Relationship between the dynamic parameters and injury severity of chest subject to impact

Modeling lung tissue dynamics and injury under pressure and impact loading

A nonlinear viscoelastic model for the lung is implemented and evaluated for high-rate loading. Principal features of the model include a closed-cell approximation of the bulk compressibility accounting for air inside the lung and a damage-injury component by which local trauma is induced by cumulative normalized internal energy and amplified by gradients of energy density. The latter feature is adapted for use in standard numerical (i.e., explicit finite element) simulations in terms of the local rate of strain energy density and the longitudinal wave speed. Injury predictions for direct loading of a block of extracted lung material, rather than the entire thorax, via pressure pulses are in reasonably close agreement with experimental observations for an extracted rabbit lung: a threshold applied pressure exists above which edema is observed experimentally, correlating with low but non-negligible damage in the numerical results. Responses to impact by cylindrical and spherical projectiles are also interrogated. Penetration depths are comparable to those observed experimentally, as is drastically increasing damage with increasing impact velocity. Damage initiates and propagates from the impact surface, with local severity of injury decreasing with distance from the impact zone, in agreement with some empirical evidence. The model predicts more severe local injury, relative to the aforementioned surface pressure loading, than what is observed experimentally. Possible reasons for the discrepancy are analyzed, and adjustments to the model, with caveats, are suggested accordingly.

Modeling of weak blast wave propagation in the lung

Blast injuries of the lung are the most life-threatening after an explosion. The choice of physical parameters responsible for trauma is important to understand its mechanism. We developed a one-dimensional linear model of an elastic wave propagation in foam-like pulmonary parenchyma to identify the possible cause of edema due to the impact load. The model demonstrates different injury localizations for free and rigid boundary conditions. The following parameters were considered: strain, velocity, pressure in the medium and stresses in structural elements, energy dissipation, parameter of viscous criterion. Maximum underpressure is the most suitable wave parameter to be the criterion for edema formation in a rabbit lung. We supposed that observed scattering of experimental data on edema severity is induced by the physiological variety of rabbit lungs. The criterion and the model explain this scattering. The model outlines the demands for experimental data to make an unambiguous choice of physical parameters responsible for lung trauma due to impact load.

Prognostic factors in victims of falls from height

OBJECTIVE

Falls from height cause significant mortality in the urban environment, but reliable prognostic factors have not been identified. Even the intuitive relation between the distance fallen and mortality rate has been questioned. Our objective was to determine factors predictive of increased mortality rate in victims of falls from height.

DESIGN

Clinical observational study, retrospective for January 1998 to May 1999 and prospective from June 1999 to September 2000.

SETTING

The study population was drawn from Seine-Saint-Denis, an urban region near Paris with 1.3 million inhabitants treated by a French out-of-hospital medical emergencies unit.

PATIENTS

Patients were victims of falls from height >3 m, age >12 yrs. Study entry was performed on the scene by an emergency physician from the medical emergencies unit.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Studied data included age, gender, circumstances of fall, height of fall, nature of the impact surface (soft or hard), transient impact preceding final impact, and part of the body touching the ground first. The primary end point was mortality. The study included 287 patients, 116 (40%) during the retrospective phase and 171 (60%) during the prospective phase. Ninety-seven patients (34%) ultimately died. In multivariate analysis, age (mean, 41.6 +/- 16.6 yrs in patients who died vs. 34.9 +/- 14.9 in survivors; odds ratio, 1.05; p < .0005); height of fall (median, 5.0; 3.8-8.0 vs. 2.0; 1.2-3.0 floors; odds ratio, 1.24; p < .0001); nature of the impact surface (hard in 39% vs. soft in 22%; odds ratio, 2.7; p < .05); and head, anterior, and lateral body surfaces touching the ground first (with respectively mortality rates of 44%, odds ratio, 16.7, p = .0001; 57%, odds ratio, 10.6, p < 0.005; 32%, odds ratio, 11.1, p < .001) were independently correlated with the final mortality rate.

CONCLUSIONS

Patient age, height of fall, impact surface nature, and body part first touching the ground are independent prognostic factors in victims of falls from height.

Modeling the Effect of Non-Penetrating Ballistic Impact As a Means of Detecting Behind Armor Blunt Trauma

BACKGROUND

According to the National Institute of Justice (NIJ) Standard 0101.04, the maximum deformation a soft armor vest can undergo without penetration is 44 mm. However, this does not take into account the effect of the pressure wave or energy transferred to the organs within the torso due to behind armor blunt trauma (BABT). Therefore, a study was undertaken to develop a finite element model (FEM) to study these effects.

METHODS

A finite element model (FEM) of the human thorax; complete with musculoskeletal structure and internal organs (heart, liver, lungs and stomach), intercostal muscle and skin, has been developed in LS-DYNA. A Kevlar vest was modeled on the chest to simulate non-penetrating ballistic impact.

RESULTS

Using a projectile modeled with a size and mass equivalent to a 9 mm (124 grain) bullet at 360 and 425 m/s, four impacts were simulated against NIJ Level II and Level IIIa Kevlar vests at the midsternum and right thorax. At the same velocity, the pressures decreased by a factor of 3 and the energy absorbed by the organs decreased by a factor of 6 for the NIJ Level II and Level IIIa vests, respectively. As the projectile velocity increased, the peak pressures increased by a factor of 3 while the energy absorbed by the organs increased by a factor of 4.

CONCLUSIONS

The resulting pressure profiles and kinetic energy exhibited by the respective organs indicate this model may be useful in identifying mechanisms of injury as well as organs at an elevated injury risk as a result of BABT.

Design and Injury Assessment Criteria for Blunt Ballistic Impacts

BACKGROUND

Less-lethal technologies are used in situations where lethal force is not warranted; however, a variety of injuries have been reported. Design and injury criteria are needed to assess the safety of these munitions.

METHODS

Injury data from ballistic impacts of cadavers were analyzed to validate design and injury criteria. Logistic regression analysis determined the predictive ability of the blunt criterion (BC) for munition design and the viscous criterion (VC) for injury risk assessment. Differences in risk for men and women were determined.

RESULTS

For a 50% risk of Abbreviated Injury Scale 2 or 3 thoracic injury, BC = 0.37 (chi = 17.71, p = 0.001) and VCmax = 0.8 m/s (chi = 11.28, p = 0.001). The 5th percentile female subject has a 36% lower tolerance to ballistic energy than the 50the percentile male subject.

CONCLUSION

The BC can be used in the development of kinetic energy munitions and the VC for testing impact injury risk. These criteria provide much needed tools for the development and progression of less-lethal munitions.

Analysis of Injury Criteria to Assess Chest and Abdominal Injury Risks in Blunt and Ballistic Impacts

BACKGROUND

The Viscous Criterion (VC) is an experimental measure developed by the automotive industry to assess injury risks for high-speed impacts. The Blunt Criterion (BC) is a prospective measure developed by the Department of Defense to predict injury from blunt projectiles.

METHODS

The range of applicability of BC was extended and compared with VC for its ability to assess injury risk using published cadaver and animal data. Department of Defense projectiles were 0.05 to 0.43 kg mass at velocities up to 86 m/s. VC data were generated from impacts with 1.75 to 23.4 kg at 3.6 to 10.2 m/s. Chest and abdominal injuries ranged from Abbreviated Injury Scale scores of 1 to 6.

RESULTS

Both criteria correlated very well with the experimental data, demonstrating correlation coefficients of R = 0.84 to 0.96. The correlation between VC and BC was R = 0.99. Logistic probability curves were derived to predict blunt impact injuries of Abbreviated Injury Scale scores of 1 to 6 for the chest and abdomen.

CONCLUSION

BC and VC are virtually identical in their ability to assess blunt and ballistic impact injury risks. They are different measures of impact energy absorbed by the body. One is predictive using input parameters, and the other measures the impact response of the body.

Release kinetics of cardiac troponin I and cardiac troponin T in effluents from isolated perfused rabbit hearts after graded experimental myocardial contusion

BACKGROUND

Few experimental studies report effects of direct contusion on cardiac enzyme release. Cardiac troponins I (cTnI) and T (cTnT) have been shown to be highly sensitive and specific markers of myocardial cell injury. This investigation was designed to determine and compare the acute effects of quantified magnitudes of blunt cardiac trauma upon release of cTnI and cTnT in comparison with creatine kinase (CK) and lactate dehydrogenase (LD).

METHODS

In 24 rabbit hearts prepared on a standard Langendorff apparatus, myocardial contusion (MC) was produced by a single blow with a ball falling from a predefined height, delivered directly to the surface of the heart. Hearts were divided into control (n = 6) and various quantified impacts: 75 mJoules (mJ) (n = 6), 100 mJ (n = 6), 200 mJ (n = 6). Coronary effluent samples for cTnI, cTnT, CK, and LD were collected at baseline, immediately after MC and 5, 15, 30, 45, and 60 minutes after MC. At the end of experiment, histologic condition was evaluated.

RESULTS

The anti-cTnI and cTnT MAbs used in the cTnI (Access) and cTnT (Elecsys) assays cross-react with cTnI and cTnT of the rabbit. The time-courses of cTnI, cTnT, CK, and LD were monophasic in form. After MC, all parameters rose significantly compared with baseline and with control group. The maximal release occurred immediately after MC. The area under the cTnI curve and the maximal cTnI concentration were linked to the contusion energy when increased at 200 mJ. Maximal concentrations and areas under cTnT, CK, LD time activity curve were not linked to the contusion energy level and showed no between-energy group differences. The correlation found between maximal cTnI and maximal cTnT concentrations was 0.70 (p = 0.0001). Histologic examination showed cellular disruption and after the more severe impact, the extent of pathologic changes was more extensive.

CONCLUSION

After graded experimental MC, maximal cTnI concentration and area under cTnI curve increase with the power of impact kinetic energy. Levels of cTnI allow a much higher accuracy in detecting the extent of myocardial injury postMC in comparison with cTnT, CK, and LD in this experimental study. These results should be consistent with the more extensive cTnI release with more severe impact in patients with blunt chest trauma. Furthermore, because specificity and time-course of release, both cTnI and cTnT should have a role in the diagnosis and evaluation of such patients.