Perception of dyspnea in asthmatics with normal lung function.

UNLABELLED: The perception of dyspnea varies widely among asthmatics and it is influenced by many factors. The aims of our study were to investigate the perception of dyspnea during methacholine-induced bronchoconstriction in asthmatics with normal lung function and to evaluate the influence of bronchial responsiveness, age and gender to dyspnea perception in these patients. A total of 192 outpatients (aged 16-77 years) with stable asthma and normal lung function were examined. Methacholine challenge test was performed to each patient. The provocative dose of methacholine that reduces forced expiratory volume in 1 sec. (FEV1) by 20% (PD20) was estimated. Dyspnea perception of bronchoconstriction was evaluated using a Borg Scale and calculating the perception score corresponding to a fall in FEV1 of 20% (PS20). According to PS20+/-1 standard deviation subjects were divided into three groups: hypoperceivers, normoperceivers and hyperperceivers. From the hypoperceivers group we set up asthmatics with PS20=0 and defined them as nonperceivers. We found out that 43 (22.4%) patients were hypoperceivers, 116 (60.4%)--normoperceivers and 33 (17.2%)--hyperperceivers. The nonperceivers presented 6.3% (n=12) of all subjects. PD20 positively correlated with PS20 (r=0.252, p<0.001). Hypoperceivers showed significantly higher bronchial hyperesponsiveness (PD20=174+/-28 microg) comparing with hyperperceivers (PD20=323+/-50 microg, p=0.013). Bronchial responsiveness to methacholine of nonperceivers (PD20= 106+/-31 microg, range 15-253 microg) was the highest and PD20 was significantly lower comparing with normoperceivers (p=0.005) and hyperperceivers (p=0.001). Age and gender had no significant effect on the perception of bronchoconstriction.
CONCLUSION: The part of asthmatics with normal lung function has impaired perception of dyspnea. Dyspnea perception depends on bronchial responsiveness, but not on age and gender of these patients.