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Modulation of vascular capacitance by angiotensin and nitroprusside: a mechanism of changes in pericardial pressure
O A Smiseth1, D E Manyari, J A Lima
1University of Calgary, Department of Medicine, Alberta, Canada.
Insights
Vasoactive drugs alter cardiac function by shifting blood volume. Angiotensin increased, while nitroprusside decreased, abdominal blood volume, affecting pericardial and left ventricular pressures.
Area of Science:
- Cardiovascular Physiology
- Pharmacology
Background:
- Left ventricular diastolic function is crucial for cardiac performance.
- Vasoactive agents can influence hemodynamics through systemic vascular effects.
Purpose of the Study:
- To investigate if vasoactive drugs modify left ventricular diastolic function.
- To test the hypothesis that blood shifts between systemic and cardiac beds alter pressures.
Main Methods:
- 10 open-chest dogs underwent anesthesia and splenectomy.
- Intravenous sodium nitroprusside and angiotensin infusions were administered.
- Blood volume changes in abdominal regions (liver, mesenteric) were measured using scintigraphy (99mTc).
- Pericardial and left ventricular pressures were monitored.
Main Results:
- Angiotensin increased aortic pressure, pericardial pressure, left ventricular end-diastolic pressure (LVEDP), and left ventricular diameter.
- Angiotensin decreased mesenteric blood volume, indicating reduced venous compliance.
- Nitroprusside decreased aortic pressure and pericardial pressure.
- Nitroprusside increased mesenteric blood volume.
Conclusions:
- Vasoactive drugs can modulate left ventricular diastolic function via alterations in systemic blood volume distribution.
- Shifts in abdominal blood volume significantly impact cardiac pressures and function.
Abstract:
The aim of the present study was to test the hypothesis that vasoactive drugs may modify left ventricular diastolic function by shifting blood between the systemic vascular bed and the heart, thereby changing pericardial and left ventricular pressure. The experiments were done in 10 open-chest, anesthetized, previously splenectomized dogs in which changes in pericardial surface pressure in response to intravenous sodium nitroprusside and angiotensin were related to changes in blood volume in the abdominal region. Blood volume was determined by blood pool scintigraphy (99mTc) and regions of interest were drawn in the liver and in the mesenteric area. Angiotensin was infused at rates that were adjusted to increase mean aortic pressure by 20 and 30 mm Hg, and nitroprusside was infused at rates to decrease mean aortic pressure by 30 and 50 mm Hg. Angiotensin increased pericardial pressure by 3 and 5 mm Hg at the respective doses and there were increments in left ventricular end-diastolic pressure (LVEDP) and left ventricular diameter (sonomicrometry). Angiotensin decreased blood volume in the mesenteric region by 14% and 17%, but did not significantly change blood volume in the liver region. Angiotensin increased portal venous pressure and decreased mesenteric blood volume, suggesting decreased mesenteric venous compliance. Nitroprusside had opposite effects: pericardial pressure was decreased by 5.5 and 6.5 mm Hg by the respective doses. The doses of nitroprusside increased blood volume in the mesenteric region by 14% and 20%, but did not significantly change blood volume in the liver region.(ABSTRACT TRUNCATED AT 250 WORDS)