see text] AB ) during exercise. We fit 11 subjects (6 males/5 females) with reflective markers and balloon catheters. Subjects completed an incremental ramp cycling test to exhaustion and a series of submaximal running trials. We found good agreement between V CW versus V t during cycling (bias = 0.002; P > 0.05) and running (bias = 0.016; P > 0.05). From rest to maximal exercise,[Formula: see text] AB increased by 84% (range: 30%-99%; [Formula: see text] AB : 1 ± 1 J/min to 61 ± 52 J/min). The relative contribution of the abdomen increased from 17 ± 9% at rest to 26 ± 16% during maximal exercise. Our study highlights and provides a quantitative measure of the role of the abdominal muscles during exercise. Incorporating the work done by the abdomen allows for a greater understanding of the mechanical tasks required by the respiratory muscles and could provide further insight into how the respiratory system functions during disease and injury. NEW & NOTEWORTHY We demonstrated that optoelectronic plethysmography (OEP) is a reliable tool to determine ventilatory volume changes during cycling and running, without restricting natural upper arm movements. Second, using OEP volumes coupled with pressure-derived measures, we calculated the work done by the rib cage and abdomen, respectively, during exercise. Collectively, our findings indicate that pulmonary mechanics can be accurately quantified using OEP, and abdominal work performed during ventilation contributes substantially to the overall work of the respiratory musculature.

Voluntary activation can be used to assess central fatigue of the diaphragm after tasks such as exercise or inspiratory muscle loading. Cervical magnetic stimulation (CMS) of the phrenic nerves elicits an involuntary contraction, or twitch, of the diaphragm. This twitch is quantified based on a measure of transdiaphragmatic pressure and can be used to evaluate diaphragm contractile function and diaphragm voluntary activation (diaphragm-VA). The test-retest reliability of diaphragm-VA using CMS is currently unknown. Thirteen participants (4 male, 9 female; aged 25 ± 3 years) performed a series of interpolated twitch manoeuvres, which included a maximal inspiratory effort against a semi-occluded mouthpiece and 2 CMS-stimuli, 1 during the inspiratory manoeuvre and 1 after when the participant returned to functional residual capacity to quantify diaphragm-VA. Intraclass correlation coefficients (ICCs) and standard error of measurement (SEM) measured between-day and within-session reliability of diaphragm-VA, respectively. Maximal diaphragm-VA values were 91% (SD: 6; SEM: 3.9) and 92% (SD: 5; SEM: 2.2) during visits 1 and 2 ( p = 0.68), respectively, and displayed "good" between-day reliability (ICC: 0.88; 95% confidence interval: 0.67-0.95; SEM: 2.7). Our results suggest that assessing diaphragm-VA using CMS is reliable in young healthy adults. Measuring diaphragm-VA may provide additional insight into the consequences and mechanisms of diaphragm fatigue. Novelty: Magnetic stimulation of the phrenic nerves can reliably measure voluntary activation of the diaphragm. Diaphragm voluntary activation can be used to provide additional insight into fatigability of the diaphragm.

To minimize transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the novel coronavirus responsible for coronavirus disease (COVID-19), the U.S. Centers for Disease Control and Prevention and the World Health Organization recommend wearing face masks in public. Some have expressed concern that these may affect the cardiopulmonary system by increasing the work of breathing, altering pulmonary gas exchange and increasing dyspnea, especially during physical activity. These concerns have been derived largely from studies evaluating devices intentionally designed to severely affect respiratory mechanics and gas exchange. We review the literature on the effects of various face masks and respirators on the respiratory system during physical activity using data from several models: cloth face coverings and surgical masks, N95 respirators, industrial respirators, and applied highly resistive or high-dead space respiratory loads. Overall, the available data suggest that although dyspnea may be increased and alter perceived effort with activity, the effects on work of breathing, blood gases, and other physiological parameters imposed by face masks during physical activity are small, often too small to be detected, even during very heavy exercise. There is no current evidence to support sex-based or age-based differences in the physiological responses to exercise while wearing a face mask. Although the available data suggest that negative effects of using cloth or surgical face masks during physical activity in healthy individuals are negligible and unlikely to impact exercise tolerance significantly, for some individuals with severe cardiopulmonary disease, any added resistance and/or minor changes in blood gases may evoke considerably more dyspnea and, thus, affect exercise capacity.

Objective: To examine the psychological mediators of exercise adherence among older adults in a group-based physical activity randomized controlled trial., Method: Older adults (≥65 years) were randomized to one of three conditions as part of the "GrOup-based physical Activity for oLder adults" (GOAL) randomized controlled trial. These included similar age same gender (SASG) and similar age mixed gender (SAMG) exercise programs that were informed by the tenets of self-categorization theory, and a "standard" mixed age mixed gender (MAMG) exercise program. Participants represented a subgroup (n = 483, Mage = 71.41 years) from the larger trial (n = 627) who completed measures of the trial's putative psychological mediators (i.e., group cohesion and affective attitudes) over the course of the 24-week exercise programs., Results: Piecewise latent growth modeling revealed different trajectories between participants in the two intervention conditions (SASG, SAMG) when compared with the comparison MAMG condition with regard to perceptions of group cohesion and affective attitudes. Results of subsequent cross-lagged panel modeling revealed that better program adherence in the two intervention conditions, when compared with the referent MAMG condition, was mediated by perceptions of group cohesion., Conclusions: The findings provide insight into how the two intervention programs differentially strengthened perceptions of group cohesion and affective attitudes over time. Consistent with self-categorization theory, the results also shed light on the role of group cohesion, in particular, as a psychological mechanism of action to promote older adults' exercise adherence behaviors. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Key Points: Under normoxic conditions, both healthy female and male diaphragms fatigue at a similar degree when matched for absolute diaphragmatic work during inspiratory loading. We investigated whether similarities in diaphragm fatigability persist under acute hypoxic conditions. We found that, in acute hypoxia, fatigue of the diaphragm is greater in women compared to men, whereas the magnitude of fatigue in normoxia did not differ between sexes. When matched for maximal diaphragm strength, women and men had a similar pressor response to work-matched inspiratory loading, independent of oxygen availability., Abstract: In normoxia, women and men display a comparable magnitude of diaphragmatic fatigue (DF) after work-matched inspiratory loading. Whether these sex similarities are maintained under acute hypoxic conditions is unknown. We investigated the influence of acute hypoxia during work-matched inspiratory pressure-threshold loading (PTL) on DF in healthy women (n = 8) and men (n = 8). Two 5 min isocapnic PTL tasks targeting a transdiaphragmatic pressure (P di ) of 92 cmH 2 O in normoxia and hypoxia (8% O 2 ) were performed on separate days (≥48 h). DF was quantified by twitch P di (P di,tw ) via cervical magnetic stimulation post-PTL. Women and men had similar maximal P di (P di,max ; women: 171 ± 16, men: 178 ± 20 cmH 2 O) and relative target workload (women: 54 ± 5%, men: 53 ± 6% P di,max ). The absolute cumulative diaphragmatic work did not differ between sexes in normoxia (women: 12,653 ± 1796 cmH 2 O s -1 , men: 13,717 ± 1231 cmH 2 O s -1 ; P = 0.202) or hypoxia (women: 11,624 ± 1860 cmH 2 O s -1 , men: 12 722 ± 1502 cmH 2 O s -1 ; P = 0.189). In normoxia, the magnitude of reduction in P di,tw post-PTL was similar between sexes (women: -21.1 ± 8.4%, men: -22.5 ± 4.9 %; P = 0.193); however, a higher degree of DF was observed in women compared to men following PTL in acute hypoxia (women: -27.6 ± 7.7%, men: -23.4 ± 9.6%, P = 0.019). We conclude that the female diaphragm is more susceptible to fatigue after inspiratory loading under acute hypoxic conditions. This finding may be related to sex differences in diaphragm muscle metabolism, such as fibre type composition, contractile properties, substrate utilisation and blood perfusion., (© 2020 The Authors. The Journal of Physiology © 2020 The Physiological Society.)

Airway luminal area (A i ) influences respiratory mechanics during dynamic exercise; however, previous studies have investigated the relationship between airway anatomy and physiological function in different groups of individuals. The purpose of this study was to determine the effect of A i on respiratory mechanics by making in vivo measures of airway dimensions and work of breathing (Wb) in the same individuals. Healthy participants (3F/2M; 23-45 years) completed a cycle exercise test to exhaustion. During exercise, Wb was assessed using an esophageal balloon catheter, while simultaneously assessing minute ventilation ( V ˙ E ). On a separate day, subjects underwent a bronchoscopy procedure to capture optical coherence tomography (OCT) measures of three airways in the right lung. Each participant's Wb- V ˙ E data were fit to a non-linear regression equation (Wb = a V ˙ E 3  + b V ˙ E 2 ) that partitions Wb into its turbulent resistive (a) and viscoelastic (b) components. Measures of A i and luminal diameter were made for the 4th-6th airway generations. A composite index of airway size was calculated as the sum of the A i for each generation and the total area of the 4th-6th generation was calculated based on Weibel's model. Constant a was significantly correlated to the Weibel model total airway area (r = -0.94, p = 0.017) and index of airway size (r = -0.929, p = 0.023), whereas constant b was not associated with either measure (both p > 0.05). We found that individuals who had the smallest A i had the highest resistive Wb and our findings provide the basis for further study of the relationship between airway size and respiratory mechanics during exercise., (© 2020 The Authors. Physiological Reports published by Wiley Periodicals LLC on behalf of The Physiological Society and the American Physiological Society.)

New Findings: What is the central question of this study? How does sternocleidomastoid blood flow change in response to increasing ventilation and whole-body exercise intensity? What is the main finding and its importance? Sternocleidomastoid blood flow increased with increasing ventilation. For a given ventilation, sternocleidomastoid blood flow was lower during whole-body exercise compared to resting hyperpnoea. These findings suggest that locomotor muscle work exerts an effect on respiratory muscle blood flow that can be observed in the sternocleidomastoid., Abstract: Respiratory muscle work influences the distribution of blood flow during exercise. Most studies have focused on blood flow to the locomotor musculature rather than the respiratory muscles, owing to the complex anatomical arrangement of respiratory muscles. The purpose of this study was to examine how accessory respiratory (i.e. sternocleidomastoid, and muscles in the intercostal space) muscle blood flow changes in response to locomotor muscle work. Seven men performed 5 min bouts of constant load cycling exercise trials at 30%, 60% and 90% of peak work rate in a randomized order, followed by 5 min bouts of voluntary hyperpnoea (VH) matching the ventilation achieved during each exercise (EX) trial. Blood-flow index (BFI) of the vastus lateralis, sternocleidomastoid (SCM) and seventh intercostal space (IC) were estimated using near-infrared spectroscopy and indocyanine green and expressed relative to resting levels. BFI SCM was greater during VH compared to EX (P = 0.002) and increased with increasing exercise intensity (P = 0.036). BFI SCM reached 493 ± 219% and 301 ± 215% rest during VH and EX at 90% peak work rate, respectively. BFI IC increased to 242 ± 178% and 210 ± 117% rest at 30% peak work rate during VH and EX, respectively. No statistically significant differences in BFI IC were observed with increased work rate during VH or EX (both P > 0.05). Moreover, there was no observed difference in BFI IC between conditions (P > 0.05). BFI SCM was lower for a given minute ventilation during EX compared to VH, suggesting that accessory respiratory muscle blood flow is influenced by whole-body exercise., (© 2020 The Authors. Experimental Physiology © 2020 The Physiological Society.)

New Findings: What is the topic of this review? Elevated demand is placed on the respiratory muscles during whole-body exercise-induced hyperpnoea. What is the role of elevated demand in neural modulation of cardiovascular control in respiratory and locomotor skeletal muscle, and what are the mechanisms involved? What advances does it highlight? There is a sympathetic restraint of blood flow to locomotor muscles during near-maximal exercise, which might function to maintain blood pressure. During submaximal exercise, respiratory muscle blood flow might be also be reduced if ventilatory load is sufficiently high. Methodological advances (near-infrared spectroscopy with indocyanine green) confirm that blood flow is diverted away from respiratory muscles when the work of breathing is alleviated., Abstract: It is known that the respiratory muscles have a significant increasing oxygen demand in line with hyperpnoea during whole-body endurance exercise and are susceptible to fatigue, in much the same way as locomotor muscles. The act of ventilation can itself be considered a form of exercise. The manipulation of respiratory load at near-maximal exercise alters leg blood flow significantly, demonstrating a competitive relationship between different skeletal muscle vascular beds to perfuse both sets of muscles adequately with a finite cardiac output. In recent years, the question has moved towards whether this effect exists during submaximal exercise, and the use of more direct measurements of respiratory muscle blood flow itself to confirm assumptions that uphold the concept. Evidence thus far has shown that there is a reciprocal effect on blood flow redistribution during ventilatory load manipulation observed at the respiratory muscles themselves and that the effect is observable during submaximal exercise, where active limb blood flow was reduced in conditions that simulated a high work of breathing. This has clinical applications for populations with respiratory disease and heart failure, where the work of breathing is remarkably high, even during submaximal efforts., (© 2020 The Authors. Experimental Physiology © 2020 The Physiological Society.)

Swimmers have a high prevalence of exercise-induced bronchoconstriction (EIB), which may be associated with repeated exposure to chlorinated pool water. The eucapnic voluntary hyperpnea (EVH) test is used to diagnose EIB; however, it fails to replicate the environmental conditions experienced by swimmers. The relationship between the composition of the EVH inspired gas and the development of EIB from swim exercise remains unclear., Purpose: This study aimed to compare the bronchoconstrictive effect of a chlorinated inspirate EVH test and swim test to a laboratory-based EVH test in swimmers., Methods: Fifteen collegiate swimmers (n = 5 male, n = 10 female; 21 ± 2 yr) completed 3 d of testing in pseudorandom order; a standard EVH test (EVHL), a pool air EVH test (EVHCl), and a swimming test (Swim). Spirometry was measured at baseline, and 3, 5, 10, 15, and 20 min after each test., Results: EVHL elicited a forced expired volume in 1 s (FEV1) fall index of -9.7% ± 6.4% compared with -6.6% ± 9.2% and -3.0% ± 7.5% after EVHCl and Swim, respectively (P < 0.05). Using Bland-Altman analysis, we found good agreement between EVHL and EVHCl (bias = -2.8, r = 0.79; P < 0.05) with poor agreement between EVHL and Swim (bias = -6.7, r = 0.20) and between EVHCl and Swim (bias = -3.9, r = 0.50; both P < 0.05). Forced expired flow between 25% and 75% lung volume and peak expired flow were significantly reduced by the EVHL compared with the EVHCl and Swim tests (P < 0.05)., Conclusions: EVHL elicits a greater forced expired volume in 1-s fall index compared with EVHCl and Swim. The unique aquatic environment of swimmers potentially protects against bronchoconstriction and should be considered in the determination of EIB.

Key Points: Diaphragm fatigue may increase the intensity (sensory dimension) and unpleasantness (affective dimension) of dyspnoea, which may partially explain why diaphragm fatigue negatively affects exercise performance. We hypothesized that diaphragm fatigue would negatively affect exercise performance via increases in both the intensity and unpleasantness of dyspnoea, and that the increase in dyspnoea would be mechanistically linked to an increase in diaphragmatic EMG (EMG di ), a surrogate measure of neural respiratory drive. Fatiguing the diaphragm prior to exercise reduced cycling performance and increased both the intensity and unpleasantness of dyspnoea. The change in submaximal dyspnoea unpleasantness was significantly correlated with the change in cycling performance. Pre-fatigue of the diaphragm did not increase EMG di during exercise and is therefore unrelated to the increase in either the sensory or affective dimension of exertional dyspnoea., Abstract: The purpose of this study was to examine the effect of diaphragm fatigue on the multidimensional components of dyspnoea and diaphragm electromyography (EMG di ) during cycling. Sixteen healthy males (age = 27 ± 5 yr, V ̇ O 2 max  = 45.8 ± 9.8 ml kg -1  min -1 ) completed two high-intensity, time-to-exhaustion cycling tests in randomized order: (i) inspiratory pressure threshold loading (PTL) prior to exercise to induce diaphragm fatigue (pre-DF) and (ii) no PTL (control). Diaphragm fatigue after PTL was confirmed via cervical magnetic stimulation of the phrenic nerves. Dyspnoea intensity and unpleasantness were measured throughout exercise with the 0-10 category-ratio Borg scale and following exercise using the Multidimensional Dyspnoea Profile (MDP). EMG di was continuously recorded via a multipair oesophageal electrode catheter. Time-to-exhaustion decreased with pre-DF vs. control (9.0 ± 5.5 vs. 10.7 ± 7.5 min, P = 0.023). Pre-DF increased dyspnoea intensity ratings by 0.6 ± 1.0 Borg 0-10 units at the highest equivalent submaximal exercise time (HESET) a participant could achieve in both conditions (P = 0.020). Dyspnoea unpleasantness ratings increased with pre-DF by 0.5 ± 1.0, 0.7 ± 1.2 and 0.9 ± 1.4 (all P < 0.05) Borg 0-10 units during the 2nd, 3rd and 4th minutes of exercise, respectively. There was a significant correlation between the change in breathing unpleasantness ratings at HESET and the change in time-to-exhaustion (r = 0.66, P = 0.006). The immediate perception domain, a combination of peak unpleasantness and specific dyspnoea descriptor intensity ratings, was the only component of the MDP that was significantly increased with pre-DF (4.3 ± 1.9 vs. 3.6 ± 1.8, P = 0.04). There were no significant differences in EMG di . In conclusion, diaphragm fatigue has negative effects on multiple domains of dyspnoea, which may partially explain why exercise performance decreases with it., (© 2020 The Authors. The Journal of Physiology © 2020 The Physiological Society.)

Chan, M, MacInnis, MJ, Koch, S, MacLeod, KE, Lohse, KR, Gallo, ME, Sheel, AW, and Koehle, MS. Cardiopulmonary demand of 16-kg kettlebell snatches in simulated Girevoy Sport. J Strength Cond Res 34(6): 1625-1633, 2020-Kettlebell lifting has become popular both as a strength and conditioning training tool and as a sport in and of itself: Girevoy Sport (GS). Although several kettlebell multimovement protocols have been analyzed, little research has attempted to quantify the aerobic stimulus of the individual events in GS, which could better inform kettlebell-related exercise prescription. The purpose of this study was to quantify the cardiopulmonary demand, assessed primarily by oxygen consumption (V[Combining Dot Above]O2) and heart rate (HR), of continuous high-intensity kettlebell snatches-under conditions relevant to GS-and to compare this demand with a more traditional graded rowing ergometer maximal exercise test. Ten male participants (age = 28.4 ± 4.6 years, height = 185 ± 7 cm, body mass = 95.1 ± 14.9 kg) completed (a) a graded-exercise test on a rowing ergometer to determine maximal oxygen consumption (V[Combining Dot Above]O2max) and maximal heart rate (HRmax) and (b) a graded-exercise test consisting of continuous 16-kg kettlebell snatches to determine peak oxygen consumption (V[Combining Dot Above]O2peak) and peak heart rate (HRpeak) during a simulated GS snatch event. Subjects achieved a V[Combining Dot Above]O2max of 45.7 ± 6.7 ml·kg·min and HRmax of 177 ± 8.3 b·min on the rowing ergometer. The kettlebell snatch test produced a V[Combining Dot Above]O2peak of 37.6 ± 4.4 ml·kg·min (82.7 ± 6.5% V[Combining Dot Above]O2max) and a HRpeak of 174 ± 10 b·min (98.0 ± 3.4% HRmax). These findings suggest that GS kettlebell snatches with 16-kg can provide an adequate aerobic stimulus to improve cardiorespiratory fitness in those with a V[Combining Dot Above]O2max of ≤51 ml·kg·min, according to aerobic training recommendations from the American College of Sports Medicine.

Purpose: To quantify the mechanical work of breathing (W b ) during an indoor rowing test in men and women. Additionally, to compare sex-based differences in the W b and its components through a rowing test., Methods: Fifteen collegiate rowers were recruited (8 women/7 men) and performed a 2000 m rowing test on a rowing ergometer. Esophageal pressure was measured during exercise via balloon catheterization, after which pressure-volume curves were used to calculate total, inspiratory resistive and elastic, and total expiratory W b ., Results: Men had significantly higher values of instantaneous and cumulative total W b at and beyond 37.5% (430.4 ± 42.5 vs. 282.1 ± 45.1 J min -1 , P < 0.05) and 62.5% (1946.8 ± 150.9 vs. 1360.1 ± 197.2 J, P < 0.05) total exercise time, respectively. However, when compared at the same minute ventilation, women had higher values of total (at and above ~ 140 L min -1 ), inspiratory resistive (at and above ~ 120 L min -1 ), and inspiratory elastic (at and above ~ 135 L min -1 ) W b , whereas men presented higher total expiratory W b compared to women at any ventilation., Conclusion: Although female rowers present higher relative values of inspiratory resistive and elastic W b , their male counterparts develop greater ventilatory efforts during a 2000 m rowing test, resulting in a larger total mechanical W b . We interpret these findings to mean that the W b reflects both anatomical (i.e., airways and lung sizes) and respiratory (i.e., minute ventilation) sex differences during rowing.

Background: Perfusion of intrapulmonary arteriovenous anastomoses (IPAVA) is increased during exercise and in hypoxia and is associated with variations in oxygen saturation (S P O 2 ), resulting in blood bypassing the pulmonary microcirculation. Sildenafil is a pulmonary vasodilator that improves S P O 2 and endurance performance in hypoxia. The purpose of this study was to determine if 50 mg sildenafil would reduce IPAVA perfusion (Q IPAVA ) and if the decrement in maximal exercise capacity (VO 2max ) in hypoxia is related to Q IPAVA . We hypothesized that during progressive levels of hypoxia at rest (F I O 2  = 0.21, 0.14, 0.12), sildenafil would increase S P O 2 and reduce bubble score (estimate of Q IPAVA ) compared to placebo, and that the decrement in VO 2max in hypoxia would be positively correlated with bubble score at rest in hypoxia. Materials and Methods: Fourteen endurance-trained men performed a graded maximal exercise test at sea level and at a simulated altitude of 3000 m, followed by two experimental visits where, after randomly ingesting sildenafil or placebo, they underwent agitated saline contrast echocardiography during progressive levels of hypoxia at rest. Results: All participants experienced a decrement in power output in hypoxia that ranged from 9% to 19% lower than sea level values. Compared to normoxia, bubble score increased significantly in hypoxia ( p  < 0.001) with no effect of sildenafil ( p  = 0.580). There was a negative correlation between S P O 2 and bubble score ( p  < 0.001). The decrement in peak power output at VO 2max in hypoxia was unrelated to IPAVA perfusion in resting hypoxia ( p  = 0.32). Several participants demonstrated Q IPAVA greater than zero in room air, indicating that arterial hypoxemia may not be the sole mechanism for Q IPAVA . Conclusion: These results indicate that the VO 2max decrement caused by hypoxia is not related to Q IPAVA and that sildenafil does not improve VO 2max in hypoxia through modulation of Q IPAVA .

New Findings: What is the central question of this study? What is the effect of age and sex on the resistive and viscoelastic components of work of breathing (W b ) during exercise? What is the main finding and its importance? The resistive and viscoelastic components of W b were higher in older adults, regardless of sex. The resistive, but not viscoelastic, component of W b was higher in females than in males, regardless of age. These findings contribute to improving our understanding of the effects of ageing and sex on the mechanical ventilatory response to exercise., Abstract: Healthy ageing and biological sex each affect the work of breathing (W b ) for a given minute ventilation ( V ̇ E ). Age-related structural changes to the respiratory system lead to an increase in both the resistive and viscoelastic components of W b ; however, it is unclear whether healthy ageing differentially alters the mechanics of breathing in males and females. We analysed data from 22 older (60-80 years, n = 12 females) and 22 younger (20-30 years, n = 11 females) males and females that underwent an incremental cycle exercise test to exhaustion. V ̇ E and W b were assessed at rest and throughout exercise. W b - V ̇ E data for each participant were fitted to a non-linear equation (i.e. W b  = a V ̇ E 3 + b V ̇ E 2 ) that partitions W b into resistive (i.e. a V ̇ E 3 ) and viscoelastic (i.e. b V ̇ E 2 ) components. We then modelled the effects of healthy ageing and biological sex on each component of W b . Overall, the model fit was excellent (r 2 : 0.99 ± 0.01). There was a significant main effect of age and sex on the resistive component of W b (both P < 0.05), and a significant main effect of age (P < 0.001), but not sex (P = 0.309), on the viscoelastic component of W b . No significant interactions between age and sex on a V ̇ E 3 or b V ̇ E 2 were noted (both P > 0.05). Our findings indicate that during exercise: (i) the higher total W b in females relative to males is due to a higher resistive, but not viscoelastic, component of W b , and (ii) regardless of sex, the higher W b in older adults relative to younger adults is due to higher resistive and viscoelastic components of W b ., (© 2019 The Authors. Experimental Physiology © 2019 The Physiological Society.)

Adult survivors of very preterm (≤32 wk gestational age) birth without (PRE) and with bronchopulmonary dysplasia (BPD) have variable degrees of airflow obstruction at rest. Assessment of the shape of the maximal expiratory flow-volume (MEFV) curve in PRE and BPD may provide information concerning their unique pattern of airflow obstruction. The purposes of the present study were to 1 ) quantitatively assess the shape of the MEFV curve in PRE, BPD, and healthy adults born at full-term (CON), 2 ) identify where along the MEFV curve differences in shape existed between groups, and 3 ) determine the association between an index of MEFV curve shape and characteristics of preterm birth (i.e., gestational age, mass at birth, duration of oxygen therapy) in PRE and BPD. To do so, we calculated the average slope ratio (SR) throughout the effort-independent portion of the MEFV curve and at increments of 5% of forced vital capacity (FVC) between 20 and 80% of FVC in PRE ( n = 19), BPD ( n = 25), and CON ( n = 20). We found that average SR was significantly higher in PRE (1.34 ± 0.35) and BPD (1.33 ± 0.45) compared with CON (1.03 ± 0.22; both P < 0.05) but similar between PRE and BPD ( P = 0.99). Differences in SR between groups occurred early in expiration (i.e., 20-30% of FVC). There was no association between SR and characteristics of preterm birth in PRE and BPD groups (all P > 0.05). The mechanism(s) of increased SR during early expiration in PRE/BPD relative to CON is unknown but may be due to differences in the structural and mechanical properties of the airways.

Key Points: The female diaphragm fatigues at a slower rate compared to that of males, with blunted cardiovascular consequences (i.e. inspiratory muscle metaboreflex). It is unclear if these findings are a function of relative or absolute diaphragmatic work. We asked if sex differences in diaphragm fatigue and the inspiratory muscle metaboreflex persisted during inspiratory loading performed at equal absolute intensities. We found that matching men and women for absolute diaphragmatic work resulted in an equal degree of diaphragm fatigue, despite women performing significantly greater work relative to body mass. Metabolite-induced reflex influences in sympathetic outflow originating from the diaphragm are attenuated in women, with potential implications for blood flow distribution during exercise., Abstract: In response to inspiratory pressure-threshold loading (PTL), women have greater inspiratory muscle endurance time, slower rate of diaphragm fatigue development, and a blunted pressor response compared to men. It is unclear if these differences are due to discrepancies in absolute diaphragm force output. We tested the hypothesis that following inspirations performed at equal absolute intensities, females would develop a similar level of diaphragm fatigue and an attenuated cardiovascular response relative to men. Healthy young men (n = 8, age = 24 ± 3 years) and women (n = 8, age = 23 ± 3 years) performed PTL whilst targeting a transdiaphragmatic pressure (P di ) of 92 cmH 2 O for 5 min. Diaphragm fatigue was assessed via twitch P di (P di,tw ) using cervical magnetic stimulation. Heart rate (HR) and mean arterial blood pressure were monitored continuously. During PTL, the absolute amount of diaphragm work was not different between men (13,399 ± 2019 cmH 2 O s) and women (12,986 ± 1846 cmH 2 O s; P > 0.05); however, women performed the PTL task at a higher relative P ¯ di /P di,max . Following inspiratory PTL, the magnitude of reduction in P di,tw was similar between men (-27.1 ± 7.2%) and women (-23.8 ± 13.8%; P > 0.05). There were significant increases in HR over time (P < 0.05), but this did not differ on the basis of sex (P > 0.05). Mean arterial blood pressure increased significantly over time in both men and women (P < 0.05); however, the rate of change was higher in men (6.24 ± 2.54 mmHg min -1 ) than in women (4.15 ± 2.52 mmHg min -1 ) (P < 0.05). We conclude that the female diaphragm is protected against severe fatigue when inspiratory work is excessive and as a result does not evoke overt sympathoexcitation., (© 2019 The Authors. The Journal of Physiology © 2019 The Physiological Society.)

Unsatisfied inspiration is commonly reported during exercise by patients with interstitial lung disease (ILD). However, the physiological basis of perceived dyspnea quality in this population has not been evaluated. We examined the relationship between dyspnea quality and indices of ventilatory-mechanical limitations during exercise in patients with fibrotic ILD. Sixteen fibrotic ILD patients (12 male) with a median age of 64 years (range 49-81), FVC 71%-predicted (51-100), and DL CO 47%-predicted (27-77) performed incremental and constant work-rate cycle exercise tests to exhaustion. Ventilatory responses were recorded at rest, throughout exercise, and at peak exercise. Dyspnea quality was serially assessed using a 4-item list from which participants selected the phrase that best described their breathing compared to rest. Increased work/effort was the dominant descriptor of dyspnea throughout exercise, but with increased selection of unsatisfied inspiration following the inflection point of tidal volume relative to ventilation. Delaying or preventing ILD patients from reaching a critically reduced IRV may have implications for symptom management., (Copyright © 2019 Elsevier B.V. All rights reserved.)

The thorax undergoes unique conditions while swimming. Hydrostatic pressure from water immersion places an external load on the thorax and increases airway resistance, and the horizontal body position results in central venous engorgement and an associated reduction in lung compliance. The aforementioned factors likely increase the work of breathing (Wb); however, this hypothesis remains untested., Purpose: This study aimed to compare Wb during freestyle swimming relative to cycling and to characterize the differences in the cardiorespiratory responses to swimming relative to cycling in the same individuals., Methods: Eight collegiate swimmers (four men and four women, age = 22 ± 2 yr) performed an incremental swim test while tethered to a resistance apparatus. On a separate day, subjects performed an incremental cycle test. During swimming and cycling, metabolic and ventilatory parameters were measured using a customized metabolic cart, and inspired Wb was quantified using an esophageal balloon catheter., Results: Swimming and cycling elicited statistically similar levels of peak oxygen uptake (3.87 ± 0.92 vs 4.20 ± 0.83 L·min, P = 0.143). However, peak minute ventilation (V˙E) (118 ± 3 vs 154 ± 25 L·min) and heart rate (164 ± 19 vs 183 ± 8 bpm) were significantly lower during swimming relative to cycling (both P < 0.05). Inspired Wb was higher at a V˙E of 50 L·min (+27 ± 16 J·min), 75 L·min (+56 ± 23 J·min), and 100 L·min (+53 ± 22 J·min) during swimming compared with cycling (all P < 0.05). Periods of interbreath apnea were observed while swimming (duration = 0.13-2.07 s)., Conclusion: We interpret our findings to mean that the horizontal body position and hydrostatic pressure on the chest wall requires swimmers to generate greater inspiratory pressures to sustain adequate V˙E during exercise.

Key Points: The effect of combined inspiratory and expiratory muscle training on resting and reflexive cardiac function, as well as exercise capacity, in individuals with cervical spinal cord injury (SCI) is presently unknown. Six weeks of combined inspiratory and expiratory muscle training enhances both inspiratory and expiratory muscle strength in highly-trained athletes with cervical SCI with no significant effect on lung function. There was a significant decrease in left-ventricular filling and stroke volume at rest in response to 45° head-up tilt, which is irreversible by respiratory muscle training. Combined inspiratory and expiratory muscle training increased peak aerobic work rate and reduced end-expiratory lung volumes during exercise, which may have implications for left-ventricular filling during exercise., Abstract: To investigate the pulmonary, cardiovascular and exercise responses to combined inspiratory and expiratory respiratory muscle training (RMT) in athletes with tetraplegia, six wheelchair rugby athletes (five males and one female, aged 33 ± 5 years) completed 6 weeks of pressure threshold RMT, 2 sessions day -1 on 5 days week -1 . Resting pulmonary and cardiac function, exercise capacity, exercising lung volumes and field-based exercise performance were assessed at pre-RMT, post-RMT and after a 6-week no RMT period. RMT enhanced maximal inspiratory (pre- vs. post-RMT: -76 ± 15 to -106 ± 23 cmH 2 O, P = 0.002) and expiratory (59 ± 26 to 73 ± 32 cmH 2 O, P = 0.007) mouth pressures, as well as peak expiratory flow (6.74 ± 1.51 vs. 7.32 ± 1.60 L/s, P < 0.04). Compared to pre-RMT, peak work rate was higher at post-RMT (60 ± 23 to 68 ± 22 W, P = 0.003), whereas exercising end-expiratory lung volumes were reduced (P < 0.017). Peak oxygen uptake increased in all athletes at post-RMT (1.24 ± 0.40 vs. 1.40 ± 0.50 l min -1 , P = 0.12). After 6 weeks of no RMT all indices returned towards baseline, with peak work rate (P = 0.037), peak oxygen uptake (P = 0.041) and end-expiratory lung volume (P < 0.034) being significantly lower at follow-up than at post-RMT. There was a significant decrease in left-ventricular end-diastolic volume and stroke volume in response to 45° head-up tilt (P = 0.030 and 0.021, respectively); however, all cardiac indices in both supine and tilted positions were unchanged by RMT. Our findings demonstrate the efficacy of RMT with respect to enhancing respiratory muscle strength, lowering exercising lung volumes and increasing exercise capacity. Although the precise mechanisms by which RMT may enhance exercise capacity remain unclear, our data suggest that it is probably not the result of a direct cardiac adaptation associated with RMT., (© 2019 The Authors. The Journal of Physiology © 2019 The Physiological Society.)

Healthy women have proportionally smaller lungs and airways compared with height-matched men. These anatomical sex-based differences result in greater mechanical ventilatory constraints and may influence the integrative response to exercise. Our review will examine this hypothesis in healthy humans in the context of dynamic whole-body exercise.

Exercise-induced arterial hypoxemia (EIAH) is characterized by the decrease in arterial oxygen tension and oxyhemoglobin saturation during dynamic aerobic exercise. Since the time of the initial observations, our knowledge and understanding of EIAH has grown, but many unknowns remain. The purpose of this review is to provide an update on recent findings, highlight areas of disagreement, and identify where information is lacking. Specifically, this review will place emphasis on ( i ) the occurrence of EIAH during submaximal exercise, ( ii ) whether there are sex differences in the development and severity of EIAH, and ( iii ) unresolved questions and future directions.

Reducing the work of breathing during exercise improves locomotor muscle blood flow and reduces diaphragm and locomotor muscle fatigue and is thought to be the result of a sympathetically mediated reflex., Aim: The aim of this study was to assess muscle sympathetic nerve activity (MSNA) when the work of breathing is experimentally lowered during dynamic exercise., Methods: Healthy subjects (n = 12; age = 29 ± 9 years) performed semi-recumbent cycling trials at 40%, 60%, and 80% of peak workload. Exercise trials consisted of spontaneous breathing, reduced work of breathing (proportional assist ventilator), followed by further spontaneous breathing (post-ventilator). MSNA was recorded from the median nerve., Results: There was no difference in work of breathing between PAV and post-PAV at 40% peak work. At 60% peak work, the ventilator significantly (P < 0.05) reduced work of breathing (103 ± 39 vs 144 ± 47 J min -1 ), sympathetic nerve activity (35 ± 5 vs 42 ± 8 burst min -1 ), and V ˙ O 2 (2.4 ± 0.5 vs 2.6 ± 0.5 L min -1 ) without influencing ventilation (86 ± 9 vs 82 ± 10 L min -1 ; P > 0.05), for PAV and post-PAV respectively. During 80% peak work (n = 8), the ventilator significantly (P < 0.05) reduced work of breathing (235 ± 110 vs. 361 ± 150 J min -1 ), MSNA (48 ± 7 vs 54 ± 11 burst min -1 ), and V ˙ O 2 (2.9 ± 0.6 vs 3.2 ± 0.7 L min -1 ) but not ventilation (121 ± 20 vs 123 ± 20 L min -1 ; P > 0.05), for PAV and post-PAV respectively. There was a significant relationship between MSNA and V ˙ O 2 (P < 0.0001) with a significant interaction due to the ventilator (P < 0.05)., Conclusion: Lowering the normally occurring work of breathing during exercise results in commensurate reductions in MSNA. Our findings provide evidence of a sympathetically mediated vasoconstrictor effect emanating from respiratory muscles during exercise., (© 2018 Scandinavian Physiological Society. Published by John Wiley & Sons Ltd.)

Key Points: The perceived intensity of exertional breathlessness (i.e. dyspnoea) is higher in older women than in older men, possibly as a result of sex-differences in respiratory system morphology. During exercise at a given absolute intensity or minute ventilation, older women have a greater degree of mechanical ventilatory constraint (i.e. work of breathing and expiratory flow limitation) than their male counterparts, which may lead to a greater perceived intensity of dyspnoea. Using a single-blind randomized study design, we experimentally manipulated the magnitude of mechanical ventilatory constraint during moderate-intensity exercise at ventilatory threshold in healthy older men and women. We found that changes in the magnitude of mechanical ventilatory constraint within the physiological range had no effect on dyspnoea in healthy older adults. When older men and women perform moderate intensity exercise, mechanical ventilatory constraint does not contribute significantly to the sensation of dyspnoea., Abstract: We aimed to determine the effect of manipulating mechanical ventilatory constraint during submaximal exercise on dyspnoea in older men and women. Eighteen healthy subjects (aged 60-80 years; nine men and nine women) completed two days of testing. On day 1, subjects were assessed for pulmonary function and performed a maximal incremental cycle exercise test. On day 2, subjects performed three 6-min bouts of cycling at ventilatory threshold, in a single-blind randomized manner, while breathing: (i) normoxic helium-oxygen (HEL) to reduce the work of breathing (W b ) and alleviate expiratory flow limitation (EFL); (ii) through an inspiratory resistance (RES) of ∼5 cmH 2 O L -1  s -1 to increase W b ; and (iii) ambient air as a control (CON). Oesophageal pressure, diaphragm electromyography, and sensory responses (category-ratio 10 Borg scale) were monitored throughout exercise. During the HEL condition, there was a significant decrease in W b (men: -21 ± 6%, women: -17 ± 10%) relative to CON (both P < 0.01). Moreover, if EFL was present during CON (four men and five women), it was alleviated during HEL. Conversely, during the RES condition, W b (men: 42 ± 19%, women: 50 ± 16%) significantly increased relative to CON (both P < 0.01). There was no main effect of sex on W b (P = 0.59). Across conditions, women reported significantly higher dyspnoea intensity than men (2.9 ± 0.9 vs. 1.9 ± 0.8 Borg scale units, P < 0.05). Despite significant differences in the degree of mechanical ventilatory constraint between conditions, the intensity of dyspnoea was unaffected, independent of sex (P = 0.46). When older men and women perform moderate intensity exercise, mechanical ventilatory constraint does not contribute significantly to the sensation of dyspnoea., (© 2018 The Authors. The Journal of Physiology © 2018 The Physiological Society.)

New Findings: What is the central question of this study? Increased respiratory muscle activation is associated with neural and cardiovascular consequences via the respiratory muscle metaboreflex. Does increased sympathetic vasoconstriction originating from the respiratory musculature elicit a reduction in blood flow to an inactive limb in order to maintain blood flow to an active limb? What is the main finding and its importance? Arm blood flow was reduced whereas leg blood flow was preserved during mild leg exercise with inspiratory resistance. Blood flow to the active limb is maintained via sympathetic control of blood flow redistribution when the respiratory muscle-induced metaboreflex is activated., Abstract: The purpose of this study was to elucidate the effect of increasing inspiratory muscle work on blood flow to inactive and active limbs. Healthy young men (n = 10, 20 ± 2 years of age) performed two bilateral dynamic knee-extension and knee-flexion exercise tests at 40% peak oxygen uptake for 10 min. The trials consisted of spontaneous breathing for 5 min followed by voluntary hyperventilation either with or without inspiratory resistance for 5 min (40% of maximal inspiratory mouth pressure, inspiratory duty cycle of 50% and a breathing frequency of 40 breaths min -1 ). Mean arterial blood pressure was acquired using finger photoplethysmography. Blood flow in the brachial artery (inactive limb) and in the femoral artery (active limb) were monitored using Doppler ultrasound. Mean arterial blood pressure during exercise was higher (P < 0.05) with inspiratory resistance (121 ± 7 mmHg) than without resistance (99 ± 5 mmHg). Brachial artery blood flow increased during exercise without inspiratory resistance (120 ± 31 ml min -1 ) compared with the resting level, whereas it was attenuated with inspiratory resistance (65 ± 43 ml min -1 ). Femoral artery blood flow increased at the onset of exercise and was maintained throughout exercise without inspiratory resistance (2576 ± 640 ml min -1 ) and was unchanged when inspiratory resistance was added (2634 ± 659 ml min -1 ; P > 0.05). These results suggest that sympathetic control of blood redistribution to active limbs is facilitated, in part, by the respiratory muscle-induced metaboreflex., (© 2018 The Authors. Experimental Physiology © 2018 The Physiological Society.)

Sildenafil is a pulmonary vasodilator that has potential to mitigate the decrement in endurance performance caused by hypoxic pulmonary vasoconstriction. The purpose of this study was to determine the effects of sildenafil on pulmonary artery pressure, cardiac output, pulse oxygen saturation, and exercise performance at moderate simulated altitude. We hypothesized that sildenafil would reduce the decline in exercise performance in hypoxia by blunting the rise in pulmonary artery pressure and causing a relative increase in cardiac output and oxygen saturation. Twelve endurance trained men performed three experimental cycling trials at sea level and simulated moderate altitude of 3,000m (FIO2 = 0.147) after ingesting either a placebo or sildenafil 50 mg capsule in a double blinded fashion. Each test consisted of a warmup period, a 15-minute steady state period at 60% of peak power output, and a 16.1 km time-trial. All subjects experienced a decline in maximal exercise capacity in hypoxia that ranged from 6% to 24%. This decline was correlated with the reduction in pulse oxygen saturation in hypoxic maximal exercise. Sildenafil had no effect on pulmonary artery pressure, cardiac output, or pulse oxygen saturation measured during steady state exercise. There was no effect of sildenafil on mean power output during the time-trial. During high intensity cycle exercise in acute, moderate hypoxia pulmonary artery pressure is unaffected by sildenafil and does not appear to influence cardiovascular function or exercise performance., Competing Interests: The authors have declared that no competing interests exist.

Women are more resistant to diaphragmatic fatigue (DF) and experience an attenuated inspiratory muscle metaboreflex relative to men. The effects of such sex-based differences on whole body exercise tolerance are yet to be examined. It was hypothesized that DF induced prior to exercise would cause less of a reduction in subsequent exercise time in women compared to men. Healthy men ( n = 9, age = 24 ± 3 yr) and women ( n = 9, age = 24 ± 3 yr) completed a maximal incremental cycle test on day 1. On day 2, subjects performed isocapnic inspiratory pressure-threshold loading (PTL) to task failure followed by a constant load submaximal time-to-exhaustion (TTE) exercise test at 85% of the predetermined peak work rate. On day 3, subjects performed the same exercise test without prior induced DF. Days 2 and 3 were randomized and counterbalanced. Magnetic stimulation of the phrenic nerve roots was used to nonvolitionally assess DF by measurement of transdiaphragmatic twitch pressure ( P di,tw ). A similar degree of DF was produced in both sexes following PTL [ P di,tw (% change from baseline): M = -24.6 ± 7.8%, W = -23.1 ± 5.4%; P = 0.54)]. There was a significant reduction in TTE with prior induced DF compared with the control condition in both men (10.9 ± 3.5 min vs. 13.0 ± 3.2 min, P = 0.05) and women (10.1 ± 2.4 min vs. 12.2 ± 3.3 min, P = 0.03) that did not differ in magnitude between the sexes (M = -15.8 ± 19.5%, W = -14.5 ± 19.2%, P = 0.89). In conclusion, DF negatively and equally impairs exercise tolerance independent of sex. NEW & NOTEWORTHY Women are more resistant to diaphragmatic fatigue (DF) relative to men. The effect of DF on exercise tolerance is currently being debated. Our findings show that DF negatively and equally affects exercise tolerance in healthy men and women. Mechanisms beyond the inspiratory muscle metaboreflex (e.g., dyspnea, central fatigue, breathing pattern) may explain the absence of a sex-based difference.

Sympathetically induced vasoconstrictor modulation of local vasodilation occurs in contracting skeletal muscle during exercise to ensure appropriate perfusion of a large active muscle mass and to maintain also arterial blood pressure. In this synthesis, we discuss the contribution of group III-IV muscle afferents to the sympathetic modulation of blood flow distribution to locomotor and respiratory muscles during exercise. This is followed by an examination of the conditions under which diaphragm and locomotor muscle fatigue occur. Emphasis is given to those studies in humans and animal models that experimentally changed respiratory muscle work to evaluate blood flow redistribution and its effects on locomotor muscle fatigue, and conversely, those that evaluated the influence of coincident limb muscle contraction on respiratory muscle blood flow and fatigue. We propose the concept of a "two-way street of sympathetic vasoconstrictor activity" emanating from both limb and respiratory muscle metaboreceptors during exercise, which constrains blood flow and O 2 transport thereby promoting fatigue of both sets of muscles. We end with considerations of a hierarchy of blood flow distribution during exercise between respiratory versus locomotor musculatures and the clinical implications of muscle afferent feedback influences on muscle perfusion, fatigue, and exercise tolerance.

Key Points: Diaphragmatic fatigue (DF) elicits a sympathetically mediated metaboreflex resulting in increased heart rate, blood pressure and limb vascular resistance. Women may be more resistant to DF compared to men, and therefore it was hypothesised that women would experience an attenuated inspiratory muscle metaboreflex during inspiratory pressure-threshold loading (PTL) performed to task failure. At the time of PTL task failure, the severity of DF was not different between sexes; however, inspiratory muscle endurance time was significantly longer in women than in men. For a given cumulative diaphragmatic force output, the severity of DF was less in women than in men. Women exhibited a blunted cardiovascular response to inspiratory resistance (i.e. metaboreflex) that may have implications for exercise tolerance., Abstract: Diaphragmatic fatigue (DF) elicits reflexive increases in sympathetic vasomotor outflow (i.e. metaboreflex). There is some evidence suggesting women may be more resistant to DF compared to men, and therefore may experience an attenuated inspiratory muscle metaboreflex. To this end, we sought to examine the cardiovascular response to inspiratory resistance in healthy young men (n = 9, age = 24 ± 3 years) and women (n = 9, age = 24 ± 3 years). Subjects performed isocapnic inspiratory pressure-threshold loading (PTL, 60% maximal inspiratory mouth pressure) to task failure. Diaphragmatic fatigue was assessed by measuring transdiaphragmatic twitch pressure (P di,tw ) using cervical magnetic stimulation. Heart rate (HR) and mean arterial pressure (MAP) were measured beat-by-beat throughout PTL via photoplethysmography, and low-frequency systolic pressure (LF SBP ; a surrogate for sympathetic vasomotor tone) calculated from arterial waveforms using power spectrum analysis. At PTL task failure, the degree of DF was similar between sexes (∼23% reduction in P di,tw ; P = 0.33). However, time to task failure was significantly longer in women than in men (27 ± 11 vs. 16 ± 11 min, respectively; P = 0.02). Women exhibited less of an increase in HR (13 ± 8 vs. 19 ± 12 bpm; P = 0.02) and MAP (10 ± 8 vs. 14 ± 9 mmHg; P = 0.01), and significantly lower LF SBP (23 ± 11 vs. 34 ± 8 mmHg 2 ; P = 0.04) during PTL compared to men. An attenuation of the inspiratory muscle metaboreflex may influence limb and respiratory muscle haemodynamics with implications for exercise performance., (© 2018 The Authors. The Journal of Physiology © 2018 The Physiological Society.)

Purpose: To characterize the effects of age, sex, and their interaction on inspiratory muscle activation patterns during exercise., Methods: Twenty younger (20-30 yr, n = 10 women) and 20 older (60-80 yr, n = 10 women) subjects performed an incremental cycle exercise test. Electromyography (EMG) of the scalene (EMGsca) and EMG of the sternocleidomastoid (EMGscm) muscles were measured using skin surface electrodes, whereas diaphragm EMG (EMGdi) and esophageal and transdiaphragmatic pressures were measured using an esophageal catheter. Electromyography data were transformed into root mean square with a 100-ms time constant. Esophageal and diaphragmatic pressure-time products were used as indices of total inspiratory muscle pressure production and diaphragmatic pressure production, respectively., Results: At absolute minute ventilations (V˙E), women and older subjects had greater EMGdi than men and younger subjects, respectively (all P < 0.05), but no differences were noted when V˙E was expressed in relative terms (all P > 0.05). Women had greater EMGsca activity than men at absolute and relative levels of V˙E (all P < 0.05). Older subjects had greater EMGsca than younger subjects when V˙E was expressed in relative (all P < 0.05) but not absolute terms (all P > 0.05). At absolute and relative levels of V˙E, women and older subjects had greater EMGscm than men and younger subjects, respectively (all P < 0.05). Women and older subjects had a greater esophageal and diaphragmatic pressure-time products at a V˙E of 70 L·min than men and younger subjects, respectively (both P < 0.05), but no differences were noted when V˙E was expressed in relative terms (all P > 0.05). No significant interactions between age and sex were noted (all P > 0.05)., Conclusions: Age and sex significantly affect inspiratory muscle activation patterns during exercise; however, the extent of the effects depends on whether comparisons are made at absolute or relative V˙E.

Background: Myocardial infarction (MI) remains under-recognized in chronic lung disease (CLD) patients. Rehabilitation health professionals need accessible clinical measurements to identify the presence of prior MI in order to determine appropriate training prescription., Objectives: To estimate prior MI in CLD patients entering a pulmonary rehabilitation program, as well as its association with heart rate parameters such as resting heart rate and chronotropic response index., Design: Retrospective cohort design., Setting: Pulmonary rehabilitation outpatient clinic in a tertiary care university-affiliated hospital., Patients: Eighty-five CLD patients were studied., Methods: Electrocardiograms at rest and peak cardiopulmonary exercise testing, performed before pulmonary rehabilitation, were analyzed. Electrocardiographic evidence of prior MI, quantified by the Cardiac Infarction Injury Score (CIIS), was contrasted with reported myocardial events and then correlated with resting heart rate and chronotropic response index parameters., Main Outcome Measurements: CIIS, resting heart rate, and chronotropic response index., Results: Sixteen CLD patients (19%) demonstrated electrocardiographic evidence of prior MI, but less than half (8%) had a reported MI history (P < .05). The Cohen's kappa test revealed poor level of agreement between CIIS and medical records (kappa = 0.165), indicating that prior MI diagnosis was under-reported in the medical records. Simple and multiple regression analyses showed that resting heart rate but not chronotropic response index was positively associated with CIIS in our population (R 2 = 0.29, P < .001). CLD patients with a resting heart rate higher than 80 beats/min had approximately 5 times higher odds of having prior MI, as evidenced by a CIIS ≥ 20., Conclusions: CLD patients entering pulmonary rehabilitation are at risk of unreported prior MI. Elevated resting heart rate appears to be an indicator of prior MI in CLD patients; therefore, careful adjustment of training intensity is recommended under these circumstances., Level of Evidence: III., (Copyright © 2018 American Academy of Physical Medicine and Rehabilitation. Published by Elsevier Inc. All rights reserved.)

Whether the large lungs of swimmers result from intensive training or genetic endowment has been widely debated. Given that peak lung growth velocities occur during puberty, this study examined if competitive swimming during puberty affected lung growth. Eleven- to fourteen-year-old healthy female competitive swimmers and controls were assessed before (PRE) and after (POST) one swimming season (7.4 ± 0.5 months). Pulmonary function testing included lung volumes, spirometry, diffusion capacity (D L , CO ), and maximal inspiratory (PI MAX ) and expiratory (PE MAX ) pressures. Ventilatory constraints, including end-expiratory lung volume, expiratory flow limitation, and utilization of ventilatory capacity, were assessed during an incremental cycling test. Swimmers (n = 11) and controls (n = 10) were of similar age, size, and sexual maturity (P > 0.05). However, swimmers compared to controls had a greater total lung capacity (PRE 4.73 ± 0.73 vs. 3.93 ± 0.46, POST 5.08 ± 0.68 vs. 4.19 ± 0.64 L; P < 0.01), peak expiratory flow (PRE 6.48 ± 0.92 vs. 5.70 ± 0.86, POST 6.97 ± 0.84 vs. 6.00 ± 0.77 L·s -1 ; P = 0.03), and PE MAX (P < 0.001). Although D L , CO was greater in swimmers (P = 0.01), differences were attenuated when expressed relative to alveolar volume (PRE 5.14 ± 0.60 vs. 5.44 ± 0.44, POST 4.91 ± 0.56 vs. 5.16 ± 0.38 mL min -1  mmHg -1  L -1 ; P = 0.20). The groups achieved a similar maximal oxygen uptake (P = 0.32), and ventilatory constraints experienced were not different (P > 0.05). Changes over time were not different between groups (P > 0.05). At the initial measurement, pubertal female swimmers had greater lung size, expiratory flows, and indices of respiratory muscle strength, but similar ventilatory constraints while cycling. One competitive swimming season did not further accentuate this enhanced lung size and function or alter ventilatory mechanics, suggesting that competitive swimming during puberty did not affect lung growth., (© 2018 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of The Physiological Society and the American Physiological Society.)

Background: Despite the health benefits of regular physical activity, across the globe older adults represent the least active section of society., Purpose: The GrOup-based physical Activity for oLder adults (GOAL) trial was a three-arm parallel randomized controlled trial (RCT) that was designed to test the efficacy of two group-based exercise programs for older adults, informed by self-categorization theory (SCT), in comparison to a standard group-based exercise program., Methods: RCT conducted in Greater Vancouver, Canada, enrolled 627 older adults (Mage = 71.57 years, SD = 5.41; 71.0% female). Participants were randomized to similar age same gender (SASG), similar age mixed gender (SAMG), or 'standard' mixed age mixed gender (MAMG) exercise group conditions. In addition to group composition, the intervention programs operationalized principles from SCT designed to foster a sense of social connectedness among participants. The primary outcome of the trial was exercise adherence behavior over 12 and 24 weeks., Results: Analyses of variance revealed that older adults randomized to the SAMG (12-weeks d = .51, p < .001; 24-weeks d = .47, p < .001) and SASG (12-weeks d = .28, p = .012; 24-weeks d = .29, p = .016) conditions adhered to a greater extent than those in the MAMG comparison condition. There were no significant differences between the SAMG and SASG conditions., Conclusions: The results provide support for the efficacy of group-based physical activity programs informed by SCT. Furthermore, the results suggest that community group-based exercise programs should attempt to engage in age-targeting but not necessarily gender-targeting among older adults. (PsycINFO Database Record, ((c) 2018 APA, all rights reserved).)

There are known sex differences in blood pressure regulation. The differences are related to ovarian hormones that influence β-adrenergic receptors and the transduction of muscle sympathetic nerve activity. Oral contraceptives (OC) modulate the ovarian hormonal profile in women and therefore may alter the cardiovascular response. We questioned if OC would alter the absolute pressor response to static exercise and influence the day-to-day variability of the response. Healthy men (n = 11) and women (n = 19) completed a familiarization day and 2 experimental testing days. Women were divided into those taking (W-OC, n = 10) and not taking (W-NC, n = 9) OC. Each experimental testing day involved isometric handgripping exercise, at 30% of maximal force, followed by circulatory occlusion to isolate the metaboreflex. Experimental days in men were 7-14 days apart. The first experimental testing in W-OC occurred 2-7 days after the start of the active phase of their OC. Women not taking OC were tested during the early and late follicular phase of the menstrual cycle as determined by commercial ovulation monitor. The increase in mean arterial pressure (MAP) during exercise was significantly lower in W-NC (95 ± 4 mm Hg) compared with men (114 ± 4 mm Hg) and W-OC (111 ± 3 mm Hg) (P < 0.05), with the differences preserved during circulatory occlusion. The rise in MAP was significantly correlated between the 2 testing days in men (r = 0.72, P < 0.01) and W-OC (r = 0.77, P < 0.05), but not in W-NC (r = 0.17, P = 0.67), indicating greater day-to-day variation in W-NC. In conclusion, OC modulate the exercise pressor response in women and minimize day-to-day variability in the exercise metaboreflex.

We examined the effects of age, sex, and their interaction on mechanical ventilatory constraint and dyspnea during exercise in 22 older (age = 68 ± 1 yr; n = 12 women) and 22 younger (age = 25 ± 1 y, n = 11 women) subjects. During submaximal exercise, older subjects had higher end-inspiratory (EILV) and end-expiratory (EELV) lung volumes than younger subjects (both P < 0.05). During maximal exercise, older subjects had similar EILV ( P > 0.05) but higher EELV than younger subjects ( P < 0.05). No sex differences in EILV or EELV were observed. We noted that women had a higher work of breathing (W b ) for a given minute ventilation (V̇e) ≥65 l/min than men ( P < 0.05) and older subjects had a higher W b for a given V̇e ≥60 l/min ( P < 0.05). No sex or age differences in W b were present at any submaximal relative V̇e. At absolute exercise intensities, older women experienced expiratory flow limitation (EFL) more frequently than older men ( P < 0.05), and older subjects were more likely to experience EFL than younger subjects ( P < 0.05). At relative exercise intensities, women and older individuals experienced EFL more frequently than men and younger individuals, respectively (both P < 0.05). There were significant effects of age, sex, and their interaction on dyspnea intensity during exercise at absolute, but not relative, intensities (all P < 0.05). Across subjects, dyspnea at 80 W was significantly correlated with indexes of mechanical ventilatory constraint (all P < 0.05). Collectively, our findings suggest age and sex have significant impacts on W b , operating lung volumes, EFL, and dyspnea during exercise. Moreover, it appears that mechanical ventilatory constraint may partially explain sex differences in exertional dyspnea in older individuals. NEW & NOTEWORTHY We found that age and sex have a significant effect on mechanical ventilatory constraint and the perception of dyspnea during exercise. We also observed that the perception of exertional dyspnea is associated with indexes of mechanical ventilatory constraint. Collectively, our results suggest that the combined influences of age and biological sex on mechanical ventilatory constraint during exercise contributes, in part, to the increased perception of dyspnea during exercise in older women.

There is evidence suggesting diaphragmatic fatigue (DF) occurs relatively early during high-intensity exercise; however, studies investigating the temporal characteristics of exercise-induced DF are limited by incongruent methodology. Eight healthy adult males (25 ± 5 yr) performed a maximal incremental exercise test on a cycle ergometer on day 1. A constant-load time-to-exhaustion (TTE) exercise test was conducted on day 2 at 60% delta between the calculated gas exchange threshold and peak work rate. Two additional constant-load exercise tests were performed at the same intensity on days 3 and 4 in a random order to either 50 or 75% TTE. DF was assessed on days 2, 3, and 4 by measuring transdiaphragmatic twitch pressure (P di,tw ) in response to cervical magnetic stimulation. DF was present after 75 and 100% TTE (≥20% decrease in P di,tw ). The magnitude of fatigue was 15.5 ± 5.7%, 23.6 ± 6.4%, and 35.0 ± 12.1% at 50, 75, and 100% TTE, respectively. Significant differences were found between 100 to 75 and 50% TTE (both P < 0.01), and 75 to 50% TTE ( P < 0.01). There was a significant relationship between the magnitude of fatigue and cumulative diaphragm force output ( r = 0.785; P < 0.001). Ventilation, the mechanical work of breathing (WOB), and pressure-time products were not different between trials ( P > 0.05). Our data indicate that exercise-induced DF presents a relatively late onset and is proportional to the cumulative WOB; thus the ability of the diaphragm to generate pressure progressively declines throughout exercise. NEW & NOTEWORTHY The notion that diaphragmatic fatigue (DF) occurs relatively early during exercise is equivocal. Our results indicate that DF occurs during high-intensity endurance exercise in healthy men and its magnitude is strongly related to the amount of pressure and work generated by respiratory muscles. Thus we conclude that the work of breathing is the major determinant of exercise-induced DF.

New Findings: What is the central question of this study? Adult survivors of preterm birth without (PRE) and with bronchopulmonary dysplasia (BPD) have airflow obstruction at rest and significant mechanical ventilatory constraints during exercise compared with those born at full term (CON). Do PRE/BPD have smaller airways, indexed via the dysanapsis ratio, than CON? What is the main finding and its importance? The dysanapsis ratio was significantly smaller in BPD and PRE compared with CON, with BPD having the smallest dysanapsis ratio. These data suggest that airflow obstruction in PRE and BPD might be because of smaller airways than CON. Adult survivors of very preterm birth (≤32 weeks gestational age) without (PRE) and with bronchopulmonary dysplasia (BPD) have obstructive lung disease as evidenced by reduced expiratory airflow at rest and have significant mechanical ventilatory constraints during exercise. Airflow obstruction, in any conditions, could be attributable to several factors, including small airways. PRE and/or BPD could have smaller airways than their counterparts born at full term (CON) owing to a greater degree of dysanaptic airway development during the pre- and/or postnatal period. Thus, the purpose of the present study was to compare the dysanapsis ratio (DR), as an index of airway size, between PRE, BPD and CON. To do so, we calculated DR in PRE (n = 21), BPD (n = 14) and CON (n = 34) individuals and examined flow-volume loops at rest and during submaximal exercise. The DR, using multiple estimates of static recoil pressure, was significantly smaller in PRE and BPD (0.16 ± 0.05 and 0.10 ± 0.03 a.u.) compared with CON (0.22 ± 0.04 a.u.; both P < 0.001) and smallest in BPD (P < 0.001). The DR was significantly correlated with peak expiratory airflow at rest (r = 0.42; P < 0.001) and the extent of expiratory flow limitation during exercise (r = 0.60; P < 0.001). Our findings suggest that PRE/BPD might have anatomically smaller airways than CON, which might help to explain their lower expiratory airflow rate at rest and during exercise and further our understanding of the consequences of preterm birth and neonatal O 2 therapy., (© 2017 The Authors. Experimental Physiology © 2017 The Physiological Society.)

Our understanding of the mechanisms of dyspnoea in fibrotic interstitial lung disease (ILD) is incomplete. The aims of this study were two-fold: 1) to determine whether dyspnoea intensity is better predicted by neural respiratory drive (NRD) or neuromechanical uncoupling (NMU) of the respiratory system in fibrotic ILD, and 2) to examine the effect of breathing 60% oxygen on NRD, NMU and dyspnoea ratings.Fourteen patients with fibrotic ILD were included. Visit 1 comprised a familiarisation incremental cycle exercise test, Visit 2 comprised a normoxic incremental cycling test to address Aim 1, and Visits 3 and 4 consisted of constant-load cycling while breathing room air or 60% oxygen to address Aim 2. Diaphragmatic electromyography (EMGdi) was used as a surrogate of NRD. NMU was calculated as the ratio between EMGdi (%max) and tidal volume (%vital capacity).On adjusted analysis, NMU and its constituents were all significantly associated with dyspnoea ratings during incremental cycling, with EMGdi having the strongest correlation. The between-treatment change in dyspnoea ratings during constant load cycling was only correlated with change in exercise endurance time and NMU.Dyspnoea more strongly reflected the level of EMGdi than NMU in fibrotic ILD. However, the improvement in dyspnoea with 60% oxygen was better predicted by improvements in NMU., Competing Interests: Conflict of interest: Disclosures can be found alongside this article at erj.ersjournals.com, (Copyright ©ERS 2018.)

Cerebral blood flow (CBF) is regulated to secure brain O 2 delivery while simultaneously avoiding hyperperfusion; however, both requisites may conflict during sprint exercise. To determine whether brain O 2 delivery or CBF is prioritized, young men performed sprint exercise in normoxia and hypoxia (P I O 2  = 73 mmHg). During the sprints, cardiac output increased to ∼22 L min -1 , mean arterial pressure to ∼131 mmHg and peak systolic blood pressure ranged between 200 and 304 mmHg. Middle-cerebral artery velocity (MCAv) increased to peak values (∼16%) after 7.5 s and decreased to pre-exercise values towards the end of the sprint. When the sprints in normoxia were preceded by a reduced P ET CO 2 , CBF and frontal lobe oxygenation decreased in parallel ( r = 0.93, P < 0.01). In hypoxia, MCAv was increased by 25%, due to a 26% greater vascular conductance, despite 4-6 mmHg lower PaCO 2 in hypoxia than normoxia. This vasodilation fully accounted for the 22 % lower CaO 2 in hypoxia, leading to a similar brain O 2 delivery during the sprints regardless of P I O 2 . In conclusion, when a conflict exists between preserving brain O 2 delivery or restraining CBF to avoid potential damage by an elevated perfusion pressure, the priority is given to brain O 2 delivery.

Background: Reduced heart rate variability (HRV), a marker of autonomic system dysfunction, has been reported in patients with chronic obstructive pulmonary disease (COPD). Yet, limited data exists on the reliability of HRV measurement in this population. Here we investigated the reliability of short-term HRV measurement performed during spontaneous breathing in patients with COPD., Methods: Thirteen individuals (8 males) with moderate-to-severe COPD (FEV 1 46±16% predicted; FEV 1 /FVC 49±13) underwent standard time and frequency domain HRV measurements derived from 5-minute electrocardiograms collected on two separate days using a SphygmoCor device. Absolute and relative reliability was assessed by a number of coefficients including within-subject random variation, systematic change in the mean, and retest correlations., Results: Within-subject coefficients of variation (CV) ranged from 4.3% to 193.4%. The intraclass correlation coefficients (ICCs) ranged from 0.72 to 0.93 for parameters related to overall HRV, and from 0.57 to 0.59 for those related to parasympathetic tone in both time and frequency domains. Mean heart rate was the only parameter that showed excellent absolute and relative reliability (CV=4.3%, ICC=0.93)., Conclusion: The HRV measurements showed overall moderate-to-substantial reliability during spontaneous breathing in COPD population. Our findings support the use of HRV parameters for diagnosis and cardiac risk assessment, but only mean heart rate can be used reliably for monitoring changes in autonomic status following rehabilitation intervention in this population., (Copyright © 2017 Sociedade Portuguesa de Pneumologia. Published by Elsevier España, S.L.U. All rights reserved.)

New Findings: What is the central question of this study? Does manipulation of the work of breathing during high-intensity exercise alter respiratory and locomotor muscle blood flow? What is the main finding and its importance? We found that when the work of breathing was reduced during exercise, respiratory muscle blood flow decreased, while locomotor muscle blood flow increased. Conversely, when the work of breathing was increased, respiratory muscle blood flow increased, while locomotor muscle blood flow decreased. Our findings support the theory of a competitive relationship between locomotor and respiratory muscles during intense exercise. Manipulation of the work of breathing (WOB) during near-maximal exercise influences leg blood flow, but the effects on respiratory muscle blood flow are equivocal. We sought to assess leg and respiratory muscle blood flow simultaneously during intense exercise while manipulating WOB. Our hypotheses were as follows: (i) increasing the WOB would increase respiratory muscle blood flow and decrease leg blood flow; and (ii) decreasing the WOB would decrease respiratory muscle blood flow and increase leg blood flow. Eight healthy subjects (n = 5 men, n = 3 women) performed a maximal cycle test (day 1) and a series of constant-load exercise trials at 90% of peak work rate (day 2). On day 2, WOB was assessed with oesophageal balloon catheters and was increased (via resistors), decreased (via proportional assist ventilation) or unchanged (control) during the trials. Blood flow was assessed using near-infrared spectroscopy optodes placed over quadriceps and the sternocleidomastoid muscles, coupled with a venous Indocyanine Green dye injection. Changes in WOB were significantly and positively related to changes in respiratory muscle blood flow (r = 0.73), whereby increasing the WOB increased blood flow. Conversely, changes in WOB were significantly and inversely related to changes in locomotor blood flow (r = 0.57), whereby decreasing the WOB increased locomotor blood flow. Oxygen uptake was not different during the control and resistor trials (3.8 ± 0.9 versus 3.7 ± 0.8 l min -1 , P > 0.05), but was lower on the proportional assist ventilator trial (3.4 ± 0.7 l min -1 , P < 0.05) compared with control. Our findings support the concept that respiratory muscle work significantly influences the distribution of blood flow to both respiratory and locomotor muscles., (© 2017 The Authors. Experimental Physiology © 2017 The Physiological Society.)