Studies on the mechanisms of stress wave propagation in the chest subjected to impact and lung injuries

A numerical simulation method of natural fragment formation and injury to human thorax

OBJECTIVE

Fragment injury is a type of blast injury that is becoming more and more common in military campaigns and terrorist attacks. Numerical simulation methods investigating the formation of natural fragments and injuries to biological targets are expected to be developed.

METHODS

A cylindrical warhead model was established and the formation process of natural fragments was simulated using the approach of tied nodes with failure through the explicit finite element (FE) software of LS-DYNA. The interaction between the detonation product and the warhead shell was simulated using the fluid-structure interaction algorithm. A method to simulate the injury of natural fragments to a biological target was presented by transforming Lagrange elements into smooth particle hydrodynamics (SPH) particles after the natural fragments were successfully formed. A computational model of the human thorax was established to simulate the injury induced by natural fragments by the node-to-surface contact algorithm with erosion.

RESULTS

The discontinuous velocities of the warhead shell at different locations resulted in the formation of natural fragments with different sizes. The velocities of natural fragments increased rapidly at the initial stage and slowly after the warhead shell fractured. The initial velocities of natural fragments at the central part of the warhead shell were the largest, whereas those at both ends of the warhead shell were the smallest. The natural fragments resulted in bullet holes that were of the same shape as that of the fragments but slightly larger in size than the fragments in the human thorax after they penetrated through. Stress waves propagated in the ribs and enhanced the injury to soft tissues; additionally, ballistic pressure waves ahead of the natural fragments were also an injury factor to the soft tissues.

CONCLUSION

The proposed method is effective in simulating the formation of natural fragments and their injury to biological targets. Moreover, this method will be beneficial for simulating the combined injuries of natural fragments and shock waves to biological targets.

An integrated physiology model to study regional lung damage effects and the physiologic response

BACKGROUND

This work expands upon a previously developed exercise dynamic physiology model (DPM) with the addition of an anatomic pulmonary system in order to quantify the impact of lung damage on oxygen transport and physical performance decrement.

METHODS

A pulmonary model is derived with an anatomic structure based on morphometric measurements, accounting for heterogeneous ventilation and perfusion observed experimentally. The model is incorporated into an existing exercise physiology model; the combined system is validated using human exercise data. Pulmonary damage from blast, blunt trauma, and chemical injury is quantified in the model based on lung fluid infiltration (edema) which reduces oxygen delivery to the blood. The pulmonary damage component is derived and calibrated based on published animal experiments; scaling laws are used to predict the human response to lung injury in terms of physical performance decrement.

RESULTS

The augmented dynamic physiology model (DPM) accurately predicted the human response to hypoxia, altitude, and exercise observed experimentally. The pulmonary damage parameters (shunt and diffusing capacity reduction) were fit to experimental animal data obtained in blast, blunt trauma, and chemical damage studies which link lung damage to lung weight change; the model is able to predict the reduced oxygen delivery in damage conditions. The model accurately estimates physical performance reduction with pulmonary damage.

CONCLUSIONS

We have developed a physiologically-based mathematical model to predict performance decrement endpoints in the presence of thoracic damage; simulations can be extended to estimate human performance and escape in extreme situations.

Ballistics for physicians: myths about wound ballistics and gunshot injuries

PURPOSE

Wound ballistics is a difficult subject. The behavior of all bullets is unpredictable but the specific effect of high velocity projectiles has been a particular source of confusion in the literature. This confusion has resulted in the likely incorrect conclusion that all high velocity wounds require massive débridement. We reviewed the entirety of the literature on this subject and concluded that high velocity weapons do not reliably create massive wounds, and judicious débridement and staged explorations may be the best treatment method for these patients.

MATERIALS AND METHODS

A MEDLINE search and retrieval were done of all pertinent references from 1966 to May 2003 concerning the field of wound ballistics. Articles initially missed in this search were obtained from the bibliography of retrieved studies. More than 70 articles and book chapters were reviewed.

RESULTS

Five common myths about the tissue effects of gunshot wounds were reviewed as well as the data that dispel these myths. Information on the effects of different bullet types, and the intended and actual effect of military rifle wounds were assessed.

CONCLUSIONS

For the majority of high velocity gunshot wounds, especially military rifles that generally fire a projectile that is meant to stay intact after impact, wound severity can be limited, even much less than that from a civilian rifle, shotgun or handgun. Judicious use of débridement during surgical exploration limits the extent of iatrogenic injury in the surgical care of these patients.