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Recent investigations of middle cerebral artery blood velocity (MCAv) kinetics at the onset of exercise have not accounted for potential dynamic changes in arterial partial pressure of carbon dioxide (P a CO 2 ) during the transient phase of exercise transitions when modeling MCAv kinetics, despite P a CO 2 having known effects on cerebrovascular tone. The purpose of our study was to determine the independent effects of mean arterial pressure (MAP) and estimated P a CO 2 (eP a CO 2 ) on mean MCAv during repeated moderate-intensity exercise transitions. We hypothesized that cerebral autoregulation would minimize the effect of sustained exercise-induced changes in MAP on mean MCAv, and that dynamic changes in eP a CO 2 would contribute to changes in mean MCAv. Eighteen young healthy adults (7 women, age: 28±5 yr) performed three exercise transitions from 25 W to 90% of the ventilatory threshold in sequence with 5 min stages. Mean MCAv increased ( p <0.001) from 25 W (60.5±14.0 cmꞏs -1 ) to 90% of ventilatory threshold (68.8±15.1 cmꞏs -1 ). MAP MCA (Δ = 14±8 mmHg, p <0.001) and eP a CO 2 (Δ = 2.7±1.8 mmHg, p <0.001) also increased with exercise intensity. Autoregressive moving average analysis isolated the independent effects of dynamic changes in MAP MCA and eP a CO 2 on MCAv, with low prediction error (mean absolute error = 1.12±0.25 cmꞏs -1 ). Calculated steady-states of the ARMA step responses were 0.13±0.15 cmꞏs -1 ꞏmmHg -1 for Δmean MCAv/ΔMAP MCA and 1.95±0.83 cmꞏs -1 ꞏmmHg -1 for Δmean MCAv/ΔeP a CO 2 . These data demonstrate that the combination of dynamic changes MAP and eP a CO 2 largely explain the MCAv response during transitions in exercise intensity.

Reduced orthostatic tolerance is common following periods of bed rest that are associated with illness or surgery, putting individuals at higher risk for syncope and falls following hospitalization. Following menopause, mechanisms of female cardiovascular regulation change, which may be associated with sex-specific responses to orthostatic stress following bed rest. The purpose of our experiment was to investigate sex differences between healthy postmenopausal women and similar-age men (age: 55-65 yr) for their orthostatic tolerance and cerebrovascular responses to standing following bed rest. Twenty-two late-middle-aged adults (11 women) completed 14 days of head-down bed rest, with half of the participants being randomized into an exercise group that performed high-intensity exercise during bed rest. Supine-to-stand tests were performed before and ∼5 h after bed rest. Women had lower orthostatic tolerance than men after bed rest (bed rest × sex interaction: P = 0.004), without a protective effect of daily exercise. Both men and women were mildly hypocapnic while supine (main effect: P = 0.019) following bed rest and had lower middle cerebral artery blood velocity (MCAv) nadirs upon standing (main effect: P = 0.027). During the third minute of standing, both men and women had lower end-tidal Pco 2 (main effect: P < 0.001) and MCAv (main effect: P = 0.002) after bed rest, but only men had increased cerebrovascular resistance index (bed rest × sex interaction: P = 0.005) and only women were hypotensive (bed rest × sex interaction: P = 0.020) compared with pre-bed rest. Accordingly, lower MCAv of postmenopausal women and men while standing after bed rest was mediated by different factors. NEW & NOTEWORTHY Postmenopausal women had lower orthostatic tolerance than similar-age men while standing post-bed rest. Both sexes exhibited lower cerebral blood velocity nadirs upon standing; however, sex-specific interactions of the determinants of cerebral perfusion (i.e., Pco 2 , cerebrovascular resistance index, and arterial pressure) were observed during prolonged standing after bed rest. These results indicate that postmenopausal women and men have different factors underlying reduced cerebral perfusion while standing after bed rest.

The human heart is very adaptable, with chamber size, wall thickness and ventricular stiffness all modified by periods of inactivity or exercise training. Herein, we summarize the cardiac adaptations induced by changes in physical activity, ranging from bed rest and spaceflight to endurance exercise training, while also highlighting how the ageing process (a long-term model of inactivity) affects cardiac plasticity. Severe inactivity during bed rest or spaceflight leads to cardiac atrophy and ventriculo-vascular stiffening. Conversely, endurance training induces eccentric hypertrophy and enhances ventricular compliance, and can be used as an effective countermeasure to prevent adverse cardiac changes during prolonged periods of bed rest or spaceflight. With sedentary ageing, the heart undergoes concentric remodelling and irreversibly stiffens at advanced age. Specifically, older adults who initiate endurance training later in life are unable to improve ventricular compliance and diastolic function, suggesting reduced cardiac plasticity with advanced age; however, lifelong exercise training prevents age-associated cardiac remodelling and maintains cardiac compliance of older adults at a level similar to those of younger healthy individuals. Nevertheless, there are still many knowledge gaps related to cardiac remodelling and changes in cardiac function induced by bed rest, exercise training and spaceflight, as well as how these different stimuli may interact with advancing age. Future studies should focus on understanding what factors (sex, age, heritability, etc.) may influence the heart's responsiveness to training or deconditioning, as well as understanding the long-term cardiac consequences of spaceflight beyond low-Earth orbit with the added stimulus of galactic cosmic radiation., (© 2024 The Author(s). The Journal of Physiology published by John Wiley & Sons Ltd on behalf of The Physiological Society.)

Bedrest as an experimental paradigm or as an in-patient stay for medical reasons has negative consequences for cardiovascular health. The effects of severe inactivity parallel many of the changes experienced with natural aging but over a much shorter duration. Cardiac function is reduced, arteries stiffen, neural reflex responses are impaired, and metabolic and oxidative stress responses impose burden on the heart and vascular systems. The effect of these changes is revealed in studies of integrative function. Aerobic fitness progressively deteriorates with bedrest and tolerance of upright posture is rapidly impaired. In this review we consider the similarities of aging and bedrest-induced cardiovascular deconditioning. We concur with many recent clinical recommendations that early and regular mobility with upright posture will reduce likelihood of hospital-associated disability related to bedrest., (Copyright © 2024 Canadian Cardiovascular Society. Published by Elsevier Inc. All rights reserved.)

Cardiovascular deconditioning and altered baroreflexes predispose returning astronauts to Orthostatic Intolerance. We assessed 7 astronauts (1 female) before and following long-duration spaceflight (146 ± 43 days) with minimal upright posture prior to testing. We applied lower body negative pressure (LBNP) of up to - 30 mmHg to supine astronauts instrumented for continual synchronous measurements of cardiovascular variables, and intermittent imaging the Portal Vein (PV) and Inferior Vena Cava (IVC). During supine rest without LBNP, postflight elevations to total peripheral resistance (TPR; 15.8 ± 4.6 vs. 20.8 ± 7.1 mmHg min/l, p < 0.05) and reductions in stroke volume (SV; 104.4 ± 16.7 vs. 87.4 ± 11.5 ml, p < 0.05) were unaccompanied by changes to heart rate (HR) or estimated central venous pressure (CVP). Small increases to systolic blood pressure (SBP) and diastolic blood pressure (DBP) were not statistically significant. Autoregressive moving average modelling (ARMA) during LBNP did not identify differences to either arterial (DBP → TPR and SBP → HR) or cardiopulmonary (CVP → TPR) baroreflexes consistent with intact cardiovascular control. On the other hand, IVC and PV diameter-CVP relationships during LBNP revealed smaller diameter for a given CVP postflight consistent with altered postflight venous wall dynamics., (© 2024. The Author(s).)

Upright posture challenges the cerebrovascular system, leading to changes in middle cerebral artery velocity (MCAv) dynamics which are less evident at supine rest. Chronic alterations in MCAv have been linked to hypoperfusion states and the effect that this may have on cognition remains unclear. This study aimed to determine if MCAv and oscillatory metrics of MCAv (ex. pulsatility index, PI) during upright posture are i) associated with cognitive function and gait speed (GS) to a greater extent than during supine rest, and ii) are different between sexes. Beat-by-beat MCAv (transcranial Doppler ultrasound) and mean arterial pressure (MAP, plethysmography) were averaged for 30-seconds during supine-rest through a transition to standing for 53 participants (73±6yrs, 17 females). While controlling for age, multiple linear regressions predicting MoCA scores and GS from age, supine MCAv metrics, and standing MCAv metrics, were completed. Simple linear regressions predicting Montreal Cognitive Assessment (MoCA) score and GS from MCAv metrics were performed separately for females and males. Significance was set to p <0.05. Lower standing diastolic MCAv was a significant ( p  = 0.017) predictor of lower MoCA scores in participants with mild cognitive impairment, and this relationship only remained significant for males. Lower standing PI was associated with slower GS ( p  = 0.027, r =-0.306) in both sexes. Our results indicate a relationship between blunted MCAv and altered oscillatory flow profiles during standing, with lower MoCA scores and GS. These relationships were not observed in the supine position, indicating a unique relationship between standing measures of MCAv with cognitive and physical functions., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Author(s).)

Background: Insufficient cardiac output in individuals with heart failure (HF) limits daily functioning and reduces quality of life. Although lower cerebral perfusion, secondary to limitations in cardiac output, has been observed during moderate-intensity efforts, individuals with HF also may be at risk for lower perfusion during even low-intensity ambulatory activities., Methods: We determined whether HF is associated with an altered cerebrovascular response to low-intensity activities representative of typical challenges of daily living. In this study, we monitored central hemodynamics and middle cerebral artery blood velocity (MCAv) and cerebral tissue oxygenation (near-infrared spectroscopy) in 10 individuals with HF (aged 78 ± 4 years; left ventricular ejection fraction 20%-61%) and 13 similar-aged controls (79 ± 8 years; 52%-73%) during 3 randomized transitions, as follows: (i) supine-to-standing; (ii) sitting-to-slow-paced over-ground walking; and (iii) sitting-to-normal-paced over-ground walking., Results: Throughout supine, sitting, standing, and both walking conditions, individuals with HF had lower cardiac index and cerebral tissue oxygenation than controls ( P < 0.05), and MCAv was lower across the range of blood pressure in HF patients ( P  = 0.051) and during walking only ( P  = 0.011). Individuals with HF had an attenuated increase in stroke volume index and cardiac index during normal-paced walking, compared to controls ( P < 0.01)., Conclusions: The indices of cerebral perfusion from MCAv and cerebral oxygenation were lower during ambulatory activities in individuals with HF; however, relationships between MCAv and blood pressure were not different between those with HF and controls, indicating no difference in static cerebral autoregulation., (© 2023 The Authors.)

Prolonged bedrest provokes orthostatic hypotension and intolerance of upright posture. Limited data are available on the cardiovascular responses of older adults to head-up tilt following bedrest, with no studies examining the potential benefits of exercise to mitigate intolerance in this age group. This randomized controlled trial of head-down bedrest (HDBR) in 55- to 65-yr-old men and women investigated if exercise could avert post-HDBR orthostatic intolerance. Twenty-two healthy older adults (11 female) underwent a strict 14-day HDBR and were assigned to either an exercise (EX) or control (CON) group. The exercise intervention included high-intensity, aerobic, and resistance exercises. Head-up tilt-testing to a maximum of 15 minutes was performed at baseline (Pre-Bedrest) and immediately after HDBR (R1), as well as 6 days (R6) and 4 weeks (R4wk) later. At Pre-Bedrest, three participants did not complete the full 15 minutes of tilt. At R1, 18 did not finish, with no difference in tilt end time between CON (422 ± 287 s) and EX (409 ± 346 s). No differences between CON and EX were observed at R6 or R4wk. At R1, just 1 participant self-terminated the test with symptoms, while 12 others reported symptoms only after physiological test termination criteria were reached. Finishers on R1 protected arterial pressure with higher total peripheral resistance relative to Pre-Bedrest. Cerebral blood velocity decreased linearly with reductions in arterial pressure, end-tidal CO 2 , and cardiac output. High-intensity interval exercise did not benefit post-HDBR orthostatic tolerance in older adults. Multiple factors were associated with the reduction in cerebral blood velocity leading to intolerance.

Nonintrusive estimation of oxygen uptake (V̇o 2 ) is possible with wearable sensor technology and artificial intelligence. V̇o 2 kinetics have been accurately predicted during moderate exercise using easy-to-obtain sensor inputs. However, V̇o 2 prediction algorithms for higher-intensity exercise with inherent nonlinearities are still being refined. The purpose of this investigation was to test if a machine learning model can accurately predict dynamic V̇o 2 across exercise intensities, including slower V̇O 2 kinetics normally observed during heavy- compared with moderate-intensity exercise. Fifteen young healthy adults (seven females; peak V̇o 2 : 42 ± 5 mL·min -1 ·kg -1 ) performed three different pseudorandom binary sequence (PRBS) exercise tests ranging in intensity from low-to-moderate, low-to-heavy, and ventilatory threshold-to-heavy work rates. A temporal convolutional network was trained to predict instantaneous V̇o 2 , with model inputs including heart rate, percent heart rate reserve, estimated minute ventilation, breathing frequency, and work rate. Frequency domain analyses between V̇o 2 and work rate were used to evaluate measured and predicted V̇o 2 kinetics. Predicted V̇o 2 had low bias (-0.017 L·min -1 , 95% limits of agreement: [-0.289, 0.254]), and was very strongly correlated ( r rm  = 0.974, P < 0.001) with the measured V̇o 2 . The extracted indicator of kinetics, mean normalized gain (MNG), was not different between predicted and measured V̇o 2 responses (main effect: P = 0.374, η p 2  = 0.01), and decreased with increasing exercise intensity (main effect: P < 0.001, η p 2  = 0.64). Predicted and measured V̇o 2 kinetics indicators were moderately correlated across repeated measurements (MNG: r rm  = 0.680, P < 0.001). Therefore, the temporal convolutional network accurately predicted slower V̇o 2 kinetics with increasing exercise intensity, enabling nonintrusive monitoring of cardiorespiratory dynamics across moderate- and heavy-exercise intensities. NEW & NOTEWORTHY Machine learning analysis of wearable sensor data with a sequential model, which utilized a receptive field of approximately 3 min to make instantaneous oxygen uptake estimations, accurately predicted oxygen uptake kinetics from moderate through to higher-intensity exercise. This innovation will enable nonintrusive cardiorespiratory monitoring over a wide range of exercise intensities encountered in vigorous training and competitive sports.

Human skeletal hemodynamics remain understudied. Neither assessments in weight-bearing bones during walking nor following periods of immobility exist, despite knowledge of altered nutrient-artery characteristics after short-duration unloading in rodents. We studied 12 older adults (8 females, aged 59 ± 3 years) who participated in ambulatory near-infrared spectroscopy (NIRS) assessments of tibial hemodynamics before (PRE) and after (POST) 14 days of head-down bed rest (HDBR), with most performing daily resistance and aerobic exercise countermeasures during HDBR. Continual simultaneous NIRS recordings were acquired over the proximal anteromedial tibial prominence of the right lower leg and ipsilateral lateral head of the gastrocnemius muscle during supine rest, walking, and standing. During 10 minutes of walking, desaturation kinetics in the tibia were slower (time to 95% nadir values 125.4 ± 56.8 s versus 55.0 ± 30.1 s, p  = 0.0014). Tibial tissue saturation index (TSI) immediately fell (-9.9 ± 4.55) and did not completely recover by the end of 10 minutes of walking (-7.4 ± 6.7%, p  = 0.027). Upon standing, total hemoglobin (tHb) kinetics were faster in the tibia ( p  < 0.0001), whereas HDBR resulted in faster oxygenated hemoglogin (O 2 Hb) kinetics in both tissues ( p  = 0.039). After the walk-to-stand transition, changes in O 2 Hb ( p  = 0.0022) and tHb ( p  = 0.0047) were attenuated in the tibia alone after bed rest. Comparisons of NIRS-derived variables during ambulation and changes in posture revealed potentially deleterious adaptations of feed vessels after HDBR. We identify important and novel tibial hemodynamics in humans during ambulation before and after bed rest, necessitating further investigation. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research., (© 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.)

Introduction: Spaceflight simulation studies like confinement in small volume habitat with limited physical activity have reported even after 60 days an abnormal arterial wall adaptation with increase thickness or stiffness. The purpose of the current study was to determine the effects on blood vessel and organ structure of 40 days of isolation in a huge habitat with intensive physical activity. Method: Data were collected from 14 individuals (7 male) who isolated in a cavern for 40-days while performing normal daily activities without time references. Ultrasound assessments were performed pre- and post-isolation using a teleoperated system with eight different acoustic windows to obtain 19 measurements on 12 different organ/vascular structures which included the common carotid artery, femoral artery, tibial artery, jugular vein, portal vein, bile duct, kidney, pancreas, abdominal aorta, cervical and lumbar vertebral distance, and Achilles tendon. Results: Common carotid artery measures, including the intima media thickness, stiffness index, and the index of reflectivity measured from the radiofrequency signal, were not changed with isolation. Similarly, no differences were found for femoral artery measurements or measurements of any of the other organs/vessels assessed. There were no sex differences for any of the assessments. Discussion: Results from this study indicate a lack of physiological effects of 40-days of isolation in a cavern, contrary to what observed in previous 60 days confinement. This suggests a potential protective effect of sustained physical activity, or reduced environmental stress inside the huge volume of the confined facility., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Arbeille, Zuj, Besnard, Mauvieux, Hingrand, Delaunay, Hughson and Clot.)

Cardiorespiratory fitness declines with age and this decline can be accelerated by inactivity and bed rest. Recovery of fitness is possible, but the timeline in 55- to 65-yr-old adults is unknown. Furthermore, the effectiveness of exercise to prevent deconditioning during bed rest is unexplored in this age group. Twenty-two adults (11 women, 59 ± 3 yr) completed 2 wk of strict 6° head-down bed rest (HDBR). Half of the participants performed approximately 1 h of daily exercises, including high-intensity interval cycling, aerobic cycling, and upper- and lower-body resistance training, whereas control participants were inactive. Step-incremental cycling tests to exhaustion were conducted pre-HDBR and at three times during the recovery phase ( day 1 or 2 , day 6 , and 4 wk) to assess peak oxygen uptake (V̇o 2 ). Peak V̇o 2 was reduced in the control group throughout the first 6 days of recovery, but did return to pre-HDBR levels by the 4-wk recovery time point (interaction: P = 0.002). In the exercise group, peak V̇o 2 was not different at any time point during recovery from pre-HDBR. Ventilatory threshold V̇o 2 (interaction: P = 0.002) and heart rate at 15 W (interaction: P = 0.055) mirrored the changes in peak V̇o 2 in each respective group. Overall, this study showed that approximately 1 h of daily exercise effectively protected 55- to 65-yr-old adults' cardiorespiratory fitness during 2 wk of HDBR. HDBR without exercise countermeasures caused substantial reductions in cardiorespiratory fitness, but fitness recovered within 4 wk of resuming daily activities. These findings highlight the importance of physical activity in late middle-age adults. NEW & NOTEWORTHY We report the complete time-course of cardiorespiratory fitness recovery back to baseline levels following 2 wk of head-down bed rest in 55- to 65-yr-old adults and found that multimodal training, consisting of high-intensity interval, aerobic and resistive exercises, performed throughout the 2 wk of head-down bed rest prevented reductions in cardiorespiratory fitness.

New Findings: What is the central question of this study? Is the attenuation of the respiratory muscle metaboreflex preserved after detraining? What is the main finding and its importance? Inspiratory muscle training increased respiratory muscle strength and attenuated the respiratory muscle metaboreflex as evident by lower heart rate and blood pressure. After 5 weeks of no inspiratory muscle training (detraining), respiratory muscle strength was still elevated and the metaboreflex was still attenuated. The benefits of inspiratory muscle training persist after cessation of training, and attenuation of the respiratory metaboreflex follows changes in respiratory muscle strength., Abstract: Respiratory muscle training (RMT) improves respiratory muscle (RM) strength and attenuates the RM metaboreflex. However, the time course of muscle function loss after the absence of training or 'detraining' is less known and some evidence suggest the respiratory muscles atrophy faster than other muscles. We sought to determine the RM metaboreflex in response to 5 weeks of RMT and 5 weeks of detraining. An experimental group (2F, 6M; 26 ± 4years) completed 5 weeks of RMT and tibialis anterior (TA) training (each 5 days/week at 50% of maximal inspiratory pressure (MIP) and 50% maximal isometric force, respectively) followed by 5 weeks of no training (detraining) while a control group (1F, 7M; 24 ± 1years) underwent no intervention. Prior to training (PRE), post-training (POST) and post-detraining (DETR), all participants underwent a loaded breathing task (LBT) to failure (60% MIP) while heart rate and mean arterial blood pressure (MAP) were measured. Five weeks of training increased RM (18 ± 9%, P < 0.001) and TA (+34 ± 19%, P < 0.001) strength and both remained elevated after 5 weeks of detraining (MIP-POST vs. MIP-DETR: 154 ± 31 vs. 153 ± 28 cmH2O, respectively, P = 0.853; TA-POST vs. TA-DETR: 86 ± 19 vs. 85 ± 16 N, respectively, P = 0.982). However, the rise in MAP during LBT was attenuated POST (-11 ± 17%, P = 0.003) and DETR (-9 ± 9%, P = 0.007) during the iso-time LBT. The control group had no change in MIP (P = 0.33), TA strength (P = 0.385), or iso-time MAP (P = 0.867) during LBT across all time points. In conclusion, RM and TA have similar temporal strength gains and the attenuation of the respiratory muscle metaboreflex remains after 5 weeks of detraining., (© 2022 The Authors. Experimental Physiology published by John Wiley & Sons Ltd on behalf of The Physiological Society.)

Hypercapnic chemosensitivity is the response to the increased partial pressure of carbon dioxide and results from central and peripheral chemosensor stimulation. The hypercapnic chemosensitivity of the peripheral chemoreceptors is potentially impacted by acute exercise, aerobic fitness, and sex. We sought to determine the peripheral chemoresponse to transient hypercapnia at rest and during exercise in males and females of various fitness. We hypothesized that 1 ) higher fitness participants would have lower hypercapnic chemosensitivity compared with those with lower fitness and 2 ) males would have a higher chemoresponse than females. Forty healthy participants (20 females) participated in one test day involving transient hypercapnic chemosensitivity testing and a maximal exercise test. Chemosensitivity testing involved two breaths of 10% CO 2 repeated five times (45 s to 1 min between repeats) at rest and the first two stages of a maximal exercise test. There was no significant difference between higher and lower aerobic fitness groups, (mean difference 0.23 ± 0.22 rest; -0.07 ± 0.04 stage 1; 0.11 ± 0.17 stage 2 L/mmHg·min) during each stage ( P = 0.472). However, we saw a significant increase in the hypercapnic response during stage 1 (0.98 ± 0.4 L/mmHg·min) compared with rest (0.79 ± 0.5 L/mmHg·min; P = 0.01). Finally, at 80 W, males had a higher chemoresponse compared with females, which persisted following body surface area correction (0.56 ± 0.2 vs. 0.42 ± 0.2 L/mmHg·min·m 2 , for females and males respectively ( P = 0.038). Our findings suggest that sex, unlike aerobic fitness, influences peripheral hypercapnic chemosensitivity and that context (i.e., rest vs. exercise) is an important consideration. NEW & NOTEWORTHY The hypercapnic chemoresponse to transient CO 2 showed an increase during acute physical activity; however, this response did not persist with further increases in intensity and was not different between participants of different aerobic fitness. Males and females show a differing response to CO 2 during exercise when compared with an iso-V̇co 2 . Our results suggest that adaptations that lead to increased aerobic fitness do not impact the hypercapnic ventilatory response but there is an effect of sex.

Objective: To develop and evaluate an accurate method for cuffless blood pressure (BP) estimation during moderate- and heavy-intensity exercise., Methods: Twelve participants performed three cycling exercises: a ramp-incremental exercise to exhaustion, and moderate and heavy pseudorandom binary sequence exercises on an electronically braked cycle ergometer over the course of 21 minutes. Subject-specific and population-based nonlinear autoregressive models with exogenous inputs (NARX) were compared with feedforward artificial neural network (ANN) models and pulse arrival time (PAT) models., Results: Population-based NARX models, (applying leave-one-subject-out cross-validation), performed better than the other models and showed good capability for estimating large changes in mean arterial pressure (MAP). The models were unable to track consistent decreases in BP during prolonged exercise caused by reduction in peripheral vascular resistance, since this information is apparently not encoded in the employed proxy physiological signals (electrocardiography and forehead PPG) used for BP estimation. Nevertheless, the population-based NARX model had an error standard deviation of 11.0 mmHg during the entire exercise window, which improved to 9.0 mmHg when the model was periodically calibrated every 7 minutes., Conclusion: Population-based NARX models can estimate BP during moderate- and heavy-intensity exercise but need periodic calibration to account for the change in vascular resistance during exertion., Significance: MAP can be continuously tracked during exercise using only wearable sensors, making monitoring exercise physiology more convenient and accessible.

Recent studies have reported a significant increase in common carotid artery (CCA) intima media thickness, wall stiffness and reflectivity to ultrasound, in astronauts, after six months of spaceflight. The hypothesis was that 4 days in dry immersion (subjects under bags of water) will be sufficient to change the CCA wall reflectivity to ultrasound similar to what observed after spaceflight. Such response would be quantified using the amplitude of the ultrasound signal returned to the probe by the target concerned. [coefficient of signal return (Rs)]. The Rs for anterior and posterior CCA wall, sternocleidomastoid muscle, intima layer and CCA lumen were calculated from the ultrasound radio frequency (RF) data displayed along each echographic line. After four days of DI, Rs increased in the CCA posterior wall (+15% +/- 10 from pre DI, p < 0.05), while no significant change was observed in the other targets. The observed increase in Rs with DI was approximately half compared to what was observed after six months of space flight (+34% +/- 14). This difference may be explained by dose response (dry immersion only four days in duration). As a marker of tissue-level physical changes, Rs provide complimentary information alongside previously observed CCA wall thickness and stiffness., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Arbeille, Greaves, Guillon and Hughson.)

Significance: The internal jugular veins (IJV) are critical cerebral venous drainage pathways that are affected by right heart function. Cardiovascular disease and microgravity can alter central venous pressure (CVP) and venous return, which may contribute to increased intracranial pressure and decreased cardiac output. Assessing jugular venous compliance may provide insight into cerebral drainage and right heart function, but monitoring changes in vessel volume is challenging., Aim: We investigated the feasibility of quantifying jugular venous compliance from jugular venous attenuation (JVA), a noncontact optical measurement of blood volume, along with CVP from antecubital vein cannulation., Approach: CVP was progressively increased through a guided graded Valsalva maneuver, increasing mouth pressure by 2 mmHg every 2 s until a maximum expiratory pressure of 20 mmHg. JVA was extracted from a 1-cm segment between the clavicle and midneck. The contralateral IJV cross-sectional area (CSA) was measured with ultrasound to validate changes in the vessel size. Compliance was calculated using both JVA and CSA between four-beat averages over the duration of the maneuver., Results: JVA and CSA were strongly correlated (median and interquartile range) over the Valsalva maneuver across participants (r = 0.986, [0.983, 0.987]). CVP more than doubled on average between baseline and peak strain (10.7 ± 4.4 vs. 25.8 ± 5.4 cmH2O; p < 0.01). JVA and CSA increased nonlinearly with CVP, and both JVA- and CSA-derived compliance decreased progressively from baseline to peak strain (49% and 56% median reduction, respectively), with no significant difference in compliance reduction between the two measures (Z = - 1.24, p = 0.21). Pressure-volume curves showed a logarithmic relationship in both CSA and JVA., Conclusions: Optical jugular vein assessment may provide new ways to assess jugular distention and cardiac function.

Physical activity was reduced during the COVID-19 pandemic, especially when lockdowns were mandated; however, little is known about the impact of these lifestyle changes on objective measures of cardiorespiratory fitness. To address this knowledge gap, we evaluated the cardiorespiratory fitness of 14 young healthy adults (4 women, age: 27 ± 6 yr) just before the pandemic and after ∼1 yr of public health measures being in place. During fitness assessments, participants performed submaximal pseudorandom cycling exercise to assess cardiorespiratory kinetics, and a 25 W·min -1 ramp-incremental cycling test to determine peak oxygen uptake (V̇o 2 ). Cluster analysis identified two subgroups of participants: those who had reduced peak V̇o 2 at the 1-yr follow-up (-0.50 ± 0.17 L·min -1 ) and those whose peak V̇o 2 was maintained (0.00 ± 0.10 L·min -1 ). Participants with reduced peak V̇o 2 also exhibited slower heart rate kinetics (interaction: P = 0.01), reduced peak O 2 pulse (interaction: P < 0.001), and lower peak work rate (interaction: P < 0.001) after 1 yr of the pandemic, whereas these variables were unchanged in the group of participants who maintained peak V̇o 2 . Regardless of changes in peak V̇o 2 , both subgroups of participants gained body mass (main effect: P = 0.002), which was negatively correlated with participants' level of self-reported physical activity level at the follow-up assessment (mass: ρ = -0.59, P = 0.03) These findings suggest that some young healthy individuals lost cardiorespiratory fitness during the pandemic, whereas others gained weight, but both changes could potentially increase the risk of adverse health outcomes and disease later in life if left unaddressed. NEW & NOTEWORTHY Some young healthy adults experienced cardiovascular deconditioning during the COVID-19 pandemic, with measurable reductions in cardiorespiratory fitness, whereas others experienced no change in fitness but gained body mass, which was related to self-reported physical activity during the pandemic.

Significant progress has been made in the development of countermeasures to attenuate the negative consequences of prolonged exposure to microgravity on astronauts' bodies. Deconditioning of several organ systems during flight includes losses to cardiorespiratory fitness, muscle mass, bone density and strength. Similar deconditioning also occurs during prolonged bedrest; any protracted time immobile or inactive, especially for unwell older adults (e.g., confined to hospital beds), can lead to similar detrimental health consequences. Due to limitations in physiological research in space, the six-degree head-down tilt bedrest protocol was developed as ground-based analogue to spaceflight. A variety of exercise countermeasures have been tested as interventions to limit detrimental changes and physiological deconditioning of the musculoskeletal and cardiovascular systems. The Canadian Institutes of Health Research and the Canadian Space Agency recently provided funding for research focused on Understanding the Health Impact of Inactivity to study the efficacy of exercise countermeasures in a 14-day randomized clinical trial of six-degree head-down tilt bedrest study in older adults aged 55-65 years old (BROA). Here we will describe the development of a multi-modality countermeasure protocol for the BROA campaign that includes upper- and lower-body resistance exercise and head-down tilt cycle ergometry (high-intensity interval and continuous aerobic exercise training). We provide reasoning for the choice of these modalities following review of the latest available information on exercise as a countermeasure for inactivity and spaceflight-related deconditioning. In summary, this paper sets out to review up-to-date exercise countermeasure research from spaceflight and head-down bedrest studies, whilst providing support for the proposed research countermeasure protocols developed for the bedrest study in older adults., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Hedge, Patterson, Mastrandrea, Sonjak, Hajj-Boutros, Faust, Morais and Hughson.)

Purpose: To determine how repeatable thoracoabdominal compartmental contributions to tidal volume (V T ) are across different intensities of exercise, and to examine if the pattern of breathing for a given minute ventilation (V̇ E ) is reproducible between constant-load and ramp exercise tests., Methods: Ten healthy adults (age: 27 ± 6 yr, peak oxygen uptake: 42 ± 5 mL min -1  kg -1 ) completed a 25 W·min -1 ramp cycling test to exhaustion and two repetitions of a step cycling test on separate days. V T , breathing rate (BR), and V̇ E were assessed using a bi-directional turbine, and thoracic and abdominal contributions to V T were measured using respiratory inductance plethysmography. Repeatability (step vs. step) and reproducibility (step vs. ramp) of responses were assessed using the intra-class correlation coefficient (ICC)., Results: The relative compartment contributions to V T during step exercise were highly repeatable for low (ICC = 0.87, p = 0.003), moderate (ICC = 0.89, p = 0.002) and heavy (ICC = 0.93, p = 0.001) exercise. Inter-individual differences in response to higher intensity exercise were observed, as two participants had significant relationships between V T and their percent compartmental contributions to V T , but five others did not. No differences were identified between ramp and step exercise tests for V T (main effect: p = 0.61) or BR (main effect: p = 0.77) at matched V̇ E for each intensity, and the pattern of breathing was reproducible for each intensity., Conclusion: These findings suggest the way young healthy adults breathe for a given V̇ E is repeatable day-to-day and reproducible between different exercise protocols., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Non-contact coded hemodynamic imaging (CHI) is a novel wide-field near-infrared spectroscopy system which monitors blood volume by quantifying attenuation of light passing through the underlying vessels. This study tested the hypothesis that CHI-based jugular venous attenuation (JVA) would be larger in men, and change in JVA would be greater in men compared to women during two fluid shift challenges. The association of JVA with ultrasound-based cross-sectional area (CSA) was also tested. Ten men and 10 women completed three levels of head-down tilt (HDT) and four levels of lower body negative pressure (LBNP). Both JVA and CSA were increased by HDT and reduced by LBNP (all p < 0.001). Main effects of sex indicated that JVA was higher in men than women during both HDT (p = 0.003) and LBNP (p = 0.011). Interaction effects of sex and condition were observed for JVA during HDT (p = 0.005) and LBNP (p < 0.001). We observed moderate repeated-measures correlations (r rm ) between JVA and CSA in women during HDT (r rm  = 0.57, p = 0.011) and in both men (r r m  = 0.74, p < 0.001) and women (r rm  = 0.66, p < 0.001) during LBNP. While median within-person correlation coefficients indicated an even stronger association between JVA and CSA, this association became unreliable for small changes in CSA. As hypothesized, JVA was greater and changed more in men compared to women during both HDT and LBNP. CHI provides a non-contact method of tracking large changes in internal jugular vein blood volume that occur with acute fluid shifts, but data should be interpreted in a sex-dependent manner., (© 2022 The Authors. Physiological Reports published by Wiley Periodicals LLC on behalf of The Physiological Society and the American Physiological Society.)

Background: Chemotherapy-induced peripheral neuropathy, a side effect of cancer treatment, presents several issues to patients, including reduced sensation and increased fall risk. Previously, massage therapy has been shown to improve chemotherapy-induced peripheral neuropathy symptoms, possibly through increased blood flow. A custom built intermittent pneumatic compression device, previously shown to increase lower leg blood flow, was tested as a plausible treatment modality., Methods: Seven cancer survivors suffering from chemotherapy-induced peripheral neuropathy were recruited. Foot sensation (Semmes-Weinstein test) as well as static (dual and tandem stance) and dynamic (timed-up-and-go) balance control tests were performed both pre and post a 5-min intermittent pneumatic compression intervention. Self-reported feedback was provided by participants following testing and 24-h later., Findings: Five participants reported positive changes in their feet immediately following intermittent pneumatic compression treatment while four of those participants reported positive changes up to 24 h after intervention. Foot sensation was unchanged regardless of location tested (P ≥ 0.23). Postural sway path length and sway area were unchanged following intervention during dual stance (P ≥ 0.14), but path length was significantly reduced (~19.9%) following intervention during tandem stance (P = 0.033). Timed-up-and-go duration was also significantly reduced (~7.0%, P = 0.012)., Interpretation: Overall, these findings demonstrate that intermittent pneumatic compression may be a plausible treatment modality for improving self-reported foot sensation as well as static and dynamic balance control. As a pilot study, this study provides sufficient context for further research exploring the efficacy of intermittent pneumatic compression as a treatment using a randomized control trial design., (Crown Copyright © 2021. Published by Elsevier Ltd. All rights reserved.)

Oxygen consumption ([Formula: see text]) provides established clinical and physiological indicators of cardiorespiratory function and exercise capacity. However, [Formula: see text] monitoring is largely limited to specialized laboratory settings, making its widespread monitoring elusive. Here we investigate temporal prediction of [Formula: see text] from wearable sensors during cycle ergometer exercise using a temporal convolutional network (TCN). Cardiorespiratory signals were acquired from a smart shirt with integrated textile sensors alongside ground-truth [Formula: see text] from a metabolic system on 22 young healthy adults. Participants performed one ramp-incremental and three pseudorandom binary sequence exercise protocols to assess a range of [Formula: see text] dynamics. A TCN model was developed using causal convolutions across an effective history length to model the time-dependent nature of [Formula: see text]. Optimal history length was determined through minimum validation loss across hyperparameter values. The best performing model encoded 218 s history length (TCN-VO2 A), with 187, 97, and 76 s yielding <3% deviation from the optimal validation loss. TCN-VO2 A showed strong prediction accuracy (mean, 95% CI) across all exercise intensities (-22 ml min - 1 , [-262, 218]), spanning transitions from low-moderate (-23 ml min - 1 , [-250, 204]), low-high (14 ml min - 1 , [-252, 280]), ventilatory threshold-high (-49 ml min - 1 , [-274, 176]), and maximal (-32 ml min - 1 , [-261, 197]) exercise. Second-by-second classification of physical activity across 16,090 s of predicted [Formula: see text] was able to discern between vigorous, moderate, and light activity with high accuracy (94.1%). This system enables quantitative aerobic activity monitoring in non-laboratory settings, when combined with tidal volume and heart rate reserve calibration, across a range of exercise intensities using wearable sensors for monitoring exercise prescription adherence and personal fitness., (© 2021. The Author(s).)

The objective was to quantify the index of reflectivity of the common carotid artery and surrounding structures, before and after 6 mo of microgravity. Our hypothesis was that structural changes in the insonated target would increase its index of reflectivity. The neck anterior muscle and common carotid artery (walls and lumen) were visualized by echography (17 MHz linear probe), and the radiofrequency signal along each vertical line was displayed. The limits of the radiofrequency data corresponding to each target (muscle, vessel wall) were determined from the B-mode image and radiofrequency trace. Each target's index of reflectivity was calculated as the proportion of backscattered energy to the whole backscattered energy along the line. After 6 mo in flight, the index of reflectivity increased significantly for both common carotid walls, while it remained unchanged for the neck muscle, carotid intima and lumen. The index of reflectivity provided additional information beyond traditional B-mode imaging., Competing Interests: Conflict of interest disclosure The authors declare no competing interests., (Copyright © 2021 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.)

Objective: An optical imaging system is proposed for quantitatively assessing jugular venous response to altered central venous pressure., Methods: The proposed system assesses sub-surface optical absorption changes from jugular venous waveforms with a spatial calibration procedure to normalize incident tissue illumination. Widefield frames of the right lateral neck were captured and calibrated using a novel flexible surface calibration method. A hemodynamic optical model was derived to quantify jugular venous optical attenuation (JVA) signals, and generate a spatial jugular venous pulsatility map. JVA was assessed in three cardiovascular protocols that altered central venous pressure: acute central hypovolemia (lower body negative pressure), venous congestion (head-down tilt), and impaired cardiac filling (Valsalva maneuver)., Results: JVA waveforms exhibited biphasic wave properties consistent with jugular venous pulse dynamics when time-aligned with an electrocardiogram. JVA correlated strongly (median, interquartile range) with invasive central venous pressure during graded central hypovolemia (r = 0.85, [0.72, 0.95]), graded venous congestion (r = 0.94, [0.84, 0.99]), and impaired cardiac filling (r = 0.94, [0.85, 0.99]). Reduced JVA during graded acute hypovolemia was strongly correlated with reductions in stroke volume (SV) (r = 0.85, [0.76, 0.92]) from baseline (SV: 79 ± 15 mL, JVA: 0.56 ± 0.10 a.u.) to -40 mmHg suction (SV: 59 ± 18 mL, JVA: 0.47 ± 0.05 a.u.; p 0.01)., Conclusion: The proposed non-contact optical imaging system demonstrated jugular venous dynamics consistent with invasive central venous monitoring during three protocols that altered central venous pressure., Significance: This system provides non-invasive monitoring of pressure-induced jugular venous dynamics in clinically relevant conditions where catheterization is traditionally required, enabling monitoring in non-surgical environments.

The objective is to develop a cuffless method that accurately estimates blood pressure (BP) during activities of daily living. User-specific nonlinear autoregressive models with exogenous inputs (NARX) are implemented using artificial neural networks to estimate the BP waveforms from electrocardiography and photoplethysmography signals. To broaden the range of BP in the training data, subjects followed a short procedure consisting of sitting, standing, walking, Valsalva maneuvers, and static handgrip exercises. The procedure was performed before and after a six-hour testing phase wherein five participants went about their normal daily living activities. Data were further collected at a four-month time point for two participants and again at six months for one of the two. The performance of three different NARX models was compared with three pulse arrival time (PAT) models. The NARX models demonstrate superior accuracy and correlation with "ground truth" systolic and diastolic BP measures compared to the PAT models and a clear advantage in estimating the large range of BP. Preliminary results show that the NARX models can accurately estimate BP even months apart from the training. Preliminary testing suggests that it is robust against variabilities due to sensor placement. This establishes a method for cuffless BP estimation during activities of daily living that can be used for continuous monitoring and acute hypotension and hypertension detection.

Background: Impaired blood pressure (BP) recovery with orthostatic hypotension on standing occurs in 20% of older adults. Low BP is associated with low cerebral blood flow but mechanistic links to postural instability and falls are not established. We investigated whether posture-related reductions in cerebral tissue oxygenation (tSO2) in older adults impaired stability upon standing, if a brief sit before standing improved tSO2 and stability, and if Low-tSO2 predicted future falls., Method: Seventy-seven older adults (87 ± 7 years) completed (i) supine-stand, (ii) supine-sit-stand, and (iii) sit-stand transitions with continuous measurements of tSO2 (near-infrared spectroscopy). Total path length (TPL) of the center of pressure sway quantified stability. K-cluster analysis grouped participants into High-tSO2 (n = 62) and Low-tSO2 (n = 15). Fall history was followed up for 6 months., Results: Change in tSO2 during supine-stand was associated with increased TPL (R = -.356, p = .001). When separated into groups and across all transitions, the Low-tSO2 group had significantly lower tSO2 (all p < .01) and poorer postural stability (p < .04) through 3 minutes of standing compared to the High-tSO2 group. There were no effects of transition type on tSO2 or TPL for the High-tSO2 group, but a 10-second sitting pause improved tSO2 and enhanced postural stability in the Low-tSO2 group (all p < .05). During 6-month follow-up, the Low-tSO2 group had a trend (p < .1) for increased fall risk., Conclusions: This is the first study to show an association between posture-related cerebral hypoperfusion and quantitatively assessed instability. Importantly, we found differences among older adults suggesting those with lower tSO2 and greater instability might be at increased risk of a future fall., (© The Author(s) 2020. Published by Oxford University Press on behalf of The Gerontological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Exercise elicits direct benefits to insulin sensitivity but may also indirectly improve glucose uptake by hemodynamic conditioning of the vasculature. The purpose of this study was to examine the modifying effect of 3 different types of exercise on the vascular response to an oral glucose challenge. Twenty healthy adults (9 women, 11 men; aged 23 ± 3 years) completed a standard oral glucose tolerance test (OGTT) at rest, as well as 1.5 hours after moderate continuous cycling exercise (30 min; 65% peak oxygen consumption), high-intensity interval cycling exercise (10 × 1 min at 90% peak heart rate), and lower-load higher-repetition resistance exercise (25-35 repetitions/set, 3 sets). Brachial and superficial femoral artery blood flow, conductance, and oscillatory shear index were measured throughout the OGTT. Regardless of rested state or exercise preconditioning, the OGTT induced reductions in brachial artery blood flow and conductance ( p  < 0.001), and transient increases in brachial and superficial femoral artery oscillatory shear index and retrograde blood flow ( p  < 0.01). Continuous cycling and resistance exercise were followed with a small degree of protection against prolonged periods of oscillatory flow. Our findings imply transient peripheral vasoconstriction and decreased limb blood flow during a standard OGTT, for which prior exercise was unable to prevent in healthy adults. Novelty: We investigated the impact of continuous, interval, and resistance exercise on the hemodynamic response to an OGTT. Our findings suggest decreased upper-limb blood flow during an OGTT is not prevented by prior exercise in healthy adults.

Purpose: Orthostatic hypotension, leading to cerebral hypoperfusion, can result in postural instability and falls in older adults. We determined the efficacy of a novel, intermittent pneumatic compression system, applying pressure around the lower legs, as a countermeasure against orthostatic stress in older adults., Methods: Data were collected from 13 adults (4 male) over 65 years of age. Non-invasive ultrasound measured middle cerebral artery blood velocity (MCAv) and finger photoplethysmography measured mean arterial blood pressure (MAP). Intermittent lower leg compression was applied in a peristaltic manner in the local diastolic phase of each cardiac cycle to optimize venous return during 1-min of seated rest and during a sit-to-stand transition to 1-min of quiet standing with compression initiated 15 s before transition., Results: During seated rest, compression resulted in a 4.5 ± 6.5 mmHg increase in MAP, and 2.3 ± 2.1 cm/s increase in MCAv (p < 0.05). MAP and MCAv increased during the 15 s of applied compression before the posture transition (2.3 ± 7.2 mmHg and 2.1 ± 4.0 cm/s, respectively, p < 0.05) with main effects for both variables confirming continued benefit during the transition and quiet stand periods., Conclusions: Application of carefully timed, intermittent compression to the lower legs of older adults increased MAP and MCAv during seated rest and maintained an elevated MAP and MCAv during a transition to standing posture. Future research could assess the benefits of this technology for persons at risk for orthostatic hypotension on standing and while walking in an effort to reduce injurious, unexplained falls in older adults.

At the onset of an exercise transition, exponential modeling to calculate a time constant (τ) is the conventional method to analyze pulmonary oxygen uptake (V̇O 2p ) kinetics for moderate and heavy exercises. A new frequency domain analysis technique, mean normalized gain (MNG), has been used to analyze V̇O 2p kinetics during moderate exercise, but has not been evaluated for its ability to detect differences in kinetics between moderate and heavy exercises. This study tested the hypothesis that MNG would detect smaller amplitude V̇O 2p responses in the heavy-exercise domain compared with moderate-exercise domain. Eight young healthy adults (3 female; age: 27 ± 6 yr; peak V̇O 2p : 43 ± 6 mL·min -1 ·kg -1 ; means ± SD) performed three bouts of pseudorandom binary sequence (PRBS) exercise for frequency analysis, with the work rate (WR) changing between 25 W and 90% ventilatory threshold (VT; L → M PRBS ), 25 W and 50% of the difference between VT and peak V̇O 2p (Δ50%; L → H PRBS ), and VT to Δ50% (VT → H PRBS ). Step exercise tests with equivalent changes in WR to the PRBS tests were performed to facilitate the comparison between MNG and τ. MNG was the highest for L → M PRBS (59 ± 7%), then L → H PRBS (52 ± 6%), and the lowest for VT → H PRBS (38 ± 7%, F (2,14)  = 129.755, P < 0.001) exercise conditions indicating slower kinetics with increasing exercise intensity that correlated strongly in repeated measures with τ from step transitions ( r rm  = -0.893). These results indicate that frequency domain analysis and MNG reliably detect differences in V̇O 2p kinetics observed across exercise intensity domains. NEW & NOTEWORTHY Mean normalized gain is able to detect differences in V̇O 2p kinetics between moderate-, heavy-, and heavy-intensity exercises from a raised WR within the same individuals. This new method of kinetic analysis may be advantageous compared with conventional V̇O 2p curve fitting, as it is less sensitive to breath-by-breath noise, it can provide useful information from a single exercise testing session, and it can be applied to nonconstant work rate exercise situations.

Vascular aging is associated with markers of cerebrovascular impairment. Whether discrete characteristics of arterial structure and function have independent and/or additive effects on cerebral hemodynamics, however, is not completely understood. We examined the association of cerebral hemodynamics with common carotid artery intima-media thickness (IMT) and pulse pressure (PP) in 61 older adults with prevalent cardiometabolic risk but no history of cerebrovascular disease. We calculated pulsatility index (PI) and hypercapnic reactivity of the middle cerebral artery, as well as global blood flow through the extracranial arteries. The dominant effects were related to hemodynamic pulsatility. In adults with metabolic syndrome, PI was related to IMT (r = 0.48, P = 0.003) after adjustment for age and sex. Without metabolic syndrome, PI was directly related to PP (r = 0.63, P = 0.003). Across the whole cohort, PP [β (95%CI) = 0.42 (0.18, 0.67), P = 0.001] and IMT [0.42 (0.18, 0.67), P < 0.001] remained significant predictors of PI, after accounting for individual cardiometabolic risk factors. The independent and combined effects of IMT and PP were tested by binarizing PP and IMT at the sample median. Participants with both IMT and PP above their respective medians had elevated PI compared with those with both vascular markers below the median [median (interquartile range) = 1.06 (0.22) vs. 0.84 (0.14), P = 0.003)]. PI was not different from the low risk group if only one of IMT or PP were above the median. Although overall vascular burden was low, moderate associations with PI persisted, suggesting pulsatile characteristics represent one of the earliest markers linking vascular aging to changes in brain health.

Efforts to better understand cardiorespiratory health are relevant for the future development of optimized physical activity programs. We aimed to explore the impact of the signal quality on the expected associations between the ability of the aerobic system in supplying energy as fast as possible during moderate exercise transitions with its maximum capacity to supply energy during maximal exertion. It was hypothesized that a slower aerobic system response during moderate exercise transitions is associated with a lower maximal aerobic power; however, this relationship relies on the quality of the oxygen uptake data set. Forty-three apparently healthy participants performed a moderate constant work rate (CWR) followed by a pseudorandom binary sequence (PRBS) exercise protocol on a cycle ergometer. Participants also performed a maximum incremental cardiopulmonary exercise testing (CPET). The maximal aerobic power was evaluated by the peak oxygen uptake during the CPET, and the aerobic fitness was estimated from different approaches for oxygen uptake dynamics analysis during the CWR and PRBS protocols at different levels of signal-to-noise ratio. The product moment correlation coefficient was used to evaluate the correlation level between variables. Aerobic fitness was correlated with maximum aerobic power, but this correlation increased as a function of the signal-to-noise ratio. Aerobic fitness is related to maximal aerobic power; however, this association appeared to be highly dependent on the data quality and analysis for aerobic fitness evaluation. Our results show that simpler moderate exercise protocols might be as good as maximal exertion exercise protocols to obtain indexes related to cardiorespiratory health. NEW & NOTEWORTHY Optimized methods for cardiorespiratory health evaluation are of great interest for public health. Moderate exercise protocols might be as good as maximum exertion exercise protocols to evaluate cardiorespiratory health. Pseudorandom or constant workload moderate exercise can be used to evaluate cardiorespiratory health.

This work presents a modelling approach to predict the blood pressure (BP) waveform time series during activities of daily living without the use of a traditional pressure cuff. A nonlinear autoregressive model with exogenous inputs (NARX) is implemented using artificial neural networks and trained to predict the BP waveform time series from electrocardiography (ECG) and forehead photoplethysmography (PPG) input signals. To broaden the range of blood pressures present in the training set, a protocol was implemented that included sitting, standing, walking, Valsalva manoeuvers, and static handgrip exercise. A five-minute interval of data in the sitting position at the end of the day was also used for training. The efficacy of the cuffless BP method for continuous BP estimation over 4.67 hours was evaluated on 3 participants for varying training data segments. A mean absolute error of 6.3 and 5.2 mmHg were achieved for systolic BP and diastolic BP estimates, respectively. Including static handgrips and Valsalva manoeuvers in the training dataset leads to better estimation of the higher ranges of BP observed throughout the day. The proposed method shows potential for estimating the range of BP experienced during activities of daily living.Clinical Relevance- Establishes a method for cuffless continuous blood pressure estimation during activities of daily living that can be used for continuous monitoring and acute hypertension detection.

Postural instability is prevalent in aging and neurodegenerative disease, decreasing quality of life and independence. Quantitatively monitoring balance control is important for assessing treatment efficacy and rehabilitation progress. However, existing technologies for assessing postural sway are complex and expensive, limiting their widespread utility. Here, we propose a monocular imaging system capable of assessing sub-millimeter 3D sway dynamics during quiet standing. Two anatomical targets with known feature geometries were placed on the lumbar and shoulder. Upper and lower trunk 3D kinematic motion were automatically assessed from a set of 2D frames through geometric feature tracking and an inverse motion model. Sway was tracked in 3D and compared between control and hypoperfusion conditions in 14 healthy young adults. The proposed system demonstrated high agreement with a commercial motion capture system (error [Formula: see text], [-0.52, 0.52]). Between-condition differences in sway dynamics were observed in anterior-posterior sway during early and mid stance, and medial-lateral sway during mid stance commensurate with decreased cerebral perfusion, followed by recovered sway dynamics during late stance with cerebral perfusion recovery. This inexpensive single-camera system enables quantitative 3D sway monitoring for assessing neuromuscular balance control in weakly constrained environments.

Purpose: Complex blood flow is commonly observed in the carotid bifurcation, although the factors that regulate these patterns beyond arterial geometry are unknown. The emergence of high-frame-rate ultrasound vector flow imaging allows for noninvasive, time-resolved analysis of complex hemodynamic behavior in humans, and it can potentially help researchers understand which physiological stressors can alter carotid bifurcation hemodynamics in vivo. Here, we seek to pursue the first use of vector projectile imaging (VPI), a dynamic form of vector flow imaging, to analyze the regulation of carotid bifurcation hemodynamics during experimental reductions in cardiac output induced via a physiological stressor called lower body negative pressure (LBNP)., Methods: Seven healthy adults (age: 27 ± 4 yr, 4 men) underwent LBNP at -45 mmHg to simulate a postural hemodynamic response in a controlled environment. Using a research-grade, high-frame-rate ultrasound platform, vector flow estimation in each subject's right carotid bifurcation was performed through a multi-angle plane wave imaging (two transmission angles of 10° and -10°) formulation, and VPI cineloops were generated at a frame rate of 750 fps. Vector concentration was quantified by the resultant blood velocity vector angles within a region of interest; lower concentration indicated greater flow dispersion. Discrete concentration values during peak and late systole were compared across different segments of the carotid artery bifurcation before, and during, LBNP., Results: Vector projectile imaging revealed that external and internal carotid arteries exhibited regional hemodynamic changes during LBNP, which acted to reduce both the subject's cardiac output (Δ - 1.2 ± 0.5 L/min, -19%; P < 0.01) and peak carotid blood velocity (Δ - 6.30 ± 8.27 cm/s, -7%; P = 0.05). In these carotid artery branches, the vector concentration time trace before and during LBNP were observed to be different. The impact of LBNP on flow complexity in the two carotid artery branches showed variations between subjects., Conclusions: Using VPI, intuitive visualization of complex hemodynamic changes can be obtained in healthy humans subjected to LBNP. This imaging tool has potential for further applications in vascular physiology to identify and quantify complex hemodynamic features in humans during different physiological stressor tests that regulate hemodynamics., (© 2019 American Association of Physicists in Medicine.)

We tested the hypothesis that transient deficits in cerebral blood flow are associated with postural sway. In 19 young, healthy adults, we examined the association between the drop in cerebral blood flow during supine-to-stand transitions, indexed by transcranial Doppler ultrasound [middle cerebral artery blood velocity at diastole (MCAdv)] and near-infrared spectroscopy [tissue saturation index (TSI)] and the center of pressure displacement while standing. Participants performed transitions under three conditions aimed at progressively increasing the drop in MCAdv, in a randomized order: 1 ) a control transition (Con); 2 ) a transition that coincided with deflation of bilateral thigh cuffs; and 3 ) a transition that coincided with both thigh-cuff deflation and 90 s of prior hyperventilation (HTC). The deficit in diastolic blood velocity (MCAdv deficit) was quantified as the difference between MCAdv and its preceding baseline value, summed over 10 s, beginning at the MCAdv nadir. Compared with Con, HTC led to greater drops in MCAdv ( P = 0.003) and TSI ( P < 0.001) at nadir. The MCAdv deficit was positively associated with the center of pressure displacement vector-average using repeated-measures correlation (repeated-measures correlation coefficient = 0.56, P < 0.001). An a posteriori analysis identified a sub-group of participants that showed an exaggerated increase in MCAdv deficit and greater postural instability in both the anterior-posterior ( P = 0.002) and medial-lateral ( P = 0.021) directions in response to the interventions. These findings support the theory that individuals who experience greater initial cerebral hypoperfusion on standing may be at a greater risk for falls. NEW & NOTEWORTHY Dizziness and risk for falls after standing might link directly to reduced delivery of oxygen to the brain. By introducing challenges that increased the drop in brain blood flow in healthy young adults, we have shown for the first time a direct link to greater postural instability. These results point to a need to measure cerebral blood flow and/or oxygenation after postural transitions in populations, such as older adults, to assist in fall risk assessment.

New Findings: What is the central question of this study? Does smartly timed intermittent compression of the lower legs alter cerebral blood velocity and oxygenation during acute orthostatic challenges? What is the main finding and its importance? Intermittent compression timed to the local diastolic phase increased the blood flux through the legs and heart after two different orthostatic stress tests. Cerebral blood velocity improved during the first minute of recovery, and indices of cerebral tissue oxygenation remained elevated for 2 min. These results provide promise for the use of lower-leg active compression as a therapeutic tool for individuals vulnerable to initial orthostatic hypotension and orthostatic stress., Abstract: Intermittent compression of the lower legs provides the possibility of improving orthostatic tolerance by actively promoting venous return and improving central haemodynamics. We tested the hypothesis that intermittent compression of 65 mmHg timed to occur only within the local diastolic phase of each cardiac cycle would attenuate the decrease in blood pressure and improve cerebral haemodynamics during the first minute of recovery from two different orthostatic stress tests. Fourteen subjects (seven female) performed four squat-to-stand transitions and four repeats of standing bilateral thigh-cuff occlusion and release (TCR), with intermittent compression of the lower legs applied in half of the trials. Blood flow in the superficial femoral artery, mean arterial pressure, Doppler ultrasound cardiac output, total peripheral resistance, middle cerebral artery blood velocity (MCAv) and cerebral tissue saturation index (TSI%) were monitored. With both orthostatic stress tests, there was a significant compression × time interaction for superficial femoral artery flow (P < 0.001). The hypotensive state was attenuated with intermittent compression despite decreased total peripheral resistance (squat-to-stand, compression × time interaction, P < 0.001; TCR, compression × time interaction, P = 0.002) as a consequence of elevated cardiac output in both tests (P < 0.001). Intermittent compression also increased MCAv (P = 0.001) and TSI% (P < 0.001) during the squat-to-stand transition and during TCR (MCAv and TSI%, compression × time interaction, P < 0.001). Intermittent compression of the lower legs during quiet standing after an active orthostatic challenge augmented local, central and cerebral haemodynamics, providing potential as a therapeutic tool for individuals vulnerable to orthostatic stress., (© 2019 The Authors. Experimental Physiology © 2019 The Physiological Society.)

Landing day symptoms from orthostatic hypotension after prolonged spaceflight can be debilitating, but severity of these symptoms can be unpredictable and highly individual. We tested the hypothesis that an impaired baroreflex response to an inflight leg cuff test could predict orthostatic intolerance on return to Earth. Eight male astronauts (44 ± 7 years of age (mean ± SD); mean mission length: 167 ± 12 days) participated in a standardized supine-to-sit-to-stand test (5 min-30s-3 min) pre- and postflight, and a 3 min thigh cuff occlusion test pre- and inflight with continuous monitoring of heart rate and arterial blood pressure. The arterial baroreflex was not changed inflight as shown by similar reductions in mean arterial pressure (MAP) response to leg cuff deflation (preflight -19 ± 2 mmHg vs. inflight -18 ± 5 mmHg). With the sit/stand test, the nadir of MAP was lower postflight (-17 ± 9 mmHg) than preflight (-11 ± 6 mmHg, p  < 0.05). A greater increase in heart rate (25 ± 7; 16 ± 3 bpm) and decrease in stroke volume (-24 ± 11; -6 ± 4 mL) occurred with sit/stand postflight than leg cuffs inflight ( p  < 0.001). Inflight testing was influenced by elevated cardiac output resulting in a smaller drop in total peripheral resistance. Two of eight subjects exhibited orthostatic hypotension during the postflight stand test; their responses were not predicted by the inflight leg cuff deflation test. These results suggest that the baroreflex response examined by inflight leg cuff deflation was not a reliable indicator of postflight stand responses., Competing Interests: Competing interestsThe authors declare no competing interests., (© The Author(s) 2019.)

We tested the hypothesis that acute changes in arterial blood pressure (BP) when astronauts moved between supine and standing posture before and after spaceflight can be tracked by beat-to-beat changes in pulse arrival time (PAT). Nine male crewmembers (45 ± 7 yr of age; mean mission length: 165 ± 13 days) participated in a standardized supine-to-sit-to-stand test (5 min-30 s-3 min) before flight and 1 day following return to Earth with continuous monitoring of ECG and finger arterial BP. PAT was determined from the R-wave of the ECG to the foot of the BP waveform. On average, modest cardiovascular deconditioning was detected by ~10 beats/min increase in heart rate in supine and standing posture after spaceflight ( P < 0.05). When looking across the full data collection period, the r 2 values between inverse of PAT (1/PAT) and systolic (SBP) and diastolic BP (DBP) varied considerably between individuals (SBP preflight 0.142 ± 0.186, postflight 0.262 ± 0.243). Individual variability was consistent during periods of transition (SBP preflight 0.284 ± 0.324, postflight 0.297 ± 0.269); however, when SBP dropped >20 mmHg, r 2 was significant in 5 of 5 preflight tests and 5 of 7 postflight tests. The standard error of the estimate based on a simple linear model during both pre- and postflight testing was 9-11 mmHg for SBP and 6-7 mmHg for DBP. Overall, the results support the hypothesis that PAT tracked dynamic changes in BP. PAT as a noninvasive, nonintrusive surrogate for changes in BP could be developed as an indicator of risk for syncope on return from spaceflight or other Earth-based applications. NEW & NOTEWORTHY Astronauts returning to Earth's gravity are at increased risk of low blood pressure on standing. Arterial pulse arrival time tracked the decrease in arterial blood pressure on moving from supine to upright posture. Nonintrusive technology providing indicators sensitive to acute changes in blood pressure could act as an early warning system to identify risk for hypotension that place astronauts, or people on Earth, at risk of impaired cognitive performance, fainting, and falls.

The purpose of this study was to determine if muscle blood flow during walking exercise and postexercise recovery can be augmented through the application of intermittent compression of the lower legs applied during the diastolic phase of the cardiac cycle. Results from four conditions were assessed: no compression (NoComp), compression during walking (ExComp), compression during postexercise recovery (RecComp), and compression applied throughout (AllComp). Superficial femoral artery (SFA) blood flow was measured (Doppler ultrasound) during rest and postexercise recovery. Mean arterial blood pressure (MAP, finger photoplethysmography) was used to calculate vascular conductance as VC = SFA flow/MAP. Near infrared spectroscopy measured changes in oxygenated (O 2 Hb) and deoxygenated hemoglobin concentration throughout the test. Compression during exercise increased SFA blood flow measured over the first 15 s of postexercise recovery (AllComp: 532.2 ± 123.1 mL/min; ExComp: 529.8 ± 99.2 mL/min) compared with NoComp (462.3 ± 87.3 mL/min P < 0.05) and corresponded to increased VC (NoComp: 4.7 ± 0.9 mL·min -1 ·mmHg -1 versus ExComp: 5.5 ± 1.0 mL·min -1 ·mmHg -1 , P < 0.05). Similarly, compression throughout postexercise recovery also resulted in increased SFA flow (AllComp: 190.5 ± 57.1 mL/min; RecComp: 158.7 ± 49.1 mL/min versus NoComp: 108.8 ± 28.5 mL/min, P < 0.05) and vascular conductance. Muscle contractions during exercise reduced total hemoglobin with O 2 Hb comprising ~57% of the observed reduction. Compression during exercise augmented this reduction ( P < 0.05) with O 2 HB again comprising ~55% of the reduction. Total hemoglobin was reduced with compression during postexercise recovery ( P < 0.05) with O 2 Hb accounting for ~40% of this reduction. Results from this study indicate that intermittent compression applied during walking and during postexercise recovery enhanced vascular conductance during exercise and elevated postexercise SFA blood flow and tissue oxygenation during recovery. NEW & NOTEWORTHY Intermittent compression mimics the mechanical actions of voluntary muscle contraction on venous volume. This study demonstrates that compression applied during the diastolic phase of the cardiac cycle while walking accentuates the actions of the muscle pump resulting in increased immediate postexercise muscle blood flow and vascular conductance. Similarly, compression applied during the recovery period independently increased arterial flow and tissue oxygenation, potentially providing conditions conducive to faster recovery.

New Findings: What is the central question of this study? Pulse contour analysis of the finger arterial pressure by Windkessel modelling is commonly used to estimate stroke volume continuously. But is it valid during dynamic changes in blood pressure? What is the main finding and its importance? Second-by-second analysis revealed that pulse contour analysis underestimated stroke volume by up to 25% after standing from a squat, and 16% after standing thigh-cuff release, when compared with aortic Doppler ultrasound estimates. These results reveal that pulse contour analysis of stroke volume should be interpreted with caution during rapid changes in physiological state., Abstract: Dynamic measurements of stroke volume (SV) and cardiac output provide an index of central haemodynamics during transitional states, such as postural changes and onset of exercise. The most widely used method to assess dynamic fluctuations in SV is the Modelflow method, which uses the arterial blood pressure waveform along with age- and sex-specific aortic properties to compute beat-to-beat estimates of aortic flow. Modelflow has been validated against more direct methods in steady-state conditions, but not during dynamic changes in physiological state, such as active orthostatic stress testing. In the present study, we compared the dynamic SV responses from Modelflow (SV MF ), aortic Doppler ultrasound (SV U/S ) and bioelectrical impedance analysis (SV BIA ) during two different orthostatic stress tests, a squat-to-stand (S-S) transition and a standing bilateral thigh-cuff release (TCR), in 15 adults (six females). Second-by-second analysis revealed that when compared with estimates of SV by aortic Doppler ultrasound, Modelflow underestimated SV by up to 25% from 3 to 11 s after standing from the squat position and by up to 16% from 3 to 7 s after TCR (P < 0.05). The SV MF and SV BIA were similar during the first minute of the S-S transition, but were different 3 s after TCR and at intermittent time points between 34 and 44 s (P < 0.05). These findings indicate that the physiological conditions elicited by orthostatic stress testing violate some of the inherent assumptions of Modelflow and challenge models used to interpret bioelectrical impedance responses, resulting in an underestimation in SV during rapid changes in physiological state., (© 2018 The Authors. Experimental Physiology © 2018 The Physiological Society.)