A long term study of pulmonary function among US refractory ceramic fibre workers.
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.


CONCLUSIONS
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.
McKay
Roy T
RT
Department of Environmental Health, University of Cincinnati College of Medicine, Cincinnati, OH 45267-0056, USA. roy.mckay@uc.edu
LeMasters
Grace K
GK
Hilbert
Timothy J
TJ
Levin
Linda S
LS
Rice
Carol H
CH
Borton
Eric K
EK
Lockey
James E
JE
D000328:Adult; D000375:Aging / Q000502:physiology; D002516:Ceramics; D004784:Environmental Monitoring / Q000379:methods; D004812:Epidemiologic Methods; D062665:Epidemiological Monitoring; D005260:Female; D005541:Forced Expiratory Volume / Q000502:physiology; D006801:Humans; D008168:Lung / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D019016:Mineral Fibers / Q000032:analysis / Q000633:toxicity*; D016273:Occupational Exposure / Q000009:adverse effects* / Q000032:analysis; D013147:Spirometry / Q000379:methods; D014797:Vital Capacity / Q000502:physiology
D019016:Mineral Fibers
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