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Respiration

a part of the life of all organisms, animal and vegetable. It is a series of chemical changes, the first of which is the absorption of oxygen into the body, and the last of which is the excretion of carbonic acid. The association of this intake of oxygen and excretion of carbonic acid with the same organs, the lungs, is due to the fact that both the food stuff and the waste stuff are gases, and not to any immediate connection between them. Necessarily any organ adapted to the diffusion of a gas from the air into the blood must also be adapted for the diffusion of a gas from the blood into the air; that is, supposing that the living membrane, of which the lung essentially consists, which separates the air from the blood, acts, so far as the diffusion of gases is concerned, as a dead membrane; even if it has any effect arising from the fact of its being a living membrane it is probable that it will behave in a similar way to both the ingoing and outgoing gases. The respiration of plants comes under the head of vegetable physiology, and the general relation of the function of respiration to the other bodily functions, under physiology.

In all animals in which the parts of the body are nourished by the circulation of a stream of food material, the blood, there must always be two distinct sets of processes to consider: (1) the maintenance of the blood in a normal state, by the supply of fresh food matter from time to time, and by the elimination of waste matter; (2) the nutrition of the individual tissues and cells of the body by the blood stream.

Applying this to the function of respiration, we shall have to consider (1) the manner in which oxygen is supplied to the blood and carbonic acid gas removed from it; (2) the manner in which the cells are able to take oxygen out of the blood and cast into it their useless carbonic acid; also the changes that take place within the cells between the intake of the oxygen and the output of the carbonic acid. These two sets of processes are usually described as the outer and the inner, or tissue, respiration. Some writers include in the term outer respiration the absorption of oxygen by the cells from the blood, and the excretion of carbonic acid into the blood, and restrict the term inner respiration to the actual changes that take place within the cells. It is evident that outer respiration corresponds to the processes of digestion and absorption to which food materials other than gaseous are subjected.

Structure of Respiratory Mechanism.- This mechanism consists of the lungs, a series of minute air chambers with a network of capillaries in the wall, the air passages from the air chambers of the RESPIRATION lungs to the outer air, and the chest walls with their muscles, which act like bellows and change the air in the lungs. The essentials of structure that a lung must possess have already been emphasized.

The simplest lung that we can imagine would be an elastic membranous bag, well supplied with blood vessels, and with a pipe connecting it with the air; the most complicated that exist are essentially of that construction, the complications that occur having for their object merely the enlarging of the surface exposed to the air. Let us begin with the air passages.

There are first the nose and mouth; these join the upper part of the gullet, known as the pharynx. From the pharynx arises the windpipe (trachea); this passes through the voice box (larynx) into the chest cavity; there it divides into two passages (the bronchi); the bronchi go on dividing again and again, generally into two; the ultimate divisions (the bronchioles) open into clusters of air chambers. The air chambers are about 1/100 inch in diameter. It has been estimated that there are some 725,000,000 of them, and that their total surface is about 2,000 square feet. The walls of the air chambers are formed of a thin membrane in which the blood and lymph capillaries ramify. Minute openings lead from the air chambers into the lymph spaces of the membrane. The membranous walls are partly formed of elastic tissue. It is this. that gives to the lungs their elasticity.

The larger air passages (trachea and bronchi) are kept open by horseshoeshaped plates of cartilage; muscles stretch between the poles of the horseshoe, complete the ring, and permit the size of the passages to vary, at the same time resisting over-distention when the internal pressure rises. These larger air passages are lined by a mucous membrane, containing mucous glands; the innermost layer is a ciliated epithelium; the cilia lash upward, and thus keep the passages free from mucus and remove foreign particles. As the passages become smaller they lose their cartilages, and the muscles form a continuous circular layer.

The lungs are invested by a membrane (the visceral pleura). At the root of the lungs this membrane is continuous with a membrane which lines the chest cavity (the parietal pleura). The space between the two is the pleural cavity; it is in reality a large lymph space, and communicates with the lymphatics of the pleura. Owing to the air pressure within the lungs the two pleuræ are closely pressed together, the lungs entirely filling the chest cavity.

The ordinary respiratory movements differ in the two sexes and at different periods of life. In young children the RESPIRATION chest is altered in size chiefly by the movements of the diaphragm, and the protrusion of the abdominal wall during inspiration is therefore very marked. In men also it is the diaphragm which is chiefly operative, but the ribs are also moved. In women it is the movement of the ribs, especially the upper ones, which is the most extensive. The respiratory rhythm is the relation of the acts of inspiration and expiration to each other as regards time. The number of respirations in a healthy person is about 14 or 18 per minute; it is greater (nearly double) in childhood. It varies according to circumstances, exercise, rest, health, disease, etc.; in disease it may fall as low as seven or rise to 100.

Though all the muscles concerned in the movements of breathing are voluntary muscles-i. e., can be made to contract by an act of will-yet respiration is normally an entirely involuntary act. This is obvious from the fact that during sleep, or during absence of consciousness caused in any way, respiration goes on as well as during wakefulness. Further, though we may at will breathe or cease to breathe, yet we cannot by any effort of the will suspend the respiratory movements for longer than at most a few minutes at a time.

History. Aristotle (384 B. C.) thought that the object of respiration was to cool the body. He observed that the warmer the animal the more rapid the breathing, and transposed cause and effect. Galen (A. D. 131-203) experimented on the mechanics of respiration, and knew something of the nervous mechanism. He believed that "soot" and water were excreted from the body by the lungs. Malpighi (1661) described the structure of the lungs. Van Helmont (1664) discovered carbonic acid; Black (1757) observed that carbonic acid is breathed out of the body. Priestley (1774) discovered oxygen. Lavoisier (1775) discovered nitrogen, found the composition of the air, and taught that the formation of carbonic acid and water resulted from the combustion that took place in the lungs. Vogel proved the existence of carbonic acid in the venous blood; Hoffman found oxygen in arterial blood. Magnus extracted and analyzed the gases of the blood in both states.

Artificial Respiration. When death is imminent owing to a cessation of the natural respiration movements, it may sometimes be averted by an imitation of them carried on regularly for some time. The methods fall into three divisions: (1) insufflation, or blowing of air into the lungs, either by the mouth or by means of bellows; (2) manual methods, in which external manipulations of the chest walls REST HARROW are made to effect the entrance and exit of air; (3) electrical stimulation of the respiratory muscles. In all cases where artificial respiration is required every moment is of importance. In Silvester's method the patient is laid on his back on a plane, inclined a little from the feet upward, and the shoulders are gently raised by a firm cushion placed under them, which also throws the head back.

The operator then grasps the patient's arms just above the elbows, and raises them till they nearly meet above the head.

This action imitates inspiration. The patient's arms are then turned down, and firmly pressed for a moment against the sides of the chest. A deep expiration is thus imitated. In Howard's method the patient is laid on his back with a cushion below the middle. The operator kneels astride his hips, places his hands with fingers spread outward over the lower part of the chest wall, and alternately bends forward, throwing his weight on the chest to imitate expiration, and springs back to allow the elastic recoil of the chest wall to imitate inspiration.

Whatever method be adopted, the movements must be gentle, regularly, and perseveringly carried on, at the rate of from 10 to 15 times in the minute. In all cases, but especially in that of persons apparently drowned, artificial respiration should be conducted in a warm atmosphere, 90° F., or even more if possible, and should be supplemented by warmth applied to the body and by vigorous friction. In other modes of death by suffocation, such as choking or strangulation, the action of the heart may continue longer, and restoration to life be therefore possible after a longer deprivation of air. See DROWNING.