expiratory

from WordNet (r) 3.0 (2006)

expiratory
    adj 1: of or relating to the breathing out phase of respiration

from The Collaborative International Dictionary of English v.0.48

Expiratory \Ex*pir"a*to*ry\, a. (Physiol.)
   Pertaining to, or employed in, the expiration or emission of
   air from the lungs; as, the expiratory muscles.
   [1913 Webster]