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The genioglossus (GG) is an extrinsic muscle of the human tongue that plays a critical role in preserving airway patency. In the last quarter century, >50 studies have reported on respiratory-related GG electromyographic (EMG) activity in human subjects. Remarkably, of the studies performed, none have duplicated subject body position, electrode recording locations, and/or breathing task(s), making interpretation and integration of the results across studies extremely challenging. In addition, more recent research assessing lingual anatomy and muscle contractile properties has identified regional differences in muscle fiber type and myosin heavy chain expression, giving rise to the possibility that the anterior and posterior regions of the muscle fulfill distinct functions. Here, we assessed EMG activity in anterior and posterior regions of the GG, across upright and supine, in rest breathing and in volitionally modulated breathing tasks. We tested the hypotheses that GG EMG is greater in the posterior region and in supine, except when breathing is subject to volitional modulation. Our results show differences in the magnitude of EMG (%regional maximum) between anterior and posterior muscle regions (7.95 ± 0.57 vs. 11.10 ± 0.99, respectively; P < 0.001), and between upright and supine (8.63 ± 0.73 vs. 10.42 ± 0.90, respectively; P = 0.008). Although the nature of a task affects the magnitude of EMG (P < 0.001), the effect is similar for anterior and posterior muscle regions and across upright and supine (P > 0.2). [ABSTRACT FROM AUTHOR]

Abstract: Upper airway muscles play an important role in regulating airway lumen and in increasing the ability of the pharynx to remain patent in the face of subatmospheric intraluminal pressures produced during inspiration. Due to the considerable technical challenges associated with recording from muscles of the upper airway, much of the experimental work conducted in human subjects has centered on recording respiratory-related activities of the extrinsic tongue protudor muscle, the genioglossus (GG). The GG is one of eight muscles that invest the human tongue (). All eight muscles are innervated by the hypoglossal nerve (cranial nerve XII) the cell bodies of which are located in the hypoglossal motor nucleus (HMN) of the caudal medulla. Much of the earlier work on the respiratory-related activity of XII motoneurons was based on recordings obtained from single motor axons dissected from the whole XII nerve or from whole muscle GG EMG recordings. Detailed information regarding respiratory-related GG motor unit activities was lacking until as recently as 2006. This paper examines key findings that have emerged from the last decade of work conducted in human subjects. Wherever appropriate, these results are compared with results obtained from in vitro and in vivo studies conducted in non-human mammals. The review is written with the objective of facilitating some discussion and some new thoughts regarding future research directions. The material is framed around four topics: (a) motor unit type, (b) rate coding and recruitment, (c) motor unit activity patterns, and (d) a compartment based view of pharyngeal airway control. [Copyright &y& Elsevier]

The tongue plays a key role in various volitional and automatic functions such as swallowing, maintenance of airway patency, and speech. Precisely how hypoglossal motor neurons, which control the tongue, receive and process their often concurrent input drives is a subject of ongoing research. We investigated common synaptic input to the hypoglossal motor nucleus by measuring the coordination of spike timing, firing rate, and oscillatory activity across motor units recorded from unilateral (i.e., within a belly) or bilateral (i.e., across both bellies) locations within the genioglossus (GG), the primary protruder muscle of the tongue. Simultaneously recorded pairs of motor units were obtained from 14 healthy adult volunteers using tungsten microelectrodes inserted percutaneously into the GG while the subjects were engaged in volitional tongue protrusion or rest breathing. Bilateral motor unit pairs showed concurrent low frequency alterations in firing rate (common drive) with no significant difference between tasks. Unilateral motor unit pairs showed significantly stronger common drive in the protrusion task compared with rest breathing, as well as higher indices of synchronous spiking (short-term synchrony). Common oscillatory input was assessed using coherence analysis and was observed in all conditions for frequencies up to ∼5 Hz. Coherence at frequencies up to ∼10 Hz was strongest in motor unit pairs recorded from the same GG belly in tongue protrusion. Taken together, our results suggest that cortical drive increases motor unit coordination within but not across GG bellies, while input drive during rest breathing is distributed uniformly to both bellies of the muscle. [ABSTRACT FROM AUTHOR]

The tongue participates in a range of complex oromotor behaviors, including mastication, swallowing, respiration, and speech. Previous electromyographic studies of the human tongue have focused on respiratory-related tongue muscle activities and their role in maintaining upper airway patency. Remarkably, the activities of human hypoglossal motor units have not been studied during the execution of voluntary maneuvers. We recorded single motor unit activity using tungsten microelectrodes in the genioglossus muscle of 10 healthy human subjects performing both slow tongue protrusions and a static holding maneuver. Displacement of the tongue was detected by an isotonic transducer coupled to the lingual surface through a customized lever arm. For protrusion trials, the firing rate at recruitment was 13.1 ± 3 Hz and increased steeply to an average of 24 ± 6 Hz, often with very modest increases in tongue protrusion. For the static holding task, the average firing rate was 16.1 ± 4 Hz, which is surprisingly high relative to limb motor units. The average coefficient of variation of interspike intervals was ∼20% (range, 10–28%). These are the first recordings of their type obtained in human subjects and provide an initial glimpse into the voluntary control of hypoglossal motoneurons during tongue movements presumably instigated by activity in the motor cortex. [ABSTRACT FROM AUTHOR]

Pulmonary ventilation during speech breathing reflects the sum of the airflow changes used to speak and to meet the metabolic needs of the body. Studying interactions between speaking and breathing may provide insights into the mechanisms of shared respiratory control. The purposes of this study were to determine if healthy subjects exhibit task-specific breathing behaviors in high respiratory drive and to document subjects' perceptions during breathing and speaking under these conditions. Ten men were studied in air and high CO[sub 2]. Magnetometers were used to estimate lung volume, rib cage and abdomen volumes, minute volume, breathing frequency, tidal volume, inspiratory and expiratory duration, and inspiratory and expiratory flow. Subjects' perceptions were assessed informally. Results indicated that the chest wall kinematic behaviors associated with breathing and speaking in high drive were similar in pattern but differed in the magnitudes of lung volume and rib cage volume events and in inspiratory and expiratory flow. Linguistic influences remained strong, but not as strong as under normal conditions. All subjects reported a heightened sense of breathing-related discomfort during speaking as opposed to breathing in high respiratory drive. We conclude that in healthy subjects breathing behavior associated with speaking in high respiratory drive is guided continuously by shared linguistic and metabolic influences. A parallel-processing model is proposed to explain the behaviors observed. [ABSTRACT FROM AUTHOR]

Purpose: This study aimed to determine if time-efficient, high-resistance inspiratory muscle strength training (IMST), comprising 30 inhalation-resisted breaths per day, improves cardiorespiratory fitness, exercise tolerance, physical function, and/or regional body composition in healthy midlife and older adults. Methods: We performed a double-blind, randomized, sham-controlled clinical trial (NCT03266510) testing 6 wk of IMST (30 breaths per day, 6 d·wk−1, 55%–75% maximal inspiratory pressure) versus low-resistance sham training (15% maximal inspiratory pressure) in healthy men and women 50–79 yr old. Subjects performed a graded treadmill exercise test to exhaustion, physical performance battery (e.g., handgrip strength, leg press), and body composition testing (dual x-ray absorptiometry) at baseline and after 6 wk of training. Results: Thirty-five participants (17 women, 18 men) completed high-resistance IMST (n = 17) or sham training (n = 18). Cardiorespiratory fitness (V̇O2peak) was unchanged, but exercise tolerance, measured as treadmill exercise time during a graded exercise treadmill test, increased with IMST (baseline, 539 ± 42 s; end intervention, 606 ± 42 s; P = 0.01) but not sham training (baseline, 562 ± 39 s; end intervention, 553 ± 38 s; P = 0.69). IMST increased peak RER (baseline, 1.09 ± 0.02; end intervention, 1.13 ± 0.02; P = 0.012), peak ventilatory efficiency (baseline, 25.2 ± 0.8; end intervention, 24.6 ± 0.8; P = 0.036), and improved submaximal exercise economy (baseline, 23.5 ± 1.1 mL·kg−1⋅min−1; end intervention, 22.1 ± 1.1 mL·kg−1⋅min−1; P < 0.001); none of these factors were altered by sham training (all P > 0.05). Changes in plasma acylcarnitines (targeted metabolomics analysis) were consistently positively correlated with changes in exercise tolerance after IMST but not sham training. IMST was associated with regional increases in thorax lean mass (+4.4%, P = 0.06) and reductions in trunk fat mass (−4.8%, P = 0.04); however, peripheral muscle strength, muscle power, dexterity, and mobility were unchanged. Conclusions: These data suggest that high-resistance IMST is an effective, time-efficient lifestyle intervention for improving exercise tolerance in healthy midlife and older adults. [ABSTRACT FROM AUTHOR]

Inspiratory resistance training (IRT) yields significant reductions in resting blood pressure and improves vascular endothelial function. Our objective was to quantify the acute effects of IRT on brachial artery flow‐mediated dilation (FMD) and shear rates (SRs) in healthy men and women. Twenty young adults (22.9 ± 3.4 years; 10 male, 10 female) completed a single bout of IRT or Rest condition in a randomized crossover design. Brachial artery FMD was performed before, 10 min after, and 40 min after the assigned condition. Brachial artery blood flow velocities were collected during IRT, separated by breathing cycle phase, and converted into SRs. FMD improved 10 min post‐IRT (+1.86 ± 0.61%; p = 0.025) but returned to baseline by 40 min post‐IRT (p = 0.002). Anterograde SR decreased by 10% and retrograde SR increased 102% during resisted inspiration, relative to baseline SR (p < 0.001). Anterograde SR increased by 7% in men and women (p < 0.001) and retrograde SR decreased by 12% in women but not men (p = 0.022) during unresisted expiration, relative to baseline SR. A single bout of IRT elicits a transient enhancement in FMD in both men and women. Acute IRT‐related enhancements in SRs may contribute to sustained improvements in FMD that have been reported previously. [ABSTRACT FROM AUTHOR]

Aging is associated with increased risk for cognitive decline and dementia due in part to increases in systolic blood pressure (SBP) and cerebrovascular dysfunction. High-resistance inspiratory muscle strength training (IMST) is a time-efficient, intensive respiratory training protocol (30 resisted inspirations/day) that lowers SBP and improves peripheral vascular function in midlife/older adults with above-normal SBP. However, whether, and by what mechanisms, IMST can improve cerebrovascular function is unknown. We hypothesized that IMST would increase cerebrovascular reactivity to hypercapnia (CVR to CO2), which would coincide with changes to the plasma milieu that improve brain endothelial cell function and enhance cognitive performance (NIH Toolbox). We conducted a 6-wk double-blind, randomized, controlled clinical trial investigating high-resistance IMST [75% maximal inspiratory pressure (PImax); 6×/wk; 4 females, 5 males] vs. low-resistance sham training (15% PImax; 6×/wk; 2 females, 5 males) in midlife/older adults (age 50-79 yr) with initial above-normal SBP. Human brain endothelial cells (HBECs) were exposed to participant plasma and assessed for acetylcholine-stimulated nitric oxide (NO) production. CVR to CO2 increased after high-resistance IMST (pre: 1.38 ±0.66 cm/s/mmHg; post: 2.31 ± 1.02 cm/s/mmHg, P = 0.020). Acetylcholine-stimulated NO production increased in HBECs exposed to plasma from after vs. before the IMST intervention [pre: 1.49 ±0.33; post: 1.73 ±0.35 arbitrary units (AU); P < 0.001]. Episodic memory increased modestly after the IMST intervention (pre: 95 ± 13; post: 103 ± 17 AU; P = 0.045). Cerebrovascular and cognitive function were unchanged in the sham control group. High-resistance IMST may be a promising strategy to improve cerebrovascular and cognitive function in midlife/older adults with above-normal SBP, a population at risk for future cognitive decline and dementia. [ABSTRACT FROM AUTHOR]

The article focuses on the role of vagal complex in food intake and swallowing. It also discusses the role of the human central nervous system in coordinating and integrating appetite, food-seeking behavior and thermoregulation with one another. Furthermore, it also features the study of Bariohay and colleagues that adds to the challenges of the hegemony of the hypothalamus thus supporting the caudal brain stem as another autonomous integrator in regulating food intake.

New Findings: What is the central question of this study? What impact does inspiratory muscle training have on systemic vascular resistance, cardiac output and baroreflex sensitivity in adult men and women? What is the main finding and its importance? Inspiratory muscle training exerts favorable effects on blood pressure, vascular resistance and perception of stress. This exercise format is well‐tolerated and equally effective whether implemented in men or women. Abstract: Previous work has shown that inspiratory muscle training (IMT) lowers blood pressure after a mere 6 weeks, identifying IMT as a potential therapeutic intervention to prevent or treat hypertension. Here, we explore the effects of IMT on respiratory muscle strength and select cardiovascular parameters in recreationally active men and women. Subjects were randomly assigned to IMT (n = 12, 75% maximal inspiratory pressure) or sham training (n = 13, 15% maximal inspiratory pressure) groups and underwent a 6‐week intervention comprising 30 breaths day−1, 5 days week−1. Pre‐ and post‐training measures included maximal inspiratory pressure and resting measures of blood pressure, cardiac output, heart rate, spontaneous cardiac baroreflex sensitivity and systemic vascular resistance. We evaluated psychological and sleep status via administration of the Cohen–Hoberman inventory of physical symptoms and the Epworth sleepiness scale. Male and female subjects in the IMT group showed declines in systolic/diastolic blood pressures (−4.3/−3.9 mmHg, P < 0.025) and systemic vascular resistance (−3.5 mmHg min l−1, P = 0.008) at week 6. There was no effect of IMT on cardiac output (P = 0.722), heart rate (P = 0.795) or spontaneous cardiac baroreflex sensitivity (P = 0.776). The IMT subjects also reported fewer stress‐related symptoms (pre‐ versus post‐training, 12.5 ± 8.5 versus 7.2 ± 9.7, P = 0.025). Based on these results, we suggest that a short course of IMT confers significant respiratory and cardiovascular improvements and parallel (modest) psychological benefits in healthy men and women. [ABSTRACT FROM AUTHOR]

Our objective was to evaluate the effects of 6-weeks high-resistance, low-volume inspiratory muscle strength training (IMST) on respiratory endurance, blood pressure (BP) and heart rate (HR) responsiveness to high respiratory workloads. Ten healthy young adults completed two constant-load resistive breathing tests to exhaustion (T lim) (target pressure =65 % maximal inspiratory pressure [PI max ]; duty cycle = 0.7; breathing frequency matched to eupnea) separated by 6-weeks high-resistance (75 % maximal inspiratory pressure, PI max), low-volume (30 inspiratory efforts/day, 5 days/week) IMST. Throughout resistive breathing trials we measured beat-to-beat changes in BP and HR, mouth pressure, inspiratory muscle work and perceived exertion. POST resistive breathing tests revealed significant gains in endurance (PRE: 362.0 ± 46.6 s vs. POST: 663.8 ± 110.3 s, p = 0.003) and increases in respiratory muscle work (PRE: −9445 ± 1562 mmHg.s vs. POST: −16648 ± 3761 mmHg.s, p = 0.069). Conversely, systolic and diastolic BP responses, HR and ratings of perceived exertion all declined. Consistent with previous observations, 6 weeks high resistance, low volume IMST lowered casual resting SBP (p = 0.002), DBP (p = 0.007) and mean arterial pressure (p = 0.001) and improved static inspiratory pressure. High resistance, low volume inspiratory muscle strength training extends respiratory endurance and attenuates BP responsiveness in healthy, recreationally-active young adults. The outcomes have implications for improved athletic performance and for attaining and/or maintaining cardiorespiratory fitness. [ABSTRACT FROM AUTHOR]

Neonates at risk for sudden infant death syndrome (SIDS) are hospitalized for cardiorespiratory monitoring however, monitoring is costly and generates large quantities of averaged data that serve as poor predictors of infant risk. In this study we used a traditional autocorrelation function (ACF) testing its suitability as a tool to detect subtle alterations in respiratory patterning in vivo. We applied the ACF to chest wall motion tracings obtained from rat pups in the period corresponding to the mid-to-end of the third trimester of human pregnancy. Pups were drawn from two groups: nicotine-exposed and saline-exposed at each age (i.e., P7, P8, P9, and P10). Respiratory-related motions of the chest wall were recorded in room air and in response to an arousal stimulus (F I O 2 14%). The autocorrelation function was used to determine measures of breathing rate and respiratory patterning. Unlike alternative tools such as Poincare plots that depict an averaged difference in a measure breath to breath, the ACF when applied to a digitized chest wall trace yields an instantaneous sample of data points that can be used to compare (data) points at the same time in the next breath or in any subsequent number of breaths. The moment-to-moment evaluation of chest wall motion detected subtle differences in respiratory pattern in rat pups exposed to nicotine in utero and aged matched saline-exposed peers. The ACF can be applied online as well as to existing data sets and requires comparatively short sampling windows (∼2 min). As shown here, the ACF could be used to identify factors that precipitate or minimize instability and thus, offers a quantitative measure of risk in vulnerable populations. [ABSTRACT FROM AUTHOR]

R3869 --> 602.7 --> Background: Age‐related declines in cardiorespiratory fitness (CRF) and exercise tolerance are major independent risk factors for cardiovascular diseases and mortality in midlife/older adults (ML/O; ≥50 years). Aerobic exercise is a well‐established strategy to improve CRF and exercise tolerance; however, adherence to time‐intensive physical activity (PA) guidelines is poor. High‐resistance inspiratory muscle strength training (IMST; 30 breaths/day against resistance, ~5 min/day) is a time‐efficient, highly adherable form of physical training but the effects of high‐resistance IMST on CRF and exercise tolerance in ML/O adults are unknown. We investigated if high‐resistance IMST would increase CRF and exercise tolerance and, if so, whether the improvements would be related to changes in circulating metabolites. Methods: Thirty‐five ML/O adults performed 6 weeks of high‐resistance IMST (75% maximal inspiratory pressure [PIMAX], n=17, 9F/8M) or Sham training (15% PIMAX, n=18, 8F/10M). Peak oxygen uptake (VO2peak) was determined with an incremental treadmill exercise test to exhaustion (modified Balke protocol). Exercise tolerance was defined as treadmill time to exhaustion (TTE). Metabolic pathways modulated by high‐resistance IMST were assessed using mass spectrometry‐based plasma metabolomics. Results: Adherence was high to both IMST and Sham training (IMST=94% of training sessions completed; Sham=90%). Body weight, body mass index (BMI), and leisure time PA levels remained stable in both groups across the intervention (all p>0.05). VO2peak was unchanged after 6 weeks of either high‐resistance IMST (pre=27.7±1.2 ml/kg/min, post=27.9±1.2 ml/kg/min; p=0.75) or Sham training (pre=27.2±1.7 ml/kg/min, post=26.7±1.6 ml/kg/min; p=0.20). However, high‐resistance IMST increased TTE by 12%, with no change after Sham (IMST: pre=540±42 sec, post=606±33 sec; Sham: pre=562±39 sec, post=553±44 sec; group*time: p=0.03). TTE increases were related to changes in 18 metabolites (all p<0.05), predominantly plasma acylcarnitines, which play key roles in energy production and fatty acid metabolism. Indeed, of the 19 carnitines measured, 11 were positively associated with TTE change post‐IMST. The strongest relations to TTE were seen with acyl‐C14:1 (R2=0.57; p<0.01), acyl‐C10 (R2=0.54; p<0.01), and acyl‐C12 (R2=0.52; p=0.01). These relations were not seen in the Sham group (all p>0.05). Conclusions: In ML/O adults, high‐resistance IMST does not increase CRF, but does improve TTE independent of changes in body weight, BMI, or PA. Improved TTE was related to changes in circulating metabolites, particularly increases in plasma acylcarnitines. These preliminary findings suggest 5 min/day of high‐resistance IMST is a promising, highly adherable mode of physical training that increases exercise tolerance and modulates metabolic pathways in ML/O adults. [ABSTRACT FROM AUTHOR]

Key points Motor units (MUs) are the fundamental element of force generation. Here we document the MU activities of the airway dilator muscle genioglossus (GG) during breathing at rest and in heavy exercise., Based on our observations we suggest that tonic MU activity, albeit with varying degrees of respiratory modulation, is the preponderant activity in the GG motoneuron pool of healthy young adults at rest in the upright position., Second, we show that exercise-driven increases in respiratory drive are associated with increased GG electromyographic activity principally due to recruitment of previously silent MUs and to a shift in the firing behaviour of already active MUs to inspiratory phase-dependent bursting., Such expiration-related inhibition may arise secondary to an exercise-related central enhancement of motoneuron excitability that amplifies the response to afferent input., Abstract The genioglossus (GG) muscle is considered the principal protruder muscle of the tongue that dilates and stiffens the pharyngeal airway. We recorded whole muscle and single motor unit (MU) activities in healthy adults performing progressive intensity exercise on a cycle ergometer. Tungsten microelectrodes were inserted percutaneously into the GG of 11 subjects (20-40 years) to record electromyographic (EMG) activities and pulmonary ventilation ( VI) at rest and at workload increments up to 300 W. Increases in respiratory drive were associated with increases in VI, mean inspiratory flow ( Vt/ Ti) and tonic and phasic components of the GG EMG activity. In contrast, individual MUs typically showed expiration-related decreases in firing as exercise intensity increased. We suggest the decrease in MU activity may occur secondary to afferent feedback from lungs/chest wall and that compensation for more negative inspiratory airway pressures generated during heavy exercise occurs primarily via recruitment of previously silent MUs. [ABSTRACT FROM AUTHOR]

R1937 --> Background: Advancing age is associated with increased risk for cardiovascular diseases (CVD), cognitive decline, Alzheimer's disease and related dementias. Part of this risk may be driven by age‐related increases in systolic blood pressure (SBP) and subsequent cerebrovascular dysfunction. Habitual aerobic exercise lowers SBP and promotes cerebrovascular health; however, lack of time and other barriers limit adherence to physical activity guidelines in the majority of adults. High‐resistance inspiratory muscle strength training (IMST; 30 inhalations/session against resistance), is a time‐efficient, highly‐adherable lifestyle intervention for lowering SBP and improving peripheral vascular function in midlife/older (ML/O; ≥50 years) adults with initial above‐normal SBP (i.e., ≥120 mmHg). However, whether IMST improves cerebrovascular function in this at‐risk population is unknown. Purpose: To determine if high‐resistance IMST improves measures of cerebrovascular function in ML/O adults with initial above‐normal SBP. We hypothesized 6 weeks of high‐resistance IMST would improve cerebrovascular function vs. low‐resistance Sham training. Methods: Cerebrovascular function was measured in 16 ML/O adults before and after 6 weeks of high‐resistance IMST (30 breaths/day, 6 days/week, 75% maximal inspiratory pressure [PIMAX]) (n=9, 4F/5M, 65 ± 3 years) or Sham training (15% PIMAX, n=7, 2F/5M, 63 ± 2 years). Middle cerebral artery blood velocity (MCAv) was measured with a 2‐MHz transcranial Doppler probe during 5 minutes each of normocapnia and hypercapnia (5% CO2, balanced nitrogen). Cerebrovascular reactivity (CVR), a measure of cerebrovascular responsiveness to a vasoactive stimulus, was determined as ΔMCAv/Δend‐tidal CO2 between normocapnia and hypercapnia and interpreted as an index of cerebrovascular health. To account for potential changes in perfusion pressure, CVR was normalized to the change in mean arterial BP from normocapnia to hypercapnia and expressed as cerebrovascular conductance index (CVCi) reactivity. Pulsatility index, a marker of cerebrovascular stiffness, was calculated as (MCAvsystole – MCAvdiastole)/MCAvmean. Results: CVR was significantly increased after 6 weeks of IMST (pre: 1.38 ± 0.22 cm/s/mmHg, post: 2.31 ± 0.34 cm/s/mmHg; p=0.04), but not Sham training (pre: 1.20 ± 0.08 cm/s/mmHg, post: 1.48 ± 0.23 cm/s/mmHg; p=0.75). As a result, CVR was higher in the IMST group vs. Sham after the intervention period (p=0.06). CVCi reactivity also was significantly higher after IMST (pre: 0.009 ± 0.002 cm/s/mmHg2, post: 0.018 ± 0.004 cm/s/mmHg2; p=0.05), but not Sham training (pre: 0.009 ± 0.001 cm/s/mmHg2, post: 0.010 ± 0.002 cm/s/mmHg2; p=0.90). Pulsatility index did not change in either group (all p>0.05). Conclusion: These preliminary findings suggest high‐resistance IMST is a promising, time‐efficient intervention for improving select measures of cerebrovascular function in ML/O adults with initial above‐normal SBP, a cohort at high risk for future CVD and cognitive decline. [ABSTRACT FROM AUTHOR]