Dynamic pulmonary hyperinflation and intrinsic PEEP (PEEPi) are known to play an important role in causing acute respiratory failure in COPD patients. In the present study, we have explored (1) the prevalence and magnitude of PEEPi in stable COPD patients, and (2) the correlation of PEEPi with respiratory mechanics and PaCO2. In 96 stable COPD patients with varying degrees of airway obstruction, we measured pulmonary flow resistance (RL), dynamic lung compliance (CLdyn), breathing pattern, arterial blood gases, and dynamic PEEPi. Dynamic PEEPi was determined as a negative deflection in esophageal pressure from the start of inspiratory effort to the onset of inspiratory flow. A significant correlation was found between dynamic PEEPi and FEVi (% predicted; r = -0.56, p less than 0.001), between PEEPi and RL (r = 0.69, p less than 0.001), and between PaCO2 and PEEPi (r = 0.6, p less than 0.001). These results indicate that increased severity of airway obstruction promotes PEEPi and concomitant dynamic hyperinflation. This implies increased inspiratory work in the face of decreased effectiveness of the inspiratory muscles as pressure generators. The present results suggest that dynamic hyperinflation may play a role in causing chronic hypoventilation in COPD patients.