Below is an instruction from Human. Write a response.
    ### Instruction:
    What causes Pulmonary Hypertension ?
    ### Response:
    Pulmonary hypertension (PH) begins with inflammation and changes in the cells that line your pulmonary arteries. Other factors also can affect the pulmonary arteries and cause PH. For example, the condition may develop if:
                
The walls of the arteries tighten.
    