The exact incidence of clinically significant pulmonary hypertension, defined as pulmonary hypertension that contributes to symptomatology and prognosis, is difficult to estimate in COPD. A prevalence of 5.8%- 13.5% in patients seems reasonable which would suggest an incidence of 1-3/10,000, which is 100 times the incidence of idiopathic pulmonary arterial hypertension.