Effect of lower body positive pressure on blood pressure, plasma atrial natriuretic factor concentration, and sodium and water excretion in healthy volunteers and cardiac transplant recipients.

The effect of one hour (40 mmHg) lower body positive pressure on blood pressure, plasma atrial natriuretic factor concentration, and urinary sodium and water excretion was studied in 10 healthy volunteers and seven cardiac transplant recipients. Both groups showed a sustained rise in blood pressure and plasma atrial natriuretic factor concentration. The healthy volunteers had a diuresis during the period of lower body positive pressure and a small natriuresis in the subsequent hour. In contrast, lower body positive pressure had no significant effect on urinary sodium and water excretion in the cardiac transplant group. The data suggest that cardiac innervation is not important as a mediator of the haemodynamic response to lower body positive pressure but is necessary for the renal response. Furthermore, small physiological rises in plasma atrial natriuretic factor concentrations do not cause a brisk natriuresis as has been reported with pharmacological plasma concentrations.