The Collaborative International Dictionary of English v.0.48:

Respiratory \Re*spir"a*to*ry\ (r?*sp?r"?*t?*r? or r?s"p?*r?-),
   a. (Physiol.)
   Of or pertaining to respiration; serving for respiration; as,
   the respiratory organs; respiratory nerves; the respiratory
   function; respiratory changes.
   [1913 Webster]

   Respiratory foods. (Physiol.) See 2d Note under Food, n.,
      1.

   Respiratory tree (Zool.), the branched internal gill of
      certain holothurians.
      [1913 Webster]

WordNet (r) 3.0 (2006):

respiratory
    adj 1: pertaining to respiration; "respiratory assistance"