East winds are reputed to be the worst for scenting conditions, and it's a wonderful excuse for poor dog work. In my experience, however, it's a mixed bag. East winds often accompany unsettled conditions. That's when gusting, direction-changing winds blow body scent all over the map. Hounds smell scent that landed on this bush or that, but they can't discern a trail.
Pointers have difficulty with bird location.
Steady east winds are not this troublesome. A Missourian was astounded when his versatile drahthaar ran downwind of a brushy fencerow without smelling a rabbit sitting in the weeds. Then the hunter noticed a peculiarity in the wind-blown leaves. They rose going over the brush, then rolled downward and back. Rabbit scent also curled back and away from the dog, like snow behind a snow fence.