The consequences of provoking a change in the sleeping position from side to prone during quiet (non-REM) and active (REM) sleep in young infants were studied in terms of ability to turn the face away from the mattress within 3 min, and in terms of ventilatory and heart rate responses in those who remained face down. Twenty-six infants were exposed to repeated tilts from the side to prone at 2.5 months, and 20 at 5 months of age. Eighteen infants were tested on both occasions. A computer-aided multichannel system was used for polysomnographic recordings. Approximately 66% of the infants did not rotate the face away from the mattress on at least one occasion. There were no significant differences in the rate of face down outcome between sleep states or ages, and no consistent pattern of final face position following repeated tilts. The face to side position was commonly accomplished after considerable difficulties involving vigorous body movements, particularly if the arm became positioned between the body and the mattress or alongside the trunk after the tilt. Apnoeas of 3-14 s in immediate response to the tilt were observed in 75% of the infants monitored electronically. In 13% of the infants, all in a face down position, the test was terminated because of increases in heart and respiratory rates, drop in oxygen saturation, or marked pallor.
Conclusions: The observed difficulties of obtaining a face to side position when suddenly exposed to the prone position during sleep, may render some young infants at risk of sudden infant death (SID).