Normal range of yearly decrease in FEV1

I work as a Occupational Health Officer in the food industry. Some of our employees are potentially exposed in certain areas to flour dust and batter mix. They work within the maximun exposure level and wear mandatory respiratory protection in the form of FFP3 masks. We perform health surviellance at a high level, which includes questionaire and spirometry at start of employment as a baseline,followed by questionaire and spirometry at 6 weeks and 13 weeks then annually. Could you please give us guidance as to what is an acceptable decrease in FEV1 levels per year?

Occupational Asthma, Worker, 2/20/2006, 2/20/2006,

This is more complicated than it appears! Spirometry is an important part of surveillance for occupational asthma, as there are some who are poor perceivers of symptoms and are missed by questionnaires, which are the most important method of screening. FEV1 increases during early adult life, reaching a peak (in non-smokers) at about the age of 25. There is then a plateau before declining at about 20-30 ml/year until about 65, after which the rate of decline may increase. For those over 30 an annual decline of over 45ml/year is abnormal. The problem is that there is inherent variability in FEV1 and a measurement error of around 160ml. It is common to have differences between 2 measurements of FEV1 of up to 400 ml in an individual without any obvious cause. I believe a reasonable action level would therefor be a fall of more than 400 ml between two measurements of FEV1 in an asymptomatic individual (who should then carry out serial measurements of PEF as per the BOHRF guidelines). In a worker with new respiratory symptoms serial measurements of PEF are indicated whatever the decrease (or increase) of FEV1 is. The analysis of FEV1 measurement over several years is of much more use. About 5 annual measurements are required to get a reasonable estimate of annual FEV1 decline. Those over 45 ml/year warrent at least highted surveillance. An alternative method of analysis is to plot the rate of FEV1 decline of a whole work group. If this is confined to those over 30 years (to remove the effect of increasing FEV1 in the young); a mean rate over 40ml/year is abnormal.

2/20/2006