Pulmonary model to predict the effects of series ventricular interaction

To fully describe the mechanisms of diastolic interaction between the right ventricle and left ventricle, it is necessary to understand how a change in right ventricular output (Qrvo) is transmitted across the pulmonary circulation. This series ventricular interaction is manifest as the temporal response in left ventricular filling (Qlvf) to a change in Qrvo. To quantify series interaction we used a three-element, two-parameter model of the pulmonary circulation. The parameters represented the pulmonary arterial and venous resistance and pulmonary vascular compliance. Using beat-to-beat values of mean pressure and flow measured at the input and output of the pulmonary circulation during the transient response to caval or pulmonary artery occlusion, we estimated the parameters for this model in eight open-chest dogs under control conditions, after autonomic blockade, and after fully opening the pericardium. From 110 separate data episodes, the average values of the pulmonary arterial and venous resistance and pulmonary vascular compliance were 0.14 +/- 0.08 mm Hg.sec/ml and 4.81 +/- 3.17 ml/mm Hg (+/- SD). These estimates were insensitive to the simultaneous effects of autonomic reflexes and direct ventricular interaction, so they uniquely measure the bulk transport properties of the pulmonary circulation. The time constant, which measures the response of Qlvf to a change in Qrvo, averaged 0.26 +/- 0.15 second, which implies that effects of series interaction on Qlvf are manifest within one beat. The model was also able to predict the dynamic response of Qlvf to changes in Qrvo and thus can be used to measure and predict the effects of series interaction in the intact cardiopulmonary system.