how much annual decline is " normal" in lung function parameters FVC, PEFR and FEV1.

I am performing health surveillance for a mixed farming group (mushroom workers, dairy, crops, poultry and welders). I am trying to look and health surveillance results logitudinally and set a "trigger" for a referral level to myself by the OHA (as well as adult onset asthma,symptoms, persistent chest illness or a positive questionnaire). How much decline can I allow in FVC and FEV1, PEFR please? Anees W, Moore VC, Burge PS, FEV1 decline in occupational asthma, Thorax, 2006;61:751-755, Hnizdo E, Yu L, Freyder L, Attfield M, Lefante J, Glindmeyer HW, The precision of longitudinal lung function measurements: monitoring and interpretation, Occup Environ Med, 2005;62:695-701,

Occupational Asthma, Health Professional, 7/15/2011, 7/22/2011,

FEV1 and FVC should increase up to about 25 years old then decrease at around 30ml/year. Patients with COPD typically decline at about 50 ml/year (which is clearly abnormal). The problem is in the measurement error (up to about 160ml within 20 mins)and the spontaneous changes over time without obvious disease. The best method is to use Spirola, a validated method for interpreting surveillance spirometry. It however generally needs about 5 years of readings in an individual to detect accelerated decline, it depends on the quality control of your spirometry (which it also measures if you have a group undergoing annual spirometry). I think you you use this anyway, it is freely available via the link http://www.cdc.gov/niosh/topics/spirometry/spirola.html. The data entry frmat takes a little getting used to. IYou can also use a rough rule of thumb of a decrease of >400 ml in FEV1. This is likely to be outside the 95% confidence interval at one year, at 2 years (at 200ml/year over 2 years) at 3 years (about 150ml/year) and 5 years (100ml/year). These are all large changes, however the average worker with occupational asthma with continuing exposure declines at over 100ml/year. There is a wide range including about 30% with no accelerated decline, these perhaps are those who may be safe to continue with reduced exposure rather than complete removal from exposure. Your main triggers for seeing workers should be your questionnaire, however there are those without reported symptoms picked up by surveillance spirometry which remains important.

7/22/2011