Peak Pressure During Volume History and Pressure–Volume Curve Measurement Affects Analysis

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Abstract
A previous volume history should be established prior to pressure- volume (P-V) curve measurement, however the effect of the volume history and the peak inspiratory pressure (PIP) during the P-V measurement has not been explored. Lung injury was created by lavage in nine sheep (25-35 kg). After stabilization, four P-V curves were sequentially obtained with PIP of 40, 50, 60, and 40 cm H2O. Prior to each P-V measurement the PIP delivered for 1 min was the same as during P-V measurement. We compared the lower inflection point (Pflex), upper inflection point (UIP), compliance below Pflex (Cstart), compliance between Pflex and UIP (Cinf), and compliance between UIP and peak pressure (Cend) for the inflation limb, and the point of maximum curvature on the deflation limb (PMC), compliance between peak pressure and PMC (Ctop), and maximum compliance (Cdef) for the deflation limb. In two sheep, Pflex at PIP 40 cm H2O could not be identified but appeared when PIP was raised. Pflex, Cstart, Cend, and Ctop were not affected by the PIP. However, UIP, PMC, Cinf, and Cdef increased as the PIP increased. Volume history and the PIP during P-V curve measurements affect both the inflation and deflation P-V curves.