<qa>  What is the ability of bosentan to reduce high blood pressure in the lungs?This study aims to determine the ability of bosentan to reduce high blood pressure in the lungs pulmonary hypertension in patients with scarring fibrosing lung disease. It is a placebo-controlled double blinded study for 16 weeks and it is proposed to follow patients in a 16 week open-label phase with bosentan therapy. 