On average , the 24-hour mean arterial pressure at 12 weeks was lower in the group receiving CPAP than in the control group ( -2.4 mm Hg ; 95 % confidence interval [ CI ] , -4.7 to -0.1 ; P = 0.04 ) or the group receiving supplemental oxygen ( -2.8 mm Hg ; 95 % CI , -5.1 to -0.5 ; P = 0.02 ) .