To clarify the relation between the vessel remodeling and the physiology of pulmonary circulation in chronic obstructive pulmonary disease (COPD), we studied the pulmonary hemodynamics at rest and during exercise (25W) and the morphology of pulmonary arteries with external diameters of 100-200 microm in ten patients with severe emphysema. The wall thickness (WT) was defined as the intima plus media. The percent WT of the external diameter (% WT) in emphysema (36.0 +/- 4.3%) was significantly increased compared with that (22.6 +/- 3.3%) in five control lungs. The % WT was not related to pulmonary arterial pressure (Ppa) at rest, but was highly correlated with exercise Ppa (r = 0.721, P = 0.02) and with deltaPpa (Ppa during exercise-Ppa at rest) (r = 0.899, P = 0.0004). These findings suggest that pulmonary artery remodeling leads to reduced recruitability and distensibility of pulmonary vessels and is closely related to exercise pulmonary hypertension.