Ventilatory responses to rebreathing in infants exposed to maternal smoking

This study assessed the effect of maternal smoking during pregnancy on vent ilatory and waking responses of infants to a respiratory challenge. This ch allenge mimicked the time-course and concentration of gases that an infant would experience rebreathing face-down into soft bedding. Control (C; n = 9 7) and smokers' infants (SM; n = 96) were studied at ages 1 and 3 mo. Asphy xial gas (hypercapnia/hypoxia) was delivered to the supine sleeping baby vi a a hood by slowly altering the inspired air: CO2 maximum 5% and O-2 minimu m 13.5%. Respiratory pattern was recorded by inductive plethysmography as t he sum of ribcage and abdominal movements. The change in ventilation with i nspired CO2 was measured over 5-6 min of the test. The slope of a linear cu rve fit relating inspired CO2 to the logarithm of ventilation was taken as a quantitative measure of ventilatory asphyxial sensitivity (VAS). Protecti ve responses were graded from 1: no waking and an estimated arterial carbon dioxide tension (PaCO2) greater than or equal to 60 mmHg (least protective ), to 4: fully awake (most protective). The results showed VAS was higher i n SM infants than controls: +0.03 (p = 0.04). The oxygen saturation (SaO(2) ) of SM infants fell -0.4% (p = 0.02) more than SaO(2) Of controls despite a greater tidal volume increase: +13.0% (p = 0.04). Overall protective resp onses were the same between groups, but grade 1, although rare, was found i n 7 SM infants and only 4 control infants; this difference was not signific ant. Conclusion: The study did not confirm the postulate that infants of mothers who smoked during pregnancy have a reduced ventilatory response or raised waking thresholds.