RESUMO
The purpose of this study was to investigate the kinetics of Vco<SUB>2</SUB>during 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 Vo<SUB>2</SUB>and Vco<SUB>2</SUB>during 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 Vo<SUB>2</SUB>, Vco<SUB>2</SUB>, and blood lactate were also determined throughout the incremental exercise. At exhaustion, mixed venous Pco<SUB>2</SUB> (PVco<SUB>2</SUB>) was determined by the CO<SUB>2</SUB>rebreathing method.<BR>1) The Vco<SUB>2</SUB>values at rest and during steady state exercise were linearly related to the Vo<SUB>2</SUB>values. When the regression line was compared with Vco<SUB>2</SUB>during the incremental exercise on the same Vo<SUB>2</SUB>, the Vco<SUB>2</SUB>during the incremental exercise below the anaerobic threshold showed lower values.<BR>2) The total sum of the difference in Vco<SUB>2</SUB>between steady state and incremental exercise was defined as CO<SUB>2</SUB>store. The calculated CO<SUB>2</SUB>store and CO<SUB>2</SUB>store per body weight were significantly related to PVco<SUB>2</SUB>at exhaustion in incremental exercise, respectively (r=0.954, r=0.954) .<BR>3) At work load below the anaerobic threshold, Vco<SUB>2</SUB>was linearly related to Vo<SUB>2</SUB>. If the Vco<SUB>2</SUB>above the anaerobic threshold is estimated from Vo<SUB>2</SUB>using the regression line obtained at work load below the anaerobic threshold, the estimated Vco<SUB>2</SUB>will be lower than the measured Vco<SUB>2</SUB>. The total sum of the difference in the Vco<SUB>2</SUB>was defined as CO<SUB>2</SUB>excess. The CO<SUB>2</SUB>excess and the CO<SUB>2</SUB>excess 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) .<BR>4) HCO<SUB>3</SUB><SUP>-</SUP>calculated from blood gases (pH and Pco<SUB>2</SUB>) 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 HCO<SUB>3</SUB><SUP>-</SUP>.<BR>5) From these results, it appeared that the expired Vco<SUB>2</SUB>during the incremental exercise consisted of the stored Vco<SUB>2</SUB>, the exceeded Vco<SUB>2</SUB>, and the produced Vco<SUB>2</SUB> (Vco<SUB>2</SUB>metabolically produced from Vo<SUB>2</SUB>) .