Meeting Abstract

34.3  Tuesday, Jan. 5  XROMM analysis of rib kinematics and intercostal muscle strain during breathing in Iguana iguana BRAINERD, E.L.*; RITTER, D.A.; DAWSON, M.M.; SULLIVAN, A.; Brown University brainerd@brown.edu

The functions of external intercostal (EI) and internal intercostal (II) muscles have been debated for centuries. In this study we used X-ray Reconstruction of Moving Morphology (XROMM) to create accurate animations of 3D rib and sternal movements during breathing in green iguanas. We measured intercostal muscle strain by mapping the attachment points of EI and II muscle fascicles onto the 3D rib models for each individual iguana, and running the XROMM animations to measure the change in distance between the fascicle attachment points during exhalation and inhalation. Green iguanas have four cervical (Cv) ribs, four sternal (St) ribs that articulate with the sternum via costal cartilages, and three ziphisternal ribs. Our x-ray videos and XROMM analysis of deep breathing movements show little movement of Cv1 and Cv2, increasing amounts of rotation in Cv3-4 and St1, the greatest rotation in St2, and gradually decreasing rotation in St3-4 and more caudal ribs. In the intercostal space between the osseous portions of St1 and St2, the EI fascicles lengthened during exhalation and shortened during inhalation, whereas between St3 and St4, the EI shortened during exhalation and lengthened during inhalation. The costal cartilages rotate posteromedially during exhalation such that the interchondral spaces all decrease in width, and subsequently increase in width during inhalation. However, the parasternal II muscle fascicles lie at steep angles (>55 degrees) to the costal cartilages, so the II fascicles lengthen during exhalation and shorten during inhalation. These results are consistent with the previously described activation patterns of the EI and II in iguanas (Carrier, 1989), and are strikingly similar to recent consensus developing on the functions of EI and parasternal II in dogs.