Session: 06-01-01: Injury and Damage Biomechanics I - Organ and Tissue Injury Biomechanics 1

Paper Number: 139657

139657 - Human Liver Injury Criteria for Behind Armor Blunt Trauma 

Introduction: Human thoracoabdominal organs are viscoelastic in terms of mechanical properties and heterogeneous in their constitutions. Their anatomical locations are different, and some are asymmetric. They have differing skeletal coverage. Their complex three-dimensional geometries are associated with varying attachments to the surrounding tissues, while they perform different physiological functions in the in vivo human. These characteristics contribute to differing responses and tolerances to external dynamic loads. It is important to subject a live animal model to impact loading, identify injury to the specific organ/region, and use statistical regression models to develop injury criteria for behind armor blunt trauma (BABT). The objective of this study is to develop liver injury criteria in the form of injury risk curves using a live animal model.

Methods: After obtaining institutional animal committee and sponsor approvals, BABT loading was applied to the liver region of each swine using a custom indenter, the design of which was based on the backface deformations from previous human cadaver tests with hard body armor. An accelerometer attached to the indenter measured acceleration signals at 500 kilohertz (kHz). A 2 kHz four-pole Butterworth filter was applied to the signals, and velocity and deflection profiles were obtained. The viscous response was calculated from the velocity and normalized deflection (based on ventral-dorsal depth at the impact region) signals and its peak magnitude, termed the viscous criterion, was obtained. Physiological parameters were monitored for six hours before euthanasia, and an autopsy was conducted. Survival analysis-based injury risk curves were developed using the viscous criterion. The quality of the injury risk curves was assessed at 10, 25, 50, 75, and 90% risk levels using 95% confidence interval bounds. It was accomplished using the normalized confidence interval size, defined as the width of the interval normalized to the mean value of the metric at the chosen risk level. Skeletal material property scaling between the swine and human ribs was used to develop human injury probability curves.

Results: Twenty live swine were each subjected to a single impact. The magnitudes of the viscous criteria at the 10, 25, and 50% risk level were 1.7, 2.3, and 3.1 meters per second (m/s), respectively, for the live swine and 2.1, 3.0, and 4.0 m/s, respectively, for the human. The quality of the risk curves, 95% confidence interval bounds, and the mean injury risk curve for both live animals and humans will be presented in the full-length paper upon acceptance.

Discussion: The live swine model was chosen due to its applicability to thoracoabdominal organ injuries and the ability to monitor injury physiology over time, a critical parameter for organ injury development. This contrasts with skeletal injuries such as rib or spine fractures that are not temporal. The swine is a proven model for impact studies in many disciplines. The viscous criterion was chosen as an injury metric because it represents the viscous nature of the trauma to internal organs, such as the liver, and is considered an underlying injury mechanism to soft tissues in impact loading scenarios. Because the sample size is limited, the current results represent any liver injury and not a specific injury severity (such as based on the American Association of Surgery for Trauma). Additional tests are needed to develop injury criteria based on liver injury severity and other thoracoabdominal organs. This is the first study to develop both live animal and human injury risk curves for liver BABT impacts, and the present results can be used to develop improved body armor and enhance Warfighter safety and mission readiness. 

Presenting Author: Narayan Yoganandan Medical College Of Wisconsin

Presenting Author Biography: Professor and ASME Fellow

Authors:

Narayan Yoganandan Medical College Of Wisconsin
Alok Shah Medical College of Wisconsin
Jared Koser Medical College of Wisconsin
Brian Stemper Medical College of Wisconsin
Lewis Somberg Medical College of Wisconsin
V. Carol Chancey U.S. Army Aeromedical Research Laboratory
B. Joseph McEntire U.S. Army Aeromedical Research Laboratory