Vicky Moore, Maritta Jaakkola, Cedd Burge, Charles Pantin, Alastair Robertson, Sherwood Burge

1. The effect of shift work on serial peak expiratory flow measurements used to diagnose occupational asthma Vicky Moore, Maritta Jaakkola, Cedd Burge, Charles Pantin, Alastair Robertson, Sherwood Burge Occupational Lung Disease Unit, Birmingham Heartlands Hospital

2. Aims • To investigate whether shift work patterns alter the PEF responses to occupational exposures. • To see if the ABC score for diagnosing occupational asthma can be applied to afternoon and night shifts. • To see how cross shift changes are affected by shift. • To see how diurnal variation is affected by shift.

3. Methods • PEF records used from occupational asthmatics (OA, n = 123) and workers with other diagnoses (Non-OA, n = 69) • Records were required to have ≥2 shift types of at least 4 days each • Only records with minimum data amounts for the ABC score / cross shift changes were used • Records with respiratory tract infections, treatment changes or known differences in exposure between shift types removed

4. Groups • The occupational asthma group had positive peak flow records on the Oasys score and diagnoses of occupational asthma, requiring a latent interval and good history. • The control group has negative peak flow records on the Oasys score and were investigated for occupational asthma, but received an alternate diagnosis. • Partially defining groups on positive / negative peak flow records affects the sensitivities and specificities quoted later.

5. Cross Shift Changes • Cross shift measurements are not a good way of diagnosing occupational asthma. • = (“last work reading” – “last reading before work”) • Large and significant circadian effect between shifts • Changes of 22 – 34 l/min, p < 0.001 • Increases in pef across day shifts, decreases across afternoon and night shifts.

8. Diurnal Variation • Diurnal variation is not a good way of diagnosing asthma or occupational asthma (95% limit of normal is 26%) • = (“highest reading” – “lowest reading”) / “predicted”, for each day • No significant changes between shifts • Using (mean work DV – mean rest DV) > 0 • Sensitivity between 70 and 78% in this study, but specificity only 26 – 48%.

9. ABC Score • Area between work and rest curves (l/min/hour) • Day shifts significantly higher than afternoon and nights for occupational asthmatics (p = 0.02, 0.03, magnitude ≈ 5 l/min/hr) • Night shifts significantly higher than afternoon shifts for controls (p = 0.04, magnitude = 5 l/min/hr) • Day shifts likely to be higher than afternoon and night but there is a lot of noise due to changed exposures, more readings before work and data quality / quantity

10. Night Shift Noise • Reduced exposure as less machines running? • Greater exposure as less supervision and less mechanical / natural ventilation? • Interpolation effect? • Sleeping? • Alcohol?

14. Results • Cross shift differences change by between 22 – 34 l/min between shift types, p < 0.001. • Using (mean work DV – mean rest DV) > 0, sensitivity was between 70 and 78%, but specificity only 26 – 48%. No significant changes between shifts. • Using ABC Score >15 l/min, sensitivity was 72 – 83% and specifity 96 – 99%. Day shifts have significantly higher scores than afternoon and night (p = 0.02, 0.03, magnitude ≈ 5 l/min/hr).

15. Conclusions • Cross shift differences vary significantly with circadian rhythm and should not be used for diagnosing OA. • DV showed no significant changes between shifts and should not be used for diagnosing OA. • Day Shifts have significantly higher ABC scores than afternoon and night shifts in those with OA. However, this varies widely between patients. • A cut off of 15L/min (found previously for day shifts only) is likely to be appropriate for all shift types.

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