Cardiopulmonary blood volume during acute blood pressure elevations in dogs.

During aortic blood flow obstructions and angiotensin infusion blood may be accumulated in the heart and the lungs because of retention or redistribution of blood from compliant regions. We measured the cardiopulmonary blood volume (CPBV) when left ventricular systolic pressure was raised by about 50 mmHg by angiotensin infusion and by balloon inflation in the ascending and descending thoracic aorta, at control inotropy and during isoproterenol infusion, in 6 anesthetized, closed-chest dogs. CPBV was calculated from determinations of cardiac output (thermodilution) and the interventricular mean transit time of ascorbate (polarographic determination). Angiotensin always increased CPBV, but the rise was greater at high than at control inotropy (16.5 +/- 4.4% and 5.1 +/- 1.2%). Balloon inflation in the descending thoracic aorta increased CPBV similarly at high and control inotropy (11.1 +/- 2.4% and 16.6 +/- 4.0%) whereas CPBV was unaltered or fell during inflation in the ascending aorta at both inotropic levels. Right and left ventricular end-diastolic pressures rose only during angiotensin infusion and balloon inflation in the descending thoracic aorta. By balloon inflation, cardiac output only fell during blood flow obstruction in the ascending aorta. Thus, an increase in CPBV during these interventions is not due to retention but is caused by redistribution of blood towards the heart.