Determinants of bronchial responsiveness at school age in prematurely born children

Bronchial hyper-responsiveness after preterm birth

Being born preterm often adversely affects later lung function. Airway obstruction and bronchial hyperresponsiveness (BHR) are common findings. Respiratory symptoms in asthma and in lung disease after preterm birth might appear similar, but clinical experience and studies indicate that symptoms secondary to preterm birth reflect a separate disease entity. BHR is a defining feature of asthma, but can also be found in other lung disorders and in subjects without respiratory symptoms. We review different methods to assess BHR, and findings reported from studies that have investigated BHR after preterm birth. The area appeared understudied with relatively few and heterogeneous articles identified, and lack of a pervasive understanding. BHR seemed related to low gestational age at delivery and a neonatal history of bronchopulmonary dysplasia. No studies reported associations between BHR after preterm birth and the markers of eosinophilic inflammatory airway responses typically found in asthma. This should be borne in mind when treating preterm born individuals with BHR and airway symptoms.

Birth weight and adult lung function: a within-pair analysis of twins followed up from birth

BACKGROUND

The aim of the study was to evaluate whether there is any association between intrauterine growth and later lung function or bronchial reactivity in early adulthood in line with Barker's hypothesis.

METHODS

Nineteen twin pairs with disproportionate intrauterine growth pattern were followed up from birth: either one of the pairs had intrauterine growth retardation (birth weight <2 SD) or the within-pair birth weight difference was >1.3 SD. Flow-volume spirometry, followed by isocapnic hyperventilation of cold air, was performed at the ages of 8-16 and 14-22 years in 1993 and 1999. Wilcoxon's matched-pairs analysis was used to compare smaller and larger twin pairs.

RESULTS

In 1993, there were no significant differences between the groups in either spirometry or cold air challenge. In 1999, such a difference was found in forced expiratory volume % (FEV%) and forced expiratory flow (FEF) at 25%-75%, the smaller twin pairs having lower values. In 1993, nine subjects reacted to cold air (>9% decrease in FEV in 1 second). In 1999, only four subjects reacted to cold air, and they all belonged to the group of smaller twins (P=0.04).

CONCLUSION

Lung function evaluated by FEV% and FEF25-75 was lower and responses to cold air were more common at the median age of 16 years in twins with impaired intrauterine growth.

Determinants of bronchial responsiveness to methacholine at school age in twin pairs

The methacholine inhalation challenge test (MIC) was used to evaluate bronchial responsiveness in 67 children who were the products of multiple pregnancies when they were 7-15 years old. At birth, 30 (45%) infants had intrauterine growth retardation (IUGR; birth weight <2 SD below normal birth weight, or birth weight difference >1.3 SD between twin-pairs), and 59 (88%) were born before 37 weeks of gestation. None of the children had doctor-diagnosed asthma. The provocative dose of methacholine causing a 20% fall in Wright's peak expiratory flow (WPEF) (PD20) was below 1,000 microg in 10 (15%) children, and they were classified as MIC responders. There were no differences in perinatal or neonatal factors between MIC responders and nonresponders; in particular, MIC responses did not differ between IUGR infants, and children with appropriate growth for gestational age (AGA) at birth. There were seven discordant pairs in which one child was a MIC responder and the other was not; 5 responders were IUGR, and 2 were AGA children (ns). Respiratory tract infections after the neonatal period were equally common in IUGR and AGA children. However, these infections were associated with later bronchial hyperresponsiveness. Doctor-diagnosed respiratory infections, numbers of antibiotic courses, episodes of otitis media, and the need for adenoidectomy, tonsillectomy, and tympanostomy were more common in MIC responders than in nonresponders. We conclude that IUGR was not associated with subsequent bronchial hyperresponsiveness in twin pairs assessed by the MIC test. A significant relationship was seen between bronchial hyperresponsiveness and infections after the neonatal period.