Pressure-volume relationships in the pulmonary "venous" system in living dogs

In this study, we examined the pressure-volume (P-V) relationships of the pulmonary "venous" (P'V') system in anesthetized living dogs, and assessed compliance by fitting the derived data of the P-V relationships to the exponential function. By definition, the P'V' system consists of the pulmonary veins and the left atrium. The pulmonary "venous" volume (P'V'V) was determined with our modified double indicator dilution method using a single injection and double sampling technique. The mean left atrial pressure (PLA) was measured directly. To observe sequential changes over a wide range of the P-V relationships, dogs were studied from the control state through the volume-loaded state with dextran. The P'V'V ranged from 3.4 to 12.2 ml X kg-1 and the PLA from 3.2 to 40.6 mmHg. We fitted the data of the P-V relationships (n = 24) to the exponential function, yielding an equation: P'V'V (ml X kg-1) = 19(1-0.833(e-0.017PLA(mmHg)). We then differentiated an above equation to estimate the slope of this curve (static compliance), giving the equation: dV/dP (ml X mmHg-1 X kg-1) = 0.269(e-0.017PLA(mmHg)). Therefore, at PLA of 10 mmHg (normal level), the compliance is 0.227 ml X mmHg-1 X kg-1. The compliance, obtained with an application of the present results in dogs to man, (disregarding expected species differences), coincides well with that in man determined with our indirect method.