Breathing discomfort in asthma: role of adaptation level.

In asthmatic patients, Helson's adaptation level theory was applied to breathing discomfort to investigate the discrepancy between the subjective severity of breathlessness and their objective airflow obstruction. The data from a signal detection methodology show a considerable loss of sensitivity in twelve asthmatic patients with permanent airflow obstruction compared to the high sensitivity of six normal subjects to the same four external resistive loads (range 2.5 to 8.0 cmH2O X l-1 X s). Furthermore, when subjective ratings are examined, the absence of any contrast effect between adjacent load intensities in asthmatics suggests that these subjects evaluate the discomfort induced by the loads with reference to a strong internal comparison (adaptation level) rather than to the experimental stimuli. There was no relationship between physiological parameters and the low sensitivity of asthmatics. Also salbutamol-induced bronchodilation in six asthmatics did not improve sensitivity or induce any contrast effect. These two observations bring out the necessity to consider the role of past experience of breathing discomfort on adaptation level and sensitivity.