Background: Orthopnea is a common feature in COPD
patients, although its nature is poorly understood.
Objective: To study the role of tidal expiratory flow
limitation (FL) in the genesis of orthopnea in patients with stable
Measurements: Tidal FL was assessed in 117
ambulatory COPD patients in sitting and supine positions using the
negative expiratory pressure method. The presence or absence of
orthopnea was also noted.
Results and conclusions: In
patients with stable COPD with tidal expiratory FL in seated and/or
supine position, there is a high prevalence of orthopnea, which
probably results in part from increased inspiratory efforts due to
dynamic pulmonary hyperinflation and the concomitant increase in
inspiratory threshold load due to intrinsic positive end-expiratory
pressure. Increased airway resistance in supine position due to lower
end-expiratory lung volume probably also plays a role in the genesis of