A constant flux of carbon dioxide injected into the airways mimics metabolic carbon dioxide in exercise.
This paper reports the expired minute-ventilation (VE) responses of 5 subjects to three step levels in a) work rate on a bicycle ergometer (30, 50, and 70 W), b) inhaled constant fraction (CF) of CO2 (3, 5, and 7%), and c) inhaled constant flux (CFlux) of CO2 (0.3, 0.4, and 0.5 l/min (STPD) injected in the inspired air-stream). Both exercise (isocapnic with regulated PETCO2) and CFlux provoke larger and similar steady-state responses in VE, than CF. Both the CF and CFlux responses are hypercapnic, but the CFlux responses show evidence of "hypercapnic regulation." VE and total CO2 input into the alveoli (i.e., VCO2 plus inhaled CO2) are excellently correlated in both the CF and the CFlux cases. However, the CFlux delivery provokes a far greater VE for a given total input of CO2 than CF, and the CFlux response resembles the VE/VCO2 plot of exercise. We conclude that CFlux inhalation of CO2 simulates the metabolic CO2 production rate of exercise, and thus the humoral aspects of exercise hyperpnea in the steady state.
Mussell
M J
MJ
Department of Information Engineering, Faculty of Engineering, Yamagata University, Yonezawa, Japan.
Paulev
P E
PE
Miyamoto
Y
Y
Nakazono
Y
Y
Sugawara
T
T
D000328:Adult; D002245:Carbon Dioxide / Q000008:administration & dosage / Q000378:metabolism*; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D006801:Humans; D007267:Injections; D008297:Male; D008875:Middle Aged; D012119:Respiration / Q000502:physiology; D014692:Ventilation-Perfusion Ratio / Q000502:physiology*
D002245:Carbon Dioxide