The pulmonary venous systolic flow pulse—its origin and relationship to left atrial pressure

OBJECTIVES The purpose of this study was to determine the origin of the pulmonary venous systolic flow pulse using wave-intensity analysis to separate forward- and backward-going waves. BACKGROUND The mechanism of the pulmonary venous systolic flow pulse is unclear and could be “suction effect” due to fall in atrial pressure (backward-going wave) or “pushing effect” due to forward-propagation of right ventricular (RV) pressure (forward-going wave). METHODS In eight patients during coronary surgery, pulmonary venous flow (flow probe), velocity (microsensor) and pressure (micromanometer) were recorded. We calculated wave intensity (dP × dU) as change in pulmonary venous pressure (dP) times change in velocity (dU) at 5 ms intervals. When dP × dU > 0 there is net forward-going wave and when dP × dU < 0 there is net backward-going wave. RESULTS Systolic pulmonary venous flow was biphasic. When flow accelerated in early systole (S1), pulmonary venous pressure was falling, and, therefore, dP × dU was negative, −0.6 ± 0.2 (x ± SE) W/m2, indicating net backward-going wave. When flow accelerated in late systole (S2), pressure was rising, and, therefore, dP × dU was positive, 0.3 ± 0.1 W/m2, indicating net forward-going wave. CONCLUSIONS Pulmonary venous flow acceleration in S1 was attributed to net backward-going wave secondary to fall in atrial pressure. However, flow acceleration in S2 was attributed to net forward-going wave, consistent with propagation of the RV systolic pressure pulse across the lungs. Pulmonary vein systolic flow pattern, therefore, appears to be determined by right- as well as left-sided cardiac events.