Barnas G M, Mills P J, Mackenzie C F, Fletcher S J, Green M D
Department of Anesthesiology, University of Maryland, Baltimore 21201.
Am Rev Respir Dis. 1992 Mar;145(3):522-6. doi: 10.1164/ajrccm/145.3.522.
Recent studies have shown that the mechanical properties of the respiratory system at normal breathing frequency in awake humans depend on tidal volume. Few measurements of respiratory system properties during anesthesia have accounted for this dependence. From measurements of airway pressure, flow and esophageal pressure, we calculated elastances and resistances of the total respiratory system (Ers and Rrs), chest wall (Ecw and Rcw), and lungs (El and Rl) in supine human volunteers during quasisinusoidal volume forcing in a normal range of breathing (250 to 800 ml) at normal breathing frequency (0.2 Hz). Measurements were made (1) with subjects awake and voluntarily relaxed; (2) after isoflurane-N2O anesthesia (end-tidal isoflurane concentration 0.3 to 0.5%); and (3) after complete muscle paralysis with vecuronium. In all conditions, Ers, Ecw, El, Rrs, and Rcw decreased at 800 ml tidal volume compared with 250 ml; Rl showed a similar decrease in awake measurements only. Compared with awake measurements, each elastance tended to increase after anesthesia, but only the increase in Ers was significant. Compared with anesthesia, there was no effect of paralysis on any measurement. We conclude that (1) tidal volume dependence of respiratory system properties in the normal range of breathing occurs in the absence of muscle activity; (2) anesthesia increases Ers and (3) respiratory muscle activity appears to be inhibited by isoflurane-N2O anesthesia at end-tidal isoflurane concentration of 0.3 to 0.5% during normocapnia.
近期研究表明，清醒人体在正常呼吸频率下呼吸系统的力学特性取决于潮气量。在麻醉期间对呼吸系统特性的测量很少考虑到这种依赖性。通过测量气道压力、流量和食管压力，我们计算了仰卧位人体志愿者在正常呼吸频率（0.2Hz）下准正弦容积驱动、正常呼吸范围（250至800ml）时全呼吸系统（Ers和Rrs）、胸壁（Ecw和Rcw）以及肺（El和Rl）的弹性和阻力。测量在以下三种情况下进行：（1）受试者清醒且自愿放松；（2）异氟烷 - N₂O麻醉后（呼气末异氟烷浓度0.3至0.5%）；（3）维库溴铵完全肌松后。在所有情况下，与250ml潮气量相比，800ml潮气量时Ers、Ecw、El、Rrs和Rcw均降低；仅在清醒测量时Rl有类似降低。与清醒测量相比，麻醉后每种弹性均有增加趋势，但只有Ers的增加具有统计学意义。与麻醉状态相比，肌松对任何测量均无影响。我们得出以下结论：（1）在无肌肉活动的情况下，呼吸系统特性在正常呼吸范围内存在潮气量依赖性；（2）麻醉使Ers增加；（3）在正常二氧化碳分压下，呼气末异氟烷浓度为0.3至0.5%时，异氟烷 - N₂O麻醉似乎抑制了呼吸肌活动。
