In 18 subjects ( age 53 + / - 8 years ) with known or suspected coronary artery disease , quantitative coronary angiography was performed before and after being randomly assigned to breathing ( 1 ) an inspired oxygen concentration ( fraction of inspired oxygen , FIO2 ) of 21 % ( room air , RA ) for 20 min ( n = 4 , controls ) or ( 2 ) an FIO2 of 15 and 10 % for 10 min each ( corresponding to altitudes of 2,500 and 5,500 m , respectively ; n = 14 ) .
