Orthopnea and tidal expiratory flow limitation in patients with stable COPD.

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 COPD. 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 orthopnea.