THE RELATIONSHIP BETWEEN PLASMA K+ AND THE VENTILATORY DRIFT DURING STEADY STATE EXERCISE

Abstract

238 Recently, potassium has been investigated as a possible metabolite involved in the control of exercise ventilation. Graded and incremental cycle tests using healthy subjects show a strong positive correlation between plasma K+ and ventilation (VE). During steady state exercise, there is an upward drift in ventilation which cannot be accounted for by lactate or expired CO2. The purpose of this study was to examine the relationship between plasma K+ levels and the ventilatory drift during steady state exercise. Participants cycled at 60% VO2 max for 30 min. VO2, VCO2, VE, plasma K+, and plasma lactate were measured each min. There was an 8% increase in both VO2 (P<0.02) and VE (P<0.03), and a 16% increase in K+ (P<0.04) between 6 and 30 min of continuous exercise. VCO2 and lactate remained unchanged. There was a significant correlation between VE and K+ (r =.97) and between VO2 and K+ (r =.97) during steady state exercise. VE and lactate over the same duration were not correlated (r =.47). These results suggest a positive relationship between increases in K+ and ventilation during steady state exercise. Whether K+ is the causative agent of the ventilatory drift, however, remains to be determined.