A Practical Physiology: A Text-Book for Higher Schools

by Albert F. Blaisdell

The visible movements of breathing vary according to circumstances. In infants the action of the diaphragm is marked, and the movements of the abdomen are especially obvious. This is called abdominal breathing. In women the action of the ribs as they rise and fall, is emphasized more than in men, and this we call costal breathing. In young persons and in men, the respiration not usually being impeded by tight clothing, the breathing is normal, being deep and abdominal.

Disease has a marked effect upon the mode of breathing. Thus, when children suffer from some serious chest disease, the increased movements of the abdominal walls seem distressing. So in fracture of the ribs, the surgeon envelops the overlying part of the chest with long strips of firm adhesive plaster to restrain the motions of chest respiration, that they may not disturb the jagged ends of the broken bones. Again, in painful diseases of the abdomen, the sufferer instinctively suspends the abdominal action and relies upon the chest breathing. These deviations from the natural movements of respiration are useful to the physician in ascertaining the seat of disease.

212. The Nervous Control of Respiration. It is a matter of common experience that one’s breath may be held for a short time, but the need of fresh air speedily gets the mastery, and a long, deep breath is drawn. Hence the efforts of criminals to commit suicide by persistent restraint of their breathing, are always a failure. At the very worst, unconsciousness ensues, and then respiration is automatically resumed. Thus a wise Providence defeats the purpose of crime. The movements of breathing go on without our attention. In sleep the regularity of respiration is even greater than when awake. There is a particular part of the nervous system that presides over the breathing function. It is situated in that part of the brain called the medulla oblongata, and is fancifully called the “vital knot” (sec. 270). It is injury to this respiratory center which proves fatal in cases of broken neck.

From this nerve center there is sent out to the nerves that supply the diaphragm and other muscles of breathing, a force which stimulates them to regular contraction. This breathing center is affected by the condition of the blood. It is stimulated by an excess of carbon dioxid in the blood, and is quieted by the presence of oxygen.

Experiment 108. To locate the lungs. Mark out the boundaries of the lungs by “sounding” them; that is, by percussion, as it is called. This means to put the forefinger of the left hand across the chest or back, and to give it a quick, sharp rap with two or three fingers. Note where it sounds hollow, resonant. This experiment can be done by the student with only imperfect success, until practice brings some skill.

Experiment 109. Borrow a stethoscope, and listen to the respiration over the chest on the right side. This is known as auscultation. Note the difference of the sounds in inspiration and in expiration. Do not confuse the heart sounds with those of respiration. The respiratory murmurs may be heard fairly well by applying the ear flat to the chest, with only one garment interposed.

Experiment 110. Get a sheep’s lungs, with the windpipe attached. Ask for the heart and lungs all in one mass. Take pains to examine the specimen first, and accept only a good one. Parts are apt to be hastily snipped or mangled. Examine the windpipe. Note the horseshoe-shaped rings of cartilage in front, which serve to keep it open.

Experiment 111. Examine one bronchus, carefully dissecting away the lung tissue with curved scissors. Follow along until small branches of the bronchial tubes are reached. Take time for the dissection, and save the specimen in dilute alcohol. Put pieces of the lung tissue in a basin of water, and note that they float.

The labored breathing of suffocation and of lung diseases is due to the excessive stimulation of this center, caused by the excess of carbon dioxid in the blood. Various mental influences from the brain itself, as the emotions of alarm or joy or distress, modify the action of the respiratory center.

Again, nerves of sensation on the surface of the body convey influences to this nerve center and lead to its stimulation, resulting in a vigorous breathing movement. Thus a dash of cold water on the face or neck of a fainting person instantly produces a deep, long-drawn breath. Certain drugs, as opium, act to reduce the activity of this nerve center. Hence, in opium poisoning, special attention should be paid to keeping up the respiration. The condition of the lungs themselves is made known to the breathing center, by messages sent along the branches of the great pneumogastric nerve (page 276), leading from the lungs to the medulla oblongata.