Bronchial responsiveness to histamine or methacholine in asthma: measurement and clinical significance.

Quantitative measurement of nonspecific bronchial responsiveness can be simply and reproducibly made by inhalation tests with histamine or methacholine. Responsiveness to histamine correlates closely with responsiveness to methacholine. The degree of responsiveness relates closely with the presence and severity of asthma. The greater the increase in responsiveness the lower the peak flow rate (PFR) on waking, the greater the improvement in PRF after bronchodilator, the greater the diurnal variation of PFR, the easier is bronchoconstriction induced by nonspecific and allergic stimuli and the more treatment is required to control symptoms. Nonspecific responsiveness can be increased by exposure to respirable allergens or occupational sensitizers, and by infection. The observations suggest that measurement can be used in clinical practice to diagnose the presence of asthma, to help assess the severity of asthma and, in the assessment of occupational asthma, to determine if exposure can heighten bronchial responsiveness.