Dehydration markedly impairs cardiovascular function in
hyperthermic endurance athletes during exercise.
Gonzlez-Alonso, Jos, Ricardo Mora-Rodraeguez, Paul R. Below, Edward F.
Coyle.
Human Performance Laboratory, Department of Kinesiology and Health
Education, The University of Texas at Austin, Austin, TX 78712
APStracts 3:0570A, 1996.
This investigation quantified the additional cardiovascular stress
encountered by imposing dehydration onto hyperthermia when endurance
athletes exercise in the heat. In addition, we attempted to quantify
the mechanisms (e.g., core hyperthermia, skin temperature and
hypovolemia) contributing to the dehydration mediated stroke volume
reduction. During two crossover trials in two separate studies,
fifteen endurance-trained cyclists (O(V,.)O2max = 4.5 0.4 l/min; mean
SD) exercised in the heat (35[acute]iC) 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 70-72% O(V,.)O2max for 30 min while: 1) euhydrated with an
esophageal temperature (Tes) of 38.30.1[acute]iC and skin temperature
(Tsk) of 34.00.2[acute]iC [meansSE; control], 2) euhydrated and
hyperthermic (Tes of 39.30.1[acute]iC; Tsk of 34.60.3[acute]iC), 3)
dehydrated and hyperthermic (Tes of 39.30.1[acute]iC, Tsk of
34.60.4[acute]iC), 4) euhydrated with Tes of 38.10.1 and Tsk of
20.90.5[acute]iC (control), 5) dehydrated with Tes of
38.10.1[acute]iC and Tsk of 20.40.4[acute]iC, and 6) condition 5
followed by restored blood volume. Compared to their corresponding
control condition, hyperthermia (1[acute]iC core temperature
increase) and dehydration (4% body weight loss) each separately
lowered stroke volume 7-82% (113 ml/beat;P < 0.05) and
increased heart rate sufficiently to prevent significant declines in
cardiac output. However, when dehydration was imposed onto
hyperthermia, the reductions in stroke volume were significantly
greater (201% or 263 ml/beat; P < 0.05) and cardiac output
declined 132% (2.80.3 l/min; P < 0.05). Furthermore, mean
arterial pressure declined 52% (52 mmHg) and systemic vascular
resistance increased 103% (0.50.1 mmHg/l/min; both P < 0.05).
When hyperthermia was prevented, all of the decline in stroke volume
with dehydration was due to reduced blood volume (200 ml). In
conclusion, these results demonstrate that the imposition of
dehydration on top of 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.
Received 6 July 1996; accepted in final form 26 November 1996.
APS Manuscript Number A670-6.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996