Abstract
In an epidemiological study, methacholine-induced bronchoconstriction was used as a physical illustration of the sensations associated with asthma. The objective of this study was to assess whether familiarity with these sensations could be used as a measure of asthma prevalence. Eight hundred and seventy six subjects aged 20-44 yrs completed a respiratory questionnaire and a measurement of airway responsiveness (the provocative dose of methacholine causing a 20% fall in forced expiratory volume in one second (PD20)). Subjects were asked about their perception of, familiarity with and description of the respiratory sensations experienced at the time of maximal bronchoconstriction. The questionnaire-derived lifetime prevalences of wheeze, chest tightness and undue breathlessness were 43, 35 and 22% respectively. Asthma medication was used by 8% and the lifetime prevalence of diagnosed asthma was 12%. Quantifiable levels of airway responsiveness were measured in 34%, and airway responsiveness in the range considered to be consistent with untreated active asthma was present in 21%. Bronchoconstriction was perceived by 59%. Perception of bronchoconstriction was associated with the magnitude of bronchoconstriction, younger age, female sex and questionnaire-reported symptoms. Of subjects able to perceive bronchoconstriction, 58% reported previous experience of (familiarity with) the associated respiratory sensations. Familiarity with the sensations of bronchoconstriction was associated with questionnaire-reported symptoms, diagnosed asthma and increasing levels of airway responsiveness. There was poor agreement between the respiratory symptoms reported by questionnaire before the methacholine test and the words used to describe respiratory sensations induced by the test. Familiarity with the sensations of methacholine-induced bronchoconstriction has all the appropriate associations of a measure of asthma prevalence and may be a useful adjunct to symptom questionnaires and airway responsiveness measurements in epidemiological studies. A sizeable number of subjects can be identified with intermediate levels of airway responsiveness, who are able to perceive bronchoconstriction and are familiar with the sensations associated with it, yet who are not recognized to suffer from asthma.
