[On the role of potassium as a limiting factor for exercise hyperpnea]

In view of the common findings that patients with pulmonary disease exhibit larger maximal exercise hyperpnea (Vmax) than their maximal voluntary ventilation (MVV), the limiting factor for the exercise loading in these patients has been considered to be excessive hyperventilation. Recently, plasma potassium released from exercising muscle has been found to effectively stimulate arterial chemoreceptors. This effect is further potentiated by the presence of hypoxia. Since patients often become hypoxemic by exercise loading, it was suspected that potassium may play a role to limit exercising capacity due to excessive stimulation of the peripheral chemoreceptors. In 1975, Kawakami et al. reported that in response to exercise loading emphysematous type patients exhibited higher potassium and lactic acid concentration than the bronchitic and mixed type COPD patients. Their findings, together with breathlessness often seen in the emphysema may be further evidence supporting the inference mentioned above.