In this study, we used across-shift change in FEVi as a measure of specific airway responsiveness to cotton dust. This method of defining cotton dust responsiveness has been used in cross-sectional studies of cotton-exposed workers. The sources of variability in such bronchial responsiveness in the mill setting may include recent viral infection, pollen exposures, biologic variation in airway smooth muscle tone, differences in inhalation patterns of workers in various jobs, and varying exposure intensity of different textile jobs. Canadian family pharmacy read Thus, we expected some variability in the magnitude of across-shift change in FEVi among cotton textile workers. Those with consistent acute responses had the most accelerated loss in lung function over the 5-year period of observation.
Acute responses at the two surveys were examined in two groups: those who “recovered” from and those who “developed” excessive across-shift changes in FEVi. Subjects with large across-shift drops in FEVi on survey 2 only had greater 5-year declines in lung function than those who had large across-shift drops in FEVi on survey 1 only. Although this may be evidence of regression to the mean in the inconsistent responders, there is a biologically plausible explanation for such a finding. Subjects with acute drops only at survey 2 include a subset who will go on to become persistent responders. In contrast, none of those with excessive drops in survey 1 only are persistent responders. Thus, a drop in preshift levels of FEVi would be more substantial for those currently (ie, at follow-up survey) developing the acute response, some of whom will go on to experience a persistent acute response. Moreover, since we reduced measurement error by discarding spirograms that did not meet reproducibility criteria at both testing sessions, it is unlikely that spuriously high results would regularly occur at the first session of the first testing day. Thus, regression to the mean is unlikely to explain the accelerated loss in lung function found in the consistent responding group. These data also suggest that although a consistent across-shift drop is associated with the largest 5-year declines, it is not a necessary precursor of chronic lung function loss.
With regard to symptoms, workers with chest tightness, chronic cough, and dyspnea at the time of first survey had the largest 5-year decline in lung function after adjusting for initial FEVi and other confounders. The significance of these findings needs further clarification, but suggest that these symptoms may be markers for significant respiratory impairment in textile workers.