Ventilatory responses to rebreathing in infants exposed to maternal smoking.
This study assessed the effect of maternal smoking during pregnancy on ventilatory and waking responses of infants to a respiratory challenge. This challenge mimicked the time-course and concentration of gases that an infant would experience rebreathing face-down into soft bedding. Control (C; n = 97) and smokers' infants (SM; n = 96) were studied at ages I and 3 mo. Asphyxial gas (hypercapnia/hypoxia) was delivered to the supine sleeping baby via a hood by slowly altering the inspired air: CO2 maximum 5% and O2 minimum 13.5%. Respiratory pattern was recorded by inductive plethysmography as the sum of ribcage and abdominal movements. The change in ventilation with inspired CO2 was measured over 5-6 min of the test. The slope of a linear curve fit relating inspired CO2 to the logarithm of ventilation was taken as a quantitative measure of ventilatory asphyxial sensitivity (VAS). Protective responses were graded from 1: no waking and an estimated arterial carbon dioxide tension (PaCO2) > or = 60 mmHg (least protective), to 4: fully awake (most protective). The results showed VAS was higher in SM infants than controls: +0.03 (p = 0.04). The oxygen saturation (SaO2) of SM infants fell -0.4% (p = 0.02) more than SaO2 of controls despite a greater tidal volume increase: +13.0% (p = 0.04). Overall protective responses were the same between groups, but grade 1, although rare, was found in 7 SM infants and only 4 control infants; this difference was not significant.


CONCLUSIONS
The study did not confirm the postulate that infants of mothers who smoked during pregnancy have a reduced ventilatory response or raised waking thresholds.
Campbell
A J
AJ
Departments of Women's and Children's Health, Otago Medical School, Dunedin, New Zealand.
Galland
B C
BC
Bolton
D P
DP
Taylor
B J
BJ
Sayers
R M
RM
Williams
S M
SM
D005260:Female; D006801:Humans; D006935:Hypercapnia / Q000209:etiology; D000860:Hypoxia / Q000209:etiology* / Q000503:physiopathology; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D009035:Mothers; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects; D012119:Respiration; D012129:Respiratory Function Tests; D012907:Smoking / Q000009:adverse effects*; D013398:Sudden Infant Death / Q000209:etiology*; D014851:Wakefulness