School of Kinesiology, University of British Columbia, Vancouver, BC, Canada.
Department of Physical Therapy, University of Florida, Gainesville, FL, USA.
J Physiol. 2021 Feb;599(4):1319-1333. doi: 10.1113/JP280704. Epub 2020 Nov 25.
Under normoxic conditions, both healthy female and male diaphragms fatigue at a similar degree when matched for absolute diaphragmatic work during inspiratory loading. We investigated whether similarities in diaphragm fatigability persist under acute hypoxic conditions. We found that, in acute hypoxia, fatigue of the diaphragm is greater in women compared to men, whereas the magnitude of fatigue in normoxia did not differ between sexes. When matched for maximal diaphragm strength, women and men had a similar pressor response to work-matched inspiratory loading, independent of oxygen availability.
In normoxia, women and men display a comparable magnitude of diaphragmatic fatigue (DF) after work-matched inspiratory loading. Whether these sex similarities are maintained under acute hypoxic conditions is unknown. We investigated the influence of acute hypoxia during work-matched inspiratory pressure-threshold loading (PTL) on DF in healthy women (n = 8) and men (n = 8). Two 5 min isocapnic PTL tasks targeting a transdiaphragmatic pressure (P ) of 92 cmH O in normoxia and hypoxia (8% O ) were performed on separate days (≥48 h). DF was quantified by twitch P (P ) via cervical magnetic stimulation post-PTL. Women and men had similar maximal P (P ; women: 171 ± 16, men: 178 ± 20 cmH O) and relative target workload (women: 54 ± 5%, men: 53 ± 6% P ). The absolute cumulative diaphragmatic work did not differ between sexes in normoxia (women: 12,653 ± 1796 cmH O s , men: 13,717 ± 1231 cmH O s ; P = 0.202) or hypoxia (women: 11,624 ± 1860 cmH O s , men: 12 722 ± 1502 cmH O s ; P = 0.189). In normoxia, the magnitude of reduction in P post-PTL was similar between sexes (women: -21.1 ± 8.4%, men: -22.5 ± 4.9 %; P = 0.193); however, a higher degree of DF was observed in women compared to men following PTL in acute hypoxia (women: -27.6 ± 7.7%, men: -23.4 ± 9.6%, P = 0.019). We conclude that the female diaphragm is more susceptible to fatigue after inspiratory loading under acute hypoxic conditions. This finding may be related to sex differences in diaphragm muscle metabolism, such as fibre type composition, contractile properties, substrate utilisation and blood perfusion.
在常氧条件下，当匹配吸气负荷时的绝对膈肌工作量时，健康女性和男性的膈肌在疲劳程度上相似。我们研究了在急性低氧条件下，膈肌疲劳的相似性是否持续存在。我们发现，在急性低氧时，女性的膈肌疲劳程度大于男性，而在常氧时，性别之间的疲劳程度没有差异。当匹配最大膈肌强度时，女性和男性在吸气压力阈值负荷（PTL）下的压力反应相似，与氧气供应无关。
在常氧条件下，女性和男性在匹配吸气负荷后表现出相当程度的膈肌疲劳（DF）。在急性低氧条件下，这些性别相似性是否维持尚不清楚。我们研究了急性低氧期间工作匹配吸气压力阈值负荷（PTL）对健康女性（n=8）和男性（n=8）的膈肌疲劳（DF）的影响。在常氧和低氧（8%O ）下，分别在 2 天（≥48 小时）进行 5 分钟的等碳酸 PTL 任务，目标是跨膈压（P ）为 92 cmH O。通过颈磁刺激在 PTL 后测量 twitch P （P ）来量化 DF。女性和男性的最大 P （P ；女性：171±16，男性：178±20 cmH O）和相对目标工作量（女性：54±5%，男性：53±6% P ）相似。在常氧（女性：12653±1796 cmH O s ，男性：13717±1231 cmH O s ；P=0.202）或低氧（女性：11624±1860 cmH O s ，男性：12722±1502 cmH O s ；P=0.189）中，性别之间的绝对膈肌工作量无差异。在常氧下，PTL 后 P 的降低幅度在性别之间相似（女性：-21.1±8.4%，男性：-22.5±4.9%；P=0.193）；然而，在急性低氧下，女性在 PTL 后观察到更高程度的 DF（女性：-27.6±7.7%，男性：-23.4±9.6%，P=0.019）。我们得出结论，女性膈肌在急性低氧条件下吸气负荷后更容易疲劳。这一发现可能与膈肌肌肉代谢的性别差异有关，例如纤维类型组成、收缩特性、底物利用和血液灌注。
