FEV1 decline acceptable values in respiratory surveillance for occupational asthma

My question concerns acceptable levels of FEV1 decline year on year so I can incorporate it into my review of my respiratory surveillance programme. My research led me to the following conclusion:“ The normal annual rate of decline in nonsmokers is 30 mls/year and is significant if greater than 90 mls/year even if the FVC and FEV1 are both greater than 80% of the expected value. The FEV1 decline over a year will not be picked up by the spirometer, making it all the more important for results to be compared with previous records wherever possible. If the FEV1 has reduced by more than 30 mls since the last spirometry then the case notes should be forwarded to an OHA/OHP for review as per company guidelines” Would you please advise if the level of acceptable FEV1 decline is is incorrect and I will amend the programme instructions

Occupational Asthma, Specialist, 7/4/2008, 7/4/2008,

This is an important and difficult area. Most agree that an annual decline in FEV1 in healthy workers is arount 20ml/year, although the predicted equations usually have a term of around 30ml/year. The point of surveillance spirometry is to pick up disease before the tests are frankly abnormal, certainly before <80% predicted is reached in a previously healthy worker, who is likely to have started well above 100%. The problem is the precision with which FEV1 can be measured, and how good your quality control for spirometry is. Quite large changes in FEV1 can occur for no obvious reason between tests, the 95% confidence interval for two tests a few weeks apart is about 180ml when done well (more than this if quality control is suboptimal). Help is at hand with a program from NIOSH called Spirola, which analyses serial FEV1 measurements in an individual and identifies deterioration in excess of 95% predicted, and provides quality control for your spirometry. The program I believe is available free of charge from NIOSH. The attached referece is rather hard work but worth a careful read. 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, Spirometry Longitudinal Data Analysis (SPIROLA) Free program to analyse longitudinal spirometry for individuals and groups. Identifies at risk individuals and measures the precision of the data. Very useful for Health Surveillance. Based on published research by Eva Hnizdo et Al. http://www.cdc.gov/niosh/topics/spirometry/spirola.html

7/4/2008