Abstract

Background: Peak expiratory flow (PEF) monitoring is frequently used to diagnose occupational asthma (OA). The variability of PEF between periods at work and away from work has not been described in workers with work-exacerbated asthma (WEA). We sought to assess and compare the diurnal variability of PEF during periods at and away from work between subjects with OA and WEA.

Methods: Workers referred for work-related asthma underwent PEF monitoring for 2 weeks at and away from work. The diagnostic of OA or WEA was subsequently made according to the respective positivity or negativity of the specific inhalation challenges. PEF mean diurnal variability was calculated during periods at and away from work. PEF graphs were also interpreted using direct visual analysis by five observers and using a computer program (Oasys-2, Expert System ) [available at: http://www.occupationalasthma.com].

Results: Thirty-four subjects were investigated (WEA, n = 15; OA, n = 19). There was a greater variability of PEF at work than away from work in both OA (19.8 ± 8.7% vs 10.7 ± 6.3%, p < 0.001) and WEA (14.2 ± 4.8% vs 10.6 ± 5.6%, p = 0.02). However, the magnitude of the variability was higher in OA than in WEA (p = 0.02). The visual interpretation of PEF or the Oasys-2 program failed to distinguish WEA from OA.

Conclusion: Although workers with OA showed a higher PEF variability than workers with WEA when at work, clinicians were unable to reliably differentiate OA from WEA using the visual interpretation of PEF graphs or the computerized analysis.

Full Text

Comments

This paper defines work-exacerbated asthma (WEA) as asthma with work-related symptoms and a negative specific challenge test. Occupational asthma (OA) was diagnosed when the challenge tests were positive, unrelated to the presence or absence of a latent interval or pre-existing asthma (including some with workplace challenge tests for both WEA and OA).There were 15 with work-exerbated asthma exposed to flour (1), latex (1), isocyanates (3), glutaraldhyde (1), triethanolamine (1) and 8 unidentified. 4 0f the 19 with occupational asthma had no identified agent. Medication was kept the same throught peak flow monitoring (2 weeks at work and 2 weeks away from work)but long acting beta agonists were stopped for specific and methacholine challenges. PEF variability was expressed as the diurnal PEF variation and calculated using thr highest amplitude percentage and the mean amplitude percentage for the work and off work days. A paired t-test was used to compare work against off work and a students t-test to compare WEA with OA. The number of days wehere diurnal variation was over 20% was also analysed as well as Oasys scores and a qualitative approach (visual analysis of PEF graphs by 5 experts). Results: Occupational asthmatics had a slightly longer duration of exposure, and both groups had increased symptoms at work. Both showed an increased diurnal variability of PEF at work compared with off work, but the OA's were slightly higher at work. A greater percentage of the occupational asthmatics showed >20% diurnal variation on more work days than the WEA's. 6 records from each group (OA and WEA) had Oasys scores >2.5. Agreement between expert vsual analysis was low (Cohen K 0.27-0.7). The discussion indicates that peak flows could not entirely differentiate between OA and WEA. The low number of Oasys positives could have been caused by the continuation of long acting beta agonists which were stopped for challenges (not written in the paper). The authors indicate that a stepwise approach to diagnosing OA is required and that although PEFs are an asset to confirming work-related problems, specific challenges are still the best method.

7/16/2008

The definition of work-exacerbated asthma in this paper is unusual, based solely on a negative specific inhalation test. Work-exacerbated asthma is usually defined as pre-existing asthma present at the time of first exposure to an occupational agent, with deterioration in the asthma on first exposure to the offending agent, which should be acting via non-specific irritant mechanisms rather than hypersensitivity. Even the most enthusiastic challengers accept that the sensitivity and specificity of specific challenge is less than 100%, making a diagnosis based on challenge testing and disregarding pre-existing asthma, latent intervals and the presence of a well recognised sensitising agent, unusual. An alternative explanation of these results is that many had occupational asthma due to hypersensitivity in the "work-exacerbated" group, and that this occupational asthma was at an earlier or less severe stage than those diagnosed as occupational asthma. This is supported by finding changes in PEF which were less marked in the work-exacerbated group, with a shorter time of exposure. The challenge testing could have been negative in these workers due to inadequate exposure which did not match that encountered at work. If the mechanism of work-exacerbated asthma is due to irritant reactions to usual exposures in the workplace, specific challenge testing should be able to reproduce this.

7/16/2008