Relationship of potassium ions and blood lactate to ventilation during exercise

Ventilatory control during exercise is a complex network of neural and humoral signals. One humoral input that has received little recent attention in the exercise literature is potassium ions [K(+)]. The purpose of this study was to examine the relationship between [K(+)] and ventilation during an incremental cycle test and to determine if the relationship between [K(+)] and ventilation differs when blood lactate [lac-] is manipulated. Eight experienced triathletes (4 of each sex) completed 2 incremental, progressive (5-min stages) cycle tests to volitional fatigue: 1 with normal glycogen stores and 1 with reduced glycogen. Minute ventilation was measured during the final minute of each stage, and blood [lac(-)] and [K+] were measured at the end of each exercise stage. Minute ventilation and [K(+)] increased with exercise intensity and were similar between trials (p > 0.5), despite lower [lac-] during the reduced-glycogen trial. The concordance correlations (R(c)) between [lac(-)] and minute ventilation were stronger for both trials (R(c) = approximately 0.88-0.96), but the slopes of the relationships were different than the relationships between [K(+)] and minute ventilation (R(c) = approximately 0.76-0.89). The slope of the relationship between [lac-] and minute ventilation was not as steep during the reduced-glycogen trial, compared with the normal trial (p = 0.002). Conversely, the slope of the relationships between [K(+)] and minute ventilation did not change between trials (p = 0.454). The consistent relationship of minute ventilation and blood [K(+)] during exercise suggests a role for this ion in the control of ventilation during exercise. Conversely, the inconsistent relationship between blood lactate and ventilation brings into question the importance of the relationship between lactate and ventilation during exercise.