Pressure to the Neck and Asphyxia Deaths - Comprehensive Forensic Notes
Pressure to the Neck and Asphyxia Deaths
Introduction to Asphyxia
Asphyxia, from the Greek meaning 'absence or lack of pulsation,' now describes interference in oxygen transfer from air to cells.
This interference can be partial (hypoxia) or complete (anoxia).
Hypoxia - oxygen levels become alarmingly low
Anoxia - oxygen levels are at zero
In forensic medicine, asphyxia often indicates a physical obstruction from mouth/nose to alveoli, but can also refer to the inability to utilize oxygen at the cellular level even without airway obstruction.
The term is frequently misunderstood, leading to attempts to standardize classification of 'asphyxia-related deaths' in forensic practice.
Classification of Asphyxia
Multiple classification schemes exist for forensic aspects of asphyxia-related deaths, but no single system is formally adopted.
Figures 11.1 and 11.2 show examples of classification schemes, the latter based on pathophysiological criteria.
Key element: users and interpreters must understand the clinical and pathological relevance of each classification and how a case fits.
This chapter focuses on physical interference with blood oxygenation via airway occlusion or pressure on the neck/chest.
Compromised oxygenation due to immersion (drowning) or toxins (e.g., carbon monoxide) are discussed elsewhere.
Asphyxiants: gases, liquids, or solids that deprive the body of oxygen by displacing it from the lungs or interfering with hemoglobin transport/mitochondrial oxidative phosphorylation.
Mechanical Asphyxial Mechanisms (Figure 11.3)
Strangulation: pressure applied to the neck by ligature or hands (Figure 11.3b-d).
Hanging: pressure applied to the neck by ligature combined with body weight (Figure 11.3e).
Choking: physical obstruction within the airways.
Compression asphyxia: pressure applied to chest/abdomen, interfering with breathing.
Smothering: physical obstruction of mouth/nose.
Non-Mechanical Asphyxial Mechanisms
Carbon monoxide poisoning: chemical interference with respiration at cellular level.
Cyanide poisoning (Table 11.1).
Other asphyxiants.
Miscellaneous Asphyxial Mechanisms
Drowning: physical interference with respiration by a liquid.
Phases and Signs of 'Asphyxia'
Traditionally, forensic textbooks describe a stereotypical sequence of events following airway obstruction, but this description is of historical interest only.
Such a sequence is not relevant to all obstructive asphyxia events or specific to a particular event, and the pathophysiology remains incompletely understood.
Asphyxia Conditions and Terminology (Table 11.1)
Lack of oxygen in inspired air: Suffocation.
Blockage of external orifices (nose/mouth): Suffocation/smothering.
Blockage of internal airways: Gagging/choking.
Compression of internal airways: Strangulation/hanging.
Limitation of chest movement: Traumatic asphyxia.
Failure of oxygen transportation (e.g., carbon monoxide poisoning).
Failure of oxygen utilization (e.g., cyanide poisoning).
Failure to Supply of adequate amounts of oxygen (e.g., due to displacement of environmental oxygen by other gases; consumption of oxygen without replacement; confinement in sewers etc.): Asphyxia.
Failure to transfer oxygen from the environment into the blood (e.g., external/ internal obstruction in smothering, choking and hanging; extrinsic/intrinsic compromise of thoracic cage function in mechanical/ traumatic asphyxia or chest wall trauma; and reduced oxygen binding capacity of the blood in carbon monoxide toxicity).
Failure of transport of oxygen due to a breakdown in supply or uptake, or a problem with blood flow due to local vascular compression reducing cerebral blood flow (e.g., hanging and strangulation).
Failure of cells to take up oxygen (e.g., cyanide impeding cellular utilisation of oxygen by damaging enzyme systems - chemical asphyxia).
Complex cases/ combined mechanisms (e.g., drowning and hanging: combined venoarterial occlusion, upper airway obstruction from lifting of the tongue, and tracheal compression etc.).
Classic Signs of Asphyxia (Not Specific)
Petechial hemorrhages: in the skin of the face and in the lining of the eyelids.
Congestion and edema: of the face.
Cyanosis: (blue discoloration) of the skin of the face.
Right heart congestion and abnormal fluidity of the blood.
None of these signs is specific to 'asphyxia'.
Ambroise Tardieu believed petechiae (Tardieu spots) were pathognomonic of suffocation, but they are not.
They may be seen in congestive cardiac failure deaths.
Raised intravascular pressure in head/neck explains the first three signs; right heart congestion and fluidity of blood are less relevant.
Importance of Petechiae
Finding petechiae in the face/neck is most important to the forensic pathologist; requires an explanation.
Requires a careful search for evidence supporting 'pressure having been applied to the neck or chest' (Figure 11.4).
Additional nonspecific findings include congestion of viscera and petechiae (Figure 11.5).
Timeframe for Petechiae Development
Time to produce congestion and petechiae in a living victim is controversial, but generally accepted to be rapid, perhaps after 10-30 seconds of compression.
Absence of petechiae (caused by leakage of blood from vessels) means death may have occurred before they could be produced if death resulted from pressure to the neck.
Absence of petechiae does not exclude compression; important in criminal trials.
Forensic Pathologist Examination
In cases of assault resulting in death, examination by a forensic pathologist is required to identify subtle evidence.
Determining the nature of an asphyxial death can be very challenging and requires a detailed review of known pre-mortem events, death scene findings, autopsy findings, and results of other post mortem investigations, including toxicological analysis.
Asphyxial Insults and Outcomes
Asphyxial insults are not necessarily fatal.
The outcome depends on the insult's nature, degree, and length of time.
Survivors may suffer no significant long-term health effects, but prolonged oxygen deprivation may result in neurological sequelae or a persistent vegetative state due to irreversible hypoxic-ischemic brain injury.
Examination of Living Survivors
In a living survivor, examination, documentation, sampling (e.g., for DNA), and investigations (radiological imaging) optimize the recovery of forensically useful evidence.
Such an examination should be made by an experienced forensic physician at the earliest opportunity.
Additional injuries unrelated to the asphyxia mechanism may have forensic significance.
May require review by an otorhinolaryngologist (ENT specialist).
Cervical arterial injuries may also be documented, resulting in stroke.
Signs and Symptoms in Survivors
Hoarseness.
Stridor (noisy breathing).
Pain and tenderness around neck.
Damage to the larynx and cartilages.
Fracture to the hyoid bone.
Dried saliva around the mouth.
Cyanosis (in the immediate period after the attack).
Types of Mechanical Asphyxial Mechanisms: Pressure to the Neck
Three types: manual strangulation, ligature strangulation, and hanging.
Rate of death varies; may be relatively 'slow' with classic signs of asphyxia or rapid with absent signs.
Effects of Circumferential or Direct Pressure
Obstruction of jugular veins: impaired venous return, cyanosis, congestion, petechiae.
Obstruction of carotid arteries: cerebral hypoxia and collapse.
Stimulation of carotid sinus baroreceptors: neurologically mediated cardiac arrest (Box 11.2, Figure 11.6).
Elevation of the larynx and tongue: closing the airway at the pharynx.
Timeframe for Loss of Consciousness and Death
Loss of consciousness can occur rapidly, possibly by 10 seconds.
Sleeper holds (vascular neck restraint) can cause loss of consciousness in under 10 seconds.
Time to produce a fatal outcome is variable; filmed hanging analysis suggests lack of recognizable respiratory movements after ~2 minutes and lack of muscle movements after ~7.5 minutes.
Factors Affecting Outcome
Effects relate to physical pressure application.
Free divers can breath-hold for >10 minutes in static apnea.
Historic animal experiments: survival up to 14 minutes following obstructive asphyxiation.
Strangulation: Manual Strangulation
Pressure to the neck using hands (or forearms/limbs).
Relatively common mode of homicide.
External Signs
Bruises and abrasions: front and sides of the neck, lower jaw.
Pattern of skin injuries is often difficult to interpret due to the dynamic nature of assault.
The signs are more pronounced in survivors or fatalities where death was not immediate.
Injury Patterns
Rounded or oval-shaped bruises (up to ~2 cm) from fingertip pressure.
Fingernail scratches: linear or crescent-shaped abrasions, imprints, or skin breaches.
Injuries can be inflicted by the assailant or victim.
'The Barleycorn Public House Murder' (Box 11.3)
Example illustrating challenges in interpreting injury patterns and determining the amount of pressure exerted.
Strangulation: Ligature Strangulation
Homicidal, suicidal, or accidental.
Pressure to the neck by an item, constricting the neck (e.g., scarf, neck-tie, belt, tights, cable tie) (Figure 11.9).
Signs
Clear demarcation of congestion, cyanosis, and petechiae above the ligature.
Ligature mark: compression and abrasion of the skin, reflecting the nature of the ligature.
Precise documentation (measurement/photography) of the ligature mark may enable comparison with putative ligature.
Wide or soft ligatures may leave little evidence of compression.
Considerations
Marks may encircle the neck horizontally; clothing/hair may cause discontinuities.
Marks may suggest crossover/knots, but no pattern suggesting a suspension point (distinguishing from hanging).
Post mortem: ligature marks are frequently seen as brown parched bands.
Accidental and suicidal ligature strangulation do occur, but homicide must be excluded.
Other Methods of Applying Pressure
Restraint techniques involving force to the neck (e.g., vascular neck restraint, choke-hold, sleeper hold, arm-lock).
Potential for fatality.
Investigations into deaths following police/security service contact often involve evaluation of potential effects of restraint techniques used prior to death.
Such techniques may or may not result in asphyxial signs or neck injury.
Many law-enforcement bodies prohibit these techniques.
The 'Choking Game'
Non-suicidal, non-autoerotic self-strangulation by adolescents to experience euphoria.
Unquantifiable risk of fatality.
Injury to Soft Tissue and Skeleton
Extent of injury varies depending on pressure applied.
Post mortem dissection should be carried out after 'drainage' of the vasculature to avoid artefactual hemorrhage (Figure 11.10).
Bruising within 'strap muscles' and injury to superior horns of thyroid cartilage are common (Figure 11.11).
Suspected fractures should be confirmed microscopically; triticeous cartilage mobility can simulate fractures.
Greater horns of the hyoid bone may also be injured, albeit less frequently than the thyroid cartilage.
Radiological techniques are effective at identifying injuries in the deceased.
Calcification/ossification of hyoid bone and thyroid cartilage occurs with age, making structures more prone to injury.
Internal neck injuries are commonly less extensive in ligature strangulation.
Case Example: 'The Disappearing Bruise' (Box 11.4)
1929 Sidney Fox case highlights the need for photographic documentation and microscopy of critical injuries.
The case illustrates the potential for misinterpreting post mortem discoloration as a bruise, known as the Prinsloo-Gordon artefact.
Hanging
Suspension of the body by the neck; material forms a ligature.
Pressure is produced by body weight.
Complete suspension is not necessary.
Ligature mark is commonly present but discontinuous at some point around the neck.
Discontinuity reflects suspension point (sides, back, or front of the neck).
If the ligature mark rises at the sides, forming an inverted V-shape at the back, the suspension point was at the back of the head (Figures 11.12 and 11.13).
Mechanism of Death
Multifactorial: venoarterial occlusion, upper airway occlusion, tracheal compression.
Absence of classical asphyxia signs suggests rapid death, raising the possibility of carotid sinus pressure and neurogenic cardiac arrest.
Judicial Execution
Involves a drop calculated to result in cervical spinal cord injury and fracture-dislocation of the cervical spine, without decapitation.
Internal Injuries
Internal injury to neck structures is frequently inconspicuous or absent in non-judicial hangings.
Other Considerations
Non-judicial hanging is frequently a suicidal act of males.
Accidental hangings can occur (e.g., entanglement with cords).
Homicides can be staged to resemble suicide.
Toxicological analysis should be performed to determine the individual's capacity for self-suspension.
Case Example: Controversial Hanging Death (Box 11.5)
The Gilfoyle case raises questions about staged homicides.
Sequelae in Survivors
No adverse sequelae, hypoxic brain damage, motor/sensory loss.
Breathing attempts with a blocked upper airway raise intrathoracic pressure, leading to pneumomediastinum and cervical emphysema.
Autoerotic Asphyxia
Fatalities occurring during solitary sexual activity involving neck compression, cerebral hypoxia, and heightened sexual response.
Terms: sexual asphyxia, sex hanging, asphyxiophilia, Kotzwarrism, autoasphyxiophilia, hypoxyphilia.
Deaths generally involve men and result from failure of safety devices or misjudgment.
Features Suggestive of Autoerotic Asphyxia
Evidence of solo sexual activity.
Private/secure location.
Evidence of previous similar activity.
No apparent suicidal intent.
Unusual props (ligatures, clothing, pornography).
Failure of a device causing death.
Additional Factors
Death often results from pressure to the neck.
Presence of classic asphyxia signs is variable.
Gags or asphyxiant substances may lead to suffocation.
Injuries suggestive of assault must be carefully investigated, and third-party involvement considered.
Obstruction or Occlusion of the Airways
Choking, suffocation, and smothering involve obstruction of the upper air passages.
Choking: Accidental ingestion of objects or food causes internal obstruction.
Bolus Obstruction
An object/substance impacted in the pharynx or larynx below the epiglottis.
Common causes: misplaced dentures, inhaled toys/marbles.
Medical practice risks: sedated/anesthetized individuals may experience airway occlusion without protective reflexes.
Law-enforcement: deaths occur when individuals attempt to swallow drug packages.
Obstruction leads to respiratory distress with congestion and cyanosis.
Cafe Coronary
Complete upper airway obstruction by a food bolus, often meat.
Sudden onset simulates acute myocardial infarction.
Large food bolus prevents breathing, speech, and coughing.
The individual may die silently and quickly, and the cause of death remains hidden until autopsy (Figure 11.14).
Suffocation and Smothering
Suffocation: A fatal reduction of oxygen concentration in the respired atmosphere, and often incorporates smothering.
Reduction can occur in decompressed aircraft cabins or grain silos.
Mechanical Obstruction
Plastic bags placed over the head (accidental, homicidal, or suicidal) (Figure 11.15).
Post mortem examination rarely reveals classic asphyxial signs.
Smothering
Physical occlusion of the nose and mouth may leave no asphyxial signs in survivors or the deceased.
Lack of Struggle
Extremes of age/intoxication may prevent struggle, resulting in no evidence of injury.
Findings
Intraoral injury (bruising, abrasion, laceration) and soft tissue dissection may reveal subcutaneous bruising (As with manual strangling, smothering may be very difficult to diagnose at post mortem examination).
Retained items/objects used to smother may have evidential value.
Saliva/DNA matching may corroborate accounts.
Pressure to the Chest or Abdomen
Compressional and positional asphyxia can result in an inability to breathe effectively.
Compressional Asphyxia
Trunk pressure (chest/abdomen) leads to breathing difficulty and death.
Examples: Workmen trapped in trenches, buried in grain silos, or crushed during events.
Traumatic/crush asphyxia is common in such situations (Box 11.6).
Positional/Postural Asphyxia
Awkward body position prevents breathing effectively.
Examples: Squeezing through railings, hanging head first over a bed.
Law-enforcement settings: Restraint in positions that prevent adequate breathing.
Those involved are usually unable to extricate themselves because of intoxication or misinterpretation of struggle as resistance.
Controversy exists regarding restraint techniques, particularly securing arms behind the back in a face-down position.
Such deaths rarely involve restraint in isolation but occur with exertion, substance misuse, and mental health problems.
The course of death represents a culmination of adverse physiological factors, making the determination of the cause of death challenging.
Restraint techniques must minimize positional asphyxia risk.
Neurological Impairment
Individuals with neurological disease can succumb to positional asphyxia.
Diagnostic criteria:
1. The deceased is discovered in a position that prevents adequate breathing/respiration (including confined positions, flexion of the head on the chest, partial or complete external airway compression, and neck compression).
2. An examination of the scene, and a review of the circumstances suggest that the deceased placed her/himself in that position, and that there is no evidence of the involvement of another individual.
3. The deceased could not remove her/himself from the position in which they were found (due to, for example, the effects of alcohol/drug intoxication, or a neurodegenerative disorder).
4. There is no evidence of internal obstruction of the airways e.g., by aspirated food or a poorly chewed impacting food bolus.
5. There is no evidence of carbon monoxide toxicity or any other suffocating gas inhalation.
6. There is no evidence of significant natural disease which could, on its own, provide an explanation for death.
The diagnostic criteria can be seen in Box 11.7.
Bethnal Green Tube Disaster
During WWII, civilians sought shelter in underground stations during bombing raids.
Panic during a siren led to a crush on a dark staircase, killing 173 people.
Autopsies attributed death to compression asphyxia, but pathologist Keith Simpson noted changes inconsistent with prolonged asphyxia, suggesting rapid death.