Mechanical basis for lingual deformation during the propulsive phase of swallowing as determined by phase-contrast magnetic resonance imaging

The tongue is an intricately configured muscular organ that undergoes a series of rapid shape changes intended to first configure and then transport the bolus from the oral cavity to the pharynx during swallowing. To assess the complex array of mechanical events occurring during the propulsive phase of swallowing, we employed tongue pressure-gated phase-contrast MRI to represent the tissue's local strain rate vectors. Validation of the capacity of phase-contrast MRI to represent local compressive and expansive strain rate was obtained by assessing deformation patterns induced by a synchronized mechanical plunger apparatus in a gelatinous material phantom. Physiological strain rate data were acquired in the sagittal and coronal orientations at 0, 200, 400, and 600 ms relative to the gating pulse during 2.5-ml water bolus swallows. This method demonstrated that the propulsive phase of swallowing is associated with a precisely organized series of compressive and expansive strain rate events. At the initiation of propulsion, bolus position resulted from obliquely aligned compressive and expansive strain, vertically aligned compressive strain and orthogonal expansion, and compressive strain aligned obliquely to the styloid process. Bolus reconfiguration and translocation resulted from a combination of compressive strain occurring in the middle and posterior tongue aligned obliquely between the anterior-inferior and the posterior-superior regions with commensurate orthogonal expansion, along with bidirectional contraction in the distribution of the transversus and verticalis muscle fibers. These data support the concept that propulsive lingual deformation is due to complex muscular interactions involving both extrinsic and intrinsic muscles.