Knowledge of the biomechanical properties of central nervous system (CNS) tissues is important for understanding mechanisms and thresholds for injury, and aiding development of computer or surrogate models of these tissues. Many investigations have been conducted to estimate the properties of CNS tissues including under shear, compressive and tensile loading, however there is much variability in this body of literature, making it difficult to separate the material properties from effects that result from a given experimental protocol. This review summarises previous studies of brain and spinal cord properties; discussing their main findings and points of difference, and displays the reported data on comparable scales. Additionally, based on the observed effects of methodological choices on reported tissue properties, recommendations for future studies of brain and spinal cord properties are made.

Study Objectives: To characterize tongue and lateral upper airway movement and to image tongue deformation during mandibular advancement.Design: Dynamic imaging study of a wide range of apnea hypopnea index (AHI), body mass index (BMI) subjects.Setting: Not-for-profit research institute.Participants: 30 subjects (aged 31-69 y, AHI 0-75 events/h, BMI 17-39 kg/m2).Interventions: Subjects were imaged using dynamic tagged magnetic resonance imaging during mandibular advancement. Tissue displacements were quantified with the harmonic phase technique.Measurements and Results: Mean mandibular advancement was 5.6 ± 1.8 mm (mean ± standard deviation). This produced movement through a connection from the ramus of the mandible to the pharyngeal lateral walls in all subjects. In the sagittal plane, 3 patterns of posterior tongue deformation were seen with mandibular advancement—(A) en bloc anterior movement, (B) anterior movement of the oropharyngeal region, and (C) minimal anterior movement. Subjects with lower AHI were more likely to have en bloc movement (P = 0.04) than minimal movement. Antero-posterior elongation of the tongue increased with AHI (R = 0.461, P = 0.01). Mean anterior displacements of the posterior nasopharyngeal and oropharyngeal regions of the tongue were 20% ± 13% and 31% ± 17% of mandibular advancement. The posterior tongue compressed 1.1 ± 2.2 mm supero-inferiorly.Conclusions: Mandibular advancement has two mechanisms of action which increase airway size. In subjects with low AHI, the entire tongue moves forward. Mandibular advancement also produces lateral airway expansion via a direct connection between the lateral walls and the ramus of the mandible.