Ventilation and ventilatory pattern during sleep in aborted sudden infant death syndrome

To assess ventilatory control during sleep in infants at risk for the sudden infant death syndrome (SIDS), we made serial measurements of resting tidal volume (Vt), respiratory cycle time (Ttot), and the ventilatory changes resulting from inhalation of 2% CO2 in aborted SIDS infants in rapid eye movement and quiet sleep and compared them to a group of normal infants during the first 4 months of life. Ventilation was measured by the barometric method, and sleep was staged using electroencephalogram, electrooculogram, and electromyogram and behavioral criteria. Although resting instantaneous minute ventilation (Vt/Ttot) was virtually the same in both groups of infants, Vt tended to be smaller (by up to 50% in the first 2 months) and Ttot tended to be shorter in aborted SIDS than in normal infants in both rapid eye movement and quiet sleep. The increase in the mean Vt/Ttot with 2% CO2 is greater by about 5 to 20% in aborted SIDS than in normal infants at 3 and 4 months of age in both sleep states. These findings, together with our previous findings that aborted SIDS infants have an increase in heart rate and a shortening of the QT interval, provide indirect evidence that infants at high risk for SIDS may have increased sympathoadrenal activity.