ISSN:
1439-6327
Keywords:
Gas exchange
;
Buffer CO2
;
Lactate
;
Bicarbonate
;
CO2 store
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract A method to estimate the CO2 derived from buffering lactic acid by HCO3 − during constant work rate exercise is described. It utilizes the simultaneous continuous measurement of O2 uptake ( $$\dot V$$ O2) and CO2 output ( $$\dot V$$ CO2), and the muscle respiratory quotient (RQm). The CO2 generated from aerobic metabolism of the contracting skeletal muscles was estimated from the product of the exercise-induced increase in $$\dot V$$ O2 and RQm calculated from gas exchange. By starting exercise from unloaded cycling, the increase in CO2 stores, not accompanied by a simultaneous decrease in O2 stores, was minimized. The total CO2 and aerobic CO2 outputs and, by difference, the millimoles (mmol) of lactate buffered by HCO3 − (corrected for hyperventilation) were estimated. To test this method, ten normal subjects performed cycling exercise at each of two work rates for 6 min, one below the lactic acidosis threshold (LAT) (50 W for all subjects), and the other above the LAT, midway between LAT and peak $$\dot V$$ O2 [mean (SD), 144 (48) W]. Hyperventilation had a small effect on the calculation of mmol lactate buffered by HCO3 − [6.5 (2.3)% at 6 min in four subjects who hyperventilated]. The mmol of buffer CO2 at 6 min of exercise was highly correlated (r = 0.925, P 〈 0.001) with the increase in venous blood lactate sampled 2 min into recovery (coefficient of variation = ±0.9 mmol·l−1). The reproducibility between tests done on different days was good. We conclude that the rate of release of CO22 from HCO3 − can be estimated from the continuous analysis of simultaneously measured $$\dot V$$ CO2, $$\dot V$$ O2, and an estimate of muscle substrate.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00392036
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