Age, fitness, and regional blood flow during exercise in the
heat.
Ho, C. W., J. L. Beard, P. A. Farrell, C. T. Minson, and W. L. Kenney.
Noll Physiological Research Center, Penn State University,
University Park, PA 16802-6900
APStracts 3:0571A, 1996.
During dynamic exercise in warm environments, the requisite increase
in skin blood flow (SkBF) is supported by an increase in cardiac
output (Qc) and decreases in splanchnic (SBF) and renal blood flows
(RBF). To examine interactions between age and fitness in determining
this integrated response, 24 men (6 per group) were recruited in 4
categories: young fit (YF; 24+/-2 yr, VO2max 62+/-2 ml.kg-1.min-1,
99th fitness %ile), young sedentary (YS; 26+/-2, 43+/-1, 45th %ile),
older fit (OF; 64+/-2, 42+/-1, 90th %ile), and older sedentary (OS;
65+/-1, 28+/-1, 30th %ile). Subjects sat at rest for 50 min, then
exercised for 20 min at 35% and 30 min at 60% VO2max at an ambient
temperature of 36 C (20% rh). Qc was measured by CO2-rebreathing, SBF
by indocyanine green clearance, and RBF by clearance of para-amino
hippurate, and forearm blood flow (FBF) by venous occlusion
plethysmography. The change in FBF was used to examine changes in
SkBF. At both exercise intensities, YF had a significantly higher-Qc
and FBF than any other group. In the older group, fitness level had
no significant effect on any measured variable. At 60% VO2max, the
young subjects had significantly greater decreases in SBF and RBF
during exercise, regardless of fitness level. Total flow redirected
from these 2 vascular beds (_SBF + _RBF) was as follows: YF: 1128+/
-69, YS: 779+/-110, OF: 568+/-68, and OS: 427+/-81 ml/min. Plasma
norepinephrine concentrations were consistent with the
vasoconstriction differences, i.e.,
YF>>YS>OF>OS. After 4 of the OS men
underwent a rigorous 4-week endurance training regimen, FBF was 35%
higher (p<0.05) at 60% of peak cycle VO2 and Qc was 10%
higher, but SBF and RBF were unchanged. During exercise at a given
(moderate) relative exercise intensity, distribution of Qc to
regional circulations is affected by age, with older men showing
smaller increases in SkBF and smaller decreases in SBF and RBF. In
young subjects the higher SkBF associated with a higher fitness level
is a function of both a higher Qc and a greater redistribution of
flow from splanchnic and renal circulations. Conversely, the
attenuated splanchnic and renal vasoconstriction in older men does
not appear to change with enhanced aerobic fitness.
Received 23 May 1996; accepted in final form 2 December 1996.
APS Manuscript Number A491-6.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996