Clinical assessment of bronchial hyperresponsiveness due to nonspecific and specific agents.

I has been recognized for many years that patients with asthma have increased levels ofbronchial responsiveness to pharmacologic, physical, and chemical stimuli. The level of responsiveness correlates reasonably with the severity of asthma.' The association between bronchial hyperrespon-siveness and bronchial asthma is not absolute. Occupational asthma may occur in the absence of hyperresponsiveness.2 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 hyperresponsive-ness 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 hyperre-sponsiveness 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 asymp-tomatic 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 floury or grain89 dusts. In these studies, bronchial hyper-reactivity was associated with the presence of respiratory symptoms75 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. Finally, the measurement of hyperreactivity has been used as a research tool to evaluate the mechanisms underlying the airway responses in occupational asthma. The role of the late asthmatic reaction rather than the immediate reaction in altering bronchial hyperreactivity has been well established. " More recently this change in airway reactivity has been shown to follow the immediate asthmatic response but precede the onset of the late asthmatic response.12 This finding has important implications with regard to the mechanisms and treatment of asthma. Methods Bronchial hyperresponsiveness may be demonstrated with a variety of constrictor stimuli, including histamine, these various stimuli, the most widely used and best evaluated are histamine and methacholine. Three protocols have been devised for measuring hyperresponsive-ness using either ofthese stimuli. The dosimeter method of Chaii uses incremental, cumulative doubling doses of methacholine or histamine, originally delivered via a De Vilbiss …