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Influence of nonlinearities on estimates of respiratory mechanics using multilinear regression analysis

journal contribution
posted on 1994-01-01, 00:00 authored by S Kano, C J Lanteri, A W Duncan, Peter Sly
To investigate the influence of nonlinearities on estimates of respiratory mechanics, differing patterns of mechanical ventilation patterns were analyzed from 8 puppies and 14 children. Respiratory mechanics were calculated using multiple linear regression to fit a linear single- compartment model, a volume-dependent single-compartment model (VDSCM), and a flow-dependent single-compartment model. The ratio of the compliance of the last 20% of the dynamic volume-pressure (V-P) curve to the total compliance (C20/C) and the contribution of a volume-dependent elastance to total elastance {� = E2(VT)/[E1 + E2)VT], where E1 + E2 is total elastance, E2 is the volume-dependent component, and VT is tidal volume} were used as the indexes of overdistension. By positioning the dynamic loops on the static V- P curves, ventilation patterns were classified as overdistended or nonoverdistended. In the overdistended group, the C20/C was significantly lower (0.71 ± 0.10 vs. 0.92 ± 0.16; P < 0.0001) and � was significantly higher (43.4 ± 15.0 vs. 0.51 ± 18.02%, P < 0.0001) than in the nonoverdistended group. The mode of ventilation (pressure controlled vs. volume controlled) and the resistive pressures that resulted in widening of the dynamic V-P loop were found to alter C20/C but not �. When the respiratory system was overdistended, i.e., ventilated up to the flattened portion of the V-P curve, the VDSCM gave more accurate estimates of respiratory mechanics. Furthermore, � calculated from VDSCM is a useful parameter for estimating respiratory system overdistension that is not affected by resistive pressures.



Journal of Applied Physiology






1185 - 1197