Kinetics of CO_2 excessive expiration in constant-load exercise

摘要

Background. The purpose of this study was to examine the kinetics of excessively expired CO_2 (V_(CO_2)excess) in response to an increase in blood lactate (La) during constant-load exercise. Methods. O_2 uptake (V_(O_2) and CO_2 output (V_(CO_2) were measured at exercise intensities of 55% and 70% of individual peak values of V_(O_2) obtained in incremental exercise. V_(CO_2) excess was obtained by multiplying the V_(O_2) obtained at 55% or 70% peak Voz by the difference between respiratory gas exchange ratios (V_(CO_2)/V_(O_2)) at 55% or 70% peak V_(O_2) and at 40% peakV_(O_2). Results. In both exercises of 55% and 70% peakV_(O_2), V_(CO_2-) excess remained constant for about the first minute, increased until about 2 min after the start of exercise, and then decreased. V_(CO_2)excess showed positive values even at 10 min after the start of exercise. The La level, on the other hand, increased during the first 5 min of exercise but did not show any significant change during the next 5 min. The values of V_(CO_2)excess were integrated from the start to the end of 10 min of exercise (CO_2excess). CO_2excess was found to be significantly related to the difference between La at 10 min after the start of exercise and at rest (ΔLa). End tidal CO_2 pressure (PETCO_2) increased and then decreased in both exercises. The difference between PETCO_2 values at peak and at 10 min after the start of exercise (ΔPETCO_2) was significantly related to CO_2excess. ΔPETCO_2 was also found to be significantly related to the increase in ΔLa. Conclusions. The kinetics of estimated V_(CO_2)excess is affected first by the increase in La and later by the decrease in PETCO_2 induced by the La increase.