SUBMODULE 5.1. GENERAL CHARACTERISTICS OF MECHANICAL ASPHYXIA
Mechanical asphyxia is disorder of external respiration resulting from mechanical obstruction of airways.
The injuring factor is a mechanical effect preventing air supply to the lungs and causing hypoxia and hypercapnia.
Mechanism of death at mechanical asphyxia
There are several periods of mechanical asphyxia, which go as follows.
Preasphyxial period begins from the moment of cessation of air supply to the lungs until there is total lack of oxygen in the blood.
Inspiratory dyspnea period. Oxygen deficiency in the body activates the inspiratory part of the medullary respiratory center. This leads to loss of consciousness and pronounced physical inactivity which rules out self-rescue.
Expiratory dyspnea period. Carbon dioxide accumulation in the body activates expiratory part of the medullary respiratory center. Smooth muscle excitation combined with sphincter relaxation results in uncontrolled defecation, urination and ejaculation.
Short-time respiratory arrest. Carbon dioxide accumulation causes total dysfunction of the medullary respiratory center and respiratory arrest.
Terminal breathing period. Persistent hypercapnia stimulates excitation of the spinal cord respiratory center. The breathing movements are infrequent, irregular, and of varying depth.
Final respiratory arrest period. Excess of carbon dioxide results in exhaustion and paralysis of the spinal cord respiratory center. Irritation of the vagus nerve center, decreased blood pressure and slowed-down heartbeat following
the cardiac arrest finish the process of asphyxia. Single heart contractions are observed in 5-20 minutes.
Common features of asphyxia. Asphyxia resulting in death is characterized by several common morphological or rapid death features: