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Re: Cardiovascular adaptation in hypoxia

Dear Editor

I read with great interest the recently published study by Shave et al.[1] in the February, 2004 issue of the British Journal of Sports Medicine. The authors found that exercise training in hypoxic environment did not affect cardiac systolic and diastolic functions. However, it is known that the characteristics of the study population (broad age range, aerobic exercise capacity) may cause significantly different diastolic Doppler parameters in subjects.

Furthermore, I believe that exercise duration is important for cardiac functions and fatigue as much as exercise distance. It should be also explained how the authors found lower E wave velocity, while higher cardiac stroke volume and output in hypoxic group before exercise.

On the other hand, Bailey et al. [2] reported that the stimulus of intermittent normobaric hypoxia invoked an additive cardioprotective effect. Although anticipated, they found a decreased power output for a given submaximal heart rate during hypoxic training because of an increased sympathoadrenerjik drive and that the hypoxic inspirate did not influence the submaximal heart rate and power output relationship.

It has been explained that the prevailing arterial hypoxemia would decrease absolute training intensity and subsequent oxygen flux and thus mask the potentially synergistic effects of hypoxic training [3]. The authors proposed that physiological adaptation to intermittent hypoxemia could have upregulated vascular reactivity, in particular, if the hypoxic stimulus was of sufficient magnitude to induce morphological changes in the endothelium.

I also believe that increased cardiovascular functional adaptations to regular exercise in athletes [4] in normobaric normoxic conditions are prevent cardiovascular injury and fatigue in hypoxic environment.

References

(1). Shave RE, Dawson E, Whyte G, George K, Gaze D, Collinson P. Effect of prolonged exercise in a hypoxic environment on cardiac function and cardiac troponin T. Br J Sports Med 2004;38:86-8.

(2). Bailey DM, Davies B, Baker J. Training in hypoxia: modulation of metabolic and cardiovascular risk factors in men. Med Sci Sports Exerc 2000;32:1058-66.

(3). Levine BD, Stray-Gundersen J. Living high-training low: effect of moderate-altitude acclimatization with low-altitude training in performance. J Appl Physiol 1997;83:102-12.

(4). Kasikcioglu E, Kayserilioglu A, Oflaz H, Akhan H. Aortic distensibility and left ventricular diastolic functions in endurance athletes. Int J Sports Med 2004;25 (In press)