Cardiac effects of splanchnic and non-splanchnic blood volume redistribution during aortic occlusions in dogs.

Translocation of blood from the lower body dilates the left ventricle during occlusion of the descending thoracic aorta and by increased activation of the Frank-Starling mechanism, stroke volume is maintained despite raised aortic blood pressure. The contributions from the splanchnic and non-splanchnic blood volumes to the left ventricular dilation were examined by ultrasonic measurements of myocardial chord length (MCL) in atropinized open-chest dogs. End-diastolic MCL rose by 2.5 +/- 0.9% during abdominal suprarenal aortic occlusion, draining blood from the non-splanchnic region, and by 7.4 +/- 1.7% during thoracic aortic occlusion draining blood from both splanchnic and non-splanchnic regions. Systolic left ventricular pressure rose by 16 +/- 3 mmHg and 76 +/- 12 mmHg, respectively. End-diastolic MCL rose by 6.0 +/- 1.2% during combined thoracic aortic and abdominal infrahepatic vena cava occlusion draining blood solely from the splanchnic region and further by 2.5 +/- 0.8% by blood drained from the non-splanchnic region after release of the vena cava occlusion. Similar results were obtained using a shunt permitting selective drainage first from the non-splanchnic region during thoracic aortic occlusion. Blood translocation from the non-splanchnic region maintains cardiac output during abdominal aortic occlusion. During occlusion of the thoracic aorta, drainage from the splanchnic region accounts for about 70% of the increase in end-diastolic MCL.