Cardiovascular reflexes during long-term converting enzyme inhibition and sodium depletion. The response to tilt in hypertensive patients.

The reflex hemodynamic and humoral response to postural change during long-term renin-angiotensin blockade (captopril) was assessed in sodium-depleted hypertensive patients. Orthostatic hypotension was not observed with head-up tilt or repeated pressure recordings. During tilt, a reflex increase of heart rate occurred (76 +/- 2 to 98 +/- 4 bpm, p less than 0.001). Home recordings demonstrated only minor changes in blood pressure with standing. To evaluate these observations, hemodynamic studies were performed during tilt at three stages of therapy: control, administration of captopril, and administration of captopril plus diuretic. With tilt, no orthostatic hypotension was noted at all three stages of therapy, despite similar peripheral pooling (-22 percent cardiac index). Maintenance of blood pressure was due to reflex increase of heart rate (44, 45 and 38 percent) and systemic resistance (34, 38 and 37 percent). The response to tilt of plasma renin activity was modified by drug therapy, but not completely blocked. This study indicated that long-term converting enzyme inhibition and sodium depletion were safe and did not appreciably blunt the cardiovascular reflexes responsible for prevention of orthostatic hypotension.