FACTORS INFLUENCING CHANGES IN CORONARY FLOW FOLLOWING SYMPATHETIC NERVE STIMULATION

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Abstract
Expts. are presented to evaluate the possible effect of physical factors upon coronary flow increases following accelerator nerve stimulation. Studies on fully dilated coronary arteries were employed to separate vascular from physical factors. Reduction in the systole/cycle (S/C) ratio produced max. increases in flow of 30%, but usually much less. Decreases of mid-diastolic intraventricular pressure of 4-5 mm. Hg probably account for only about 5% increases in flow. Decreases in systolic and diastolic cardiac volume probably are without effect upon coronary flow. There is no evidence from these expts. that the heart massages blood through itself except for flow increases due to shifts in the S/C ratio. Increases in coronary flow after nerve stimulation are not passive changes due to increased cardiac output and elevations of aortic pressure. The observed flow changes probably result chiefly from active coronary vasodilatation.
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