Journal of Applied Physiology, Vol 65, Issue 5 2090-2096, Copyright © 1988 by American Physiological Society

ARTICLES

Role of lungs and inactive muscle in acid-base control after maximal exercise

J. M. Kowalchuk, G. J. Heigenhauser, M. I. Lindinger, G. Obminski, J. R. Sutton and N. L. Jones
Department of Medicine, McMaster University Health Sciences Centre, Hamilton, Ontario, Canada.

The pulmonary responses and changes in plasma acid-base status occurring across the inactive forearm muscle were examined after 30 s of intense exercise in six male subjects exercising on an isokinetic cycle ergometer. Arterial and deep forearm venous blood were sampled at rest and during 10 min after exercise; ventilation and pulmonary gas exchange variables were measured breath by breath during exercise and recovery. Immediately after exercise, ventilation and CO2 output increased to 124 +/- 17 1/min and 3.24 +/- 0.195 l/min, respectively. The subsequent decrease in CO2 output was slower than the decrease in O2 intake (half time of 105 +/- 15 and 47 +/- 4 s, respectively); the respiratory exchange ratio was greater than 1.0 throughout the 10 min of recovery. Arterial plasma concentrations of Na+, K+, and Ca2+ increased transiently after exercise. Arterial lactate ion concentration ([La-]) increased to 14-15 meq/l within 1.5 min and remained at this level for the rest of the study. Throughout recovery there was a positive arteriovenous [La-] difference of 4-5 meq/l, associated with an increase in the arteriovenous strong ion difference ([SID]) and by a large increase in the venous Pco2 and [HCO3-]. These findings were interpreted as indicating uptake of La- by the inactive muscle, leading to a fall in the muscle [SID] and increase in plasma [SID], associated with an increase in muscle PCO2. The venoarterial CO2 content difference was 38% greater than could be accounted for by metabolism of La- alone, suggesting liberation of CO2 stored in muscle, possibly as carbamate.(ABSTRACT TRUNCATED AT 250 WORDS)

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