Background Cross-sectional studies have shown declines in lung function among refractory ceramic fibre (RCF) workers with increasing fibre exposure. This study followed current and former workers (n=1396) for up to 17 years and collected 5243 pulmonary function tests.
Methods Cumulative fibre exposure and production years were categorised into exposure levels at five manufacturing locations. Conventional longitudinal models did not adequately partition age-related changes from other time-dependent variables. Therefore, a restricted cubic spline model was developed to account for the non-linear decline with age.
Results Cumulative fibre >60 fibre-months/cc showed a significant loss in lung function at the first test. When results were examined longitudinally, cumulative exposure was confounded with age as workers with the highest cumulative exposure were generally older. A longitudinal model adjusted by age groups was implemented to control for this confounding. No consistent longitudinal loss in lung function was observed with RCF exposure. Smoking, initial weight and weight increase were significant factors.
Conclusion No consistent decline was observed longitudinally with exposure to RCF, although cross-sectional and longitudinal findings were discordant. Confounding and accelerated lung function declines with ageing and the correlation of multiple time-dependent variables should be considered in order to minimise error and maximise precision. An innovative statistical methodology for these types of data is described.
- lung function
- refractory ceramic fibre
- exposure assessment
- lung function
- Accepted 6 January 2010
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Funding The Refractory Ceramic Fiber Coalition (2300 N Street NW, Room 6178, Washington, DC USA 20037) provided funding for this study.
Competing interests James E Lockey has received grants from the Refractory Ceramic Fiber coalition through the University of Cincinnati College of Medicine for directing and analysing the data of the medical surveillance program and for salary support of contributing faculty and support staff. Eric K Borton, Carol H Rice, Linda Levin and Timothy Hilbert have received research funding from the Refractory Ceramic Fiber Coalition for participation in the medical surveillance program. Grace K LeMasters has received funding as a research investigator for the Refractory Ceramic Fiber Coalition and for the presentation of preliminary results of the medical surveillance program and for salary support. Roy T McKay has received faculty salary support from the Refractory Ceramic Fiber Coalition for his role in the design and analysis of this study.
Patient consent Obtained.
Ethics approval This study was conducted with the approval of the University of Cincinnati Institutional Review Board.
Provenance and peer review Not commissioned; externally peer reviewed.
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