Ventilatory sensitivity to mild asphyxia: prone versus supine sleep position.

AIMS

To compare the effects of prone and supine sleep position on the main physiological responses to mild asphyxia: increase in ventilation and arousal.

METHODS

Ventilatory and arousal responses to mild asphyxia (hypercapnia/hypoxia) were measured in 53 healthy infants at newborn and 3 months of age, during quiet sleep (QS) and active sleep (AS), and in supine and prone sleep positions. The asphyxial test mimicked face down rebreathing by slowly altering the inspired air: CO(2), maximum 5% and O(2), minimum 13.5%. The change in ventilation with inspired CO(2) was measured over 5-6 minutes of the test. The slope of a linear curve fit relating inspired CO(2) to the logarithm of ventilation was taken as a quantitative measure of ventilatory asphyxial sensitivity (VAS). Sleep state and arousal were determined by behavioural criteria.

RESULTS

At 3 months of age, prone positioning in AS lowered VAS (0.184 prone v 0.269 supine, p = 0.050). At newborn age, sleep position had no effect on VAS. Infants aged 3 months were twice as likely to arouse to the test than newborns (p = 0.013). Placing infants prone as opposed to supine increased the chances of arousal 1.57-fold (p = 0.035).

CONCLUSION

Our findings show 3 month old babies sleeping prone compared to supine have poorer ventilatory responses to mild asphyxia, particularly in AS, but the increased prevalence of arousal is a protective factor.