Blood pressure and heart rate responses to sudden changes of
gravity during exercise.
Linnarsson, D., C. J. Sundberg, B. Tedner, Y. Haruna, J. M. Karemaker,
G. Antonutto, and P. E. Di Prampero.
Environmental Physiology Laboratory, Dept of Physiology and
Pharmacology, Karolinska Institutet, Stockholm, Dept of Health
Administration, Tokyo University, Tokyo, Japan, Dept of Physiology,
University of Amsterdam, Amsterdam, The Netherlands, Dept of
Biomedical Science and Technology, University of Udine, Udine,
Italy
APStracts 2:0471H, 1995.
Heart rate (HR) and blood pressure responses to sudden changes of
gravity during 80-100 W leg exercise were studied. One group was
exposed to sudden changes between 1.0 and 0 g in the head-to-foot
direction (Gz+), starting upright and with repeated 30 sec long tilts
to supine. Another group was exposed to sudden Gz+ changes between
1.8 and 0 g in an aircraft performing parabolic flight. Arterial
blood pressure at the level of the carotid (carotid distending
pressure, CDP) showed a large transient increase by 27 to 47 mmHg
when Gz+ was suddenly decreased and a similar drop when Gz+ was
suddenly increased. Heart rate displayed a reverse pattern with
larger transients (-22 to -26 min-1) in response to Gz+ decreases and
more sluggish changes of lower amplitude in the other direction.
Central blood volume as estimated from transthoracic impedance
(1/TTI) varied in concert with Gz+. A model is proposed in which HR
responses are described as a function of CDP and 1/TTI following a
time delay of 2.3-3.0 sec and including a low pass filter function
with time constants of 0.34-0.35 sec for decreasing heart rates and
time constants of 2.9-4.6 sec for increasing heart rates. The
sensitivity of the carotid component was on the order of -0.8 to -1.0
min-1 x mmHg-1 (4 to 7 msec x mmHg-1). The cardiopulmonary
baroreceptor component was an additive input but of modest relative
importance during the initial HR responses. For steady state HR
responses, however, our model suggests that inputs from carotid and
cardiopulmonary receptors are of equal importance.
Received 29 December 1994; accepted in final form 9 October 1995.
APS Manuscript Number H1144-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95