Modulation of baroreflex sensitivity and spectral power of blood
pressure by heat stress and aging.
Stauss, Harald M., Donald A. Morgan, Karl E. Anderson, Michael P.
Massett, and Kevin C. Kregel.
Department of Exercise Science, The University of Iowa, Iowa City,
Iowa 52242 and Department of Physiology, Humboldt University -
Charit\351 Berlin, 10115 Berlin, Germany
APStracts 3:0384H, 1996.
To investigate the effects of hyperthermia and aging on baroreceptor
-heart rate reflex sensitivity (BRS), cardiovascular parameters were
recorded during a progressive rise in core temperature in conscious
mature and senescent Fischer 344 rats. BRS was calculated from
spontaneous changes in blood pressure and inter-beat interval. Low
(LF, 0.01-0.20 Hz) and mid (0.2-0.5 Hz) frequency blood pressure
power (MF) were also determined. In both age groups, hyperthermia
caused an increase in blood pressure, renal resistance, and LF but no
changes in renal nerve activity, while a tachycardia was only
observed in the older rats. Increase in BRS (0.80 \006 0.14 versus
1.72 \006 0.34 msec/mmHg, p <0.05) and MF (3.10 \006 0.55 versus
7.81 \006 1.89 mmHg 2, p <0.05) and a positive correlation
between BRS and MF (r=0.50, p <0.01) were observed with heating
in mature but not senescent rats. These results indicate that LF,
which increased with elevated core temperature, may be modulated by
thermal stimuli. The augmented BRS in the mature group may contribute
to the hemodynamic adjustments that occur with hyperthermia, while
the lack of an increase in BRS during heat stress in the senescent
group suggests that baroreceptor reflex modulation is impaired with
aging. The positive correlation between BRS and MF in mature rats
together with the lack of an increase in renal sympathetic nerve
activity indicates that MF may reflect the modulating influence of
the efferent sympathetic portion of the baroreceptor reflex loop on
arterial blood pressure, rather than merely the activity of the
peripheral sympathetic nervous system.
Received 22 May 1996; accepted in final form 22 August 1996.
APS Manuscript Number H467-6.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 19 September 1996