Roussos C, Fixley M, Gross D, Macklem P T
J Appl Physiol Respir Environ Exerc Physiol. 1979 May;46(5):897-904. doi: 10.1152/jappl.1979.46.5.897.
The time (tlim) required to produce inspiratory muscle fatigue was measured in five normal subjects breathing at functional residual capacity (FRC) against a variety of high inspiratory resistive loads. In every breathing test the subjects generated with each inspiration a mouth pressure (Pm) that was a predetermined fraction of maximum Pm (Pmmax). They continued breathing until they were unable to generate this Pm. The Pm/Pmmax that could be generated indefinitely (Pmcrit) was around 60%. The inspiratory power output at that level of breathing was 6.6 kg.m/min (Wcrit). In three of those subjects the same experiment was conducted at an end-expiratory volume of FRC + one-half inspiratory capacity (1/2IC). The higher lung volume was actively maintained by the subjects watching end-expiratory transpulmonary pressure on an oscilloscope. For any fraction of the maximum mouth pressure at FRC + 1/2IC (Pm'max), tlim was shorter than FRC. Pmcrit decreased to 30% Pm'max and Wcrit to 2.6 kg.m/min. Monitoring the abdominal pressure revealed that the contribution of the diaphragm and intercostal accessory muscles alternated in time, possibly postponing the onset of fatigue.
在五名正常受试者以功能残气量（FRC）呼吸对抗各种高吸气阻力负荷的情况下，测量了产生吸气肌疲劳所需的时间（tlim）。在每次呼吸测试中，受试者每次吸气时产生的口腔压力（Pm）是最大Pm（Pmmax）的预定比例。他们持续呼吸，直到无法产生该Pm。能够无限期产生的Pm/Pmmax（Pmcrit）约为60%。在该呼吸水平下的吸气功率输出为6.6 kg·m/min（Wcrit）。在其中三名受试者中，在呼气末容积为FRC + 一半吸气容量（1/2IC）时进行了相同的实验。受试者通过观察示波器上的呼气末跨肺压来主动维持较高的肺容积。对于FRC + 1/2IC时最大口腔压力的任何比例（Pm'max），tlim均短于FRC时。Pmcrit降至30% Pm'max，Wcrit降至2.6 kg·m/min。监测腹压发现，膈肌和肋间辅助肌的贡献随时间交替，这可能推迟了疲劳的发生。
