In-vivo analysis of thoracic mechanical response under belt loading: The role of body mass index in thorax stiffness

Abstract

Thoracic injuries are a major cause of mortality in frontal collisions, especially for elderly and obese people. Car occupant individual characteristics like BMI are known to influence human vulnerability in crashes. In the present study, thoracic mechanical response of volunteers quantified by optical method was linked to individual characteristics. 13 relaxed volunteers of different anthropometries, genders and age were submitted to non-injurious sled tests (4 g, 8 km/h) with a sled buck representing the environment of a front passenger restrained by a 3-point belt. A resulting shoulder belt force was computed using the external and internal shoulder belt loads and considering shoulder belt geometry. The mid sternal deflection was calculated as the distance variation between markers placed at mid-sternum and the 7th vertebra spinous process of the subject. Force-deflection curves were constructed using resulting shoulder belt force and midsternal deflection. Average maximum chest compression was 7.9±2.3% and no significant difference was observed between overweight subjects (BMI≥25 kg/m²) and normal subject (BMI<25 kg/m²). The overweight subjects exhibited significantly greater resultant belt forces than normal subjects (715±132 N vs. 527±111 N, p<0.05), higher effective stiffness (30.9±10.6N/mm vs. 19.6±8.9 N/mm, p<0.05) and lower dynamic stiffness (42.7±8.71 N/mm vs. 61.7±15.5 N/mm, p<0.05).

Optimal design of continuously inflated airbag for 12-year-old child occupants with various sitting postures

“…15 The contact area between the continuously inflated airbag and the thorax is larger than that between the shoulder strap and the thorax, which leads to the great reduction of the THPC . This conclusion is consistent with the research of Poulard et al and Untaroiu et al 52,53…”

“…15 The contact area between the continuously inflated airbag and the thorax is larger than that between the shoulder strap and the thorax, which leads to the great reduction of the THPC. This conclusion is consistent with the research of Poulard et al and Untaroiu et al 52,53 Under Condition 2 and Condition 6, the HIC 15 and T 3ms in the optimized case increase compared with the three-point safety belt case, but these values are far less than the corresponding threshold value of 437.2 and 52.1g. The reasons for the increase in the HIC 15 and T 3ms are as follows: (1) On the one hand, before the collision, the 12-year-old child occupant is in the slouched sitting posture, the gravitational potential energy of the backward-leaning upper torso can offset part of the kinetic energy generated by the forward rotation of the upper torso in the frontal collision; on the other hand, the upper torso is always restrained by the shoulder strap of the three-point safety belt so that the head and thorax do not contact the other objects; eventually causing the HIC 15 and T 3ms to be lower.…”