Disclosures Nothing as it pertains to this lecture Speaker s Bureau for Sanofi and Bristol Myers Squibb Disclaimer The opinions expressed in this lect

Transcription

1 The Physics of Explosive Blast Traumatic Brain Injury Geoffrey Ling, M.D., Ph.D. Colonel, Medical Corps, US Army Program Manager, DARPA Professor and Interim Chair, Neurology, USUHS Director, Neuro Critical Care, WRAMC

2 Disclosures Nothing as it pertains to this lecture Speaker s Bureau for Sanofi and Bristol Myers Squibb Disclaimer The opinions expressed in this lecture are those of the presenter alone. They do not nor should they be interpreted as endorsements by the U.S. Army, Dept. of Defense, or any other agency of the Federal Government.

3 OIF (2007)

4 OEF (2009)

5 Explosive Blast Injury Categories Four categories of blast injury: Primary Caused by the direct blast energy Crush injuries, lacerations, hemorrhage common Secondary Caused by projectiles and other hazards created by the blast Rubble, building fragments, shrapnel, etc. Tertiary Inertial injuries caused by personnel being propelled by the blast (being thrown) Quaternary Inhalation, burns, and anything else not described by first three

6 Explosive Blast TBI Wide spectrum of neurological effects have been described Mild TBI Subtle cognitive deficits, neurobehavior changes, mood and affect issues Both can occur together Moderate TBI Loss of consciousness, overt structural damage Severe TBI Severe neurological deficits, subarachnoid hemorrhage, vascular changes (acute and chronic)

7 Mild TBI Pt suffered blast TBI from about 8 feet away Wearing helmet/armor No LOC but confusion/amnesia for at least 15min (Grade 2 concussion) CT: normal Persistent neuro cognitive deficits on Day #2 (transfer) Frontal lobe based tasks (digit span, word list generation) Normal by Day 7, returned to duty

8 Moderate TBI (low velocity shrapnel) Pt exposed to mortar explosion and struck by frag Day #14, fully recovered

9 IED Blast TBI (Severe) Pt suffered TBI from IED Pt underwent extensive surgery including hemicraniectomy 10 day ICU care, complicated course Recovered to awake, following commands, extubated tx to civilian rehab

10 Delayed Blast Related Vasospasm Figure 6 ACA Absent ACA Filling Post Angioplasty Supraclinoid ICA Severe Vasospasm a b Close to 50% of patients of cohort of WRAMC with severe blast TBI showed angiographic evidence of delayed vasospasm

11 What is the mechanism of injury? What is the physics?

12 Shock front formation Wave at point a is propagating into undisturbed media Wave at point b is propagating into a local zone of compressed media b a t = t 1 b a t = t 2 b a t = t 3 S. Parks, ORA, Inc point b eventually catches up to a steepening the wavefront

13 Air blast shock front Initial disturbance of media (air) caused by detonation Shock front is a discontinuous change in air properties Shock front heats the air to 1000 s of degrees Primary cause of personnel burns from blast, not fireball Shock heating is a principle mechanism of blast energy dissipation primary shock reflected shock S. Parks, ORA, Inc

14 Blast Wave

15 Airblast signatures Free field blast signature Friedlander shape Shock wave followed by decay of the pulse to a negative phase Shock front Negative phase Complex blast signature Many reflected components Quasi static component Target loaded from multiple directions Reflected peaks Quasi static pressure All real world blast signatures will have features of both S. Parks, ORA, Inc

16 Free field ideal blast Source: TM P S () t t t = PSO 1 to A e Friedlander equation ( t t A ) θ Airburst of spherical, uncased explosives approach ideal case Deviation from ideal presence of ground, reflecting surfaces, multiphase flow, ejecta, fireball, weapon casing S. Parks, ORA, Inc

17 Complex blast No closed form solution many empirical equations to predict Multiple peaks from reflecting surfaces Empirical simulation software or CFD/hydrocodes Geometry is most significant factor defining the pressure profile Sensor at this location Non responding concrete structure S. Parks, ORA, Inc

18 Crater Ejecta Delivers significantly more impulse and loading over airblast and fragments alone More destructive than simple blast prediction based on NEW 0 msec 6 msec 31 msec 63 msec 252 msec 948 msec Show movie: Crater formation OF 26 detonation (030107_01) S. Parks, ORA, Inc

19 Blast / Ejecta Loading Soil ejecta imparts over twice the impulse of air blast alone S. Parks, ORA, Inc

20 State of the Art Bowen Richmond Curves Current metrics of blast injury are Binary: alive or dead Evaluate pessure damage to the lungs Do not address TBI Some unstudied characteristics of explosions: Rapid temperature change Environmental chemical composition changes Electromagnetic pulse Kinetic energy transfer Lethality vs Pressure

21 Typical damage thresholds Peak Overpressure (psi) Impact Window glass breaks Concrete shatters, wood splinters Bricks shear >10.0 Lung damage % eardrum rupture % lethality % lethality > % lethality Without body armor

22 Paradox Many blast related TBI cases Few blast lung cases in isolation Few blast bowel cases

23 Return to first principles What is the mechanism of injury? Is it more than pressure alone What is the continuum of this disease?

24 WRAIR/ORA Experimental Environments BWG Swine are exposed to blast in three environments Large scale blast wave generator: Creates operationally relevant levels of blast overpressure HMMWV blast test surrogate: Allows for study of complex blast in high interest small enclosed environment Urban warfare blast test arena: Replicates blast effects from detonation in enclosed spaces Large scale blast wave generator: BWG blast wave (1 kg explosive): Actual free field blast wave created by open air detonation or artillery shell IED Creates free field blast wave exposure to high levels with minimal explosive weight Free field blast exposure occurs with any open air detonation of an IED free field is relevant for study Explosive = 90/10 mix of nitromethane/ triethylamine (TNT equivalent of 1.0) Free field characteristic

25 WRAIR/ORA Experimental Environments HMMWV Swine are exposed to blast in three environments Large scale blast wave generator: Creates operationally relevant levels of blast overpressure HMMWV blast test surrogate: Study complex blast in high interest small enclosed environment Urban warfare blast test arena: Replicates blast effects from detonation in enclosed spaces HMMWV surrogate: animal location opening HMMWV surrogate blast wave ( 0.5 KG explosive) Charge set under surrogate, simulates blast breach into driver side floorboard complex characteristic Creates complex blast with multiple reflected peaks characteristic of exposure to IED blast inside up armored HMMWV

26 WRAIR/ORA Experimental Environments Urban warfare test arena Swine are exposed to blast in three environments Large scale blast wave generator: Creates operationally relevant levels of blast overpressure HMMWV blast test surrogate: Study complex blast in high interest small enclosed environment Urban warfare blast test arena: Replicates blast effects from detonation in enclosed spaces Urban warfare blast test arena (under construction operational 15 July 2008) animal location Complex blast wave created by similar structure (blue) Charge set around corner opening Creates complex blast with multiple reflected peaks characteristic of exposure to IED blast inside or between buildings Generally a larger volume with more vent paths than encountered in vehicles Distinctly different power spectrum than vehicle blast

27 OUTCOMES Gait Analysis EEG near infrared strobe (NIR) camera CAMERA Arena: capture volume Cognitive Spatial Memory Histopathology DMS sample PRE BLAST POST BLAST delay General and neurophysiology Cerebral autoregulation Serum and CSF Protein Analysis Cerebral Angiography Bioreactor with 3 D tissue constructs Auricul ar artery Ascend ing pharyn geal artery

28 ARA Protocol/Schedule IRB Protocol Approved: subjects and controls June course Four pressure gauges, one inertial cube, and one air sampler per subject, personnel borne Two free field pressure gauges September course: Same as above and: Four free field thermal flux sensors EMP sensors still being refined for implementation without disruption of tests Inertia Cube Helmet Pressure Gage Vest Pressure Gage Data Acquisition System Cameras Camera Scale Charge Main Rm IronMan Hall IronMan Task Months from Start J F M A M J J A S O N D IRB Protocol Preparations Contract Award 1 Preparation Invitation Letter 1.1 Project Planning 1.2 Institutional Review Board Approvals 1.3 Test Subject Selection 1.4 Schedule Coordination with USMC 1.5 Test Equipment Acquisition 1.6 Logistics 1.7 Dry Run 2 Execution 2.1 Training Session #1 (June 6 through June 22) 2.2 Training Session #2 (September 5 through September 21) 3 Data Analysis 3.1 Post Processing of Individual Test Data 3.2 Statistical Analyses 3.3 Data Integration (Blind Reviews, Sessions #1 and #2) 4 Reporting and Communications 4.1 Reporting Kickoff Briefing Interim Briefing Data Report form Training Session Interim Briefing after Training Session Data Report form Training Session Interim Briefing after Training Session Final Briefing Status Reports (Monthly) Draft Final Report Final Report 4.2 Communications Instrumentation Coordination Telecons TT TTTT TTTT TT TTTT T Neurocognitive Evaluation Coordination Telecons T T T T T T Data Analysis Team Meetings TT TT TT TT T Telecon Solid Completed Clear To Be Done

29 Evaluation Techniques and Insights Vestibular/Auditory Neuro Imaging Human ALL STUDIES ARE NON INVASIVE Quantico, VA: Breacher Training Facility Personnel worn pressure gauges, inertial cubes and air samplers, and free field pressure gauges September measurements will add thermal flux sensors, EMP sensors Toxic Gas Loads on Personnel Neruoimaging T1/T2 weighted, FLAIR fmri Diffusion tensor Environment Standard USMC Breacher training exercises Neuro Behavior Computer based TBI testing Reaction time Mood affect Cognitive processing Clinical testing Clinical interviews PTSD/Brain injury scale scoring

30 Preliminary Results Pre Clinical Blast thresholds associated with increasing severities of injury are identified Limited* TBI: predominantly inflammation with no neuronal damage, can persist for many days/weeks, neurobehavior effects resolve over time Moderate TBI: neuron damage, functional deficits Severe TBI: widespread neuronal death, vasospasm, diffuse cerebral edema, significant deficits and death Clinical Standard USMC breacher training does not lead to TBI Below a threshold, repeated exposures can be tolerated without leading to TBI *Limited TBI may or may not be equivalent to mild TBI, a it is defined clinically.

31 Conclusion Explosive blast related TBI covers a wide spectrum The coupling of pressure waves to the brain is, in part, the cause The long term sequelae of explosive blast TBI has yet to be fully characterized