Dehydration markedly impairs cardiovascular function in hyperthermic endurance athletes during exercise

Abstract

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 (VO2max) = 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% VO2max for 30 min while 1) euhydrated with an esophageal temperature (T(es)) of 38.1-38.3 degrees C (control); 2) euhydrated and hyperthermic (39.3 degrees C); 3) dehydrated and hyperthermic with skin temperature (T(sk)) of 34 degrees C; 4) dehydrated with T(es) of 38.1 degrees C and T(sk) of 21 degrees C; and 5) condition 4 followed by restored blood volume. Compared with control, hyperthermia (1 degrees C T(es) 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 (approximately 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.

Fluid Balance During Training in Elite Young Athletes of Different Sports

“…It is well documented that even moderate levels of dehydration increase physiological strain, most likely via disproportionately elevation in heart rate and a concomitant reduction in cardiac output, resulting in body’s inability to dissipate heat (12, 13). Furthermore, water losses ≥ 2% of total body weight impair significantly exercise and skill performance (1, 5) both in laboratories and field studies as well as mental performance in hot environments (7, 27, 28).…”

Educational intervention on water intake improves hydration status and enhances exercise performance in athletic youth

“…It has been shown that losses as small as 2% of body weight (BW) increase significantly physiologic strain (Gonzalez-Alonso et al, 1995), decrease exercise performance (Montain & Coyle, 1992; Gonzalez-Alonso et al, 1997) and hinder the thermoregulatory advantages conferred by high aerobic fitness (Cadarette et al, 1984) and heat acclimatization (Sawka et al, 1983). …”

Hydration Status as a Predictor of High-altitude Mountaineering Performance

“…Hydration likely plays a role in successful high-altitude mountaineering because the body experiences fluid shifts when dehydrated that result in increased cardiovascular strain as plasma volume declines [20]. Impaired cardiovascular function leads to diminished cutaneous blood flow and subsequently a diminished ability to dissipate heat to the environment, [21] which can occur from high-exertion activities even in cold alpine conditions.…”