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The Journal of Sports Medicine and Physical Fitness 2020 Jul 28

DOI: 10.23736/S0022-4707.20.11012-0


language: English

Effect of 3% CO2 inhalation on respiratory exchange ratio and cardiac output during constant work-rate exercise

Takahide KATO 1 , Takaaki MATSUMOTO 2, Stanley M. YAMASHIRO 3

1 Department of General Education, National Institute of Technology, Toyota College, Toyota, Japan; 2 Laboratory for Exercise Physiology and Biomechanics, School of Health and Sport Sciences, Chukyo University, Toyota, Japan; 3 Department of Biomedical Engineering, Viterbi School of Engineering, University of Southern California, Los Angeles CA, USA


BACKGROUND: The aim of this study was to examine whether the decrease in respiratory exchange ratio (RER) during constant work-rate exercise (CWE) with 3% carbon dioxide (CO2) inhalation could be caused by the combination of the decrease in CO2 output (VCO2) and the increase in oxygen uptake (VO2). In addition, we investigated the effect of 3% CO2 inhalation on cardiac output (Q) during CWE.
METHODS: Seven males (VO2 max: 44.1 ± 6.4 mL/min/kg) carried out transitions from low-load cycling (baseline; 40w) to light intensity exercise (45% VO2max; 89.3 ± 12.5 W) and heavy intensity exercise (80% VO2 max; 186.5 ± 20.2 W) while inhaling normal air (Air) or an enriched CO2 gas (3% CO2, 21% O2, balance N2). Each exercise session was 6 min, and respiratory responses by Douglas bag technique and cardiac responses by thoracic bio-impedance method were measured during the experiment.
RESULTS: Ventilation for 3% CO2 was higher than for Air through the experiment (P < 0.05). Steady and non-steady state RER and VCO2 for 3% CO2 were less than for Air in both light and heavy intensities (P < 0.05), but VO2 and Q did not differ between the two conditions.
CONCLUSIONS: 3% CO2 inhalation induced the decrease in RER during CWE at light and heavy intensities, which was due to the decrease in VCO2. The promoted ventilation with 3% CO2 did not lead to the increase in VO2. Moreover, 3% CO2 inhalation did not affect Q during CWE at light and heavy intensities.

KEY WORDS: Hypercapnia; Respiratory exchange ratio; Cardiac output; Exercise

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