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Cardiopulmonary blood volume during acute blood pressure elevations in dogs
Insights
Blood flow obstructions and angiotensin infusion increase cardiopulmonary blood volume (CPBV) by redistributing blood toward the heart, not by retention. This finding clarifies circulatory dynamics during cardiovascular stress.
Area of Science:
- Cardiovascular Physiology
- Hemodynamics
- Integrative Biology
Background:
- Aortic obstructions and angiotensin can alter blood distribution, potentially accumulating blood in the heart and lungs.
- Understanding cardiopulmonary blood volume (CPBV) changes is crucial for comprehending circulatory responses to altered hemodynamics.
Purpose of the Study:
- To investigate the mechanisms of cardiopulmonary blood volume (CPBV) changes during experimentally induced aortic blood flow obstructions and angiotensin infusion.
- To differentiate between blood retention and redistribution as causes for CPBV alterations.
Main Methods:
- Cardiopulmonary blood volume (CPBV) was measured in anesthetized dogs using thermodilution for cardiac output and polarographic determination for interventricular mean transit time.
- Left ventricular systolic pressure was increased via angiotensin infusion or balloon inflation in the ascending/descending thoracic aorta.
- Measurements were taken at control inotropic state and during isoproterenol infusion.
Main Results:
- Angiotensin infusion consistently increased CPBV, with a greater rise observed at higher inotropic states.
- Balloon inflation in the descending thoracic aorta increased CPBV, irrespective of inotropic state.
- Inflation in the ascending aorta did not alter or decreased CPBV, indicating obstruction.
- Elevated ventricular pressures and altered cardiac output were observed depending on the location of obstruction.
Conclusions:
- Increased cardiopulmonary blood volume (CPBV) during aortic obstructions and angiotensin infusion is primarily due to blood redistribution towards the heart.
- The findings challenge the notion of simple blood retention and highlight the dynamic nature of circulatory adjustments.
Abstract:
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.