Kinetics of mixed venous CO2 pressure in incremental-load exercise

The purpose of the present study was to examine the kinetics of mixed venous CO_2 pressure (Pvco_2) in incremental-load exercise. Pvco_2 seemed to indicate a linear increase after a somewhat slow increase. CO_2 Store phase appearing in expiration of CO_2 (stored CO_2) was calculated from the data of 0_2 uptake (VO_2), CO_2 output (Pvco_2) and work rate. The stored CO_2 indicated a linear increase after a time delay. The stored CO_2 also significantly related to Pvco_2. When kinetics of Pvco_2 at light exercise intensity was supposed from stored CO_2, Pvco_2 seemed to indicate a linear increase with a time delay. Excessive expired CO_2 (excess CO_2) was calculated from the data of VO_2 and work rate. The excess CO_2 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 Pvco_2 was unchanged. This result was considered to be related to the excessive CO_2 expiration corresponding to the increase of blood lactate. Thus, within the present results and assumptions, it seemed that Pvco_2 indicated a linear increase with a time delay without the effect of lactate increase in incremental-load exercise.