Exercise-induced rise in arterial potassium in patients with chronic heart failure - Relation to excessive exercise ventilation

Objectives: In patients with chronic heart failure (CHF), exercise is frequently associated with skeletal muscle fatigue and breathlessness due to heightened ventilatory response, The exercise-induced rise in potassium, which is released frost the exercising skeletal muscle, has been implicated in ventilatory control during exercise. The aim of the present study was to determine whether the exercise-induced rise in arterial potassium is altered in patients with CHF and to examine the relationship between increased exercise ventilation and exercise-induced hyperkalemia in patients with CHF. Methods and results: We evaluated 88 patients with CHF (25 patients were in class I, 35 in class II, and 28 in class III according to the New York Heart Association functional classification) and 14 normal subjects, Subjects performed symptom-limited ergometer exercise while expired gas, al arterial blood gas, and arterial potassium were analyzed, The increases in ventilation (Delta(V) over dot (E)), effective alveolar ventilation (Delta(V) over dot A), and carbon dioxide output (Delta(V) over dot (CO2)) from rest to peak exercise decreased as the severity of CHF advanced. The ratio of Delta(V) over dot (E) to Delta(V) over dot (CO2) was significantly elevated in class III patients, although there was no difference in the ratio of Delta(V) over dot A to Delta(V) over dot (CO2) among the four groups. Rest and exercise arterial P-CO2 did not differ among the four groups and was controlled within the normal range. The increase in arterial potassium (Delta K+) from I est to peak exercise was markedly reduced as the severity of CHF advanced: (mean +/- SD) 1.70 +/- 0.32 mmol/L in normal subjects; 1.46 +/- 0.27 mmol/L in class I patients; 1.15 +/- 0.24 mmol/L in class II patients; and 0.78 +/- 0.24 mmol/L in class III patients. The ratios of Delta(V) over dot A or Delta(V) over dot (CO2) to Delta K+ were not different among the four groups. The ratio of Delta(V) over dot (E) to Delta K+, however, was significantly greater in patients in class III than in normal subjects or patients in class I or II. Conclusions: The Delta K+ from rest to peak exercise was markedly reduced as the severity of CHF advanced, The increased exercise ventilation due to increased physiologic dead space in severe CHF was not accompanied by the corresponding augmentation of exercise-induced hyperkalemia. Exercise-induced hyperkalemia does not contribute to the increased ventilatory drive to keep normal arterial P-CO2 during exercise in the presence of increased physiologic dead space in severe CHF.