Pulmonary hypertension refers to high blood pressure in the lungs. It is a complex health condition and a relatively rare disease that affects people of different ages and ethnic groups.The rare lung disorder occurs when the blood pressure in the pulmonary arteries rises far above normal levels and the walls of the pulmonary arteries become thicker. There are many different types of pulmonary hypertension and sometimes, the cause is unknown.The detailed pulmonary hypertension processes are: