In the revised HRQoL model, multiple factors can affect
functional status. For example, functional capacity can be
directly affected by biological function and by symptoms,
and functional performance can be affected by characteristics
of the individual and the environment. In people with
COPD, functional capacity can be limited by ventilatory capacity
and by symptoms of dyspnea or leg fatigue. However,
symptoms alone do not fully account for the decrease
in functional capacity. If symptoms are severe enough, they
might interfere with day-to-day levels of activity, which
might cause a patient to become sedentary and physically
deconditioned (decline in functional status). But the extent
of the decline in day-to-day activities also could be influenced
by individual characteristics, such as self-efficacy and
motivation for physical activity, or by social environmental
factors, such as social support for physical activity and
community safety.