It has been recognized for many years that patients with asthma have increased levels of bronchial responsiveness to pharmacologic, physical, and chemical stimuli. The level of responsiveness correlates reasonably with the severity of asthma. The association between bronchial hyperresponsiveness and bronchial asthma is not absolute. Occupational asthma may occur in the absence of hyperresponsiveness. In community surveys, hyperresponsiveness has been detected in up to 14% of random samples of the population. In those studies, the most important determinants of responsiveness were positive skin test responses to common allergens in the young and smoking habits in the older subjects. There is evidence that bronchial hyperresponsiveness is also increased after upper respiratory tract infections in subjects not considered to be asthmatic; however, this would not appear to influence outcome significantly in community studies.
The epidemiologic measurement of bronchial hyperresponsiveness in an occupational setting is in its infancy. Already different methods and protocols are being used in field studies, which will make comparison between studies potentially difficult.
The value of such studies also must be prospectively evaluated. It is possible that hyperreactivity in an asymptomatic individual may prove to be a predisposing factor in the development of occupational asthma or bronchitis. A small number of cross-sectional studies have measured airways reactivity in the evaluation of work forces exposed to flour or grain- dusts. In these studies, bronchial hyperreactivity was associated with the presence of respiratory symptoms and with current or past exposure to dust.’ The measurement of hyperresponsiveness has also proved valuable in following the recovery of individuals with occupational asthma.