Maturation of ventilatory response to hypoxia in puppies during sleep

Using the barometric method, we studied the maturation of the ventilatory response to steady-level hypoxia (FIO2 = 15%O2) during sleep in 37 beagle puppies. In rapid-eye-movement (REM) sleep, instantaneous minute ventilation (VT/Ttot) and mean inspiratory time (VT/TI) increased, and inspiratory time (TI) and expiratory time (TE) were shortened in response to hypoxia at all the ages studied (14, 19, 24, 29 days). In quiet sleep, however, VT/Ttot decreased, and TE and Ttot were prolonged at 14 days in response to the same hypoxic stimulus. There was no change in VT/Ttot at 19 and 24 days of age, but VI/Ttot and VT/TI increased, and TI and TE were shortened at 29 days of age in response to hypoxia in the same sleep state. The mean arterial O2 tension (PaO2) dropped during hypoxia to about 45 Torr, and the mean arterial CO2 tension (PaCO2) decreased, and the mean pH increased at all ages in both REM and quiet sleep. We conclude that in beagles puppies 1) the ventilatory response to hypoxia matures at a slower rate in quiet than in REM sleep and depends primarily on timing rather than volume mechanisms: and 2) in response to hypoxia, the regulation of blood gases in REM sleep may be achieved differently from that in quiet sleep in early life.