Vassiliou M, Peslin R, Saunier C, Duvivier C
Unité 14 de Physiopathologie Respiratoire, Institut National de la Santé et de la Recherche Médicale, Université H. Poincaré Nancy 1, Vandoeuvre-les-Nancy, France.
Eur Respir J. 1996 Apr;9(4):779-86. doi: 10.1183/09031936.96.09040779.
We have previously observed large phasic variations of respiratory mechanical impedance in chronic obstructive pulmonary disease (COPD) patients mechanically-ventilated for acute respiratory failure, and postulated that they were due to expiratory flow limitation (EFL). The aim of this study was to test that assumption experimentally and to assess the value of impedance for automatic and noninvasive detection of EFL during mechanical ventilation. The study was performed: 1) in a mechanical analogue, including a flow-limiting element; and 2) in eight anaesthetized and paralysed rabbits, before and during histamine infusion. In both instances, EFL was obtained by lowering the expiratory pressure, using a computer-controlled ventilator; the absence of flow increase when expiratory pressure was further lowered was taken as evidence of EFL. Impedance was measured by applying 15 Hz oscillations at the airway opening. Its real (Re) and imaginary (Im) parts were measured separately during the inspiratory and the expiratory phases, and their differences were related to the mean inspiratory modulus. With the analogue, EFL was accompanied by large decreases both of Re and Im during the expiratory phase. In the rabbits, phasic variations of Re were variable in sign and were not significantly different with and without EFL. In contrast, EFL systematically and specifically decreased Im during the expiratory phase. A threshold of -50% provided a sensitivity of 96% and a specificity of 100% for detecting EFL. The observed phasic variations may be explained by airway wall shunt properties. The study suggests that a large decrease of the imaginary part of impedance during the expiratory phase is a sensitive and specific index of expiratory flow limitation during artificial ventilation.
我们之前观察到，因急性呼吸衰竭接受机械通气的慢性阻塞性肺疾病（COPD）患者的呼吸机械阻抗存在大幅度的相位变化，并推测这是由于呼气气流受限（EFL）所致。本研究的目的是通过实验验证这一假设，并评估阻抗在机械通气期间自动无创检测EFL的价值。该研究在以下两种情况下进行：1）在包含限流元件的机械模拟装置中；2）在八只麻醉并麻痹的兔子身上，于输注组胺之前和期间进行。在这两种情况下，使用计算机控制的呼吸机通过降低呼气压力来实现EFL；当呼气压力进一步降低时气流未增加被视为EFL的证据。通过在气道开口处施加15 Hz的振荡来测量阻抗。在吸气和呼气阶段分别测量其实部（Re）和虚部（Im），并将它们的差值与平均吸气模量相关联。在模拟装置中，EFL伴随着呼气阶段Re和Im的大幅下降。在兔子身上，Re的相位变化符号不定，在有和没有EFL的情况下无显著差异。相比之下，EFL在呼气阶段系统性且特异性地降低了Im。-50%的阈值在检测EFL时的灵敏度为96%，特异性为100%。观察到的相位变化可能由气道壁分流特性来解释。该研究表明，呼气阶段阻抗虚部的大幅下降是人工通气期间呼气气流受限的敏感且特异指标。
