Although the FEV1 is very popular,
it may be an older index of flow limitation. Other
methods, including the tidal volume over the envelope
in the flow-volume loop or the negative expiratory
pressure during tidal breathing, should be compared
against any measurements of clinical or laboratory dyspnea.
The present study was also limited by the small
number of participants and distinct male preponderance
of the subjects. Although the latter is typically
observed in subjects with COPD in Japan, generalization
of these results to women with COPD may be
uncertain.