AMMONIA RESPONSE TO EXERCISE IN PATIENTS WITH CONGESTIVE-HEART-FAILURE

Objective-To assess energy depletion in skeletal muscle in patients wi th congestive heart failure by measuring blood purine metabolites duri ng exercise and, at the same time, determine the implications of the a mmonia response to exercise in these patients. Setting-Tottori Univers ity Hospital, Yonago, Japan. Patients-49 heart failure patients (New Y ork Heart Association (NYHA) grades I-III) and 16 normal subjects. Mai n outcome measures-Blood lactate, ammonia, and hypoxanthine levels wer e measured during exercise with expired gas analysis. Results-In norma l exercising subjects as well as in each heart failure subgroup, the a mmonia threshold was significantly higher than both the lactate thresh old [control: 21.8 (SD 5.3) v 17.4 (3.3) ml/kg/min; NYHA class I: 18.9 (3.8) v 15.5 (2.6); class II: 14.8 (2.5) v 12.7 (2.4); class III: 13. 5 (2.6) v 11.8 (2.5)] and the ventilatory threshold (P < 0.01). The di fference between the ammonia and lactate thresholds was noted in all n ormal subjects and in all heart failure patients. The ammonia threshol d, however, was significantly lower in heart failure patients than in normal subjects and it decreased with increasing NYHA class (P < 0.01) . Maximum ammonia levels were lower in the hear failure group and decr eased further with higher NYHA clasifications [control: 198 (52) mg/dl ; NYHA class I: 170 (74); class II: 134 (58); class III: 72 (15); P < 0.01]. There were significant correlations between maximum ammonia val ues and maximum lactate, oxygen consumption, and hypoxanthine levels ( r = 0.74, 0.48, and 0.87, respectively; P < 0.001). Conclusions-The am monia threshold may reflect the onset of ATP depletion in exercising s keletal muscles, as opposed to the onset of anaerobic respiration. It seems therefore that energy depletion in skeletal muscles during exerc ise occurs after attaining the anaerobic threshold. Both aerobic and a naerobic capacities of skeletal muscle are reduced in patients with co ngestive heart failure.