2001 年 50 巻 1 号 p. 129-138
It is known that lactic anions and hydrogen ions (H+) produced during intense exercise are partly transported or diffused from muscle to blood resulting in the production of non-metabolic CO2 through the bicarbonate buffering system. The purpose of the present study was to examine the reliability of the estimation of non-metabolic CO2 output using respiratory gas analysis during incremental exercise. Six healthy subjects underwent an incremental pedaling exercise test accompanied by respiratory gas and arterial blood sampling. The rate of non-metabolic CO2 output (VCO2-NM) was calculated by subtracting projected metabolic VCO2 from actual VCO2 after CO2 threshold (CT) . CT was determined using a modified V-Slope method. Bicarbonate (HCO3-), pH, CO2 partial pressure and lactate concentration were measured from arterial blood samples using automatic analyzers. The kinetics of VCO2-NM and HCO2- were compared throughout the exercise test. VCO2-NM was significantly correlated with HCO3-decrease after CT (r=0.976, p<0.001) and the kinetics of VCO2-NM and HCO3- decrease were similar during exercise. Furthermore, the amount of non-metabolic CO2 output (NM-CO2) calculated integrating VCO2-NM above CT was significantly correlated with the difference in HCO3-between CT and exhaustion (r=0.929, p<0.01) and with the difference in arterial blood pH between rest and exhaustion (r=0.863, p<0.05) . However, NM-CO2 was not significantly related to maximum ventilation (r=0.111, ns) . These results suggest that the estimation of non-metabolic CO2 output during incremental exercise proposed in the present study is reliable. It was also suggested that the primary factor which influenced nonmetabolic CO2 output during incremental exercise was the addition of H+ into blood and not hyperventilation.