Factors associated with airway responsiveness to methacholine in asthmatic children and their families

AIM: Investigate factors associated with methacholine responsiveness in a population of asthmatic families. DESIGN: Exhaled nitric oxide (eNO), skin prick test (SPT), spirometry and log methacholine dose response slope (DRS) were measured in families with an asthma-affected sibling pair aged between 7 and 35 years. RESULTS: 230 subjects (54 Families) were recruited. 118 (51%) were male and 112 (49%) were female. Of 124 siblings, 59 (48%) were female, 116 (94%) were asthmatic and 34 (27.4%) SPT negative. Of 106 parents, 57 (53.8%) were asthmatic and 32 (30.2%) were SPT negative. DRS was the dependent variable in a linear regression model with stepwise consideration of parameters: log- FEV FVC, PEF, FEF 35.75, age, height, weight, eNO and FEF 25.75 /FVC, sex, SPT, serum IgE, wheezy episodes and years of cough. In 58 subjects aged less than 12 years, DRS was associated with FEV| (b=-2.24,p=0.005) and eNO (b=0.371,p=0.021). In 40 subjects aged 12-16 years, DRS was associated with male sex (b=0.347, p=0.005) and eNO (b=0.411, p=0.002). In 26 subjects aged 16-27 years, DRS was associated with wheezy episodes (b=O.OOI, p=0.025) and eNO (b=0.427, p=0.001).In 22 subjects aged 35-40 years, DRS was associated with FEF 25.75 /FVC (b=-1.172, p=0.006). In 84 subjects aged 40-58 years, DRS was significantly associated with age, years of cough, FEF and eNO. CONCLUSIONS: The methacholine DRS is associated with different variables when grouping the study subjects into different ages. Associations vary across age when symptoms, atopy, parameters of airway function and body size are considered.