Cardiovascular responses to handgrip isometric exercise in patients following cardiac transplantation

The effects of cardiac denervation on the hemodynamic responses to isometric handgrip contraction were studied in patients 1--5 years after allograft cardiac transplantation. The objective of these studies was to determine the role of cardioacceleration and myocardial contractility on the increase in systemic arterial pressure during isometric exercise. Initially, noninvasive measurement of brachial artery pressure and heart rate during 60 seconds of isometric exercise at 50% of maximal voluntary contraction (50% MVC) were recorded in 23 cardiac transplant patients, 18 ischemic heart disease patients, and 15 healthy controls. While the increases in arterial pressure were not significantly different among the three groups and the heart rate response for the healthy controls and ischemic heart disease patients were similar, the transplant patient's heart rate remained essentially unchanged. In an attempt to determine the mechanisms for the increase in arterial pressure, despite any increase in heart rate in transplant patients, we recorded left ventricular volumes before and at the end of 50% MVC using fluoroscopy of tantalum midwall myocardial markers in seven cardiac transplant recipients and seven nontransplant cardiac surgery patients. The rise in arterial pressure during isometric exercise in both groups of patients resulted from a significant increase in peripheral vascular resistance but not in stroke volume or cardiac output. These data demonstrate that the rise in arterial pressure observed during isometric exercise can be achieved by increased peripheral vascular resistance alone in patients who lack the capacity to increase heart rate or stroke volume.