Cardiovascular response to submaximal exercise in sustained
microgravity.
Shykoff, B. E., L. E. Farhi, A. J. Olszowka, D. R. Pendergast, M. A.
Rokitka, C. G. Eisenhardt, and R. A. Morin.
Department of Physiology, State University of New York at Buffalo,
Buffalo, NY 14214
APStracts 2:0528A, 1995.
Cardiac output (Q x ), heart rate (HR), blood pressure (BP) and oxygen
consumption (V x O2) were measured repeatedly, both at rest and at
two levels of exercise in 6 subjects during microgravity exposure.
Exercise was at 30% and 60% of the workload producing the
individual's maximum oxygen consumption at 1 G (30% ex, 60% ex).
Three of the subjects were on a 9-day flight, SLS-1 (Spacelab Life
Sciences 1) and 3 on a 15-day flight, SLS-2. We found no temporal
differences during the flights. Thus, we have combined all
microgravity measurements to compare inflight values (FL) with erect
(E) or supine (S) control. At rest, Q x (FL) was 126% of Q x (E)
(p<0.01) but not different from Q x (S), and HR(FL) was 81% of
HR(E) (p<0.01) and 91% of HR(S) (p<0.05). Thus, resting
stroke volume (SV) in flight was 155% of SV(E) (p<0.01) and 109%
SV(S) (p<0.05). Resting mean arterial blood pressure (MAP) and
diastolic pressure were lower in flight than erect (p<0.05).
Exercise values were considered as functions of V x O2. The increase
of Q x with V x O2 in flight was less than that at 1 G (slope 3.5 vs
6 L/min/L/min). SV(FL) fell with increasing V x O2 while SV(E) rose
and SV(S) remained constant. The BP response to exercise was not
different inflight from E or S. We conclude that true microgravity
causes a cardiovascular response different from that seen during any
of its putative simulations.
Received 13 February 1995; accepted in final form 14 November
1995.
APS Manuscript Number A176-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 8 December 95