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Medical Education Division |
Operational Medicine 2001
Field Medical Service School
Student Handbook
INJURY
MECHANISMS FROM CONVENTIONAL WEAPONS
FMST 0424 06 DEC 99
TERMINAL LEARNING OBJECTIVES: 1. Given the injury mechanisms from conventional weapons, identify the human body’s response to injury from conventional weapons, per the references. (FMST. 04.24) ENABLING LEARNING OBJECTIVES 1. Without the aid of references, given a list, select the correct statement which explains the energy exchange process between a projectile and the human body, per the student handbook. (FMST.04.24a) 2. Without the aid of references, given a list, select the correct definition of cavitation, per the student handbook. (.04.24b) 3. Without the aid of references, given a list, select the types of cavitation, per the student handbook. (FMST.04.24c) 4. Without the aid of references, given a list, select the correct definition of a low velocity missile, per the student handbook. (FMST.04.24d) 5. Without the aid of references, given a list, select the correct definition of a high velocity missicle, per the student handbook. (FMST.04.24e) 6. Without the aid of references, given a list, select the damage to the body caused by a low velocity missile, per the student handbook. (FMST.04.24f) 7. Without the aid of references, given a list, select the damage to the body caused by a high velocity missile, per the student handbook. (FMST.04.24g) OUTLINE: THE
ENERGY EXCHANGE PROCESS The amount of damage to the human body caused by a projectile depends on the amount of kinetic energy transferred to the tissue and the area of the body it penetrates. Of these two factors, the amount of kinetic energy that is transferred to the tissue is the greatest indicator of potential damage. The amount of kinetic energy transferred to the tissue by a given mass is more a factor than the mass. A high-velocity bullet of a small mass has the potential to cause more damage than a knife of larger mass. The kinetic energy formula explains why:
Kinetic Energy = (Mass_x_Velocity x Velocity) / 2 Translation: The size of the projectile is unimportant, what is important is the speed at which the projectile contacts the body part. The greater the speed the more potential there is for damage. CAVITATION Definition: Cavity left by projectile as it passes through the tissues in the body. Explanation: As a projectile contacts and passes through the body it imparts motion to the tissue in its tract, and these fly off radially, imparting their momentum in turn to the surronding tissue. The particles of tissue moving away from the projectile track, even after the projectile has passed, must then form a vacuum or cavity. This cavitation is the basis of the explosive effects. The enormous extent of the cavity or vacuum thus formed depends soley upon the velocity of the tissue moving outward from the track of the bullet. A wound consist of a permanent cavitation the hollow path left by the projectile as it cuts through the body (this is what we see when we treat the wound). It also has the surrounding tissue that was stretched by a temporary cavitation, the size of the temporary cavity is determined by energy transfer the larger the energy transfer the larger the wound (this is what we do not see because it takes place first).
AK 47. This was the standard rifle used by the
communist forces in Vietnam and is used today very widely throughout the world.
The long path through tissue before marked yaw begins (about 25 cm) explains the
clinical experience that many wounds from this weapon resemble those caused by
much lower velocity handguns. HIGH AND LOW VELOCITY MISSILES The amount of energy impacting the body is determined by the mass, size and velocity of the missile. Velocity is the primary factor which determines the energy that a missile expends. The terms "high velocity" and "low velocity" are arbitrary with a dividing line from 2,000 to 2,500 feet per second. Most commonly, 2,000 feet per second is the dividing line and will be used throughout this course of instruction. A. LOW-VELOCITY MISSILES 1. DEFINTION-Any missile traveling at less than 2,000 feet per second ie.Knives, bayonets, bullets, rocks, sticks, glass, etc. 2. DAMAGE- No significant energy is transferred to tissues, therefore only local tissue is damaged and only minimal debridement is required. B. HIGH-VELOCITY MISSILES 1. DEFINTION- Projectiles traveling faster than 2,000 feet per second. The single most important thing to understand is that they are totally different from wounds that you may have previously encountered. The amount of damage sustained will vary greatly depending on the individual characteristics of each missile and its angle of impact. 2. DAMAGE a. The damage will correspond to the density of the involved tissues. b. Muscles will be severely damaged. c. Lung tissue will be minimally damaged. d. Tissues of varying density (fascia or bone) may divert missile direction resulting in a bizarre wound tract. e. A permanent wound tract will occur - damage not immediately apparent on first observation. f. A large cavity 30 to 40 times the size of the missile is created within the body. g. Even more damage occurs when bone is fragmented and acts as secondary missiles. h. Cavity formation disrupts tissue, ruptures blood vessels and nerves, and may fracture bones away from the missile path. i. Adjacent tissues are hurled forward, laterally, and then backwards. j. Exit wounds are usually larger than entrance wounds. NOTE: High and low velocity missile wounds vary from simple closed contusions to devastating open wounds with a physical appearance that will mislead you into believing that the extent of the injury is minimal, but is actually extensive STUDENT REFERENCES Textbook of Military Medicine Part1 Volume 5 Trauma Nursing Core Course Field Medical Service School
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