Abstract

Some workers with occupational asthma appear to tolerate regular falls in lung function better than others. We hypothesise that this relates to their ability to perceive changes in airflow obstruction. Perception of breathlessness was assessed by measuring perceived breathlessness on a visual analogue scale (VAS) 4 times during a methacholine test. The slope of the regression line of percent fall in FEV1 vs. changes in VAS were used to divide 81 workers with objective evidence of occupational asthma (from serial PEF plots) into tertiles of high, intermediate and low perceivers. Changes in airflow obstruction at home and work were assessed using 2-hourly plots of PEF for at least 3 weeks. The Oasys plotter was used to calculate the differences in mean daily PEF and area under the curve for 2-hourly PEF between days at and away from work. Mean diurnal variation in PEF on workdays was also calculated. There was a significant correlation between VAS score and % fall in FEV1 (p=0.015) There was no relationship between the index of perception and baseline FEV1 % predicted, atopy or smoking. High, Intermediate and low perceivers had similar responses to occupational exposure; mean daily work-rest PEF (19;21;16 l/min), area under the 2-hourly PEF curve (268;316;203 l/min/day) and diurnal PEF variation on workdays (15;19;16 %mean). There was no significant correlation between the PEF variables and the perception index when all workers were considered together.

Conclusion
Perception of breathlessness as assessed during methacholine challenge was unrelated to the magnitude of PEF changes during tolerated work-exposure in a group with occupational asthma.

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