INCREASED RENAL AND FOREARM VASOCONSTRICTION IN RESPONSE TO EXERCISE AFTER HEART-TRANSPLANTATION

Objective-To test the hypothesis that the loss of the inhibitory effec t of the cardiac ventricular afferent fibres on the vasomotor centre w ould result in increased vasoconstrictor drive to the forearm and rena l vascular beds during supine exercise in heart transplant recipients. Design-Comparison of regional haemodynamic response to exercise in he art transplant recipients and two age matched control groups. Setting- Regional heart transplant unit. Patients and methods-Orthotopic heart transplant recipients (n = 10), patients with NYHA class II heart fail ure (n = 10), and normal controls (n = 10) underwent short duration ma ximal supine bicycle exercise. Main outcome measures-Simultaneous meas urements were made of heart rate, systemic blood pressure, oxygen cons umption (VO2), forearm blood flow, and renal blood flow. Forearm blood flow was measured by forearm plethysmography and renal blood flow by continuous renal vein thermodilution. Results-The peak forearm vascula r resistance was significantly greater in the transplant group than in the controls (mean (SEM) 75 (18) v 40 (7) resistance units, p < 0.05) . The percentage fall in renal blood flow at peak exercise was signifi cantly greater in heart transplant recipients than in the controls (44 % (4%) v 32% (4%), p < 0.05) as was the percentage increase in renal v ascular resistance (transplants: 116% (19%) v controls: 78% (17%), p < 0.05). Regional haemodynamics during exercise in the heart failure gr oup were not significantly different from those in the controls. Concl usions-These findings suggest that surgical division of the cardiac ve ntricular afferent fibres results in increased vasoconstrictor drive t o the kidneys and non-exercising muscle during exercise. This mechanis m may contribute to persistent exercise limitation and renal impairmen t after heart transplantation.