Dyspnea is multifactorial, but static lung hyperinflation
and its increase during exercise (dynamic hyperinflation)
is believed to be the most important in subjects with
chronic obstructive pulmonary disease (COPD) [1-3]. It
has been reported that indices related to hyperinflation,
such as the inspiratory capacity (IC), are more closely
related to exercise tolerance and dyspnea than the
forced expiratory volume in 1 second (FEV1) or forced
vital capacity (FVC) [4-8]. The Borg scale is frequently
used during exercise as a marker of laboratory dyspnea
in physiological investigations to evaluate this relationship.
Furthermore, Casanova and colleagues proved that
static lung hyperinflation estimated by the inspiratory
capacity-to-total lung capacity (IC/TLC) ratio is a predictor
of all-cause and respiratory mortality in patients
with COPD, independent of the FEV1 [9].