Contributions of blood drainage from the liver, spleen and intestines to cardiac effects of aortic occlusion in the dog

By occluding the descending thoracic aorta, blood transferred from the lower to the upper part of the body increases left ventricular end-diastolic volume and maintains stroke volume despite a rise in systolic left ventricular pressure (LVP) of about 60 mmHg. Seventy percent of the blood drained stems from the splanchnic circulation. To examine which splanchnic organs contribute to the cardiac effects, selective occlusions were performed during ultrasonic measurements of spleen and liver dimensions and left ventricular myocardial chord length (MCL) in atropinized, open-chest dogs. Drainage of 15 +/- 2 ml from the spleen accounted for 18 +/- 4% of the increase in end-diastolic MCL, whereas liver dimensions remained unaltered. Similar results were obtained during aortic occlusion at high inotropy (isoproterenol infusion). It was ascertained by occlusion of the coeliac and mesenteric arteries that about 50% of the cardiac response to aortic occlusion was due to drainage from the intestines and the aorta. Liver blood volume could be reduced by combined occlusion of the aorta and portal vein or coeliac and mesenteric arteries and was sensitive to changes in pressure in the inferior vena cava, did not contribute to the cardiac response to aortic occlusion.