Proceedings of the British Thoracic Society

In 33 asthmatics (17 males) estimates of breathlessness during exercise were compared with lung volumes, peak flow (PEF) variation, six minute walking distance (6-MWD) and disability (MRC dyspnoea scale).The patients' mean age was 44 years (range 17-70), mean FEV, was 85% predic- ted (range 33-118%).Lung volumes (VC, RV, TLC, RV/TLC) were measured spiro- metrically and by helium dilution.PEF was recorded twice daily for 14 days.Variation in PEF was estimated using the amplitude or the standard deviation of the daily variation as a percentage of the mean or as a percentage of predicted PEF.Exercise was performed on a cycle ergometer.A one minute increment protocol was followed with work rates selected according to size and sex.Minute ventila- tion (VE) and dyspnoea were measured every minute.Dyspnoea was measured using the modified Borg scale and defined as "an uncom- fortable need to breathe."The mean number of work increments was 10 (range 6-14).The median r value for the dyspnoea/VE relation- ship was 0-88 (range 0-0 99).In three patients r was < 0-8; these were excluded from further analysis.The dyspnoea/VE relationship was normalised between patients by fitting height, sex, and a height-sex term to the regression.None of the measurements of lung volume, spirometry, or peak flow correlated with the dyspnoea/VE relationship (p > 0 3 in all cases).6MWD was negatively correlated with dyspnoea/VE (p = -0-46, p = 0-014) and MRC dyspnoea grade was positively correlated (p 0 38, p = 0 034).These results indicate that patients giving low scores for breathlessness relative to ventilation (after adjustment for height and sex) indicated less disability and walked faster than patients who indicated high levels of dyspnoea.These findings suggest that patients' perception of the level of their dyspnoea during exercise may condition their exercise tolerance and ensuing disability, but dyspnoea perception appears to be unrelated to disturbances in lung volumes and measures of airflow limitation.