DEVELOPMENT OF OASYS-2 - A SYSTEM FOR THE ANALYSIS OF SERIAL MEASUREMENT OF PEAK EXPIRATORY FLOW IN WORKERS WITH SUSPECTED OCCUPATIONAL ASTHMA

Background - Serial peak expiratory flow (PEF) measurement is usually the most appropriate first step in the confirmation of occupational as thma, Visual assessment of the plotted record is more sensitive and sp ecific than statistical methods so far reported. The use of visual ana lysis is limited by lack of widespread expertise in the methods. A com puter assisted diagnostic aid (OASYS-2) has been developed which is ba sed on a scoring system developed from visual analysis. This removes t he requirement for an experienced interpreter and should lead to the m ore widespread use of the technique. Methods - PEF records were collec ted from workers attending an occupational lung disease clinic for inv estigation of suspected occupational asthma and from workers participa ting in a study of respiratory symptoms in a postal sorting office. PE F records were divided into two development sets and two gold standard sets. The latter consisted of records from workers in which a final d iagnosis had been reached by a method other than PEF recording. An exp erienced observer scored individual work and rest periods for the two development set PEF records; linear discriminant analysis was used to compare measurements taken from development set 1 records with visual scores. Two equations were produced which allowed prediction of scores for individual work or rest periods. The development set 2 was used t o determine how these scores should be used to produce a whole record score. The first gold standard set was used to determine the whole rec ord score which best separated those with and without occupational ast hma. The second set determined the sensitivity and specificity of the chosen score. Results - Two hundred and sixty eight PEF records were c ollected from 169 workers and divided into two development sets (81 an d 60 records) and two gold standard sets (60 and 67 records). Linear d iscriminant analysis produced equations predicting the score for work periods incorporating five indices of PEF change and one for rest peri ods using seven indices. These equations correctly predicted the score for development set 1 work and rest periods on 61% of occasions (kapp a = 0.47). The whole record score for development set 2 records, after weighting for definite or definitely no occupational effect, correlat ed with the visual score (correlation coefficient 0.86). Comparison wi th gold standard set 1 identified a cut off which proved to have a sen sitivity of 75% and a specificity of 94% for an independent diagnosis of occupational asthma when applied to gold standard set 2. Conclusion s - These results suggest that the sensitivity and specificity of anal ysing PEF records for occupational asthma using OASYS-2 approaches tha t of visual analysis, but it should be absolutely reproducible. The pe rformance of OASYS-2 is more specific and approaches the sensitivity o f other statistical methods of analysis. The evaluation of a large num ber of PEF records from workers exposed to different sensitising agent s suggests that these results should be robust and should be repeatabl e in clinical practice.