Buffering of respiratory variations in venous return by right ventricle: a theoretical analysis.

The role of the right ventricle (RV) in buffering systemic venous return, thereby dampening respiratory-induced variations, left ventricular (LV) stroke volume, and systemic arterial pressure variations was examined using a computer model of the cardiovascular system. Respiration was simulated by cyclical variations in intrathoracic and abdominal pressures (cycle time 5 heartbeats), causing a 43-ml fluctuation in venous return per heartbeat (mean 71 ml) compared with fluctuations of 19 ml in RV stroke volume, 6 ml in pulmonary venous flow, and only 3 ml in LV stroke volume. On a percentage basis, the RV provided 56% of the total buffering of systemic venous return, the lungs another 30%, whereas the LV only 7%. A 10-fold increase in RV diastolic compliance increased the RV stroke volume variations from 26 to 57% of the venous return variations; a 10-fold increase in RV elastance increased them from 24 to 60%, whereas decreasing pulmonary arterial pressure from 28 to 10 mmHg increased them from 28 to 56%. The results also suggest that an underrecognized function of the RV is to buffer systemic venous return and thereby keep LV stroke volume relatively constant.