Department of Pneumology, University Hospital Freiburg, Killianstrasse 5, D-79106 Freiburg, Germany.
Respir Physiol Neurobiol. 2011 Apr 30;176(1-2):14-20. doi: 10.1016/j.resp.2011.01.009. Epub 2011 Jan 31.
The diaphragm was postulated to fatigue relatively early during exhaustive whole body exercise without further loss in contractility as exercise proceeds towards task failure. Diaphragmatic contractility was investigated prior/during/after exhaustive whole body exercise until task failure by using lung volume corrected twitch transdiaphragmatic pressure (TwPdi(c)) during magnetic phrenic nerve stimulation (every 45s). Eleven cyclists exercised to exhaustion (workloads ≥85% maximal oxygen uptake; 20.7±9.8min). Individual post hoc calculation of TwPdi(c) was conducted (diaphragmatic contractility versus lung volume). Diaphragmatic fatigue (i.e. TwPdi reduction baseline/recovery ≥10%) occurred in 9/11 subjects (82% "fatiguers"; baseline/recovery TwPdi(c) -16±13%, p<0.01). Fatiguers TwPdi(c) was: baseline: 2.99±0.40kPa, exercise-onset: 2.98±0.41kPa, initial third: 2.80±0.67kPa, second third: 2.54±0.55kPa, final third-task failure: 2.51±0.44kPa, recovery: 2.50±0.52kPa. Diaphragmatic contractility and lung volume (rest) were strongly related (r(2)=0.98, mean TwPdi(c) gradient 0.78kPa/l). To conclude, diaphragmatic contractility (lung volume corrected) decreases relatively early (initial two thirds) during exhaustive exercise and remains preserved towards task failure. This confirms previous assumptions postulating that respiratory performance is sustained without further fatigue of the primary inspiratory muscle.
膈肌在全身衰竭性运动中，在进一步收缩力丧失之前，可能会较早疲劳，随着运动向衰竭进行。在进行全身衰竭性运动直至任务失败的过程中，通过在磁神经刺激时使用肺活量校正的膈神经 twitch 跨膈压（TwPdi(c)）（每 45 秒一次）来研究膈神经收缩力。11 名自行车运动员进行衰竭性运动（工作量≥85%最大摄氧量；20.7±9.8min）。对每个个体进行事后 TwPdi(c)的计算（膈神经收缩力与肺活量的关系）。11 名运动员中有 9 名（82%的“疲劳者”）出现膈神经疲劳（即 TwPdi 降低基线/恢复≥10%）。疲劳者的 TwPdi(c)为：基线：2.99±0.40kPa，运动开始时：2.98±0.41kPa，初始第三阶段：2.80±0.67kPa，第二三阶段：2.54±0.55kPa，最后三阶段-任务失败：2.51±0.44kPa，恢复：2.50±0.52kPa。膈神经收缩力和肺活量（休息时）之间具有很强的相关性（r(2)=0.98，平均 TwPdi(c)梯度为 0.78kPa/l）。综上所述，在全身衰竭性运动中，膈神经收缩力（肺活量校正）在早期（前两个三分之一）就会较早下降，并且在接近任务失败时仍然保持不变。这证实了之前的假设，即呼吸性能在没有主要吸气肌进一步疲劳的情况下得以维持。
