To do with the processes of breathing and supplying the body with the oxygen it needs to survive, e.g., respiratory muscles are the muscles needed to breathe.
Found on http://www.encyclo.co.uk/local/20560
Re·spir'a·to·ry adjective (Physiol.) Of or pertaining to respiration; serving for respiration; as, the respiratory organs; respiratory nerves; the respiratory function; respiratory changes. Respiratory foods . (Physiol.) See 2d Note under Found on http://www.encyclo.co.uk/webster/R/63