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Human Performance Laboratory, Department of Kinesiology and Health Education, The University of Texas at Austin, Austin, Texas 78712
Received 16 July 1996; accepted in final form 26 November 1996.
González-Alonso, José, Ricardo
Mora-Rodríguez, Paul R. Below, and Edward F. Coyle.
Dehydration markedly impairs cardiovascular function in
hyperthermic endurance athletes during exercise. J. Appl. Physiol. 82(4): 1229-1236, 1997.
We
identified the cardiovascular stress encountered by superimposing
dehydration on hyperthermia during exercise in the heat and the
mechanisms contributing to the dehydration-mediated stroke volume (SV)
reduction. Fifteen endurance-trained cyclists [maximal
O2 consumption
(
O2 max) = 4.5 l/min] exercised in the heat for 100-120 min and either became dehydrated by 4% body weight or remained euhydrated by drinking
fluids. Measurements were made after they continued exercise at 71%
O2 max for 30 min
while 1) euhydrated with an
esophageal temperature (Tes) of
38.1-38.3°C (control); 2)
euhydrated and hyperthermic (39.3°C);
3) dehydrated and hyperthermic with
skin temperature (Tsk) of
34°C; 4) dehydrated with
Tes of 38.1°C and Tsk of 21°C; and
5) condition
4 followed by restored blood volume. Compared with
control, hyperthermia (1°C Tes
increase) and dehydration (4% body weight loss) each separately
lowered SV 7-8% (11 ± 3 ml/beat;
P < 0.05) and increased heart rate
sufficiently to prevent significant declines in cardiac output.
However, when dehydration was superimposed on hyperthermia, the
reductions in SV were significantly (P < 0.05) greater (26 ± 3 ml/beat), and cardiac output declined 13% (2.8 ± 0.3 l/min). Furthermore, mean arterial
pressure declined 5 ± 2%, and systemic vascular resistance
increased 10 ± 3% (both P < 0.05). When hyperthermia was
prevented, all of the decline in SV with dehydration was due to reduced
blood volume (~200 ml). These results demonstrate that the
superimposition of dehydration on hyperthermia during exercise in the
heat causes an inability to maintain cardiac output and blood pressure
that makes the dehydrated athlete less able to cope with hyperthermia.
cardiovascular strain; stroke volume; cardiac output; blood pressure
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