Slowed glycogen utilization enhances exercise endurance in patients with heart failure

OBJECTIVES The objective of the study was to investigate the impact of alte ration of glycogen stores and metabolism on exercise performance in patient s with heart failure. BACKGROUND In normal subjects, muscle glycogen depletion results in increas ed exertional fatigue and reduced endurance. Skeletal muscle biopsies have revealed reduced glycogen content in patients with congestive heart failure (CHF). Whether glycogen depletion contributes to reduced endurance and abn ormal ventilation in these patients is unknown. METHODS Bicycle exercise tests with measurement of respiratory gases were p erformed following dietary manipulations to induce glycogen depletion (60% protein, 40% fat) and dow glycogen utilization (60% carbohydrate, 30% fat, 10% protein) in 13 patients with CHF (left ventricular ejection fraction 22 +/- 6%; age 48 +/- 9 years) and 7 control subjects (age 45 +/- 5 years). M aximal exercise, exercise at 75% of peak workload until exhaustion and 1-mi n cycles of supramaximal exercise at 133% of peak were performed on three o ccasions over a two-week period. RESULTS Significant changes in resting respiratory quotients (RQs) in norma l (Baseline: 0.78 +/- 0.03; Depleted: 0.69 +/- 0.05) and CHF subjects (Base line: 0.84 +/- 0.05; Depleted: 0.72 +/- 0.05) were observed (both p < 0.05) . Peak VO2 (oxygen consumption) in both groups was unchanged. The ventilato ry response to exercise was analyzed by correlating CO2 production (VCO2) t o minute ventilation (VE) in each test. The slopes of these correlations we re not affected in either group. With glycogen depletion, exercise enduranc e was reduced from 17 to 6.1 min (57 +/- 19%) in normal subjects versus a r eduction of 9.4 to 8.1 min (11 +/- 19%) in patients (p < 0.05). With slowed glycogen use, CHF patients increased exercise endurance from 9.4 to 16.5 m in (65%) versus 17 to 20.6 min (18%) in normal subjects (p < 0.05). CONCLUSIONS Glycogen depletion minimally affects maximal exercise performan ce, endurance or ventilation in CHF patients, whereas slowed glycogen utili zation markedly enhances exercise endurance. Therapeutic interventions that increase or slow use of glycogen stores may have clinical benefit. (C) 199 9 by the American College of Cardiology.