Effect of head-up tilt on subcutaneous blood flow during the course of acute myocardial infarction.

1. Central and local regulation of subcutaneous blood flow in the forearm was studied in the acute phase of myocardial infarction. 2. Blood flow was measured by the local 133Xe-washout technique. 3. The vasoconstrictor response to increase in venous transmural pressure was not present on day 1 after coronary occlusion but gradually recurred during days 2, 3 and 7. 4. Passive 30 degrees head-up tilt induced a vasoconstriction in subcutaneous tissue. There was no difference in this response at any time during the course of acute myocardial infarction. The vasoconstriction could be blocked by proximal nervous blockade. 5. Thus a decrease in baroreceptor activity induced by head-up tilt enabled a marked neurogenically mediated vasoconstriction in subcutaneous tissue, indicating that orthodromic impulse activity in sympathetic fibres can be further increased even on day 1 of acute myocardial infarction.