Does resistive loading decrease diaphragmatic contractility before task failure?
Does resistive loading decrease diaphragmatic contractility before task failure?
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DOI：
10.1152/jappl.1998.85.3.1103
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发表时间：
1998-09-01
影响因子：
3.3
通讯作者：
Tobin, MJ
中科院分区：
文献类型：
--
作者：
Laghi, F;Topeli, A;Tobin, MJ
在承受导致任务失败的负荷时，尚不清楚横隔膜疲劳是逐渐发展还是仅在任务失败时发生。我们假设，在任务失败之前，递增负荷会导致横隔肌收缩能力的进行性下降。10名受试者产生60%的最大跨膈压(PDI(Max))，持续2分钟、4分钟，直到任务失败。记录负荷前、负荷后20min和末次负荷后20h的最大呼气末压力(pdi(Max))、非增强和增强呼气末收缩压(pdi(Tw))，以及CO2刺激时呼吸肌的募集模式。在任务失败方案的第4分钟，吸气努力的感觉比之前的C-min方案的同一时间更大。令人惊讶的是，增强的PDI(Tw)和PDI(Max)在加载2min后下降，并在加载4min和任务失败后进一步下降，非增强的PDI(Tw)在加载4min和任务失败后下降。在二氧化碳激发期间，胃压对潮气呼吸的贡献随着前一负荷期的持续时间而递减，而呼气肌募集则递增。任务失败后类似于20小时的休息时间不足以使呼吸肌招募的这些变化或疲劳引起的横隔肌收缩的变化正常化。总而言之，在承受机械负荷的同时，在任务失败之前，横隔膜就会逐渐疲劳，当受到挑战时，胸腔到横隔膜对潮气呼吸的贡献和呼气肌的募集随着前一次负荷的持续时间而增加。
While sustaining a load that leads to task failure, it is unclear whether diaphragmatic fatigue develops progressively or occurs only at task failure. We hypothesized that incremental loading produces a progressive decrease in diaphragmatic contractility ever before task failure. Ten subjects generated 60% of maximal transdiaphragmatic pressure (Pdi(max)) for 2 min, 4 min, and until task failure. Before loading, 20 min after each period of loading, and similar to 20 h after the last period of loading, Pdi(max), nonpotentiated and potentiated Pdi twitch pressure (Pdi(tw)), and the pattern of respiratory muscle recruitment during a CO2 challenge were recorded. Sensation of inspiratory effort at the 4th min of the task-failure protocol was greater than at the same time in the preceding C-min protocol. Surprisingly, potentiated Pdi(tw) and Pdi(max) were reduced after 2 min of loading and decreased further after 4 min of loading and after task failure; nonpotentiated Pdi(tw) was reduced after 4 min of loading and after task failure. The gastric pressure contribution to tidal breathing during a CO2 challenge decreased progressively in relation to duration of the preceding loading period, whereas expiratory muscle recruitment progressively increased. A rest period of similar to 20 h after task failure was not sufficient to normalize these alterations in respiratory muscle recruitment or fatigue-induced changes in diaphragmatic contractility. In conclusion, while sustaining a mechanical load, the diaphragm progressively fatigued, ever before task failure, and when challenged the rib cage-to-diaphragmatic contribution to tidal breathing and recruitment of the expiratory muscles increased pari passu with duration of the preceding loading.