Session: 07-01-01: Injury Risk Assessment due to Blunt Impact

Paper Number: 172733

Blunt Cardiac Trauma Risk Curve and Threshold Development Using Ovine Finite Element Models 

Blunt cardiac trauma, or BCT, can occur due to blunt impacts to the chest from motor vehicle crashes, projectiles impacting protective equipment, and sports impacts. Within high velocity blunt impacts in particular, the chest wall experiences a very small, localized deformation at a very high rate, leading to internal injuries such as BCT. Clinically, BCT is difficult to diagnose due to the range of injuries and symptomology that patients may present with. Minimal work has been published regarding BCT injury thresholds, particularly at the organ level, in high velocity blunt trauma.

The objective of this study is to develop strain-based injury thresholds for three types of BCT injuries: cardiovascular instability, prolonged arrhythmia, and asystole. This was completed using subject-specific ovine thoracic finite element models that were matched to experimental impacts (N = 41). During in vivo experiments, male Katahdin sheep were impacted on the right lateral side between the seventh and eighth ribs following all protocols approved by the Temple University Institutional Animal Care and Use Committee (N = 41). The boundary conditions for each impact included the angle from the perpendicular vector from the spine, where positive angles point caudally (-2 to 25°), the velocity at which the impactor impacted the subject (40 or 70 m/s), and the depth of the impact (19-59 mm). A total of 9 subjects experienced asystole, 15 experienced prolonged arrhythmia, and 16 experienced cardiovascular instability, where 14 subjects had at least two of the defined injuries. 17 subjects had no cardiac trauma. The subject-specific simulations included matching each subject and the boundary conditions each subject experienced. The mass and the dimensions of each of the subject-specific finite element models match the outer dimensions of each of the experimental subjects, some of which had experienced BCT.  

Two data sets were statistically analyzed using survival analysis to determine the best metrics for predicting injury. Prior to survival analysis, potential metrics and injury outcomes were investigated to check statistical associations (α = 0.05). The first data set were metrics that can be measured experimentally during in vivo experiments – force, energy, impulse, impact angle, and impact depth. No metrics were associated with cardiovascular instability outcomes. Force, energy, and impulse were all considered associated with asystole and prolonged arrhythmia outcomes. For both asystole and prolonged arrhythmia, peak energy was determined to be the best fitting metric for experimental metrics.

The second set were cardiac strains in three different regions – the right atria, the right side of the heart, and the whole heart. A total of seven metrics were investigated – maximum and minimum principal strain, maximum principal strain rate, maximum principal strain x strain rate, maximum shear stress, and absement maximum and minimum principal strain. There were no statistical associations between any of the metrics or regions for cardiovascular instability, however, there were associations for each region for the remaining injury categories (asystole and prolonged arrhythmia). Across all three regions and the remaining injury categories, maximum principal strain rate was considered the best metric. The 50% risk thresholds ranged from 80.3 to 177.8 1/s, depending on region and type of injury. Prolonged arrhythmia had lower threshold values than asystole, and the right atria region had lower values than the right side and whole heart regions. These thresholds can be utilized in future work in areas such as translational injury studies and in protective equipment development to ensure low BCT injury risk to better protect the wearer.

Presenting Author: Patricia Thomas Wake Forest University School of Medicine

Presenting Author Biography: At the time of abstract submission, Patricia Thomas is a PhD candidate at Wake Forest University School of Medicine. Her research areas include injury biomechanics, finite element modeling, and material characterization, primarily focused on military applications.

Authors:

Patricia Thomas Wake Forest University School of Medicine
Fang-Chi Hsu Wake Forest University School of Medicine
Marla Wolfson Temple University Lewis Katz School of Medicine
F. Scott Gayzik Wake Forest University School of Medicine