Overall "gain" of the respiratory control system in normoxic humans awake and asleep

With the addition of external dead space in normoxia, PCO2-ventilation response and CO2 production were determined in 10 healthy male subjects. Overall "gain" (G) of the respiratory control system was calculated from the slope of the CO2-response curve (S) and that of the metabolic hyperbola (SL) at alveolar partial pressure of CO2 (PACO2) of the respective experimental run. We found that 1) despite the depression of ventilation during non-rapid-eye-movement (NREM) sleep, G was generally not changed due to decreased SL, although considerable individual variations were seen; 2) effects of external dead space on PACO2 change during sleep and wakefulness were similar in magnitude; and 3) the above PACO2 changes experimentally induced agreed well with the predicted values estimated from G. Contrary to general opinion, these results demonstrated that overall gain of the respiratory control system is generally not depressed during NREM sleep in normal healthy subjects.