Ventilation, CO2 Production, and CO2 Exposure Effects in Conscious, Restrained CF‐1 Mice

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Abstract
Respiratory rate (f), tidal volume (VT) and carbon dioxide production (VECO2) were measured in restrained, conscious CF‐1 mice. Mean f ± S.D. and mean VT ± S.D. were 270 ± 8 breaths/min. and 0.123 ± 0.024 ml (STPD) for male, and 274 ± 15 breaths/min. and 0.115 ± 0.023 ml (STPD) for female mice, respectively. VEO2 was obtained from a rebreathing (closed loop) system. The maximum VECO2 (STPD) amounted to 95.5 ± 15.4 ml/(kg min.) in males and to 72.7 ± 4.2 ml/(kg min.) in females. The CO2 concentration in the closed loop system increased slowly during a 30 min. rebreathing period and reached a concentration of about 2.7%. No effect was seen on f and on VT. Dynamic (abrupt) exposure up to 10.3% CO2 had no effect on f in male mice, whereas VT increased from 112% (2.3% CO2) to 181% (10.3% CO2). The estimated O2 concentrations decreased from 20.5% to 18.7% with increasing CO2 exposure. The equivalent CO2 experiments with O2 kept at 16% by N2 administration showed that the lower O2 concentration added an additional drive on the respiratory centre.