Towards a new method for the measurement of bronchial responsiveness in infancy
Neonatal bronchial responsiveness (BR) predicts childhood asthma and decreased lung function. Examination of neonatal BR, on a larger scale than has previously been possible, would enable investigation of prenatal lung development to BR, in order to examine the relationship between foetal environment and airway function, the genetic epidemiology of BR, the role of BR in airway disease and postnatal lung development, and the classification of airway disease into phenotypes in infancy.;The aim of this project was to develop a test of bronchial responsiveness suitable for use in unsedated infants in a domiciliary setting, as a prelude to population studies. Current techniques involve prolonged procedures, carried out under sedation in a laboratory setting.;Resistance by interruption (Rint) has been comprehensively evaluated in infants in the course of this work. Feasibility has been demonstrated in unsedated infants and the entire process of obtaining data from initial approach to parents to laboratory success rates examined. For the first time, Rint measurements have been obtained in unsedated infants in the community. Preliminary reference values have been generated.;Rint and another technique applicable in unsedated infants, the high speed interrupter technique (HIT) were compared with the rapid thoracoabdominal compression (RTC) method in the context of a bronchial challenge test with doses of 0.9%, 2% and 4% saline. Following saline challenge, complex changes in HIT were found, which discount it as a suitable test for bronchial challenge, but have added to theories of the physiology of infant wheezing.;Large decreases in Rint were demonstrated after saline challenge, which may be explained by the dynamic nature of infant breathing patterns, which were also examined.;In summary, both techniques (HIT and Rint), originally proposed for use in assessment of BR in unsedated infants have been excluded from use in this context, and their use lies elsewhere.