Running, breathing and visceral motion in the domestic rabbit (Oryctolaguscuniculus): Testing visceral displacement hypotheses

The relative motion of the visceral mass may be important to ventilation du ring running. A visceral piston hypothesis predicts that, during galloping, cranial motion of the liver during expiration and caudal motion of the liv er during inspiration may characterize efficient quadrupedal mammalian loco motion. Although a theoretical model based on vibration mechanics casts dou bt on this prediction, only limited direct measurements of visceral mass mo tion during galloping have been reported. In the present study, mechanical interactions between running, breathing and liver oscillations in the domes tic rabbit are recorded using synchronized videographic, cineradiographic a nd pneumotachographic techniques; The analysis focuses on the variation ire locomotor-respiratory coupling (LRC) and on the relative position of the l iver. Results from running rabbits show (1) variation in phase angle betwee n the locomotor and respiratory periods that is inconsistent with the 1:1 L RC ratio that has been reported for other galloping mammals; (2) a tendency towards a 1:1 LRC ratio at higher speeds and stride frequencies; and (3) t hat the relative motion of the liver is caudal during expiration and crania l during inspiration, which is inconsistent with the visceral piston hypoth esis. The data presented here are generally consistent with the theoretical vibration mechanics model for liver motion and with a pneumatic stabilizat ion hypothesis that the lungs serve an important role in the stabilization of the thorax during locomotion.