Lack of oxygen in the blood from the air or a violation of its utilization in the body itself causes oxygen starvation.
Oxygen starvation of organs and tissues - anoxia until complete cessation of oxygen uptake, determined by the term "hypoxia".
Hypoxia is one of the most important pathogenic and tanatogennyh factors for various diseases and extreme conditions, and therefore is a universal medical problem. Currently, it is customary to distinguish at least 6 types of hypoxia, developing due to various reasons:
1) exogenous hypoxia occurs due to a decrease in the partial pressure of oxygen in the inhaled air;
2) respiratory hypoxia develops due to respiratory diseases, and more often from mechanical obstructions;
3) circulatory - occurs due to hemodynamic disturbances, as a rule, in relation to diseases of the cardiovascular system;
4) hemic - it is the consequence of reducing the oxygen capacity of the blood, abundant blood loss, blood diseases or blockade of hemoglobin to form carboxyhemoglobin, methemoglobin, etc .;
5) tissue - occurs due to a violation of biological oxidation processes, that is most pronounced when exposed to cyanide ;
6) mixed hypoxia is observed most often as a result of a combination of the above-mentioned pathogenetic mechanisms.
The pace of development is divided into acute hypoxia that develops and leads to death in a matter of seconds or minutes, subacute (a few hours), chronic - lasting for months or even years. In forensic practice, the most common form of acute respiratory hypoxia that occurs as a result of mechanical obstacles that have long called mechanical asphyxia.
In most mechanical obstacles to respiration originate from external factors, but in some cases they may be caused by diseases (diphtheria, laryngeal edema, glottic spasm or bronchial compression or closure airway tumor et al.).
Based on the nature of mechanical factors, constitute an obstacle to breathing and the peculiarities of their impact, distinguish different kinds of mechanical asphyxia.
Asphyxia from compression: 1) strangulation - asphyxia due to compression of the neck (hanging, strangulation noose, strangling hands); 2) compression asphyxia (from compression of the chest and abdomen).
Asphyxia from closing holes and respiratory tract: 1) obturazionnaya (by closing the mouth and nose openings, closing the airways foreign bodies, from the closing fluid airway drowning ); 2) aspiration - from the closing of the respiratory tract food and vomit, blood.
In forensic practice in the first place in frequency should asphyxia from compression of the neck loop or hands, other types of apnea are much rarer.