The presence of symptoms of chronic bronchitis
was a weak but significant factor related to survival,
as shown in Table 6. Whether it is related to
mortality in patients with COPD remains controversial.
18–20 According to the Copenhagen study,18
chronic mucus hypersecretion played no major role
as a prognostic indicator, although it was significantly
associated with hospitalization.9 The study18 suggested
that predictors of hospitalization might not
necessarily be predictors of subsequent prognosis.
Although the present study was not performed to
investigate the significance of chronic mucus hypersecretion
as a prognostic factor, this should be
studied in the future.