Most studies11–13 on mortality among patients with
COPD have reported that FEV1 is the strongest
factor related to survival and that other factors, with
the exception of age, are minor.11 Dyspnea, which is
the subjective perception of respiratory discomfort,
is a result of complex and multifocal mechanisms.14
These include abnormalities in the respiratory control
system, neurochemical receptors, ventilation,
respiratory muscles, gas exchange, and so on.14 Dyspnea
can vary among patients with the same degree
of airway obstruction.15 In the present study, there
were significant differences in age and arterial blood
gas measures as well as pulmonary function between
the groups delineated on the basis of the level of
dyspnea. As shown in Tables 4, 5, classification by
the level of dyspnea was considered to be more
discriminating with respect to various factors than
classification of disease severity based on airway
obstruction. Dyspnea may reflect more comprehensive
information than airway obstruction in patients
with COPD. Previously, some studies16 have suggested
that dyspnea could be used as one of the
prognostic factors in patients with COPD. However,
to our knowledge, this is the first report of mortality
among patients with COPD that compared the
categorization of patients with COPD on the basis of
the level of dyspnea vs airway obstruction.