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A and B: continuous recordings of fraction of inspired CO2 (
) and predicted arterial Pco2 (
) responses to hypercapnia (5% CO2) at rest and during exercise (Ex) in 1 representative subject. Hypercapnia was started at time 0. C: group-averaged sum of CO2-response delay (t0) and time constant (τ) of 
and predicted 
exponential fitting curves at rest and during exercise. Values are means ± SE. *P < 0.05 vs. 
. †P < 0.05 vs. rest.
