Chen R C, Yan S
Meakins-Christie Laboratories, McGill University and Montreal Chest Institute of Royal Victoria Hospital, Montreal, Quebec, Canada.
Am J Respir Crit Care Med. 1999 Mar;159(3):720-7. doi: 10.1164/ajrccm.159.3.9803044.
Dynamic hyperinflation loads the inspiratory muscles by increasing end-expiratory lung volume (EELV) and imposing intrinsic positive end-expiratory pressure (PEEPi), the latter behaving as an inspiratory threshold load (ITL). The major purpose of this study was to describe the independent effects of the imposed ITL and changes in operating lung volume on the perception of inspiratory difficulty. In eight healthy subjects, independent increases in EELV and ITL were induced by continuous positive airway pressure (CPAP) and external ITL applications, respectively; increase in both EELV and PEEPi (thus the imposed ITL) was induced by application of positive end-expiratory pressure (PEEP). The perceived inspiratory difficulty increased significantly when either EELV or ITL was increased, and was always greater during combined increase in EELV and the imposed ITL (during PEEP) than when either factor was increased independently, suggesting that the imposed ITL and EELV each contribute independently to inspiratory difficulty. Inspiratory difficulty of each subject under all conditions was then fitted into a step-forward multiple regression model. The imposed ITL was a significant contributor to inspiratory difficulty in all subjects and was the first parameter to be selected in six of the eight subjects. When the results of all the subjects were pooled, the imposed ITL alone explained 40% of variations in inspiratory difficulty. Adding the change in end-inspiratory lung volume (DeltaEILV) to the model explained an additional 24% of variations in inspiratory difficulty. The coefficients (slopes) of the imposed ITL and DeltaEILV were 0.21 +/- 0.02 cm H2O-1 and 0.051 +/- 0.006 %IC-1, respectively. It is concluded that under our experimental conditions, the imposed ITL is a better predictor for explaining the variability of the perceived inspiratory difficulty than the operating lung volume.
动态肺过度充气通过增加呼气末肺容积（EELV）并施加内源性呼气末正压（PEEPi）来负荷吸气肌，后者表现为吸气阈值负荷（ITL）。本研究的主要目的是描述施加的ITL和肺容积变化对吸气困难感知的独立影响。在8名健康受试者中，分别通过持续气道正压通气（CPAP）和外部ITL施加独立增加EELV和ITL；通过施加呼气末正压（PEEP）来诱导EELV和PEEPi（从而施加的ITL）两者增加。当EELV或ITL增加时，感知到的吸气困难显著增加，并且在EELV和施加的ITL联合增加期间（PEEP期间）总是比任一因素单独增加时更大，这表明施加的ITL和EELV各自独立地导致吸气困难。然后将所有条件下每个受试者的吸气困难情况拟合到逐步多元回归模型中。施加的ITL是所有受试者吸气困难的重要影响因素，并且是8名受试者中有6名首先选择的参数。当汇总所有受试者的结果时，仅施加的ITL就解释了吸气困难变化的40%。将吸气末肺容积变化（DeltaEILV）添加到模型中又解释了吸气困难变化的另外24%。施加的ITL和DeltaEILV的系数（斜率）分别为0.21±0.02 cm H2O-1和0.051±0.006 %IC-1。得出的结论是，在我们的实验条件下，与肺容积相比，施加的ITL是解释感知到的吸气困难变异性的更好预测指标。
