Cl. Heaps et al., HYPOHYDRATION CAUSES CARDIOVASCULAR DRIFT WITHOUT REDUCING BLOOD-VOLUME, International journal of sports medicine, 15(2), 1994, pp. 74-79
To determine the effect of hydration on cardiovascular drift (i.e.; in
creased heart rate and reduced stroke volume) during exercise in a 21
degrees C environment, nine subjects were studied while cycling at 65%
of peak oxygen consumption when euhydrated and while still hypohydrat
e, following exercise-induced dehydration and a 2h rest/rehydration pe
riod. Subjects dehydrated by exercising in the heat (32 degrees C) unt
il body weight was reduced 2.5%. On two separate occasions following e
xercise, subjects either received no fluid or ingested a volume of wat
er equal to 100% of the fluid lost during exercise. Following the 2h r
est/rehydration period, 65 +/- 6% of the ingested water was retained a
nd thus the subjects were hypohydrated by 0.9 +/- 0.1%, compared to be
ing hypohydrated by 2.8 +/- 0.1% when no fluid was ingested. Despite t
hese differences in whole body hydration, blood volume during exercise
remained at euhydrated levels when hypohydrated by 0.9% and 2.8%. How
ever, the degree of cardiovascular drift was graded in proportion to h
ypohydration. Compared to the responses when euhydrated, heart rate wa
s elevated 10 +/- 2 and 18 +/- 2 bt/min, whereas stroke volume was red
uced 9 +/- 3 and 18 +/- 2 ml/bt, respectively, when hypohydrated by 0.
9% and 2.8% during the water and no fluid trials (p < 0.05 for all com
parisons). These observations indicate that cardiovascular drift durin
g exercise in a 21 degrees C environment is graded in proportion to hy
dration and under these conditions, not due to reductions in blood vol
ume.