Potassium as a respiratory signal in humans

Six renal transplant recipients underwent a series of incremental exercise experiments. Minute ventilation (V̇E), carbon dioxide production rate (V̇CO₂), and arterial blood chemistry were measured at rest and while subjects exercised on a stationary bicycle. Four of the subjects performed a similar experiment while exercising on a static rowing machine. Within each subject, arterial potassium concentration ([K⁺](a)) was linearly related to V̇CO₂ and V̇E during exercise. The slope of the relationship between [K⁺](a) and V̇CO₂ was similar in the cycling and rowing experiments. This implies that the absorption of potassium by resting muscle does not significantly limit the arterial hyperkalemia seen during exercise. When V̇E, V̇CO₂, and [K⁺](a) were measured 1 and 5 min after the end of cycling there was no correlation, whereas V̇E continued to be closely correlated with V̇CO₂. The relationship demonstrated between change in [K⁺](a) and V̇CO₂ in these experiments is compatible with change of [K⁺](a) acting as a respiratory signal during exercise but not during recovery from exercise in humans.