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shock heating mechanism of blast
- -cause by passage of shock front (initial disturbance of air) through the air
- shock front heats the air to 1000s of degrees
- -primary cause of burn injuries from blast, not fireball, which is actually the coolest part of the explosion
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impluse
- -main parameter that correlates to damage done by the blast
- -pressure/time
- -you can graph the pressure and see it spike, decay and then go slightly negative, area under the curve is the impulse
- -**better predictor of injury than peak pressure**
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blast signature
- -positive and negative phase of pressure
- -signature is graph showing impulse
- -most blast signatures are complex, not "free field", due to reflections of waves off surfaces
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reflected blast pressure
- -reflected pressure is greater than incident pressure, greater than the "predicted" blast pressure, because you add reflected to normal
- -the biologically relevant pressure
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Categories of Blast Injury
- primary: cause by direct blast energy
- secondary: projectiles from the blast
- tertiary: from being propelled by blast and hitting something
- quaternary: other- inhalation, burns
*all happen together
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Bowel and Blast injury
- most susceptible
- -edema, hemorrhage, laceration and ruptuer
- -progress to perforation
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Solid Organs and Blast Injury
- liver and kidney
- -more resistant than gas containing organs
- -lacerations and fractures
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Lungs and Blast Injury
- -leading cause of death
- -gas exacerbates injury ( like bowel)
- -cause by barotrauma, compression then decompression, putting alveoli under tension, either rupturing them or damaging membranes, causing fluid leakage --eduma and hemorrhage
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Heart and Blast Injury
- -air emboli leading to infarcts
- -bruising can occur
- -myoelectric disruption
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Identifying Blast Lung Injury
- -respiratory difficulty
- -one side worse then the other
- -crackles
- -decrease oxygen sat
- -see fluid in lungs on radiograph
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Head and Blast Injury
- Ear: not lethal, but low threshold of injury
- Eye: a secondary blast problem
- Brain/CNS: more sensitive than previously thought, skull is not rigid, blast wave coupling a concern
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Transient Neurotrauma Effects
- -apnea, bradycardia, hypotension
- - can be fatal if left alone**
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Acute Neurotrauma Effects
- -edema, pial hemorrhage, increased ICP
- "blast brain"
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Chronic Neurotrauma Effects
-degenerative cascade leading to injured/dead axons, neurons, astrocytes
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Near-Term Post Blast Systemic Physiology
- Traid of Vagally Mediated Transient Symptoms:
- 1. HR drop
- 2. O2 sat drop
- 3. respiratory rate drop
--then the values recover
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