Orthotopic cardiac transplantation reverses abnormal reflex regulation of the microvasculature in the lower leg.

OBJECTIVE

The aim was to investigate the effect of cardiac transplantation on reflex control of lower leg subcutaneous blood flow.

METHODS

The reflex regulation of subcutaneous blood flow of the lower leg was studied in 11 patients following orthotopic cardiac transplantation, in 11 patients with severe congestive heart failure (New York Heart Association functional class III or IV), and in 11 healthy subjects. Four patients were studied before and after cardiac transplantation. Cause of heart failure was classified as idiopathic dilated cardiomyopathy in all heart failure patients and in all the cardiac transplant patients before transplantation. Blood flow was measured by the local 133xenon washout method in the supine position and during 45 degrees head up tilt.

RESULTS

When performing head up tilt without activation of the local nervous venoarteriolar axon reflex in patients with congestive heart failure, the relative subcutaneous blood flow increased abnormally, by 50(SD 25)%, but in patients after cardiac transplantation a normal decrease was seen [-28(13)%, p < 0.001]. The responses in the transplant group were similar to those observed in normal controls with a decrease in blood flow [-32(15)%; NS]. Head up tilt with simultaneous activation of the local venoarteriolar axon reflex increased blood flow [31(22)%] in patients with heart failure as compared to the decrease in blood flow found in the transplants [-44(17)%, p < 0.001]. The decrease of blood flow was not significantly different between the transplant group and control subjects [-53(19)%; NS].

CONCLUSIONS

These results indicate that abnormal reflex regulation in severe congestive heart failure with peripheral vasodilation of the lower leg during orthostasis is reversed and even normalised after cardiac transplantation. The haemodynamic consequence may be a regaining of an oedema-protective mechanism that eliminates the stress (capillary hypertension) on the microcirculation seen in severe heart failure.