Relationships between duration of asthma and asthma severity among children in the Childhood Asthma Management Program (CAMP)

Background: Many factors, including heredity, atopic status, and environment, have been implicated in the determination of asthma severity, Relatively little is known about the degree to which asthma duration influences asthma severity. Objective: The Childhood Asthma Management Program (CAMP), consisting of 1041 children (age 8.9 +/- 2.1 years at enrollment) with mild-to-moderate asthma, offers an opportunity to examine the relationship between asthma duration and asthma severity. Methods: By using the extensive CAMP baseline cross-sectional data on asthma duration, spirometry, bronchial responsiveness, symptomatology and markers of atopy, univariate and multivariate regression models were used to evaluate whether asthma duration is associated with asthma severity, Results: Duration of asthma in the study cohort from time of diagnosis until randomization into CAMP ranged from 0.3 to 12.1 years (mean, 5.0; SD, 2.7; median,4.8). Asthma duration is associated in univariate analyses both with lower levels of several lung functions (P<.001), including methacholine bronchial reactivity (natural log [In] FEV1PC20, mg/mL; r = -0.112), prebronchodilator and postbronchodilator percent predicted FEV1 (r= -0.176 and r = -0.130, respectively), and prebronchodilator and postbronchodilator FEV1/forced vital capacity (FVC) (%) (r = -0.237 and r= -0.211, respectively), as well as higher levels of symptoms (symptom scare: r = 0.117, P <.001) and borderline greater use of albuterol fur symptoms (r= 0.058, P =.064) during a 28-day screening period before randomization. Simple linear regression detected the following differences in lung functions per gear of asthma duration: In FEV1PC20, -0.050 mg/mL/y; prebronchodilator FEV1-0.907 percent predicted/y; and prebronchodilator FEV1/FVC, -0.729 percent predicted/y. After controlling for potential explanatory variably (atopy, Inflammatory markers, household Der p 1 levels, anti-inflammatory medication use, and clinical center), regression models revealed that the duration of asthma remained significantly and independently associated with In FEV1PC20 (P =.004) prebronchodilator percent predicted FEV1 (P =.043), and prebronchodilator and postbronchodilator FEV1/FVC (%) (P <.001), as well as being positively associated with mean daily symptom score (P <.001) and albuterol use for symptoms (P=.003) during a 28-day screening period. Duration was also found to be significantly associated with physician/nurse assessment of asthma severity and other historical measures-of medication use. Conclusions: These data demonstrate that asthma duration is associated with loner lung function, greater methacholine responsiveness, more asthma symptomatology, and greater use of as-needed albuterol, which are all measures of asthma severity As such, early diagnosis and intervention mag be necessary to ameliorate these adverse effects of persistent asthma.