Effects of Acetylcholine on Hemodynamics and Blood Oxygen Saturation in Mitral Stenosis
Acetylcholine was infused into the main pulmonary artery in a dose of 2 to 12 mg. per minute to 18 patients with mitral stenosis of rheumatic origin. The drug produced significant arterial oxygen desaturation in nine patients. This was associtaed with (a) a decrease in pulmonary resistance and pulmonary arterial pressure, (b) an increase in cardiac index and stroke index, and (c) an increase in "central" blood volume. The changes in the above parameters were minimal or in opposite direction in those patients who showed no significant desaturation.
The data did not lend support to the explanation that arterial desaturation during acetylcholine infusion was due to (a) decreased alveolar ventilaton, (b) focal bronchoconstriction, or (c) opening of pulmonary arteriovenous shunts bypassing the alveoli.
Evidence is presented to show that the most likely mechanism of the decline in arterial oxygen saturation during acetylcholine infusion was an increased pulmonary blood flow in pre-existing poorly ventilated regions of the lungs as a consequence of pulmonary arteriolar dilatation. These changes resulted in a significant lowering of the arterial blood oxygen tension and content, and a considerable widening of the alveolar-arterial oxygen gradient.
- © 1961 American Heart Association, Inc.