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 (VE) and arterial K+ (Ka+) are similar, suggesting that changing Ka+ may lead to the phenomenon of the ventilatory threshold through its action on the peripheral chemoreceptors. 2. Expiratory ventilation, oxygen consumption, CO2 production (VE, VO2, VCO2), arterialized venous PCO2 (Pav, CO2; see Methods), pH (pHav), K+ (Kav+) and lactate were measured during incremental exercise tests undertaken by six normal male subjects under control conditions and during lactic acidosis following severe exercise (experimental trial). 3. A ventilatory threshold, associated with a period of isocapnic buffering, was observed under both control and experimental conditions. During the control trial, plots of Kav+ against VO2 showed an inflexion close to the ventilatory threshold. Throughout the experimental trial Kav+ rose linearly relative to VO2. In both control and experimental trials Kav+ concentrations were similar at the ventilatory threshold. 4. These results suggest that the pattern of change of Ka+ cannot account for the phenomenon of the ventilatory threshold. The possibility that the peripheral chemoreceptor response is non-linear above a critical value of Ka+ requires further investigation.