Two variants of occupational asthma separable by exhaled breath nitric oxide level.

UNLABELLED: Exhaled nitric oxide (FE(NO)) has been used as a marker of asthmatic inflammation in non-occupational asthma, but some asthmatics have a normal FE(NO). In this study we investigated whether, normal FE(NO) variants have less reactivity in methacholine challenge and smaller peak expiratory flow (PEF) responses than high FE(NO) variants in a group of occupational asthmatics. METHODS: We measured FE(NO) and PD(20) in methacholine challenge in 60 workers currently exposed to occupational agents, who were referred consecutively to a specialist occupational lung disease clinic and whose serial PEF records confirmed occupational asthma. Bronchial responsiveness (PD(20) in methacholine challenge) and the degree of PEF change to occupational exposures, (measured by calculating diurnal variation and the area between curves score of the serial PEF record in Oasys), were compared between those with normal and raised FE(NO). Potential confounding factors such as smoking, atopy and inhaled corticosteroid use were adjusted for. RESULTS: There was a significant correlation between FE(NO) and bronchial hyper-responsiveness in methacholine challenge (p = 0.011), after controlling for confounders. Reactivity to methacholine was significantly lower in the normal FE(NO) group compared to the raised FE(NO) group (p = 0.035). The two FE(NO) variants did not differ significantly according to the causal agent, the magnitude of the response in PEF to the asthmagen at work, or diurnal variation. CONCLUSIONS: Occupational asthma patients present as two different variants based on FE(NO). The group with normal FE(NO) have less reactivity in methacholine challenge, while the PEF changes in relation to work are similar.

Improving the quality of peak flow measurements for the diagnosis of occupational asthma.

INTRODUCTION: Serial measurements of peak expiratory flow (PEF) are recommended in the evidence-based review list as the first stage in objective confirmation of occupational asthma. Different centres have reported widely different success in obtaining records of sufficient data quantity for diagnosis. We investigated different methods of instruction and determined the return rate and quality of the resulting record for the diagnosis of occupational asthma. METHODS: Consecutive new referrals were recruited from a specialized occupational lung disease clinic and requested to carry out serial PEFs for the assessment of suspected occupational asthma. Requests to carry out the records were either from written postal instructions or personal instruction from a PEF specialist. Record quality received from other clinicians was also analysed separating those using dedicated occupational forms, and those submitting on graph type forms. RESULTS: The postal return rate was 56% and the personal rate 85%. The number of records fulfilling all the data quality criteria were similar in the postal and personal groups (55 and 59%, respectively). Pre-existing records from other clinics plotted from graph charts (fulfilling all criteria) were only adequate in 23%, compared with 61% adequate for pre-existing records plotted from occupational forms. Failure of the record to contain consecutive work periods of > or =3 workdays was the most common failure. CONCLUSION: The return rate of PEFs for diagnosing occupational asthma is better when patients have been given specific instructions from a PEF specialist and the data quantity better when recorded on a dedicated form.

Use of pulmonary function tests in the diagnosis of occupational asthma.

OBJECTIVE: To discuss the different methods of assessing lung function measurements for the diagnosis of occupational asthma, focusing in particular on serial peak expiratory flow rate (PEFR) monitoring, including details on how PEFR records should be kept, plotted, and analyzed and limitations of the method. DATA SOURCES: Published studies on the use of diagnostic methods in occupational asthma, expert opinion, and recently obtained data from studies performed at a large occupational lung disease clinic. STUDY SOURCES: The expert opinion of the author was used to select the relevant data for review. RESULTS: Objective methods are necessary for the diagnosis of occupational asthma, since clinical history alone is not a satisfactory means of diagnosis. Serial PEFR monitoring has a high diagnostic sensitivity and specificity for occupational asthma and is more useful than evaluation of cross-shift change in forced expiratory volume in 1 second or change in nonspecific bronchial hyperresponsiveness. Interpretation is best performed by expert visual evaluation of plots of maximum, mean, and minimum daily PEFR readings. CONCLUSIONS: Despite some limitations of the method, serial PEFR monitoring is usually the most appropriate first-line investigation in workers suspected of having occupational asthma.