Maturation of ventilation and ventilatory pattern in normal sleeping infants.

Noninvasive studies of ventilation and ventilatory pattern were performed serially in 15 normal infants in the first 4 mo of life during REM and quiet sleep with the barometric method. We measured tidal volume (VT), total respiratory cycle time (Ttot), inspiratory time (Ti), expiratory time (TE), mean inspiratory flow (VT/TI), and respiratory "duty cycle" (TI/Ttot). Vt, Ttot, TI, TE, VT/TI, and VT/Ttot but not TI/Ttot increased with age. In all age groups, Ttot, TI, and TE but not VT/TI were greater in quiet than in REM sleep. In the first 2 mo of life, VT was greater in quiet than in REM sleep; in the older infants, VT/Ttot was smaller in quiet than in REM sleep. TI/Ttot was not dependent on sleep state. Thus, because VT/Ttot = VT/TI X TI/Ttot, the increase in VT/Ttot with age results from an increase in mean inspiratory flow rather than from changes in respiratory "duty cycle". Further, the "on-switching" as well as the "off-switching" of inspiratory activity depends on sleep state.