Advances in the Use of Inhalation Provocation Tests in Clinical Evaluation

¹ From McMaster University and St. Joseph's Hospital, Hamilton, Ontario, Canada

Recent advances in the use of inhalation provocation tests in the clinical evaluation of asthma have been made with methacholine and histamine tests. The tests can be better standardized and the results more accurately interpreted. The ease of stimulation of bronchoconstriction by methacholine and histamine (bronchial responsiveness) relates closely to the presence and the degree of variable airflow obstruction that occurs spontaneously or is triggered by natural stimuli. Responsiveness can be heightened by bronchial infection and by exposure to allergens or sensitizing chemicals, such as toluene diisocyanate, and can be reduced by treatment. These observations indicate three uses of the tests in clinical practice. First, they can be used to validate the presence of hyperresponsiveness which, when spirometric study is normal, is synonymous with the presence of asthma. Second, they can be used to quantify the severity of hyperresponsiveness which relates closely to the amount of bronchodilator réquired to treat asthma. Finally, they can be used to measure a change in responsiveness, which is useful to document occupational asthma (defined as hyperresponsiveness caused by materials at work), and to optimize the treatment required to reverse or reduce hyperresponsiveness as much as possible.