EXERCISE-INDUCED RISE IN ARTERIAL POTASSIUM IS ENHANCED IN PATIENTS WITH IMPAIRED EXERCISE TOLERANCE

We assessed the changes in arterial potassium concentration during exe rcise and recovery in relation to exercise tolerance in patients with impaired exercise tolerance. Sixteen patients with cardiac disease wer e subjected to a cardiopulmonary exercise test on a cycle ergometer. A rterial potassium and lactate concentrations were measured every minut e during and after exercise, and ventilatory threshold (VT) and lactat e threshold (LT) were identified. Before exercise, arterial potassium concentration was 3.8 +/- 0.3 mEq/l. It increased to 4.1 +/- 0.3 mEq/l at LT (p < 0.002 versus at rest), to 4.2 +/- 0.3 mEq/l at VT, and to 4.8 +/- 0.5 mEq/l at peak exercise (p < 0.001 versus at LT, p < 0.001 versus at VT). At an exercise intensity equivalent to 30, 40, 50 or 60 % of predicted maximum oxygen uptake, the increase in arterial potassi um showed a negative and significant correlation with %LT (r=-0.62 sim ilar to-0.72, p < 0.01 similar to 0.05) and %VT (r=-0.62 similar to-0. 75, p < 0.001 similar to 0.05), where %LT and %VT represent the ratios of LT and VT to the predicted maximum oxygen uptake, respectively. Th ere was a good correlation between the rate of fall in potassium conce ntration during recovery and its increase during exercise. It was conc luded that in patients with impaired exercise tolerance, the greater t he degree of exercise intolerance, the greater the increase in arteria l potassium concentration during exercise, and the steeper the fall in potassium concentration during recovery. Because the rise in potassiu m concentration during exercise and its fall during recovery were grea ter when the exercise level exceeded the anaerobic threshold, exercise levels below the anaerobic threshold are recommended for patients wit h cardiac diseases.