Analysis of the Primate “Squeeze‐back” Swallowing Mechanism using X‐ray Reconstruction of Moving Morphology and Fluoromicrometry

Abstract

The primate hyolingual apparatus is a complex composite of a muscular hydrostat and a floating bone that is essential for feeding. In particular, the characteristic elevation (i.e., the “squeeze‐back” mechanism) and retraction of the tongue base during swallowing may be important in flipping the epiglottis to protect the laryngeal inlet. However, the link between hyolingual muscle behavior and hyolingual kinematics is poorly supported by in vivo data. Tongue base elevation and retraction could be due to one or a combination of three mechanisms thanks to its redundant morphology: intrinsic tongue muscles inducing hydrostatic deformation, extrinsic muscles moving the whole tongue, or hyoid elevation and protraction deforming the tongue. We evaluated these possibilities using a macaque model system. We implanted two rhesus macaques (one male, one female) with tantalum beads and filmed them during feeding using biplanar videofluoroscopy for X‐ray Reconstruction of Moving Morphology and fluoromicrometry workflows to measure hyoid kinematics, tongue deformation, and muscle length change with high spatiotemporal resolution. The results of general linear models demonstrate significant effects of hyoid movement and hydrostatic deformation on tongue base elevation, while all three mechanisms predict tongue base retraction (p < 0.001). Future directions include incorporating electromyography to understand how hyolingual muscle activity, especially active shortening, generates to tongue movement. These findings not only give insight into the biomechanics of the hyolingual apparatus, but they are also relevant for dysphagia rehabilitation as they suggest that more muscles are involved in tongue base retraction‐‐and perhaps epiglottic flipping‐‐than previously thought.Support or Funding InformationThis research was supported by the NIH (R01 DE023816‐03 and T32 HD007009‐41) and the NSF (MRI 1338066).