Asphyxia (Gr.), literally 'pulselessness,' but usually applied to the condition resulting from the blood in the body no longer being brought into the proper relations to the atmospheric air by respiration, so as to allow a sufficiently free exchange of carbonic acid for oxygen (see RESPIRATION). Asphyxia, or suspended respiration, may result from several causes. No air, or but a scanty supply, may be admitted, as in strangulation, drowning, choking, or disease in the windpipe; the chest may be prevented from expanding either from a superincumbent weight or paralysis, as when a man breaks the upper part of his neck above the phrenic nerve, thus paralysing the diaphragm; and again, although there may be every capacity for respiration, the air itself may be in fault, and contain too little oxygen or too much carbonic acid in proportion to other elements. Aquatic animals may be asphyxiated either by depriving the water they inhabit of oxygen, or impregnating it with excess of carbonic acid.
When from any of the above causes asphyxia occurs, the respiratory movements become quicker and more forcible than normal, and additional muscles are brought into action till the respiratory acts merge in general convulsions. Meanwhile consciousness has been lost; the blood, unable to circulate freely through the lungs in consequence of its imperfect oxygenation, accumulates in them, in the right side of the heart, and in the veins, and the skin becomes livid. The short convulsive stage is followed by one of comparative quiescence, in which respiratory efforts more natural in appearance are made, but become slower and weaker till they stop altogether. The heart continues to beat feebly for a short time after all other movements have ceased.
After death the blood is very dark in colour. It remains fluid, or nearly so, and consequently gravitates very readily to the part of the body which happens to be most dependent. The right side of the heart is found distended with fluid blood, the left nearly empty. The lungs are usually, though not always, much congested.
In man death occurs in from a minute and a half to five minutes after complete deprivation of oxygen. Some persons, no doubt, as the Ceylon divers, can by habit do without a fresh supply of air for a longer period; and some diving animals have an arrangement of blood-vessels by which they are enabled to be under water for a long time. Restoration of asphyxiated persons may be attempted with hopes of success at a very long period after apparent death. The object of all methods is of course to fill the lungs with fresh air. For a description of these, see RESPIRATION (ARTIFICIAL).