Transient responses to CO₂ breathing of human subjects awake and asleep

¹ Department of Environmental Medicine, The Johns Hopkins University, Baltimore, Maryland

Ventilation and end-tidal Pco₂ were studied in six subjects awake and asleep (following the ingestion of 200–300 mg sodium pentobarbital) during oxygen breathing and the administration and withdrawal of 4% CO₂ in oxygen. During the control period as well as steady-state CO₂ breathing, ventilation was significantly lower in asleep than in awake subjects. There was no significant difference between sleep and wakefulness in end-tidal Pco₂ or in the slope of the ventilatory response to 4% CO₂. The transient responses of ventilation and end-tidal Pco₂ of the group as a whole were similar in sleep and wakefulness. Ventilation changed more slowly than did end-tidal Pco₂. End-tidal Pco₂ overshot beyond the steady-state CO₂ breathing value at the onset of CO₂ breathing; and undershot below the control value during recovery. The magnitudes of both the overshoot and undershoot of end-tidal Pco₂ were correlated significantly to the slope of the ventilatory response to 4% CO₂, in the whole group awake and asleep.