Peak oxygen consumption increased 2.0 mLkg ( -1 ) min ( -1 ) ( from 28.7 to 30.7 mLkg ( -1 ) min ( -1 ) ) in the bosentan group compared with 0.6 mLkg ( -1 ) min ( -1 ) ( from 28.4 to 29.0 mLkg ( -1 ) min ( -1 ) ) in the placebo group ( P = 0.02 ) .