RELATIONSHIP BETWEEN LACTATE AND AMMONIA THRESHOLDS IN HEART-TRANSPLANT PATIENTS

The purpose of this investigation was to study the relationship betwee n both blood ammonia thresholds (AmT) and lactate thresholds (LT) duri ng dynamic exercise in cardiac transplant patients (CTPs). Eleven male patients who had undergone orthotopic cardiac transplantation (age: 5 4+/-11 years, mean+/-SD; height: 165.1+/-6.6 cm; body mass: 78.3+/-16. 1 kg) participated in this study. Each of them performed a bicycle erg ometer test (ramp protocol) until volitional fatigue. During each test , gas exchange parameters and ECG responses were determined continuous ly. In addition, blood lactate and ammonia concentrations were measure d every 2 min for determination of both LT and AmT, respectively. Peak values of oxygen uptake (V over dot o(2)), respiratory exchange ratio , ventilation, and heart rate averaged 15.9+/-3.03 mL . kg(-1). min(-1 ), 1.02+/-0.06, 46.69+/-5.69 L . min(-1), and 124+/-16 beats per minut e, respectively. However, blood concentrations of lactate and ammonia at peak exercise were 3.7+/-0.4 mmol . L(-1) and 85.6+/-31.7 mu g . dL (-1), respectively. LT and AmT were detected in 8 (72.7% of total) and 9 (81.8% of total) of 11 subjects, respectively. No significant diffe rences were found between mean values of LT and AmT, when both were ex pressed either as V over dot o(2) (10.01+/-1.19 vs 10.5+/-2.38 mL . kg (-1) . min(-1), respectively) or as percent V over dot o(2) peak (64.6 2+/-11.362 vs 66.48+/-9.19%, respectively). In addition, LT and AmT we re significantly correlated (p<0.05) when both mere expressed either a s V over dot o(2) (mL . kg(-1) . min(-1)) or as percent V over dot o(2 ) peak (r=0.70 and r=0.68, respectively). Our findings suggest that in CTPs, both LT and AmT occur at similar workloads, probably as a resul t of skeletal muscle alterations associated with chronic deconditionin g and immunosuppressive therapy.