Pulmonary hypertension (PH or PHTN) is a condition of increased blood pressure in the arteries of the lungs.[7] Symptoms include shortness of breath, fainting, tiredness, chest pain, swelling of the legs, and a fast heartbeat.[7][2] The condition may make it difficult to exercise.[7] Onset is typically gradual.[8] According to the definition at the 6th World Symposium of Pulmonary Hypertension in 2018, a patient is deemed to have pulmonary hypertension if the pulmonary mean arterial pressure is greater than 20mmHg at rest, revised down from a purely arbitrary 25mmHg, and pulmonary vascular resistance (PVR) greater than 3 Wood units.

Reference
Wiki: Chronic hypoxic pulmonary hypertension