Impact Tolerance and Resulting Injury Patterns in the Baboon: Air Force Shoulder Harness—Lap Belt Restraint

The tolerance to abrupt linear deceleration (-GX) and impact trauma patterns resulting from the use of the Air Force shoulder harness-lap belt restraint were investigated. Eightynine deceleration tests were performed with 37 adult male baboons. Peak sled decelerations ranged from 6.5-134 g. The stopping distance varied from 0.5-3.5 ft at 6 in increments. LD₅₀s were calculated to be 102, 103, and 98 g for the 0.5, 2.0, and 3.5 ft stopping distances, respectively. Since the deceleration pulses were similar, the results imply that for the exposure range of these tests, impact lethality is dependent upon magnitude of peak sled deceleration, irrespective of the pulse duration, sled velocity, or stopping distance. At all stopping distances, the primary cause of death was lower brainstem or cervical spinal cord trauma. The pelvic, abdominal, and thoracic injury patterns were significantly different at the various stopping distances. Animals impacted at the 0.5 ft stop typically displayed no significant injuries other than head-neck trauma. The predominant injuries at the 2.0 ft stop included pelvic and abdominal myorrhexis, intestinal herniation, urinary bladder rupture, and pelvic fractures in addition to luxation of cervical through thoracic vertebrae. At the 3.5 stop animals received extensive muscular and skeletal injuries of the pelvic, abdominal, and thoracic regions. Brainstem hemorrhage was a significant finding, but there was no evidence of luxation or fractures of cervical vertebrae.