Respiratory alkalemia during exercise reduces angina threshold.

The effect of hyperventilation-induced alkalemia on angina threshold was evaluated in nine subjects who had a consistent pattern of chest pain and ST segment depression during exercise. For this study, the subjects performed graded bicycle exercise to angina during normal breathing and during hyperventilation. The maximum workload achieved was not significantly different between normal breathing and hyperventilation exercise. However, in five subjects who had arterial alkalemia during hyperventilation exercise (mean pH = 7.52), the heart rate X blood pressure product (HR X BP) at angina was 224 X 10(2) compared with 240 X 10(2) during normal breathing exercise (P less than 0.05). Four subjects appeared to hyperventilate, but were not alkalemic (mean pH = 7.40). Their HR X BP at angina was not significantly different between the two exercise periods (288 X 10(2) vs 284 X 10(2). In conclusion, the threshold for angina during exercise fell in the five patients in whom hyperventilation caused alkalemia. This finding suggests that the alkalemia interfered with myocardial oxygen supply.