THE PERCEPTION OF BREATHLESSNESS IN ASTHMA

Abstract

Perception of breathlessness as a function of airflow obstruction was studied in 45 asthmatic subjects using a category scaling technique. Airflow obstruction and breathlessness were induced by inhalations of histamine acid phosphate in twofold-increasing concentrations from 0.03-16 mg/ml. The FEV1 [1-s forced expiratory volume] was measured after each inhalation of histamine, and the subject was asked to rate his symptoms of breathlessness. Breathlessness increased as the FEV1 decreased but, despite a close linear relationship in all subjects (mean r = 0.88 .+-. 0.15 SD), there was a considerable variation in the severity of breathlessness for any particular degree of airflow obstruction (mean intercept, 0.50 .+-. 0.89 SD). The increase in sensory magnitude with increasing airflow obstruction did not show the same degree of variability (mean slope, 0.13 .+-. 0.06 SD). The variability in breathlessness in asthmathic patients is likely to have many components. Two of these components were identified. First, there was less respiratory distress in those subjects in whom airflow obstruction was present at the onset of the study. The presence of airflow obstruction at this time does not result in a reduction in sensation for further increases in airflow obstruction as might be expected from discrimination studies. Second, there was a significant relationship (P < 0.01) between bronchial responsiveness and the magnitude of respiratory distress. Those subjects highly responsive to histamine experienced less respiratory distress than the less responsive subjects.