Kinetics of CO(2) excessive expiration in constant-load exercise.
BACKGROUND
The purpose of this study was to examine the kinetics of excessively expired CO(2) (VCO(2) excess) in response to an increase in blood lactate (La) during constant-load exercise.


METHODS
O(2) uptake (VO(2) ) and CO(2) output (VCO(2) ) were measured at exercise intensities of 55% and 70% of individual peak values of Vo2 obtained in incremental exercise. VCO(2) excess was obtained by multiplying the Vo2 obtained at 55% or 70% peakVoz by the difference between respiratory gas exchange ratios (VCO(2) /Vo(2) ) at 55% or 70% peak VO(2) and at 40% peakVO(2) .


RESULTS
In both exercises of 55% and 70% peakVO(2) , VCO(2) excess remained constant for about the first minute, increased until about 2 min after the start of exercise, and then decreased. VCO(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 VCO(2) excess were integrated from the start to the end of 10 min of exercise (CO(2) excess). CO(2) excess was found to be significantly related to the difference between La at 10 min after the start of exercise and at rest (DLa). 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 (DPETCO(2) ) was significantly related to CO(2) excess. DPetco2 was also found to be significantly related to the increase in DLa.


CONCLUSIONS
The kinetics of estimated VCO2excess is affected first by the increase in La and later by the decrease in PETCO(2) induced by the La increase.
Yano
T
T
Laboratory of Exercise Physiology, Graduate School of Education, Hokkaido University, Sapporo, Japan. yano@edu.hokudai.ac.jp
Horiuchi
M
M
Yunoki
T
T
Ogata
H
H
D000328:Adult; D002245:Carbon Dioxide / Q000097:blood*; D015444:Exercise / Q000502:physiology*; D006801:Humans; D007700:Kinetics; D019344:Lactic Acid / Q000097:blood*; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology; D011659:Pulmonary Gas Exchange / Q000502:physiology*
D002245:Carbon Dioxide; D019344:Lactic Acid