Diaphragm Recruitment Increases during a Bout of Targeted Inspiratory Muscle Training

Experimental Physiology

Dominelli

et al. 2017

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What is the central question of this study? This study is the first to measure objectively both inspiratory and expiratory muscle fatigue after inspiratory resistive loading to determine whether the expiratory muscles are activated to the point of fatigue when specifically loading the inspiratory muscles. What is the main finding and its importance? The absence of abdominal muscle fatigue suggests that future studies attempting to understand the neural and circulatory consequences of diaphragm fatigue can use inspiratory resistive loading without considering the confounding effects of abdominal muscle fatigue. Expiratory resistive loading elicits inspiratory as well as expiratory muscle fatigue, suggesting parallel coactivation of the inspiratory muscles during expiration. It is unknown whether the expiratory muscles are likewise coactivated to the point of fatigue during inspiratory resistive loading (IRL). The purpose of this study was to determine whether IRL elicits expiratory as well as inspiratory muscle fatigue. Healthy male subjects (n = 9) underwent isocapnic IRL (60% maximal inspiratory pressure, 15 breaths min , 0.7 inspiratory duty cycle) to task failure. Abdominal and diaphragm contractile function was assessed at baseline and at 3, 15 and 30 min post-IRL by measuring gastric twitch pressure (P ) and transdiaphragmatic twitch pressure (P ) in response to potentiated magnetic stimulation of the thoracic and phrenic nerves, respectively. Fatigue was defined as a significant reduction from baseline in P or P . Throughout IRL, there was a time-dependent increase in cardiac frequency and mean arterial blood pressure, suggesting activation of the respiratory muscle metaboreflex. The P was significantly lower than baseline (34.3 ± 9.6 cmH O) at 3 (23.2 ± 5.7 cmH O, P < 0.001), 15 (24.2 ± 5.1 cmH O, P < 0.001) and 30 min post-IRL (26.3 ± 6.0 cmH O, P < 0.001). The P was not significantly different from baseline (37.6 ± 17.1 cmH O) at 3 (36.5 ± 14.6 cmH O), 15 (33.7 ± 12.4 cmH O) and 30 min post-IRL (32.9 ± 11.3 cmH O). Inspiratory resistive loading elicits objective evidence of diaphragm, but not abdominal, muscle fatigue. Agonist-antagonist interactions for the respiratory muscles appear to be more important during expiratory versus inspiratory loading.

Section: Discussionmentioning

confidence: 99%

“…Peak root mean square data were analysed during inspiration by manually selecting EMG signals to avoid the influence of cardiac artifact on EMG measurements of the respiratory muscles (Ramsook et al . ).…”

Section: Methodsmentioning

confidence: 97%

Influence of inspiratory resistive loading on expiratory muscle fatigue in healthy humans

Peters

Experimental Physiology

Dominelli

et al. 2017

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“…Subjects were instructed to breathe using their diaphragm in order to minimize the recruitment of accessory inspiratory muscles (Ramsook et al . ). The task was terminated at the 5 min mark for all subjects.…”

Section: Methodsmentioning

confidence: 97%

“…The target inspiratory pressure was displayed on a computer screen to provide continuous visual feedback. Subjects were instructed to breathe using their diaphragm in order to minimize the recruitment of accessory inspiratory muscles (Ramsook et al 2016). The task was terminated at the 5 min mark for all subjects.…”

Section: Inspiratory Pressure-threshold Loadingmentioning

confidence: 99%

Diaphragm fatigue and inspiratory muscle metaboreflex in men and women matched for absolute diaphragmatic work during pressure‐threshold loading

Geary

The Journal of Physiology

McDonald

et al. 2019

Key points The female diaphragm fatigues at a slower rate compared to that of males, with blunted cardiovascular consequences (i.e. inspiratory muscle metaboreflex). It is unclear if these findings are a function of relative or absolute diaphragmatic work. We asked if sex differences in diaphragm fatigue and the inspiratory muscle metaboreflex persisted during inspiratory loading performed at equal absolute intensities. We found that matching men and women for absolute diaphragmatic work resulted in an equal degree of diaphragm fatigue, despite women performing significantly greater work relative to body mass. Metabolite‐induced reflex influences in sympathetic outflow originating from the diaphragm are attenuated in women, with potential implications for blood flow distribution during exercise. Abstract In response to inspiratory pressure‐threshold loading (PTL), women have greater inspiratory muscle endurance time, slower rate of diaphragm fatigue development, and a blunted pressor response compared to men. It is unclear if these differences are due to discrepancies in absolute diaphragm force output. We tested the hypothesis that following inspirations performed at equal absolute intensities, females would develop a similar level of diaphragm fatigue and an attenuated cardiovascular response relative to men. Healthy young men (n = 8, age = 24 ± 3 years) and women (n = 8, age = 23 ± 3 years) performed PTL whilst targeting a transdiaphragmatic pressure (Pdi) of 92 cmH2O for 5 min. Diaphragm fatigue was assessed via twitch Pdi (Pdi,tw) using cervical magnetic stimulation. Heart rate (HR) and mean arterial blood pressure were monitored continuously. During PTL, the absolute amount of diaphragm work was not different between men (13,399 ± 2019 cmH2O s) and women (12,986 ± 1846 cmH2O s; P > 0.05); however, women performed the PTL task at a higher relative trueP¯di/Pdi,max. Following inspiratory PTL, the magnitude of reduction in Pdi,tw was similar between men (−27.1 ± 7.2%) and women (−23.8 ± 13.8%; P > 0.05). There were significant increases in HR over time (P < 0.05), but this did not differ on the basis of sex (P > 0.05). Mean arterial blood pressure increased significantly over time in both men and women (P < 0.05); however, the rate of change was higher in men (6.24 ± 2.54 mmHg min−1) than in women (4.15 ± 2.52 mmHg min−1) (P < 0.05). We conclude that the female diaphragm is protected against severe fatigue when inspiratory work is excessive and as a result does not evoke overt sympathoexcitation.

“…Subjects were instructed to breathe diaphragmatically as natural breathing strategies during resistive inspirations can preferentially target accessory inspiratory muscles (Ramsook et al . ). The task was terminated when subjects failed to generate the target inspiratory pressure for four consecutive breaths or the second occasion of three missed consecutive breaths despite verbal encouragement.…”

Section: Methodsmentioning

confidence: 97%

Sex differences in diaphragmatic fatigue: the cardiovascular response to inspiratory resistance

The Journal of Physiology

Archiza

Guenette

et al. 2018

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Diaphragmatic fatigue (DF) elicits reflexive increases in sympathetic vasomotor outflow (i.e. metaboreflex). There is some evidence suggesting women may be more resistant to DF compared to men, and therefore may experience an attenuated inspiratory muscle metaboreflex. To this end, we sought to examine the cardiovascular response to inspiratory resistance in healthy young men (n = 9, age = 24 ± 3 years) and women (n = 9, age = 24 ± 3 years). Subjects performed isocapnic inspiratory pressure-threshold loading (PTL, 60% maximal inspiratory mouth pressure) to task failure. Diaphragmatic fatigue was assessed by measuring transdiaphragmatic twitch pressure (P ) using cervical magnetic stimulation. Heart rate (HR) and mean arterial pressure (MAP) were measured beat-by-beat throughout PTL via photoplethysmography, and low-frequency systolic pressure (LF ; a surrogate for sympathetic vasomotor tone) calculated from arterial waveforms using power spectrum analysis. At PTL task failure, the degree of DF was similar between sexes (∼23% reduction in P ; P = 0.33). However, time to task failure was significantly longer in women than in men (27 ± 11 vs. 16 ± 11 min, respectively; P = 0.02). Women exhibited less of an increase in HR (13 ± 8 vs. 19 ± 12 bpm; P = 0.02) and MAP (10 ± 8 vs. 14 ± 9 mmHg; P = 0.01), and significantly lower LF (23 ± 11 vs. 34 ± 8 mmHg ; P = 0.04) during PTL compared to men. An attenuation of the inspiratory muscle metaboreflex may influence limb and respiratory muscle haemodynamics with implications for exercise performance.