PERCEPTION OF DYSPNEA DURING ACUTE CHANGES IN LUNG-FUNCTION IN PATIENTS WITH EITHER ASTHMA OR COPD

The aim of the study was to evaluate the relationship between several lung function indices and perceived dyspnoea during bronchoconstrictio n. Acute changes in lung function were induced by inhaled histamine fo llowed by terbutaline, in 12 asthmatics and 12 subjects with chronic o bstructive pulmonary disease (COPD). A bipolar visual analogue scale ( VAS), allowing subjects to report either improvement or worsening when moving off from a 'nochange' midpoint, was used to rate shortness of breath. Large swings in ratings were seen in all asthmatics and in sev en out of 12 COPD subjects (high perceivers). Using linear regression of VAS rating against parallel change in lung function, on a within-su bject basis, the highest degree of correlation between dyspnoea and ob jective response was found to involve the change in specific inspirato ry resistance (sRin) in the asthmatics. In the five low perceivers, th e ability to discriminate an increase in airway obstruction, estimated as the VAS/change in lung function slope, was very poor. Using a step wise multiple regression analysis, the sensation of dyspnoea was found to be significantly related to the FEV(1) and the sRin in the asthmat ics, to the inspiratory vital capacity and the maximal inspiratory flo w at 50% FVC (MIF(50)) in the COPD subjects with high perception, and to the MIF(50) in the COPD subjects with low perception.