Effect Of 3% Co2 Inhalation On Vo2 And Vco2 Kinetics During Heavy Intensity Exercise

Hypercapnic gas (HC) inhalation increases ventilation (VE) and decreases the respiratory exchange ratio during constant work-rate exercise (CWE) at heavy intensity. Hypoxia (HP) increases the time constant (τ) of oxygen uptake (VO2) in phase II during CWE at heavy intensity. Thus, it was hypothesized that HC inhalation alters VO2 and carbon dioxide output (VCO2) kinetics during CWE at heavy intensity. PURPOSE: This study tested the hypothesis that HC inhalation altered τVO2 and τVCO2 during CWE at heavy intensity. METHODS: Seven healthy males (23 ± 2 yrs) carried out the incremental maximum exercise tests while breathing; 1) ambient air (Air); 2) HC (21% O2, 3% CO2, N2 = balance); or 3) HP (16% O2, N2 = balance). Each subject performed CWE at 80%VO2max intensity for 6 min on three occasions. Subjects breathed Air, HC, or HP from 10 min before the start of exercise until the end of the exercise. τVO2, τVCO2, and τVE in phase II were estimated with a nonlinear least-squares fitting procedure. Statistical analysis was performed by one-way ANOVA with a post hoc test. RESULTS: τVO2 for HP was significantly higher than for Air (28.5 ± 5.6 vs. 21.7 ± 4.1 sec, p < 0.05), while τVO2 for HC (26.2 ± 5.9 sec) was not significantly different from Air and HP. The amplitude of VCO2 for HC was significantly less than for Air and HP (2222 ± 284 vs. 2919 ± 334 vs. 2872 ± 410 ml/min, p < 0.05), but τVCO2 for HC was not significantly different from Air and HP (44.2 ± 5.6 vs. 45.8 ± 17.5 vs. 40.5 ± 8.5 sec). The baseline of VE for HC was significantly higher than for Air and HP (16.9 ± 2.4 vs. 11.6 ± 1.8 vs. 11.0 ± 2.0 L/min, p < 0.05), but τVE for HC was not significantly different from Air and HP (53.5 ± 13.5 vs. 50.5 ± 10.2 vs. 50.2 ± 10.4 sec). CONCLUSIONS: 3% CO2 gas inhalation led to increased VE at rest and decreased VCO2 during CWE at heavy intensity but had no impact on both VO2 and VCO2 rising dynamics in phase II. This work was supported in part by JSPS KAKENHI Grant Number 21K11463. This work was supported in part by JSPS KAKENHI Grant Number 21K11463