In this article, Mechanical Engineer & Biomechanics Expert, Dr. Carolyne Albert explains the ways in which brain hypoxia can occur as a result of mechanical forces and reviews the questions that a biomechanical analysis can answer in a legal dispute.
The Biomechanics of Oxygen Deprivation to the Brain – Expert Overview
Tissues, such as the brain, require oxygen to survive and function. Brain hypoxia is a condition in which brain cells are not supplied sufficient oxygen. Some medical conditions (e.g., pneumonia, bronchial asthma, or chronic obstructive pulmonary disease) have been associated with a risk of hypoxia, but brain hypoxia can also result from mechanical causes, such as:1,2
- Airway obstruction by inhalation of a foreign object
- External obstruction of the mouth and nose
- Compression of the chest or abdomen restricting respiratory movements
- Compression of the neck
Biomechanics is the science that deals with the response of the body to external or internal forces. Injuries, such as brain anoxia, can result from specific forces applied on the body. A competent biomechanical engineer can apply fundamental principles of physics and engineering to the evidence of a case to investigate the forces experienced during an event, and how these forces compare to those necessary to cause a claimed diagnosed injury.
During normal breathing, coordinated forces from the diaphragm and muscles of the ribcage (intercostal muscles) move air in and out of the lungs cyclically. During inhalation, these muscles contract to expand the thoracic cavity, which decreases the air pressure in the lungs and results in air flow through the airways (nose or mouth, pharynx, larynx, and trachea) and into the lungs (Figure 1). During exhalation, these muscles relax allowing the lungs to return to their unstretched size. Inside the lungs, oxygen diffuses from small air sacs (alveoli) into adjacent blood capillaries, from which oxygen is delivered to tissues through the circulatory system.
Compression of the chest, e.g., from the torso being trapped under a heavy object or wedged between objects, can interfere with volumetric expansion of the thoracic cavity and impair breathing. Impaired breathing can reduce or stop air flow into the lungs and result in hypoxia from a low oxygen content in the blood (hypoxemia).
Compression of the neck, e.g., from an inappropriate chokehold maneuver or the neck pressing against an object, can obstruct airways resulting in hypoxemia and/or obstruct blood flow to the brain. The brain obtains its oxygenated blood supply from the internal carotid arteries and the vertebral arteries. The internal carotid arteries originate from the common carotid arteries and make their way to the brain through the base of the skull (Figure 2). The common carotid arteries are located at the left and right sides of the anterior aspect (front) of the neck. Pressure applied to the common carotid arteries can reduce blood flow and oxygen supply to the brain.3
In some situations, hypoxia occurs when a person is immobilized in a position that obstructs their airways and/or interferes with respiratory movements. This type of situation is sometimes called positional asphyxia. Young children and other individuals with limited motor skills are at risk of positional asphyxia due to their inability to reposition themselves if their airways become obstructed. For example, a position in which an infant’s head is flexed (bent forward) onto its chest can cause severe airway narrowing.4
Injury Causation Disputes
A biomechanical analysis applies fundamental principles of engineering and physics, knowledge of anatomy and physiology, and fundamentals of tissue mechanics to investigate the cause of injuries in a variety of situations. In a legal dispute involving mechanically induced brain hypoxia, a biomechanical engineer can investigate the cause of the injury and questions such as:
- What was the position and orientation of the person during the incident?
- How did that person come to be in that position?
- What were the forces acting on the person’s body?
- What anatomic structures were compressed and/or otherwise deformed by those forces?
- How were the type and direction of force necessary to cause oxygen deprivation generated?
- How much force was necessary to result in the oxygen deprivation?
Complementary Practice Areas in Causation Disputes
Depending on the fact pattern of your case, it may be beneficial to involve an expert in another practice area to address questions of liability. Experts in fields such as supervision, product liability, premises safety, police practices, and others often work alongside our biomechanical engineers to provide a comprehensive forensic approach to the matter at hand. Contact us or submit an inquiry to be connected with the expert(s) most suited to your case.
Biomechanical Engineering Investigations
Biomechanical experts at Robson Forensic offer a scientific approach to injury causation analysis in a variety of contexts, including motor vehicle collisions, sports and recreation injury, workplace injury, and falls. Our biomechanical experts can apply their understanding of injury biomechanics together with principles of physics with and engineering to determine whether an injury is consistent with the physical evidence and descriptions of an event.
For more information, contact the author of this article or submit an inquiry.
Mechanical Engineer & Biomechanics Expert
Dr. Albert is a mechanical engineer with expertise in pediatric and adult orthopedic biomechanics, and materials engineering. She is an adjunct research professor at Marquette University with over 15 years of experience in biomedical and materials engineering research. She has presented her research at national and international scientific conferences, and her work is published in the Journal of Biomechanics, Bone, Clinical Biomechanics, and the Journal of Bone and Joint Surgery.
- Bhutta BS, Alghoula F, and Berim I. Hypoxia. [Updated 2021 Aug 7]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2001 Jan-.
- Sauvageau A and Boghossian E. Classification of asphyxia: the need for standardization. Journal of Forensic Sciences, 2010:55(5), p.1259-1267.
- Mitchell JR, Roach DE, Tyberg JV, Belenkie I, and Sheldon RS. Mechanism of loss of consciousness during vascular neck restraint. Journal of Applied Physiology 2012:112, p.396-402.
- Tonkin SL, Vogel S, Bennet L, and Gunn AJ. Positional upper airways narrowing and an apparent life threatening event. N Z Med J. 2002;115: 193–194