Reliability of the Estimation of Non-Metabolic CO2 Output During Incremental Exercise / 体力科学

ABSTRACT

It is known that lactic anions and hydrogen ions (H<SUP>+</SUP>) produced during intense exercise are partly transported or diffused from muscle to blood resulting in the production of non-metabolic CO<SUB>2</SUB> through the bicarbonate buffering system. The purpose of the present study was to examine the reliability of the estimation of non-metabolic CO<SUB>2</SUB> 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 CO<SUB>2</SUB> output (VCO<SUB>2</SUB>-NM) was calculated by subtracting projected metabolic VCO<SUB>2</SUB> from actual VCO<SUB>2</SUB> after CO<SUB>2</SUB> threshold (CT) . CT was determined using a modified V-Slope method. Bicarbonate (HCO<SUB>3</SUB><SUP>-</SUP>), pH, CO<SUB>2</SUB> partial pressure and lactate concentration were measured from arterial blood samples using automatic analyzers. The kinetics of VCO<SUB>2</SUB>-NM and HCO<SUB>2</SUB><SUP>-</SUP> were compared throughout the exercise test. VCO<SUB>2</SUB>-NM was significantly correlated with HCO<SUB>3</SUB><SUP>-</SUP>decrease after CT (r=0.976, p<0.001) and the kinetics of VCO<SUB>2</SUB>-NM and HCO<SUB>3</SUB><SUP>-</SUP> decrease were similar during exercise. Furthermore, the amount of non-metabolic CO<SUB>2</SUB> output (NM-CO<SUB>2</SUB>) calculated integrating VCO<SUB>2</SUB>-NM above CT was significantly correlated with the difference in HCO<SUB>3</SUB><SUP>-</SUP>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-CO<SUB>2</SUB> was not significantly related to maximum ventilation (r=0.111, ns) . These results suggest that the estimation of non-metabolic CO<SUB>2</SUB> output during incremental exercise proposed in the present study is reliable. It was also suggested that the primary factor which influenced nonmetabolic CO<SUB>2</SUB> output during incremental exercise was the addition of H<SUP>+</SUP> into blood and not hyperventilation.