Treprostinil administration by inhalation

A method of treating pulmonary hypertension comprising:

• administering by inhalation to a human suffering from pulmonary hypertension a therapeutically effective single event dose of a formulation comprising from 200 to 1000 μg/ml of treprostinil or a pharmaceutically acceptable salt thereof with a pulsed ultrasonic nebulizer that aerosolizes a fixed amount of treprostinil or a pharmaceutically acceptable salt thereof per pulse, said pulsed ultrasonic nebulizer comprising an opto-acoustical trigger that allows said human to synchronize each breath to each pulse, said therapeutically effective single event dose comprising from 15 μg to 90 μg of treprostinil or a pharmaceutically acceptable salt thereof delivered in 3 to 18 breaths, wherein the fixed amount of treprostinil or its pharmaceutically acceptable salt for each breath inhaled by the human comprises at least 5 μg of treprostinil or its pharmaceutically acceptable salt.