ABSTRACT
Objective Direct impact is a common mechanism of injury for blunt thoracic injury, and if resulting thoracic injury is severe the mortality may be as high as 10% ～ 25% . We aim to develop a mechanical device for animal impact injury experiment, so as to establish a rodent model of severe thoracic injury. Method A spring operated mechanical device for animal impact injury experiment was developed. The device allowed for accurate controlled delivery of impact force to specific areas of the chest well, at specific velocities and degrees of chest compression. Eghty-four male Sprague-Dawley rats were anaesthetized and underwent left carotid artery cannulation. They were randomly divided into seven groups and given the following treatment: group A (Control group) were subjected to sham impact; group B to G animals were subjected to impacts on the right lateral superior chest at different velocities and degrees of chest wall compression. ( B 3 m/s, 20%; C 3 m/s 40%; D 6 m/s 20%; E 6 m/s 40%; F 9 m/s 20%; G 9 m/s 40%). Arterial blood gas samples were taken just before injury, and at 2 and 12 post injury. All rats were sacrificed at 12 hours and their degree of thoracic injury rated. Pathological examination of injured lung tissue was also performed. Results The device was able to deliver impact forces accurately, with ＜ 4% deviation from desired velocity and ＜ 3 mm deviation from target area of impact. Other than the control group, all animals experienced significant hemodynamic changes immediately post impact. Arterial blood gas analysis detected significant hypocapnia in groups B and C. Significant hypoxemia and hypocapnia was detected in groups D, E and F. In groups B,C,D and F, die impact produced a mild thoracic injury with low mortality rate at 12 hours. In group E, the impact produced severe thoracic injury with mortality rate of 33.33% at 12 hours. Group C animals sustained the most serious thoracic injury with mortality rate of 83.33% at 12 hours. Pathological examination revealed injuries from direct trauma as well as secondary lung injuries. Conclusions Our device was able to repetitively deliver accurate and precise impact forces to rats and allows us to establish a rodent model of severe thoracic injury firm blunt trauma. We found that with our device, impact force at velocity of 6 m/s and 40% chest compression produced the most severe lung injury in rats.This helps us establish a rodent model of severe thoracic injury which can be use for future research in severe blunt thoracic trauma and the secondary lung injuries.