Kinetics of Mixed Venous CO₂ Pressure in Incremental-Load Exercise

Abstract

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.