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The control of cardiac chronotropic function in hypobaric hypoxia
J P Richalet1, R Kacimi, A M Antezana
1Association pour la Recherche en Physiologie de l'Environnement, U.F.R. Médecine, Bobigny, France.
International Journal of Sports Medicine
|October 1, 1992
Summary
Altitude hypoxia alters heart rate regulation by desensitizing beta-adrenoceptors (beta AR) and increasing parasympathetic activity. This limits myocardial oxygen consumption, benefiting the heart during exercise at high altitudes.
Area of Science:
- Cardiovascular Physiology
- Altitude Medicine
- Neuroendocrinology
Background:
- High altitude exposure triggers increased adrenergic activity.
- Reduced maximal heart rate and chronotropic response occur above 3500m.
- This is linked to beta-adrenoceptor (beta AR) desensitization and/or heightened parasympathetic activity.
Purpose of the Study:
- Investigate the effects of chronic hypoxia on cardiac receptor density and function.
- Elucidate the mechanisms behind altered heart rate regulation during high-altitude exposure.
- Determine the impact on myocardial oxygen consumption.
Main Methods:
- Examined beta AR density in rat ventricle and human lymphocytes.
- Assessed adenylate cyclase activity in rat right ventricle.
- Measured adenosine A1 and muscarinic receptor density and affinity in rat myocardium.
Main Results:
- Chronic hypoxia decreased beta AR density in rat left ventricle and human lymphocytes.
- Adenylate cyclase activity decreased in the rat right ventricle.
- Rat myocardium showed decreased adenosine A1 receptors and increased muscarinic receptors with higher affinity.
Conclusions:
- Hypoxia modulates multiple receptors controlling cardiac chronotropic activity.
- Combined receptor effects limit myocardial oxygen consumption.
- This adaptation is beneficial, particularly during strenuous exercise at high altitudes.