Application and interpretation of forced expiratory manoeuvres in infancy
This thesis comprised a series of population-based studies, based on two separate cohorts of healthy preterm and term infants, undertaken to examine factors determining respiratory function during infancy, together with the development of sex-specific reference data for maximal expiratory flow at functional residual capacity (V'maxFRc). 108 preterm infants without respiratory disease were recruited to investigate whether, after adjustment for body size, respiratory function in the neonatal period is reduced in those exposed to maternal smoking prenatally. At -36 weeks post-menstrual age, and prior to any postnatal smoke exposure, breathing patterns were altered and V'maxFRc reduced in those whose mothers smoked antenatally, in white compared with black infants and in boys compared with girls. Repeat measures of V'maxFRc in a subset of this preterm cohort (n=24) showed that, despite similar size-corrected values shortly after birth, at 1 year corrected postnatal age V'maxFRc was significantly lower (-2 Z score) than in term infants, with marked 'tracking' of lung function between test occasions, suggesting that preterm delivery per se may adversely affect subsequent airway development. Using the raised volume technique, airway function was assessed in 234 term infants (98 with low birth weight for gestational age SGA ). At 6 weeks postnatal age, after adjusting for relevant covariates including body size, airway function was significantly lower among SGA infants, in boys compared with girls and in those exposed to maternal smoking antenatally. Follow-up measurements at -8-9 months in 80 infants (32 SGA) of non-smoking mothers demonstrated considerable 'tracking' of airway function, with forced expired volume in 0.4 s (FEV04) being -9% lower in SGA infants throughout the first year (95% CI: 2% to 16%). These results suggest that adverse prenatal events may constrain lung development with potential long-term effects of respiratory health. In summary, maternal smoking during pregnancy, sex, preterm delivery and being born SGA may exert independent effects on airway function during infancy.