Gas exchange, blood lactate and plasma catecholamines during incremental exercise in hypoxia and normoxia. Hughson, R. L., H. J. Green, and M. T. Sharratt. Department of Kinesiology, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
APStracts 2:0220A, 1995.
The interrelationships among blood lactate (La-b) and plasma norepinephrine (Nepi) and epinephrine (Epi) were studied simultaneously with measures of ventilation (E) and gas exchange during incremental exercise to exhaustion in 9 healthy young men. We wanted to observe if the tight coupling that exists during normoxic exercise between [La-b] and both [Nepi] and [Epi] would also be found in hypoxia (FIO2 = 0.14). In addition, we used recently advocated methods of V-slope (CO2 vs. O2) to select ventilatory threshold (Tvent) and log-log transformation of [La-b] and O2 to select lactate threshold (TLa-b). Peak O2 was reduced from 4164+/-184 ml/min in normoxia to 3635+/-144 ml/min in hypoxia (P<0.05). The increase in [La-b] was linearly related to the increases in both [Nepi] and [Epi] in the normoxic and hypoxic tests (r = 0.92-0.96). Estimates of O2 at Tvent were significantly greater than those at TLa-b in both normoxia and hypoxia, but these estimates were poorly correlated (r = -0.11 -0.46). Each of Tvent and TLa-b was reduced by hypoxia. Visual interpretation of Tvent by examination of E vs. O2 and E/O2 vs. O2 did not differ from TLa-b, but they were less than Tvent by the V -slope method (P<0.05) yet, all were poorly correlated. The tight coupling between the increase in [La-b] and the increase in plasma catecholamines might indicate a common mechanism for increase or a causative link. Tvent and TLa-b provided estimates of the general trend in the data, but the poor correlation between them questions the utility of attempting to predict one from the other. 

Received 16 September 1994; accepted in final form 12 May 1995.
APS Manuscript Number A972-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 May 1995.