Canadian Journal of Anesthesia, Vol 23, 111-124, Copyright © 1976 by Canadian Anesthesiologists' Society

The Effects of Age on Baroreceptor Reflex Function in Man

¹ Department of Anaesthesia, University of Manitoba, Winnipeg, Manitoba, Canada
² Department of Anaesthesia, University of California, San Francisco, California, U.S.A. 94122

The relationship of age to baroreceptor reflex activity was determined in 35 healthy volunteers ranging in age from 19 to 65 years. Intra-arterial catheters were placed and blood pressure and pulse rate responses of each subject were observed during a Valsalva maneuver (31 subjects) and during the Pressor Test (33 subjects ). The Valsalva maneuver consisted of a forced expiration sufficient to raise a column of mercury 40 torr for 10 seconds. This resulted in a reduction in pulse pressure (Baroreceptor stimulus) during the maneuver followed by a transient overshoot in diastolic pressure (response) following its termination. In comparison to younger subjects, older subjects had a greater reduction in pulse pressure but similar overshoot in diastolic pressure. The pressor test consisted of observing the effect of increasing systolic blood pressure (stimulus) on pulse duration (response) following the intravenous administration of phenylephrine. By relating each systolic pressure to the immediately succeeding R-R interval, a linear relationship was found. Its slope expressed in milliseconds of R-R interval change per torr increase in systolic pressure is an index of baroreflex function. Older subjects have less cardiac slowing compared to younger subjects and a hyperbolic relationship exists between age and slope (r = 0.84, p < 0.05). These tests indicate that baroreceptor reflex function decreases with aging.