Biomechanical response of the pediatric abdomen, part 1: development of an experimental model and quantification of structural response to dynamic belt loading.

The abdomen is the second most commonly injured region in children using adult seat belts, but engineers are limited in their efforts to design systems that mitigate these injuries since no current pediatric dummy has the capability to quantify injury risk from loading to the abdomen. This paper develops a porcine (sus scrofa domestica) model of the 6-year-old human's abdomen, and then defines the biomechanical response of this abdominal model. First, a detailed abdominal necropsy study was undertaken, which involved collecting a series of anthropometric measurements and organ masses on 25 swine, ranging in age from 14 to 429 days (4-101 kg mass). These were then compared to the corresponding human quantities to identify the best porcine representation of a 6-year-old human's abdomen. This was determined to be a pig of age 77 days, and whole-body mass of 21.4 kg. The sub-injury, quasistatic response to belt loading of this porcine model compared well with pediatric human volunteer tests performed with a lap belt on the lower abdomen. A test fixture was designed to produce transverse, dynamic belt loading on the porcine abdomen. A detailed review of field cases identified the following test variables: loading location (upper/lower), penetration magnitude (23%-68% of initial abdominal depth), muscle tensing (yes/no), and belt penetration rate (quasistatic, dynamic 2.9 m/s - 7.8 m/s). Dynamic tests were performed on 47 post-mortem subjects. Belt tension and dorsal reaction force were cross-plotted with abdominal penetration to generate structural response corridors. Subcutaneous stimulation of the anterior abdominal muscle wall stiffened the quasistatic response significantly, but was of negligible importance in the dynamic tests. The upper abdomen exhibited stiffer response quasistatically, and also was more sensitive to penetration rate, with stiffness increasing significantly over the range of dynamic rates tested here. In contrast, the lower abdomen was relatively rate insensitive. To our knowledge, this is the only dynamic structural characterization study on a comprehensively developed experimental model of the 6-year-old human abdomen. The structural corridors developed here should lead to the development of both mechanical (i.e., crash dummies) and computational pediatric models that are more useful for assessing injurious levels of belt penetration into the abdomen.