to determine if a relationship existed between the site of airway obstruction and the mechanisms of exercise-induced asthma , we studied the predominant site of flow limitation , as determined by the mid-vital capacity ratios of maximal expiratory flow with air ( vmax air ) and 80 % helium-20 % oxygen ( vmax he-o2 ) , before and after physical exertion in 12 asthmatics .
C1875235
helium
C0030054
o2