Orthopnea and tidal expiratory flow limitation in patients with stable COPD

Background: Orthopnea is a common feature in COPD patients, although its na ture is poorly understood. Objective: To study the role of tidal expiratory flow limitation (FL) in th e genesis of orthopnea in patients with stable COPD. Measurements: Tidal FL was assessed in 117 ambulatory COPD patients in sitt ing 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 orthopn ea, which probably results in part from increased inspiratory efforts due t o dynamic pulmonary hyperinflation and the concomitant increase in inspirat ory threshold load due to intrinsic positive end-expiratory pressure. Incre ased airway resistance in supine position due to lower end-expiratory lung volume probably also plays a role in the genesis of orthopnea.