Clarke, Jane Rebecca; (1996) Bronchial responsiveness during the first year of life. Doctoral thesis (M.D), UCL (University College London).

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Abstract

In older children and adults, asthma is associated with increased bronchial responsiveness (BR). In order to test the hypothesis that BR in the neonatal period is a risk factor for subsequent lower respiratory illness (LRI), a cohort of term healthy infants of atopic parents was studied during their first year of life, with questionnaires and lung function measurements. Using the "squeeze" technique to generate partial forced expiratory flow volume curves, VmaxFRc, the maximal flow at functional residual capacity, was calculated. BR to histamine aerosol was determined and expressed as PC30, the provoking concentration of histamine which induced a 30% fall in VmaxFRc- Functional residual capacity (FRC), was measured using a small infant spirometer and the helium dilution technique. In a parallel study, a group of "asthmatic" infants and a group with severe chronic lung disease of prematurity (CLD) were studied during tidal breathing, to evaluate technically simpler methods of lung function assessment. During histamine challenge tidal breathing parameters and non-invasive measurements of oxygenation were recorded and any changes applied to BR assessment. Both neonatal lung function and BR were risk factors for LRI in the first year of life. In boys, LRI was associated with decreased VmaxFRc, whereas in girls it was associated with increased levels of BR in the neonatal period. By the age of six months, both boys and girls with LRI had decreased lung function, but differences in BR were no longer apparent. Tidal expiratory flow measurements were less sensitive than forced expiratory flow measurements in detecting differences between health and disease, only falling outside the normal range in infants with CLD. During bronchial challenge, change in oxygenation, measured by a reduction in transcutaneous oxygen tension, was a less sensitive index of bronchial responsiveness in healthy infants than in infants with a history of recurrent LRI.

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