EXOGENOUS STIMULI AND CIRCADIAN PEAK EXPIRATORY FLOW VARIATION IN ALLERGIC ASTHMATIC-CHILDREN

The influence of exogenous factors in the home on the circadian variat ion of airway obstruction has not been fully assessed in children with asthma. The aim of the present study was to investigate the contribut ion of exogenous stimuli to the degree of peak expiratory flow (PEF) v ariability during 24 h. Fifty-five children (33 boys and 22 girls; mea n age, 9.3 +/- 1.7 yr) with symptoms of asthma, increased bronchial re sponsiveness, and a solitary allergy to house dust mite (HDM) particip ated. Their asthma symptoms were well-controlled for at least 4 mo wit h daily inhaled corticosteroids (ICS) and beta(2)-adrenergic drugs if needed. Symptoms, peripheral blood eosinophils, total IgE, and specifi c IgE to HDM were assessed. Spirometry and PC20 histamine were perform ed. PEF amplitudes during 24 h (highest minus lowest as a percentage o f the day's mean value) were obtained at home during and 6 d after wit hdrawal of ICS. Dust samples were collected from the total area of the living rooms, bedrooms, mattresses (n = 25), and classrooms to obtain the HDM allergen (HDMA) exposure to Der p I and Der p II. Family smok ing habits, presence of pets, and types of floor-covering were recorde d on a checklist. Mean PEF amplitude did not increase after withdrawal of ICS, but absolute PEF values were significantly lower (p 0.05) at midnight and 4:00 A.M. Twenty-six children (47%) were exposed to envir onmental tobacco smoke (ETS), and 23 (42%) kept pets. Mattresses conta ined significantly higher amounts of HDMA compared with other location s. PEF amplitude after withdrawal of ICS was significantly higher in c hildren exposed to ETS, a pet, or a high HDMA level in their mattress than in children who were not exposed (ETS: 29.7% [3.9 to 56.6] versus 19.4% [0.0 to 56.6], p < 0.05; pets: 31.4% [9.7 to 52.5] versus 21.9% [0.0 to 56.6], p < 0.05; high HDMA level in the mattress: 35.5% [10.2 to 56.6] versus 21.4% [3.9 to 56.6], p < 0.05). These factors combine d with age and PC20 histamine and its interaction with ETS, especially in mild to moderate asthma, explained 48.4% of the variance of the PE F amplitude after withdrawal of ICS. Exogenous stimuli such as exposur e to ETS, pets, and high HDMA levels in mattresses contribute to an in creased circadian PEF amplitude after withdrawal of ICS and therefore to nocturnal worsening of asthma in HDM-allergic asthmatic children. M oreover, ETS exposure seems to especially worsen PEF variability in ch ildren with mild to moderately severe bronchial responsiveness.