Laghi F, Topeli A, Tobin M J
Division of Pulmonary and Critical Care Medicine, Edward Hines, Jr., Veterans Administration Hospital, and Loyola University of Chicago Stritch School of Medicine, Hines, Illinois 60141, USA.
J Appl Physiol (1985). 1998 Sep;85(3):1103-12. doi: 10.1152/jappl.1998.85.3.1103.
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 (Pdimax) for 2 min, 4 min, and until task failure. Before loading, 20 min after each period of loading, and approximately 20 h after the last period of loading, Pdimax, nonpotentiated and potentiated Pdi twitch pressure (Pditw), 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 4-min protocol. Surprisingly, potentiated Pditw and Pdimax were reduced after 2 min of loading and decreased further after 4 min of loading and after task failure; nonpotentiated Pditw 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 approximately 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.
在承受导致任务失败的负荷时，尚不清楚膈肌疲劳是逐渐发展还是仅在任务失败时才出现。我们假设递增负荷会在任务失败前就使膈肌收缩力逐渐下降。10名受试者分别以最大跨膈压（Pdimax）的60%进行2分钟、4分钟的负荷，直至任务失败。在负荷前、每次负荷期后20分钟以及最后一次负荷期后约20小时，记录Pdimax、非增强和增强的膈肌抽搐压力（Pditw）以及二氧化碳激发试验期间呼吸肌募集模式。任务失败方案第4分钟时的吸气努力感觉大于前一个4分钟方案中同一时间的感觉。令人惊讶的是，负荷2分钟后增强的Pditw和Pdimax降低，负荷4分钟后以及任务失败后进一步降低；非增强的Pditw在负荷4分钟后以及任务失败后降低。在二氧化碳激发试验期间，胃压对潮气量呼吸的贡献相对于前一个负荷期的持续时间逐渐降低，而呼气肌募集则逐渐增加。任务失败后约20小时的休息期不足以使呼吸肌募集的这些改变或疲劳引起的膈肌收缩力变化恢复正常。总之，在承受机械负荷时，膈肌在任务失败前就逐渐疲劳，并且当受到刺激时，胸廓对膈肌的潮气量呼吸贡献和呼气肌募集与前一个负荷期的持续时间同步增加。
