Lake F R, Finucane K E, Hillman D R
Department of Pulmonary Physiology, Sir Charles Gairdner Hospital, Nedlands, Western Australia, Australia.
Respir Physiol. 1999 Dec 1;118(2-3):149-61. doi: 10.1016/s0034-5687(99)00065-1.
To quantify any mechanical inhibitory effect of nasal intermittent positive pressure ventilation (IPPV) on inspiratory activity of the diaphragm we ventilated five conscious relaxed subjects on two occasions at respiratory rates similar to quiet breathing (QB) and at three levels of applied pressure (Pappl)--6, 9 and 12 cmH2O, each during hypocapnia (P(CO2) allowed to decrease) and eucapnia (CO2 added to inspired gas). Diaphragm activity was assessed from transdiaphragmatic pressure (esophageal and gastric balloons) and diaphragm EMG (surface electrodes) both integrated with time (integral(Pdi x dt) and integral(EMGdi x dt), respectively). Neural inspiratory time (Tin) was measured as onset to peak of the integral(EMGdi x dt) signal. Relative to QB, integral(Pdi x dt) was 50-69% less during eucapnic IPPV 6-12 cmH2O (P < 0.005) and 67-85% less during hypocapnic IPPV (P < 0.005). Tin decreased (P < 0.05) with IPPV and, on ceasing IPPV, there was apnoea (prolonged expiratory time) on 23 of 27 occasions; these changes were independent of P(CO2). Integral(EMGdi x dt) decreased (P < 0.05) at Pappl 12 cmH2O during eucapnia and at all Pappl during hypocapnia. The repeatability of integral(EMGdi x dt) was substantially less than integral(Pdi x dt) (F = 42, P << 0.01). We conclude that, during non-invasive IPPV in awake healthy subjects mechanical factors are of major importance in inhibiting inspiratory activity of the diaphragm.
为了量化经鼻间歇正压通气（IPPV）对膈肌吸气活动的任何机械抑制作用，我们在两种情况下对五名清醒放松的受试者进行通气，呼吸频率与安静呼吸（QB）相似，施加压力（Pappl）分三个水平——6、9和12 cmH₂O，每次在低碳酸血症（允许P(CO₂)降低）和正常碳酸血症（向吸入气体中添加CO₂）期间进行。通过经膈压（食管和胃气囊）和膈肌肌电图（表面电极）评估膈肌活动，二者均与时间积分（分别为积分(Pdi×dt)和积分(EMGdi×dt)）。神经吸气时间（Tin）测量为积分(EMGdi×dt)信号从开始到峰值的时间。与QB相比，在正常碳酸血症的IPPV 6 - 12 cmH₂O期间，积分(Pdi×dt)减少了50 - 69%（P < 0.005），在低碳酸血症的IPPV期间减少了67 - 85%（P < 0.005）。Tin随IPPV降低（P < 0.05），停止IPPV时，27次中有23次出现呼吸暂停（呼气时间延长）；这些变化与P(CO₂)无关。在正常碳酸血症时，Pappl为12 cmH₂O时积分(EMGdi×dt)降低（P < 0.05），在低碳酸血症时所有Pappl水平下积分(EMGdi×dt)均降低。积分(EMGdi×dt)的可重复性明显低于积分(Pdi×dt)（F = 42，P << 0.01）。我们得出结论，在清醒健康受试者的无创IPPV期间，机械因素在抑制膈肌吸气活动中起主要作用。
