Role of lungs and inactive muscle in acid-base control after maximal exercise.
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)
Kowalchuk
J M
JM
Department of Medicine, McMaster University Health Sciences Centre, Hamilton, Ontario, Canada.
Heigenhauser
G J
GJ
Lindinger
M I
MI
Obminski
G
G
Sutton
J R
JR
Jones
N L
NL
D000136:Acid-Base Equilibrium; D000328:Adult; D001769:Blood / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism; D006801:Humans; D007773:Lactates / Q000378:metabolism; D019344:Lactic Acid; D008168:Lung / Q000378:metabolism*; D008297:Male; D009132:Muscles / Q000378:metabolism*; D010101:Oxygen Consumption; D005082:Physical Exertion; D011659:Pulmonary Gas Exchange
D007773:Lactates; D002245:Carbon Dioxide; D019344:Lactic Acid