Arterial and cardiopulmonary baroreflexes in 60-69 vs. 18-36 year
old humans.
Shi, Xiangrong, Kevin M. Gallagher, Rita M. Welch-O'connor, and Brian
H. Foresman.
Departments of Physiology and Medicine, University of North Texas
Health Science Center, Fort Worth, Texas 76107
APStracts 3:0052A, 1996.
The purpose of this study was to investigate the carotid baroreflex
and cardiopulmonary baroreflex responsiveness in older humans during
central hypovolemia. Eleven healthy young (aged 18 to 36 years) and
eleven normotensive older (aged 60 to 69 years) individuals were
assessed using heart rate (HR) and mean arterial pressure (MAP)
responses to neck pressure and neck suction during rest and lower
body negative pressure (LBNP) of -15 torr. In addition, the slope of
forearm vascular resistance (FVR) to central venous pressure (CVP)
during LBNP 0, -5, -10, -15 and -20 torr, was assessed as the reflex
response to non-hypotensive central hypovolemia. Baseline HR, MAP,
FVR and CVP were not significantly different between the young and
older subjects. In addition, carotid baroreflex function was not
different between the groups. LBNP -15 torr affected neither HR nor
MAP, whereas it decreased CVP and increased FVR, in both groups. The
slopes of FVR/CVP were similar in the young (-3.6+/-0.3 PRU/mmHg) and
older (-3.7+/-0.6 PRU/mmHg) subjects. LBNP augmented the carotid-HR
reflex gain from -0.39+/-0.04 to -0.47+/-0.03 bpm/mmHg (p<0.03)
and the carotid-MAP reflex gain from -0.26+/- 0.02 to -0.42+/-0.04
mmHg/mmHg (p<0.04) in the young subjects. In the older subjects
there was no difference between the control and -15 torr LBNP in
either carotid-HR (-0.35+/-0.08 vs. -0.35+/-0.09 bpm/mmHg) or
carotid-MAP (-0.33+/-0.10 vs. -0.33+/-0.07 mmHg/mmHg) gains. These
data indicate that the augmented carotid baroreflex during central
hypovolemia observed in the young individuals was absent in the older
subjects. We concluded that there was no difference in the discrete
baroreflex function between the two age groups. However, since the
interaction of the cardiopulmonary baroreceptors with the carotid
baroreflex function was absent in the older subjects, we suggest that
the central integration of afferent neural inputs from the discrete
(i.e., cardiopulmonary and carotid) baroreceptors was altered with
aging.
Received 13 March 1995; accepted in final form 10 January 1996.
APS Manuscript Number A273-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 25 January 96