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Mechanical asphyxia — hanging, strangulation, airway obstruction and chest compression
Mechanical asphyxia covers situations in which an external force prevents oxygen supply — pressure on the neck (hanging, ligature strangulation, manual strangulation), obstruction of the mouth and nose or the airway, and compression of the chest — and the autopsy findings depend on the mechanism and are sometimes minimal, so the scene and circumstances are essential.
Why it matters in the exam
The exam tests the difference between a hanging mark and a ligature-strangulation mark and the meaning of petechial haemorrhages. In hanging the mark rises obliquely towards the knot, does not encircle the whole neck, usually lies above the thyroid cartilage and becomes dry and hard like parchment; livor concentrates in the lower limbs. In complete hanging, where pressure also occludes the arteries, the face is usually pale and petechiae are few. In ligature strangulation the mark is horizontal, encircles the whole neck, lies lower, and above it there is facial congestion and many petechiae in the conjunctivae and facial skin, because the veins are occluded before the arteries.
Manual strangulation shows small crescent-shaped fingernail abrasions (also from the victim trying to pull the hand away), round fingertip bruises, haemorrhage in the neck muscles on layered dissection and sometimes fractures of the horns of the hyoid bone or thyroid cartilage; in young people bones and cartilages are flexible, so fractures are less common. Petechiae are not specific to asphyxia: they also occur with vomiting, resuscitation, heart failure and deep livor in the head.
Chest compression (traumatic asphyxia), as in a crowd crush on stairs or under a heavy weight, causes bluish congestion of the face and neck above the compressed area, many petechiae and sometimes a sharp line between the congested and the pale area. Positional asphyxia occurs when the body is trapped in a position that prevents breathing, mainly with intoxication, and in prone restraint with pressure on the back. Obstruction with a plastic bag or a pillow may leave no sign at all, so the scene is decisive.
Key points
- Hanging: an oblique mark rising to the knot.
- Ligature strangulation: a horizontal encircling mark with congestion and petechiae.
- Manual strangulation: fingernail abrasions, round bruises, sometimes a hyoid fracture.
- Chest compression: congestion above the compressed area.
- Petechiae are not specific; the scene is decisive.
Summary table
| Mechanism | Mark on neck or body | Petechiae | Additional finding |
|---|---|---|---|
| Hanging | Oblique, rising to knot, above thyroid cartilage, dry | Few in complete hanging | Livor in legs and hands |
| Ligature strangulation | Horizontal, encircling, lower | Many, with facial congestion | Haemorrhage in neck muscles |
| Manual strangulation | Fingernail abrasions, round bruises | Usually many | Hyoid and thyroid fractures, less often in the young |
| Chest compression | Bluish congestion above the compressed area | Very many | Crowd crush, heavy weight |
| Mouth and nose obstruction | Sometimes none | Variable | The scene is decisive |
A free exam question
בנתיחת צעיר שהופנה לבדיקה בחשד לניסיון אובדני , נמצא בקיבה גוש אפרפר הנראה כמורכב מעשרות טבליות .בטפטוף ברזל כלורי (Ferric Chloride) על אחת הטבליות , פני השטח שלה הפכו לסגלגלים-כחולים . אילו מהממצאים הבאים לא צפוי להימצא בנתיחה ובבדיקות העזר? (the question as examined, in Hebrew)
- א. פטכיות בקרום הנסיובי (סרוזה )של האיברים הפנימיים
- ב. ריכוז מינימלי שנחשב כקטלני- 500 מ"ג/ליטר
- ג. כיב קטן ברירית הקיבה שבאה במגע עם טבליה
- ד. נמק מרכזי בכבד
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Sources
- Knight's Forensic Pathology, 4th edition (2016) — Suffocation and asphyxia; fatal pressure on the neck
- Spitz and Fisher's Medicolegal Investigation of Death, 5th edition (2020) — Asphyxia
- Sauvageau A, Boghossian E. Classification of asphyxia, Journal of Forensic Sciences, 2010 — Proposed classification
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.