Pulmonary circulation in low cardiac output syndrome following open heart surgery.

The pulmonary circulation of 41 patients with low cardiac output syndrome (LOS) in the recovery period following open heart surgery was studied. Cardiac indices (CI) of these patients in LOS was 1.64 +/- 0.28 (Mean +/- SD) L/min X m2 and increased to 2.60 +/- 0.50 L/min X m2 after the stabilization of hemodynamic conditions. Mean pulmonary arterial pressure, pulmonary arteriolar resistance index (PARI) and total pulmonary resistance index (TPRI) in the condition of LOS were very high and significantly decreased after recovery from LOS, although the mean left atrial pressure showed no significant change. The correlation coefficient (r) between CI and PARI was found to be -0.574. High Pao2 with reductions of alveolar-arterial oxygen tension difference (A-aDo2) and physiological pulmonary shunt ratio (Qs/Qt) in LOS significantly decreased concomitant with significant increases in both A-aDo2 and Qs/Qt after the stabilization of the hemodynamic condition. Moderate correlations were obtained between CI and Pao2 (r = -0.478), and high correlations were established between CI and physiological pulmonary shunt flow (Qps) (r = 0.747). These studies showed that pulmonary vasoconstriction was playing a major role in the elevation of pulmonary vascular resistance in LOS, which eventually leads to the reduction of intrapulmonary shunting.