Respiratory responses to hypoxia/hypercapnia in small for gestational age infants influenced by maternal smoking.
OBJECTIVE
To determine any variation in the respiratory responses to hypoxia/hypercapnia of infants born small for gestational age (SGA) to smoking and to non-smoking mothers.


METHODS
A total of 70 average for gestational age (AGA) infants (>36 weeks gestation, >2500 g, >25th centile for gestational age, and no maternal smoking), and 47 SGA infants (<10th centile for gestational age) were studied at 1 and 3 months of age, in quiet and active sleep. Respiratory test gases were delivered through a Perspex hood to simulate face down rebreathing by slowly allowing the inspired air to be altered to a CO(2) maximum of 5% and O(2) minimum of 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).


RESULTS
There was no significant difference in VAS between the AGA and SGA infants (0.25 v 0.24). However within the SGA group, VAS was significantly higher (p = 0.048) in the infants whose mothers smoked during pregnancy (0.26 (0.01); n = 24) than in those that did not (0.23 (0.01); n = 23). The change in minute ventilation was significantly higher in the smokers than the non-smokers group (141% v 119%; p = 0.03) as the result of a significantly larger change in respiratory rate (8 v 4 breaths/min; p = 0.047) but not tidal volume.


CONCLUSIONS
Maternal smoking appears to be the key factor in enhancing infants' respiratory responses to hypoxia/hypercapnia, irrespective of gestational age.
Galland
B C
BC
Department of Women's and Children's Health, Otago Medical School, University of Otago, PO Box 913, Dunedin, New Zealand. barbara.galland@stonebow.otago.ac.nz
Taylor
B J
BJ
Bolton
D P G
DP
Sayers
R M
RM
D005260:Female; D005865:Gestational Age; D006801:Humans; D006935:Hypercapnia / Q000209:etiology*; D000860:Hypoxia / Q000209:etiology*; D007223:Infant; D007231:Infant, Newborn; D007236:Infant, Small for Gestational Age; D008297:Male; D011247:Pregnancy; D012120:Respiration Disorders / Q000209:etiology*; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects*