The results of our study do not support the hypothesis that cellulose fiber exposure has a separate or specific effect on lung function. However, a clear separation of specific fiber and dust effects is not possible due to methodologic problems (different units). The interpretation has to take into account the fact that fibers are part of the total dust amount. The parameter estimates with relation to cumulative dust-years and fiber-years reveal similar results (Table 4).
It is still unknown if the effects on lung function described in the literature and those found in this study are reversible or persistent. Some results from different exposure settings suggest that deterioration of lung function parameters is an across-shift effect that is reversible. Christiani et al described a link between across-shift decline of FEV1 and 5-year decline of FEV1 in cotton workers. Across-shift decline was predictive for chronic effects > 5 years. In our study, no information was available on across-shift changes of lung function. The analyses were performed within one shift. Further evidence for across-shift changes after organic dust exposure was found in a study in poultry workers. Exposure concentrations associated with significant across-shift pulmonary function decrements were 2.4 mg/m total dust, 0.16 mg/m respirable dust, 614 EU/m endotoxin, and 12 ppm ammonia. The dust concentrations were considerably lower than those in our study.
In our study, both FVC and FEV1 decreased with increasing exposure. FEV1%FVC did not change significantly, with only a slight increase showing that FVC decreased more than FEV1. Moreover, the prevalence of clinically relevant decreased FVC (< 80% predicted) rose with increasing exposure. This might be a sign of a restrictive pattern, which has not been described in the literature so far, and that could be due to early fibrotic effects. To clarify this question, lung volume measurements and chest radiograph or thin-section CT, which is more sensitive, would be helpful to detect possible interstitial disease.