Comparative Effects of Volume Loading on Pulmonary Venous Flow in Dogs with Normal Heart and with Myocardial Ischemia

The influences of cardiac loading conditions and left ventricular performance on pulmonary venous flow are poorly understood. The authors studied the effects of volume loading on the pattern of pulmonary venous flow in normal and ischemic hearts. Thirteen anesthetized dogs were equipped with a transit-time ultrasonic flow probe around the left upper pulmonary vein. In 6 of the dogs, the left anterior descending artery was ligated to induce myocardial ischemia. The remaining 7 dogs had normal hearts. Heart rate was fixed at 110 beats/minute by right atrial pacing. Dextran was infused from the femoral vein until mean left atrial pressure increased 3 mm Hg above the baseline value in both groups. In normal heart, systolic pulmonary venous flow volume (SI) increased significantly, but early diastolic flow volume (DI) did not show a significant change during volume loading. The ratio of SI/DI increased significantly (1.12 +/- 0.34 vs 2.11 +/- 0.49, P < 0.05). After ligation of the left anterior descending artery, the SI and DI decreased significantly. The ratio of SI/DI did not show a significant change (0.88 +/- 0.32 vs 0.87 +/- 0.30, ns). In dogs with myocardial ischemia, volume loading caused increases in the SI and DI. However, no significant change was observed in the ratio of SI/DI (0.87 +/- 0.30 vs 0.97 +/- 0.36, ns). These findings demonstrate that left ventricular performance influences the alteration in pulmonary venous flow pattern that is caused by systemic volume loading.