GAS-EXCHANGE, BLOOD LACTATE, AND PLASMA-CATECHOLAMINES DURING INCREMENTAL EXERCISE IN HYPOXIA AND NORMOXIA

The interrelationships among blood lactate (La-) and plasma norepineph rine (NE) and epinephrine (Epi) were studied simultaneously with measu res of ventilation (VE) and gas exchange during incremental exercise t o exhaustion in nine healthy young men. We wanted to observe whether t he tight coupling that exists during normoxic exercise between the con centrations of La- ([La-]) and of both NE and Epi would also be found in hypoxia (inspired O-2 fraction = 0.14). In addition, we used recent ly advocated methods of V slope [CO2 output vs. O-2 uptake (VO2)] to s elect the ventilatory threshold (VT) and log-log transformation of [La -] and VO2 to select the lactate threshold (LT). Peak VO2 was reduced from 4,164 +/- 184 ml/min in normoxia to 3,635 +/- 144 ml/min in hypox ia (P < 0.05). The increase in [La-] was linearly related to the incre ases in both NE and Epi concentrations in the normoxic and hypoxic tes ts (r = 0.92-0.96). Estimates of VO2 at VT were significantly greater than those at LT in both normoxia and hypoxia, but these estimates wer e poorly correlated (r = -0.11-0.46). VT and LT were reduced by hypoxi a. Visual interpretation of the VT by examination of VE vs. VO2 and VE /VO2 vs. VO2 did not differ from the LT, but they were less than the V Ts by the V-slope method (P < 0.05); yet, all were poorly correlated. The tight coupling between the increase in [La-] and the increase in p lasma catecholamines might indicate a common mechanism for the increas e or a causative link. VT and LT provided estimates of the general tre nd in the data, but the poor correlation between them questions the ut ility of attempting to predict one from the other.