漸増負荷運動中における非代謝性CO₂排出量の評価の信頼性

抄録

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.