Clinical interpretation of airway response to a bronchodilator. Epidemiologic considerations.
Airways responsiveness to a bronchodilator is frequently measured to assist in determining the cause of respiratory symptoms. Clinically, a greater than 15% improvement in the FEV1 is often used to define the "increased" response indicative of asthma. However, unlike other tests of lung function, reference standards derived from "healthy" members of a general population sample have never been reported. As part of a health survey carried out in Alberta, Canada, 2,609 subjects completed a standardized respiratory symptom questionnaire and had FEV1 measured before and 20 min after inhaling terbutaline sulfate via a 750-ml spacer device. Among asymptomatic never-smoking subjects with a FEV1 greater than 80% of predicted, the upper 95th percentile of bronchodilator response (BDR), when expressed as 100 x (FEV1 postBDR - FEV1 preBDR)/predicted baseline FEV1 averaged 9%. This value remained remarkably stable across gender, age (7 to 75 yr), and height groups, and deviated to 6% only when baseline FEV1 was greater than 120% of predicted. Consistent with other respiratory function variables, in which the upper limit of normal is often defined as the upper 95th percentile, our population-derived reference values provide a conceptual definition of BDR that can easily be applied to define "increased" response in the clinical setting.
Dales
R E
RE
Department of Epidemiology and Biostatistics, McGill University, Montreal, Quebec, Canada.
Spitzer
W O
WO
Tousignant
P
P
Schechter
M
M
Suissa
S
S
D000293:Adolescent; D000328:Adult; D000368:Aged; D000395:Air Pollutants, Occupational / Q000009:adverse effects; D001993:Bronchodilator Agents / Q000494:pharmacology*; D002648:Child; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D013726:Terbutaline / Q000494:pharmacology
D000395:Air Pollutants, Occupational; D001993:Bronchodilator Agents; D013726:Terbutaline