[Effects of hypoxia on the coronary circulation and myocardial metabolism]

The effects of hypoxia on coronary flow (Qcor) and myocardial metabolism differ according to whether the situation is acute, and transient, or chronic and prolonged (chronic hypoxia at high altitudes). Acute hypoxia induces a marked increase in Qcor which is associated, in the case of severe hypoxia, with the production of lactate and pyruvate in the coronary venous blood, indicating abnormal aerobic metabolism of the myocardium, blocked by the lack of oxygen. A study of the effects of chronic hypoxia at high altitudes (HA) carried out at 3700 metres in 17 normal subjects revealed a significant decrease (of 24 to 28 per cent) in Qcor in comparison with a group of 12 normal subjects studied at sea level, using the same method (method of KETY-SCHMIDT with N2O and tritiated water method). The finding at HA of a decrease in myocardial oxygen consumption for a given external cardiac work load in comparison with the sea level group would suggest an increase in left ventricular work yield. Associated with other favourable changes in the myocardium (increase in terminal and capillary circulation, quantitative and qualitative improvement in the respiratory enzyme chain) the apparently beneficial effects of chronic hypoxia at HA may be suggested as a means for the prevention of coronary disease.