Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) pulmonary arterial hypertension ?
    ### Response:
    Pulmonary arterial hypertension is a progressive disorder characterized by abnormally high blood pressure (hypertension) in the pulmonary artery, the blood vessel that carries blood from the heart to the lungs. Pulmonary arterial hypertension is one form of a broader condition known as pulmonary hypertension.
    