[The influence of LAP and cardiac output on the pulmonary gas exchange. Intraoperative studies in cardio-surgical patients (author's transl)].

In 21 patients haemodynamic parameters and pulmonary gas exchange were investigated after open heart surgery with cardio-pulmonary bypass (aortic valve replacement, AVR (n = 8); mitral valve replacement, MVR (n = 6); aorto coronary bypass; ACB (n = 7). For describing gas exchange function of the lung the O2-CO2 diagram was used. Stepwise increase of left atrial pressure (LAP) was followed by increasing cardiac output (CO) only in the AVR and ACB groups, whereas in the MVR group CO did not increase. Rising venous admixture (Qs/Qt) under these circumstances was related to CO only in the AVR and ACB groups. In the MVR group Qs/Qt did not change. Qs/Qt is related to low VA/Q areas in the lung. Increased CO leads to rising Qs/Qt from these low VA/Q-areas.