EXERCISE-INDUCED CHANGES IN PLASMA POTASSIUM AND THE VENTILATORY THRESHOLD IN MAN

1. It has been reported that, during incremental exercise testing, the patterns of change in ventilation (V-E) and arterial K+ (K-a(+)) are similar, suggesting that changing K-a(+) may lead to the phenomenon of the ventilatory threshold through its action on the peripheral chemor eceptors. 2. Expiratory ventilation, oxygen consumption, CO2 productio n (V-E, V-o2, V-co2) arterialized venous P-co2 (P-av,P-co2; see Method s), pH (pH(av)), K+ (K-av(+)) and lactate were measured during increme ntal exercise tests undertaken by six normal male subjects under contr ol conditions and during lactic acidosis following severe exercise (ex perimental trial). 3. A ventilatory threshold, associated with a perio d of isocapnie buffering, was observed under both control and experime ntal conditions. During the control trial, plots of K-av(+) against V- o2 shosved an inflexion close to the ventilatory threshold. Throughout the rose linearly relative to V-o2. In both control and experimental trials K-av(+) concentrations were similar at the ventilatory threshol d. 4. These results suggest that the pattern of change of K-a(+) canno t account for the phenomenon of the ventilatory threshold. The possibi lity that the peripheral chemoreceptor response is non-linear above a critical value of K-a(+) requires further a investigation.