Figure 4

Reproducibility of O ₂ and CO ₂ manipulations using the new breathing circuit. Manipulations consisted of two runs of the 18-minute schedule described in ref [7]. O₂ (top) and CO₂ (bottom) respiratory traces (grey) were modeled as described in Material and Methods to obtain end-tidal (ET) levels (black). Pure O₂ was administered during 3 minutes in two different instances, inducing an approximate 600 mmHg increase in the fractional concentration of ETO₂. A 5%CO₂ mixture was also administered in two different instances, lasting 2 minutes each, which induced an approximate 10 mmHg increase in the fractional concentration of ETCO₂. We also observed small changes in ETO₂ and ETCO₂ when the CO₂ and, respectively, O₂ were administered. When not breathing one of the above gas compositions, the subject breathed medical air.