Article,
A New Method to Analyze Lung Compliance when Pressure–Volume Relationship is Nonlinear
American Journal of Respiratory and Critical Care Medicine, (1998)
Abstract
Changes in dynamic lung compliance during inspiration and expiration cannot be modeled accurately with conventional algorithms. We developed a simple method to analyze pressure–volume (P/V)relationships under condition of nonlinearity (APVNL) and tested it in a lung model with known resistance and nonlinear P/V relationship. In addition, pulmonary mechanics in 22 infants, 11 of themwith nonlinear P/V relationships, were analyzed with the new method. The findings were comparedwith those obtained by a recently introduced algorithm, multiple linear regression analysis (MLR) ofthe equation of motion. The APVNL method described the changing compliance (C) of the lungmodel accurately, whereas the MLR method underestimated C especially in the first half of thebreath. In infants the MLR method gave highly variable, often nonphysiological C values in the begin-ning of a breath. In contrast, the coefficient of variability of measurements obtained by the APVNLmethod was significantly smaller (p < 0.02), and the indices of model-fit showed better agreementbetween calculated and observed pressure than for the MLR method (p < 0.02). We conclude that theAPVNL method accurately describes nonlinear P/V relationships present during spontaneous breathing or mechanical ventilation. The method may be helpful in identifying and preventing pulmonary overdistention.
