- results from exchange of energy between object and human body, without intrusion of the object through the skin
- most common cause of trauma death and disability.
- energy exchange results in crush, tear, stretch injuries below the skins surface
- branch of physics dealing with objects in motion and energy exchanges that occur as these onjects collide.
- The two basic principles of kinetics
- laws of inertia
- energy conversation
- Newtons first law
- bodies in motion will remain in motion unless acted upon by an outside force; bodies at rest will remain at rest unless acted upon by an outside force
Energy & Energy Conservation
- Energy is defined as the ability to do work
- Energy can neither be created or destroyed
- Newton’s second law
- states that force strength is related to an objects weight (mass) and the rate of its change in velocity.
Force = Mass x Acceleration (or deceleration) / 2
- the energy of an object in motion
- it is a function of the objects mass and velocity.
KE = Mass(weight) x Velocity(speed)2 /2
Biomechanics of Trauma
- is the investigation of the injury process
- examines kinetic energy forces as they progress from body’s exterior to the internal organs and structures
- bound by lawas of physics: inertia, force, and energy conservation
- occurs as blunt object abruptly halts a portion of the body while inertia causes the remaining anatomy to continue in motion
- results in one tissue or organ being pushed into another, compressing it and damaging small blood vessels, connective tissues, and cell structures within.
- opposite of compression
- protein fobers that hold tissues together are pulled and injured or torn
- happens when tissues are pulled away from one another
- Hollow organs filled with fluid/air stretch laterally as pressure brings anterior and posterior walls of organ together (ie plastic bag under foot)
- occurs alon the edges of the impacting force or at organ attachments
- 34,500 deaths annually
- Events of impact - 4 major collisions in MVA
- Vehicle Collision
- Body Collision
- Organ Collision
- Secondary Collisions
- *Additional Impacts
- begins when vehicle strikes (or is struck) by another object
- vehicles KE (kinetic Energy) causes damage as it converts to heat and mechanical energy
- 2nd Collision in MVA
- occurs when occupants within vehicle strike interior of vehicle
- Occupants KE is transformed into initial tissue deformity
- restraints and safety features work to decelerate occupants and impact strength
- Occurs as occupants body collides and tissues within body collide into one another
- Causes compression, stretching, tearing and shearing.
- occurs when vehicle occupant is impacted my objects traveling within vehicle
- objects continue to trave at vehicles initial speed
- occur when vehicle recieves a second impact
- can be from deflection into other objects or struck by other vehicles in the accident
- can cause new injuries or further the seriousness of those already recieved
Restraints: Seat Belts
- prevents occupants continued independent movement during collision
- lessesns the chance for ejection
- helps slow occupants with vehicle
- if lap belt is worn too high, abdominal compression, and spinal fractures to T12 - L2 may result
- if worn too low - hip dislocation may take place
- does not provide protection for head and neck movement
Restraints: Supplemental Restraint Systems (SRS)
- aka: Airbags
- extreemely effective for initial frontal collisions but not susequent/secondary collisions
- residue from airbag deployment may cause irritation but can be relieved with gentle irrigation
- always check for dash and steering wheel deformity
Restraints: Child Safety Seats
- <2yrs children should be placed in rear seat facing backward
- >2yrs seated forward in mini seat facing forward
- children in adult’s lap are not protected during collision
Restraints: Head Rests
- designed to prevent unopposed reward motion during rear-end collision
- protects agains violent backward head rotation and neck extention - Whiplash injury
- Intrusion suggests increased KE may have reached the patient
- Intrusion associated with lateral impact is frequent due to reduced crumple zone
- Lateral impact has very high occupant mortality
Types of auto impacts
Frontal - 62%
Lateral - 23% - higer mortality rate
Rear-End - 7%
Collision: 4 Modes of patient travel
- up and over
- down and under
- lap and shoulder belts help occupant decelerate with the vehicle
- Limits interior impact and energy associated with it
- occupant tenses legs in prep. for impact causing upper body to pivot forward and up
- steering wheel can cause femur fx
- steering wheel decelerates abdominal contents causing hollow-organ rupture and liver laceration
- increased abdominal pressure can cause diaphram to rupture
- lower chest may fx and become flail
- head impacts windshield = soft tissue, facial fx’s, and internal bleeding
- head striking windshield may result in hyperextention/hyper flexion or axial loading - as Cervical vertebrae collapse or compress
- a large proportion of vehicular deaths are attributed to up and over
compression force on the c-spine resulting in collapse of vertebral column support elements
- unrestrained occupant slides downward as vehicle comes to stop
- knees striking dash absorb initial impact resulting in knee, femur, hip dislocations and fractures
- Upper body then contact the lower steering wheel (higher on chest than up-and over)
- Resulting injuries: flail chest, blunt cardiac trauma, aortic tears
- If neck strikes steering wheel, tracheal and vascular injury may result
- Paper-Bag Syndrome may cause pneumothorax and pulmonary contusion
Paper Bag Syndrome
- As driver antipates impact they takes deep breath
- during collision aschest strikes steering wheel, pressure in chest results from compression of chest.
- resulting in pneumothorax and pulmonary contusions
- The up and over pathway may lead to ejection of unrestrained occupant
- victim experiences two impacts:
- contact with interior of vehicle
- impact with environment
- responsible for 27% of vehicular deaths
- most commonly associated with frontal impact of unrestrained occupant
- modern vehicle design to absorb impact forces
- collapse happens more gradually
- reduces forces expressed onto occupants
- “T-Bone” - 90 degree impact
- greater likelihood of intrusion
- higer percentage of fatality
- typical injuries
- lateral fx of ribs (instead of anterior)
- diphram rupture
- pulmonary contusion
- head turns toward impact, vertebrae fx due to rapid lateral, twisting motion
- skull strikes side window
- splenic injury to driver
- liver injury to passenger
- heart like head, due to poor attachment in thoracic cavity, moves toward impact, can cause Aortic dissection or delamination of intima
- vehicle is struck at an angle: left-front, right-front, right-rear, left-rear
- most likely to induce rotation
- injuries are generally less serious due to deflection
Rear End Impact
- collision force pushes the auto forward
- body propells forward with vehicle; neck rotates backward; when vehicle comes to rest, neck snaps forward creating “whip-lash” injury
- proper placement of head rest mitigates backward snapping motion
- improper placement of head rest can cause extreme hyperextension and hyperflexion
- normally caused by change in elevation or affecting vehicles with high centers of gravity
- commonly results in ejection or partial ejection of occupants
- initial injuries are compounded by subsequent impacts
Vehicle Collision Analysis
- vehicle hazards : oil, hot fluids, caustic substances, jagged objects, gasoline
- traffic, weather
Vehicle Collision Analysis : Hybrid Vehicles
- risk of electrocution: current ranges between 36 & 550 volts
- unexpected movement: silent electric propulsion may engage - remove proximity FOB (>16ft) or ensure ignition is off
Vehicle Collision: Evaluate factors
- relative sizes of impacting vehicles or objects
- occupant interior impacts
- deformed steering wheel
- dented dash
- deformities of pedals = feet ankle injuries
- restraints used
- position of head rests
Vehicle collision analysis: intoxication
- consider possibility of drugs or alcohol
- 50% of fatals involve intoxication
- may be hard to differentiate between AMS and intoxication
- evidence of attempt to stop?
Blunt Trauma to head and body cavity accounts for ___% of vehiculat mortality.
pay particular attention to ABC’s
look carefully at areas where your index of suspicion suggests injury
- How did objects collide?
- From what direction did they come?
- What Speed were they traveling?
- Similar sized?
- Secondary Collisions?
- Wet pavement/poor visibility?
- Windshield? Bloody/star shaped? Penetrated by patients head?
- Steering Wheel Collapsed/deformed?
- Dash Dented?
- Seatbelts/SRS systems/Head rests?
- Frontal - head on
- Bike dips down, throwing rider up and forward
- handlebars catch lower abdomen/pelvis; femur fx wehn higher trajectory
- Angular - oblique angle
- riders lower extremity is trapped between bike and object struck
- can result in crushed or open wounds to femur, knee, ankle or foot
- Sliding - lays bike down (experienced rider)
- bike absorbs initial impact
- reduces chance of ejection
- increased abrasions, minor lacerations
- Ejection - commonly most serious
- injuries due to collisions with bike, object, ground
- skull/head injury
- spinal fractures
- internal thoracic
- abdominal injury
- extremity fxs
- helmets reduce incidence and severity by 50%
- leathers protect against soft tissue injuries, but hide underlying contusions, fxs, and internal injuries
Pedestrian Collisions: Adult vs Pedi
- Adults turn away - laterally to oncoming vehicle
- Initial Impact is low on body resulting in tib/fib fxs,
- Legs then displaced resulting in lateral knee ligamental injuries
- Lateral upper body crashes onto hood resulting in femur fx’s, lateral chest injuries, and upper extremity injuries
- Victim then slides up toward windshield where possible head, neck, and shoulder injuries.
- Further injuries or complications of other injuries may be caused by striking ground
- children typically turn toward the vehicle
- injuries higher up on body; bumper strikes femurs or pelvis
- due to lower center of gravity children are usually thrown infront of the vehicle and run over or pushed to the side
- if child is thrown upward injuries will be similar to an adult
Off Road Collisions : Snowmobiles
- injuries similar to autos but with out restrain systems
- limited crumple zones for impact absorption
- typically result in
- crush - secondary to rollover
- glancing blows from obstructions
- head & neck trauma from hidden wires
- collisions with autos, other snowmobiles, stumps or rocks
- Trauma often complicated by cold exposure and hypothermia
Off Road Collisions : Watercraft
- typically result of impact with other watercraft or obstructions
- not designed to absorb impact or provide passenger restraint
- serious injuries despite lower speeds than autos
- potential for complications due to drowning, boat sinking and hypothermia (water draws heat from body 20x faster than air
Off road collisions : ATV’s
- injuries similar to motorcycles and snowmobiles
- inexperienced riders
- capeability to travel off-road at fast speeds
- high center of gravity = likelihood of roll over
- expected injuries include:
- upper/lower extremity fxs
- head & spine injury
- most common form of blunt trauma
- increased risk in young or elderly
- a fall is the release of stored gravitational energy
- Newton’s second law: the more rapid the deceleration the greater the force and resulting injury
- Feet first falls transfer energy through: calcaneus, tiba, femur, pelvis, lumbar spine
- the lumbar spine is especially prone because it is the only skeletal component suporting the entire upper body
- If person attemps to break fall with outstretched arm injuries may include
- wrist, choulder, and clavicle injuries
- A backward fall may result in
- pelvic, thoracic, or head injury
- classified as a fall of 3x heigth
- 20 feet in adults
- 10 feet in children
- focus attention of potential internal injuries; rapid decelleration causes organs to be compressed, displaced, and twisted
- ie ligamentum arteriosum rupture = exsanguination
Criteria for evaluating a fall
- fall heigth
- anatomic point of impact
- force of impact
- impact surface
- transmission pathway of forces through skeleton
- fracture sites
- possible internal injuries
Geriatric fall considerations
- increased age =
- decreased coordination
- muscle & bone strength
- bones may break during normal activities
- sometimes a break may cause a fall; rather than a fall that causes a break
- Consider circumstances of fall and patients preexisting medical conditions
Blast Injuries : Explosion
- occurs when an agent or environment combusts
- Conventional explosion = fuel and oxidizing agent combine instantaneously
- Heat from the breakdown/restablisment of chemical bonds creates a pressure differential between agent and surrounding air.
- This heat & pressure differential produces several MOI
- pressure wave
- blast wind
- displacement of persons near blast
- As combustible agent ignites it superheats surrounding air, increasing the pressure of the exploding cloud
- The rapid increase in pressure compresses adjacent air, repeating as it gets further away from ignition point creating a pressure wave.
- This thin wave (blast overpressure, moves slightly faster than speed of sound) results in breif but drastic increase then decrease in air pressure
- When explosion occurs in confined space, ie bus, or interior of building, confined space aids in rapid pressure release and enhances potential for injury and death
- Water is a noncompressible medium that transmitts the blast overpressure efficently and aids in compression, decompression injuries, (water increases lethal range of blast 3 fold
- overpressure does not affect fluid or sold organs, however it does compress/decompress air in air filled organs
- eardrums/bowels, sinuses, and lungs
- as well as TBI
- Lying on ground with feet toward blast will aid in lessening effects of pressure wave
- travels just behind pressure wave
- lasts longer than pressure wave
- outward mvmt of air and gases from epicenter
- causes much less damage but may displace debris or victims
- military ordnance, pipe bomb or container that bursts apart form during an explosion
- flechettes on military missles and ordnance help keep the projectile on-track
- IED’s are often filled with scraps of metal, nails, ballbearings, and screws that become projectiles when blast takes place
- debris from a blast may be powerful enough to remove limbs or cause serious open wounds
- The overpressure and blast wave may be powerful enough to physically propel victims away from the blast’s epicenter
- Personnel then become projectiles which seffer blunt and penetrating trauma from impact with ground, other objects, debris or other o personnel
Confined Space Explosions & Structural Collapse
- because the pressure wave radiates outward in all directions, the energy disipates quickly
- in a confined space, because pressure wave is contained, it maintains it’s energy longer
- pressure waves are reflected off surfaces and when they meet overpressure greatly increases
- the structure also adds debris and collapse elements to the explosion resulting in penetrating, blunt and crush injuries
- structural collapse makes extrication difficult for rescuers and difficult to locate victims
- additional hazzards include: additional collapse, electrocution, fire, secondary explosion of leaking gas or fuel.
- explosions produce tremendous heat
- flash burns for those close to detonation may produce superficial or partial thickness burns
- blast may ignite combustable materials such as clothing and and debris which are typically more extensive burns
Types of Blast Injuries
- primary blast injuries are caused by the heat of the explosion and the overpressure weave
- pressure injuries are the most serious and life-threatening because they damage air filled spaces: ears, sinuses, bowel, and lungs
- burns are limited unless caused by a secondary combustion (clothes or fuels collateral to the blast)
Types of Blast Injuries
- secondary blast injuries are caused by projectiles
- may be more severe than primary blast injuries
- may range further than blast wave
- may cause multiple penetrations and cause severe bleeding
Types of Blast Injuries
- Tertiary injuries include thase resulting from personnel displacement and stuctural collapse
- Victims displaced may suffer blunt and penetrating trauma from being thrown
- When structural collapse is involved crush injuries may be present
- Crush injuries may cause soft, skeletal, nervous, vascular, and organ destruction.
Types of Blast Injuries
- include any other injuries caused by explosion mechanism
- include: Crush Injuries, burns, asphyxia, toxic exposures, and exacerbations of preexisting conditions or chronic illness
Blast Injury Assessment
- If possible, determine if blast was result of terrorism. Be suspicious of other explosive devices
- be aware of radiological (dity bomb) potential
- evaluate the scene for secondary hazards: gas leaks, electrical wires, sharp debris, and further structural collapse
- implement incident command and employ disaster triage focusing on most severly injured
- Most common injury in an explosion is lung injury
- anticipate lung injury with any significant blast injury
- High index of suspicion for anyone with hearing loss or epistaxis
- monitor lungs for crakles or respiratory congestion
- consider O2 and early airway protection
- Hearing loss can produce anxiety, reassure patients
Blast Injury Care: Lungs
- most frequent life-threatening pressure injury
- extreme pressure ruptures the alveolar walls resulting in inflammation, fluid accumulation, hemorrhage, and even air directly into bloodstream
- Fluid accumulation makes lungs less elastic and air movement more difficult
- If air directly enters the capillaries it can create emboli that travel to heart and brain causing stroke like symptoms, MI or death
- Patient may have progressively worsening crackles, dyspnea, or hemoptysis
- If necessary to ventilate be aware: PPV may push air into the vascular system and create emboli or push air into pleural space causing pneumothorax
- If possible place patient in Left lateral recumbant position with head slightly down to discourage air traveling up the carotid to the brain
Blast Injury Care: Abdomen
- blast wave may also damage the air filled bowel causing possible hemorrhage and rupture
- Rupture leads to peritonitis
- Abdominal compression may push abdominal contents out of penetrating wounds resulting in abdominal evisceration
- Be alert for S&S of shock; provide rapid transport and fluid resuscitation is necessary
Blast Injury Care: Ears
- Eustachian tube provides a mechanism for equalizing small atmospheric pressure changes
- Rapid pressure changes rupture tympanic membrane or fracture hearing bones resulting in acute hearing loss
- Hearing loss is frequently temporary, but can be permanent
- commonly produced by: extreme exertion, fatigue, or direct trauma forces
- injuries can be secondary toacceleration/deceleration, compression, rotation, hyperextension, or hyperflexion
- injuries leave behind soft tissue damage to the skin, muscle, connective tissue, tendons, ligaments, skeletal long bones, spinal coulmn, and internal injuries to solid or hollow organs
- If collision results in any LOC, ensure individual is evaluated by emergency department
- Protective gear reduces chance for significant injury by can be contributing factor in injury: cleats locked to turf when struck; helmet difficulty to assess cspine
- athletic trainers knowledge of athlete and common injuries can be valuable resource
- may result from structural collapse, or in industrial or agricultural injury where limb is caught in machinery
- hemorrhage may be internal, external or mixed
- compounded if crushing force is left in place for extended period of time causing anerobic metabolism and tissue death
- release of toxins when blood flow returns may causecardiac arrhythmias or serious damage to the kidneys
- Pre hospital care may include: sodium bicarb abd other meds to combat acidosis, limit damage and improve kidney function
- Blunt trauma to a large muscle mass like calf, thigh, forearm or arm, may cause the muscle to swell more quickly than the connective (fascial) tissue that contains it can accomidate
- The pressure inside the fascial tissue limits the blood flow to muscle tissue
- Surgical treatment of fasciotomy is used to alleviate pressure within compartment
- pain that is disproportional may present within 3-4 hours and is indicative of this injury
The first tissue of the body to experience the effect of trauma is _____?
The most common cause of blunt trauma is ___?
A physical energy exchange from an object or surface transmitted through the skin into the body’s interior describes ______.
As you double the speed of an object, its ability to cause trauma is ______.
In determining the potential for trauma caused by an object, you need to examine (3 things).
The objects Speed, weight, and stopping distance.
Examples of solid organs are _______.
Blunt trauma cancreate internal injuries from organ movement within the body cavities. Which organ can be lacerated by the ligamentum teres?
The ligamentum teres hepatis (round ligament) represents the remnant of the fetal umbilical vein. The round ligament therefore only exists in mammals. Prenatally and for a month or two after birth, the umbilical vein is patent, subsequently degenerating to fibrous tissue, the round ligament.
- divides the left part of the liver into medial and lateral sections
The draining of blood to the point at which life cannot be sustained is called _________.
Air bags work much differently than seat belts and are extremely effective for ______crashes.
The childs _____makes protection in vehicle crashes difficult.
Frontal impacts produce four pathways of patient travel. Injuries in the down and under pathway most commonly include ________.
The ______ pathway accounts for over half of the deaths in vehicular crashes.
When a _____ impact occurs, the index of suspicion for serious and life-threatening internal injuries must be higher than vehicle damage alone suggests.
The anatomic region most commonly injured in the rear-end impact is the _______.
Blasts create overpressure waves that move outward from the explosion source. As an overpressure wave passes by the human body, a brief byt drastic increase in air pressure occurs. Because of this, the paramedic needs to concentrate assessment on possible ________ injuries.
hollow organ injuries
In trauma associated with a blast, assessment should include a high index of suspicion for _________.
When a patient has respiratory compromise due to a blast injury, forceful ventilation can create ______.
If possible transport in Left lateral Recumbant with head slightly downward to discourage emboli from traveling to brain.
In crush injuries, toxins released into the central circulation can cause ________.
The study of impact is related to a branch of physics called
The anticipation of injuries based upon the analysis of the collision mechanism is referred to as the
index of suspicion
T/F Penetrating trauma is the most common type of trauma associated with patient mortality.
F - Blunt Trauma is
The tendency of an object to remain at rest or remain in motion unless acted upon by an
external force is
Two autos accelerate from a stop sign to a speed of 30 miles per hour, the first one by normal
acceleration and the second when it was struck from behind by another vehicle. Assuming that
both vehicles have the same weight, which vehicle gained the most kinetic energy?
Both vehicles gained the same kinetic energy.
Which of the following is an example of energy dissipation from an auto accident?
A. Sound of the impact
B. Bending of the structural steel
D. Internal injury to the occupant
C. Heating of the compressed steel
E. All of the above
E. All of the above
Which of the following increases the kinetic energy of an object most quickly?
The temperature of the object
Increasing object mass
Increasing object speed
Decreasing object mass
Decreasing object speed
Increasing object speed
Blunt trauma may cause
rupture of the bowel
contusion of the liver or kidneys.
bursting of the alveoli.
crushing of blood vessels.
What are common causes of blunt trauma?
In which order do the events of an auto collision usually occur?
T/F - The major effect of the seat belt during the auto collision is to slow the passenger with the auto.
A supplemental restraint system (SRS) refers to what?
What restraint systems is likely to induce hand fractures?
Driver-side air bags
T/F - While less convenient than a child carrier, holding a child in the arms is relatively safe except
in the most severe of crashes.
The type of auto impact that occurs most frequently is?
Which type of auto impact occurs least frequently?
The down-and-under pathway is most commonly associated with which type of auto collision?
T/F - When analyzing the lateral-impact injury mechanism, you must assign a higher index of
suspicion for serious life-threatening injury than with other types of impact.
What injuries are associated with significant lateral impact?
T/F - With oblique impacts, the seriousness of injury is often less than vehicle damage would suggest.
The most common injury associated with the rear-end impact is to the
head and neck
What are hazzards hazard commonly associated with auto collisions?
Sharp glass or metal edges
Downed power lines
T/F - With modem vehicle construction that incorporates crumple zones, you can dependably use
the amount of vehicular damage to approximate the patient injuries inside.
In fatal collisions, about what percentage of the drivers are legally intoxicated?
The most common body area associated with vehicular mortality is the
In motorcycle accidents, the highest index of suspicion for injury should be directed at the
Use of a helmet in a motorcycle crash reduces the incidence of head injury by about
T/F - In an auto-versus-child pedestrian accident, you would expect the victim to turn toward the impact.
T/F - In addition to the danger of trauma, the boating collision patient is also likely to suffer possible
hypothermia and drowning.
Severe injury is generally associated with a fall from
three times the patient’s own height.
What are mechanisms that can cause patient injury in a blast?
The pressure wave
The patient being thrown into objects
Underwater detonation of an explosive generally increases its lethal range by
T/F A victim’s orientation to the blast does not affect the nature and severity of the injuries he
sustains from an explosion.
The arrow-shaped projectiles in military-type explosives that are designed to extend the injury
power of a bomb are called
T/F - When victims are within a structure that contains an explosion, such as a building, the effects
of the blast are concentrated and the severity of the expected injuries increases.
Which of the following are secondary blast injuries?
A. Heat injuries
B. Pressure injuries
C. Projectile injuries
D. Injuries caused by structural collapse
E. Both A and B
C. Projectile Injuries
T/F - If you suspect that a blast was a terrorist act, you should be cautious of secondary explosive
devices intended to injure rescue personnel.
The most serious and common traumas associated with explosions affect the
T/F - When ventilating the victim of a severe blast, you should use forceful deep ventilations with
the bag-valve mask because doing this will ensure good chest expansion.
Sports injuries are frequently caused by
The capacity to do work is termed
T/F - Blunt trauma does not cause injury beneath the skin.
Auto collisions account for about what number of deaths each year?
Places the events of an auto collision in the order in which they occur?
What advancements have played a substantial role in reducing highway-collision-related deaths?
Passenger air bags
Driver air bags
T/F - The seat belt is very effective at reducing injuries related to intrusion into the auto passenger compartment.
What are some injuries that air-bag inflation may cause?
The up-and-over pathway is most commonly associated with which auto collision type?
T/F - When analyzing the frontal-impact injury mechanism, the paramedic should assign a higher
index of suspicion for serious life-threatening injury than with other types of impacts.
The type of injury most commonly associated with the rear-end impact is
T/F - When you encounter the intoxicated patient, the mechanism of injury analysis becomes even
The helmet reduces the incidence of head injury by about what percent?
T/F - In the auto/adult pedestrian collision, you would expect the victim to turn away from the impact.
T/F - In the terms of physics, a fall is nothing more than the release of stored gravitational energy.
T/F - A victim standing and facing the epicenter of a blast is more likely to sustain serious injury than a
victim lying on the ground with his feet toward the blast epicenter.
T/F - Shrapnel is small, arrow-like objects within a bomb casing that extend its injury potential and range.
What are primary blast injuries?
Heat & Pressure Injuries
T/F - The closer a victim was to the blast epicenter, the higher should be the paramedic’s index of
suspicion for more serious injuries.
T/F - Ear injuries associated with an explosion, even those affecting as much as one-third of the
eardrum with a tear, may improve with time.
Sports injuries are frequently associated with what mechanisms?