An envelope of linear and rotational head motion during everyday activities

Various studies have characterized head kinematics in specific everyday activities by looking at linear and/or rotational acceleration characteristics, but each has evaluated a limited number of activities. Furthermore, these studies often present dissimilar and sometimes incomplete descriptions of the resulting kinematics, so the characteristics of normal everyday activities as a whole are not easily collectively summarized. The purpose of this study was to evaluate the literature investigating head kinematics associated with everyday activities and to generate a comprehensive kinematic boundary envelope describing these motions. The envelope constructed constitutes the current state of published knowledge regarding 'normally occurring' head accelerations. The envelope of kinematics represents activities commonly encountered and posing zero to minimal risk of injury to healthy individuals. Several kinematic measures, including linear accelerations, rotational velocities, and rotational accelerations, one may encounter as a result of normal everyday activities are summarized. A total of 11 studies encompassing 49 unique activities were evaluated. Examples of activities include sitting in a chair, jumping off a step, running, and walking. The peak resultant linear accelerations of the head reported in the literature were all less than 15 g, while the peak resultant rotational accelerations and rotational velocities approach 1375 rad/s2 and 12.8 rad/s, respectively. The resulting design envelope can be used to understand the range of acceleration magnitudes a typical active person can expect to experience. The results are also useful to compare to other activities exposing the head to motion or impact including sports, military, automotive, aerospace and other sub-injurious and injurious events.

Evaluation of Deep Brain Stimulation (DBS) Lead Biomechanical Interaction with Brain Tissue

The current study aims to examine the effect of material properties on implanted leads used for deep brain stimulation (DBS) using finite element (FE) analysis to investigate brain deformation around an implanted DBS lead in response to daily head accelerations. FE analysis was used to characterize the relative motion of the DBS lead in a suite of fifteen cases sampled from a previously derived kinematic envelope representative of everyday activities describing translational and rotational pulse shape, magnitude, and duration. Load curves were applied to the atlas-based brain model (ABM) with a scaled Haversine acceleration pulse in four directions of rotation: + X, - Y, + Y, and + Z. In addition to the fifteen sampled cases, six experimental cases taken from a previous literature review were also simulated for comparison. The current investigation found that there was very little difference in brain response for the DBS leads with two different material properties. In general, the brain and DBS lead experienced the greatest deformation during rotation about the Z axis for similar load cases. In conclusion, this study showed that there was no significant difference in implanted DBS lead deformation based on lead material properties.