Kinetics of mixed venous CO2 pressure in incremental-load exercise

The purpose of the present study was to examine the kinetics of mixed venous CO2 pressure (PvCO2) in incremental-load exercise. PvCO2 seemed to indicate a linear increase after a somewhat slow increase. CO2 store phase appearing in expiration of CO2 (stored CO2) was calculated from the data of O2 uptake (VO2), CO2 output. (VCO2) and work rate. The stored CO2 indicated a linear increase after a time delay. The stored CO2 also significantly related to PvCO2. When kinetics of PvCO2 at light exercise intensity was supposed from stored CO2, PvCO2 seemed to indicate a linear increase with a time delay. Excessive expired CO2 (excess CO2) was calculated from the data of VO2 and work rate. The excess CO2 significantly related to the increase of blood lactate. The blood lactate seemed to start to increase at around 1080 kpm/min. In spite of this change, a linear increase of PvCO2 was unchanged. This result was considered to be related to the excessive CO2 expiration corresponding to the increase of blood lactate. Thus, within the present results and assumptions, it seemed that PvCO2 indicated a linear increase with a time delay without the effect of lactate increase in incremental-load exercise.