Pressure flow and pressure volume relations in the entire pulmonary vascular bed of the dog determined by two port analysis

To quantify the resistance and particularly the capacitance properties of the entire pulmonary vascular bed, isolated perfused lungs of nine dogs were studied. In each dog, with a fixed endotracheal pressure of 5 mm Hg, the arterial pressure flow and pressure volume relations were determined while venous pressure was fixed at constant values of 2, 5, and 8 mm Hg. In the same dogs, the venous pressure flow and pressure volume relations were also obtained when arterial pressure was fixed at constant values of 15 and 20 mm Hg. The arterial and venous pressure flow relations could be regarded as linear around the physiological ranges of arterial and venous pressures; however, at very low pressures, these relations became nonlinear. The arterial and venous pressure volume relations were also approximately linear within the physiological pressure ranges. The mean arterial compliance was 0.1798 ml/mm Hg kg^-1 and was independent of venous pressures. The venous compliance values were 0.1236 and 0.0955 ml/mm Hg kg^-1 for arterial pressures of 15 and 20 mm Hg, respectively. The sums of the arterial and venous compliances were 0.3034 and 0.2753 ml/mm Hg kg^-1 for arterial pressures of 15 and 20 mm Hg, respectively. These values were nearly identical to the mean total compliance, 0.3265 ml/mm Hg kg^-1, measured in a separate series of experiments in the same dogs. Therefore, the data obtained in these experiments using two port analysis techniques represent the compliances and the resistance of the entire pulmonary vascular bed around the normal operating pressures and flows.