The purpose of this study was to investigate the kinetics of Vco₂during incremental exercise. The subjects were 7 males, age 21-28 years, exercised at two steady state work loads (540 kpm/min, 810 kpm/min) and incremental work load which was increased stepwise by every 1 min from 180 kpm/min to exhaustion. The Vo₂and Vco₂during steady state exercise (4 to 5 min) were determined by the Douglas bag method and arterialized blood samples were taken for lactate (LA) analysis and blood gas analysis. The Vo₂, Vco₂, and blood lactate were also determined throughout the incremental exercise. At exhaustion, mixed venous Pco₂ (PVco₂) was determined by the CO₂rebreathing method.
1) The Vco₂values at rest and during steady state exercise were linearly related to the Vo₂values. When the regression line was compared with Vco₂during the incremental exercise on the same Vo₂, the Vco₂during the incremental exercise below the anaerobic threshold showed lower values.
2) The total sum of the difference in Vco₂between steady state and incremental exercise was defined as CO₂store. The calculated CO₂store and CO₂store per body weight were significantly related to PVco₂at exhaustion in incremental exercise, respectively (r=0.954, r=0.954) .
3) At work load below the anaerobic threshold, Vco₂was linearly related to Vo₂. If the Vco₂above the anaerobic threshold is estimated from Vo₂using the regression line obtained at work load below the anaerobic threshold, the estimated Vco₂will be lower than the measured Vco₂. The total sum of the difference in the Vco₂was defined as CO₂excess. The CO₂excess and the CO₂excess per body weight were significantly related to ΔLAmax (the difference between LA at 3rd min after exhastion and LA at exercise below the anaerobic threshold), respectively (r=0.870, r=0.930) .
4) HCO₃^-calculated from blood gases (pH and Pco₂) was significantly related to LA (r=-0.902) . The increase of 1 mM/1 in LA was corresponding to the decrease of 0.843 mEq/l in HCO₃^-.
5) From these results, it appeared that the expired Vco₂during the incremental exercise consisted of the stored Vco₂, the exceeded Vco₂, and the produced Vco₂ (Vco₂metabolically produced from Vo₂) .