Page:Encyclopædia Britannica, Ninth Edition, v. 20.djvu/495

RESPIRATION 477 Normal Respiration. If the naked body of a person asleep or in perfect inactivity be carefully watched, it will be found that the anterior and lateral Avails of the chest move rhythmically up and down, while air passes into and out of the nostrils (and mouth also if this be open) in correspondence with the movement. If we look more closely we shall find that with every uprising of the chest walls the membranous intercostal portions sink slightly as if sucked in, while at the same time the flexible walls of the abdomen bulge as if protruded by some internal force. If respiration be in the slightest degree hurried these motions become so marked as to escape the attention of no one. The elevation of the chest walls is called inspira- tion, their depression expiration. Inspiration is slightly shorter than expiration, and usually there is a slight pause or momentary inaction of the chest between expiration and the following inspiration. Apparatuses for measuring the excursion of a given point of the chest wall during respiration are called thoracometers or stethometers. Appa- ratuses for recording the movements of the chest are called stetkograp/is or pneumographs. Frequency of Respiration. The frequency of respiration during perfect rest of the body is 16 to 24 per minute, the pulse rate being usually four times the rate of respiration ; but the respiratory rhythm varies in various conditions of life. The following are the means of many observations made by Quetelet : at the age of one year the number of respirations is 44 per minute ; at 5 years, 26 ; from 15 to 20 years, 20; from 25 to 30, 16; from 30 to 50, 18'1. Muscular exertion always increases the frequency of respira- tion. The higher the temperature of the environment the more frequent is the respiration. Bert has shown that with higher atmospheric pressures than the normal the frequency of respiration is diminished while the depth of each inspira- tion is increased. The frequency of respiration diminishes until dinner time, reaches its maximum within an hour of feeding, and thereafter falls again ; if dinner is omitted, no rise of frequency occurs. The respiratory act can be inter- rupted at any stage, reversed, quickened, slowed, and vari- ously modified at will, so long as respiration is not stopped entirely for more than a short space of time ; beyond this limit the will is incapable of suppressing respiration. Depth of Respiration. The depth of respiration is measured by the quantity of air inspired or expired in the act ; but the deepest expiration possible does not suffice to expel all the air the lungs contain. The following measure- ments have been ascertained, and are here classified accord- ing to the convenient terminology proposed by Hutchinson. (1) Residual air, the volume of air remaining in the chest after the most complete expiratory effort, ranges from 100 to 130 cubic inches. (2) Reserve or supplemental air, the volume of air which can be expelled from the chest after an ordinary quiet expiration, measures about 100 cubic inches. (3) Tidal air, the volume of air taken in and given out at each ordinary respiration may be stated at about 20 cubic inches. (4) Complemental air, the volume of air that can be forcibly inspired over and above what is taken in at a normal inspiration, ranges from about 100 to 130 cubic inches. By vital capacity, which once had an exaggerated importance attached to it, is meant the quantity of air which can be expelled from the lungs by the deepest possible expiration after the deepest possible inspiration ; it obviously includes the complemental, tidal, and reserve airs, and measures about 230 cubic inches in the Englishman of average height, i.e., 5 feet 8 inches (Hutchinson). It varies according to the height, body weight, age, sex, position of the body, and condition as to health of the subject of observation. Vital capacity is estimated by means of a spiromcter, a grad- uated gasometer into which air may be blown from the lungs. The residual air, which for obvious reasons cannot be actually measured, may be estimated in the following way (Harless, Grehant). At the end of ordinary expiration, apply the moutk to a mouth-piece communicating with a vessel filled with pure hydrogen, and breathe into and out of this vessel half a dozen times until, in fact, there is reason to suppose that the air in the lungs at the time of the experiment has become evenly mixed with hydrogen. Then ascertain by analysis the proportion of hydrogen to expired air in the vessel and estimate the amount of the air which the lungs contained by the following formula : =p : 100; where V=volume of air in the lungs at the time of experiment, u= volume of the vessel containing hydrogen, p = proportion of air to hydrogen in the vessel at the end of the experiment. V, then, is the volume of air in the lungs after an ordinary expiration ; that is, it includes the residual and the reserve air ; if we subtract from this the amount of reserve air ascertained by direct measurement, we obtain the 100-130 cubic inches which Hutchinson arrived at by a study of the dead body. Volume of Respiration. It is clear that the ventilation of the lungs in ordinary breathing does not merely depend on the quantity of air inspired at each breath, but also on the number of inspirations in a given time. If these two values be multiplied together we get what might be called the volume of respiration (Athmungsgrosse, Eosenthal) in contra- distinction to depth of respiration and frequency of respira- tion. Various instruments have been devised to measure the volume of respiration, all more or less faulty for the reason that they compel respiration under somewhat ab- normal conditions (Rosenthal, Gad, Panum, Bering). From the data obtained we may conclude that the respiratory volume per minute in man is about 366 cubic inches (6000 cubic centim.). In connexion with this subject it may be stated that, after a single ordinary inspiration of hydrogen gas, 6-10 respirations of ordinary air must occur before the expired air ceases to contain some trace of hydrogen. Types of Respiration. The visible characters of respira- tion in man vary considerably according to age and sex. In men, while there is a moderate degree of upheaval of the chest, there is a considerable although not preponderating degree of excursion of the abdominal walls. In women the chest movements are decidedly most marked, the excur- sion of the abdominal walls being comparatively small. Hence we may distinguish two types of respiration, the costal and the abdominal, according to the preponderance of movement of one or the other part of the body wall. In forced respiration the type is costal in both sexes, and so it is also in sleep. The cause of this difference between men and women has been variously ascribed (a) to con- striction of the chest by corsets in women, (6) to a natural adaptation to the needs of childbearing in women, and (c) to the greater relative flexibility of the ribs in women per- mitting a wider displacement under the action of he inspiratory muscles. Certain Concomitants of Normal Respiration. If the ear be placed against the chest wall during ordinary respiration we can hear with every inspiration a sighing or rustling sound, called "vesicular," which is pro- bably caused by the expansion of the air vesicles ; and with every expiration a sound of a much softer sighing character. In children the inspiratory rustle is sharper and more pronounced than in adults. If a stethoscope be placed over the trachea, bronchi, or larynx, so that the sounds generated there may be separately communicated to the ear, there is heard a harsh to-and-fro sound dur- ing inspiration and expiration which has received the name of " bronchial." In healthy breathing the mouth should be closed and the ingoing current should all pass through the nose. When this happens the nostrils become slightly expanded with each inspiration, probably by the action of the M.