Anatomy and Physiology of Respiratory Organs

SECTION I. PRELIMINARY POINTS PERTAINING TO THE ANATOMY AND PHYSIOLOGY OF THE RESPIRATORY APPARATUS. Tue study of diseases affecting the respiratory apparatus involves, as a point of de organs, and functions which this apparatus embraces. To this ture, acquaintance with the several structures, pre- paratory knowledge it is presumed, of course, the reader has already given more or less attention; but it will be useful to review certain points pertaining to the anatomy and physiology of this portion of the organism, which will be found to have direct and intimate patho- logical relations. To these points this section will be mainly limited, omitting details other than those of special importance in their bear- ings on the subjects to be subsequently considered. The respiratory apparatus comprises Ist, the thoracic parietes, inclusive of the diaphragm; 2d, the pulmonary organs contained within the thoracic cavity ; 3d, the canal or tube leading from the lungs to the pharynx, consisting of the primary bronchi and their subdivisions, the trachea, and larynx. The throat, mouth, and nasal passages, although involved in respiration, are rather adjuncts of the respiratory apparatus than constituents of it, their construction having more direct reference to other functions. 2 18 ANATOMY AND PHYSIOLOGY. I. Tue Troractc Parretes. The portion of the skeleton called the thorax is composed of the l vertebrae, the ribs, and the bones of the sternum, forming by a truncated do. their union, together with their intervening cartilag cone, designed to protect the organs which it contains, and to be subservient to certain movements concerned in respiration, The bony arches, the ribs, exelusive of the two last on each side (reckon- ing, as is usual, from the summit of the cone downward), are joined, either to the sternum, or to each other, by cartilages to which the walls of the chest are in a great measure indebted for their elasticity and mobility. The superior seven ribs joined to the sternum are called the true ribs, and the remaining five on each side are dis- tingnished as the false ribs. The two lowest on each side, from the fact that their anterior extremities are disconnected from those situated above them, as well as from each other, are known as the floating ribs. The elasticity of the costal cartilages is greatest in early life; it becomes impaired, as a general rule, in proportion to age, and with advanced years may be nearly lost in consequence of ossification. Under these circumstances the alternate iner diminution of the thoracic capacity with the two acts of r so far as the successive expansion and contraction of the thoracic walls are therein involved, must of necessity be in some measnre restrained. The direction of the first rib is nearly horizontal. The remainder haye an oblique direction downward, the obliquity inereasing with each inferior rib. Below the third rib the costal cartilages also have an oblique direction, but not corresponding to that of the ribs. At a short distance from the point of their attachment to the ends of the ribs, they pursue an upward direction to their sternal connections. Hence a line coincident with the axis of these ribs, forms with a line passing through the axis of their cartilages, an angle which obtuse with cach inferior rib. The length of the costal cartilages also increases successively with the three lowest of the true ribs. These anatomical poin ., the oblique downward direction of the ribs and the oblique upward direction of the costal cartila provisions for the respiratory movements, so far as these movements relate to the anterior and lateral portions of the chest. With the its force is voluntarily less s, are act of inspiration, more especially when THE THORACIC PARIETHS. 19 augmented, the lateral and antero-posterior diameters are increased. This is effected chiefly by the elevation of the ribs, by which their obliquity is diminished, causing them to approximate and even attain toa horizontal direction, tending thus to bring the ribs and the costal cartilages on a continuous line, diminishing or abolishing the angle formed by the union of the ribs and cartilages. After the cessation of the motive power which effects these changes, in other words, with the act of expiration, the elasticity of the cartilages suffices to restore the costal angle which es sive condition of the chest. These movements are abnormally increased and diminished in consequence of different forms of disease. A change, also, as regards the oblique direction of the ribs is attendant on certain sts in a pa thoracie affections, viz., pleurisy with a large accumulation of liquid in the pleural sac; the presence of liquid and gi s in pneumo-hydro- thorax, and in some cases of dilatation of the air-cells or vesicular emphysema. In connection with these affections the same changes are mechanically produced which are effected by a forcible act of in- spiration, with the important difference, that while the enlargement of the chest in the latter case is but for an instant, in the former case it persists so long as the morbid conditions which have induced it continue. The margins of the ribs are not in contact, but separated, leaving what are termed the éntercostal spaces. In consequence of the pro- gressively iner bs the inter- costal spaces are broader in front than behind. Under different morbid conditions these spaces are increased and diminished in ing obliquity in the direction of the r width, The former is incident to the aceumulation of a large quan- tity of liquid in the chest, the latter to contraction of the chest following the removal of this liquid by absorption or otherwise. In the female skeleton the upper ribs are more widely separated than in the male, and they possess also, relatively, a greater degree of mobility. This anatomical difference in the two sexes has relation to the greater part which the summit of the chest takes in the respiratory movements in the female. The inter al spaces, when the thorax is invested with the soft parts, are filled with muscular substance, which is concerned in carrying on the respiratory movements. ‘The intervening muscular layers are depressed below the level of the ribs, caus which are called the ¢ntercostal depressions. In persons with small or moderate adipose deposit, these depressions are apparent on ng furrows, 20 ANATOMY AND PHYSIOLOGY, the surface, being observable especially in front and laterally, at the lower part of the chest. They are every ible, exeept in the portions covered hy the scapule, in cases of great ema- ciation. A change as respects this anatomical point oceurs in cer- where vis tain morbid conditions, viz., when there is an accumulation of a Jarge quantity of liquid in certain cases of pleuritis, or an aceumu- Jation of liquid and air in pneumo-hydrothora Under these cir- cumstances the intercostal depre: hed, and the inter- yening integument may even project beyond the level of the ribs when avery large quantity of liquid or air is contained in the pleural The scapule and clavicles, with the soft parts, give to the thorax a shape quite different from that which it presents divested of these appendages. Compared toa trnneated cone, the base is now above. These superadded bones, ccrtain muscles investing portions of the thoracie wa in the way of exploring the che ions are abol , and, in the female, the mammary gland, offer obstacles for the physical signs of disease, which will be noticed hereafter in connection with the consideration of these signs. The partition wall separating the chest from the abdomen is the tendino-museular septum, the diaphragm, springing from the lumbar vertebrie, from the first to the fourth inclusive, and attached to the amined from below it forms a vaulted or arched roof of the abdominal eavity, its upper urface having a correspond- tending into the thoracic cavity on eel side. The ola | to “ashich this convexity rises in the two sides is not equal, being greater in the right than in the left side. In the former it rises as high as the fourth intercostal space; in the latter to a level with the fifth rib. Thus the right chest has a vertical diameter somewhat less than that of the left. Accumulation of liquid within the pleural sae, and dilatation of the air-cells in some cases of.emphy- sema, may cause, mechanically, depression of the diaphragmatic arch; and, on the other hand, enlargement of the liver on the right side, and, on the left side, enlargement of the spleen, or distension of the stomach, will produce an elevation above the normal height. The contraction of the muscular portion of the diaphragm di- minishes its vaulted form, depressing it to a plane, thereby extend- ing the vertical diameter of the thoracie space. In this way it becomes the most important agent in the act of inspiration, resuming its convexity with the act of expiration, These movements are liable nferior ribs. THE THORACIC PARIETES, 21 to be restrained, or arrested by: various affections which will be presently mentioned. Considered as divided into lateral halves, the thoraci¢ parietes on the two sides, not only as respects the skeleton, but when invested with the soft parts, should be nearly symmetrical, so that any con- siderable deviation in this point of view denotes either present disease, or deformity. An exception relates to the semicircular measurement at the middle and inferior portion of the chest. The right side usually, but not invariably, measures somewhat more than the left, the average difference being about half an inch. Of 133 cases of persons in good health in which measurements were made by Woillez, the right semi-circumference exceeded the left in 97; the left exceeded the right in 9, and both sides were equal in 27. The greater size of the right side, as determined by measurement, is usually attributed to the presence of the liver on that side. The facts presented by the author just named, however, seem to show that it depends, in a measure at least, on the greater use of the right upper extremity, which is habitual with most persons. In no instance in which the persons were right-handed did the left exceed the right side in measurement; on the other hand, of five cases in which the persons were left-handed, in three the left side exceeded the right, and in the remaining two cases both sides were equal. Ina per- fectly symmetrical chest the shoulders should be ou the same level; and in the male the nipples, situated on the fourth rib or in the fourth intercostal space, should be on the same transverse line and equidistant from the centre of the sternum, The general law of metry as regards correspondence in similar portions of the chest on the two sides is of importance in determining the existence of intra- thoracie d ; and, with reference to the application of this law, it is to be borne in mind that certain past affections are liable to leave deviations more or less permanent. The most common cause of defor- mity is spinal curvature, which may be sufficient to disturb the sym- metry of the two sides without existing toa degree to be noticed unless a careful comparison be instituted. Cases of slight lateral curvature depressing the shoulder and nipple of one side (oftener the right than the left side), approximating the margins of the ribs, and diminishing the semi-cireumference, are very frequent, and liable, withont special attention, to be overlooked. Certain di to marked alterations in the conformation on one side. This is true especially, as will be seen hereafter, of chronic pleuritis. The chest m- ases within the chest lead 22 ANATOMY AND PHYSIOLOGY. on one or both sides may he deformed in various ways irrespective of spinal curvature. Thus the sternum may project unnaturally, causing the “chicken” or “pigeon breast,” or it may be more or less depressed; there may be flattening on one side, produced per- haps by pressure from the arm of the nurse in early infancy; con- traction at the lower part of the chest in females, occasioned by tight lacing; distortions from fractures or other injuries, ete. These deviations from symmetry are sufficiently obvious, and will not there- fore escape notice. Practically they are of great importance in de- termining certain of the physical signs of existing disease. The greater portion of these signs, as will be seen hereafter, being based on the assumption that, irrespective of present disease, the two sides of the chest are symmetrical, it is obviously important to determine, in individual cases, to what extent the law of symmetry holds good. The researches of Woillez' show that chests presenting in all par- ticulars complete regularity of conformation are found in ouly the proportion of about twenty of every hundred persons. Deviations from symmetry, either disconnected from disease (physiological), or resulting from previous morbid conditions (pathological), therefore, exist toa greater or less extent, in a large proportion of individuals. This fact would impair very materially the value of physical ex- ploration were it not practicable, as it generally is, to determine whether deviations which may be discovered are due to present disease, or existed previously. The respiratory movements involve certain points important to be premised in addition to those already noticed. A complete respiration, as is well known, comprises two acts, viz., an act of inspiration, and an act of expiration. In health, after adult age, the respirations are repeated from 14 to 20 times per minute, the habitual frequency varying considerably within healthy limits in different individuals, The frequency is somewhat greater jn females than in males, and still greater in children. Deviations as regards the frequency of the respirations, exceeding the limits of health, ure important symptoms of discase, In various affections compromising the function of himatosis, the frequency of the res- pirations is considerably increased, rising for example in bronchitis naller tubes, to 30, 40, 50, 60, or even a still greater affecting the s 14 Recherches pratiques sur Vingpeetion et In mensuration de la poitrine, con- sidérées comme imoyens din > Paris, 1887, Archives Générales de Médecine, 3tme Série, sostiques complémentaires de la percussion et de Panseultation tome i, p. 73. THE THORACIC PARIETES. 23 number, per minute. On the other hand, an abnormal diminution in frequency accompanies certain morbid conditions of the nervous system which affect indircetly the respiration. ‘Thus, the respirations are morbidly infrequent, or slow, in apoplexy, and in coma however induced. The immediate object of the act of éapiration is the enlargement of the thoracic space, the air rushing in to fill the vacuum thus created within the air-cells and tubes of the lungs. This enlargement is effected by means of muscles attached to the thoracic walls, on the one hand, and, on the other hand, by the depression of the diaphragm. The immediate object of expiration is to restore the chest to the dimensions it naturally assumes when not acted on by the dilating muscle. beyond that point, thus causing expulsion of the air received by the act of inspiration. The simple restoration of the chest is due mainly to the elasticity of the dilated parts, but contraction beyond the dimensions which it naturally assumes, is effected by exp muscles. ‘The movements incident to the two acts, respectively, in ordinary or tranquil respiration; the modifications exhibited when the breathing is exaggerated or forced; the normal differences to be observed in different persons; the variations duc to age, sex, ete., are physiological points, not only interesting in themselves, but of utility in order to appreciate the aberrations associated with diseases of the respiratory apparatus. In bestowing ation on these points I shall not detain the reader with minute descriptions, still less engage in discussions relative to the mechanism of respira- tion, which, however much of interest they may possess for one desirous of investigating the subject fully, are not of special im- portance as preparatory to entering on the study of the physical exploration of the chest. In ordinary breathing, in the male, the diaphragm is usually the more important, and indeed sometimes almost the sole eflicient agent. The diaphragmatic movements are indicated by a percep- tible rising and falling of the abdomen. But in certain diseases these movements are to a greater or less extent restrained, and they may even be completely arrested. ‘They are notably diminished in acute peritonitis, being unconsciously repressed in consequence of the pain which they occasion; and they are mechanically pre- vented by a great quantity of liquid within the peritoneal sac, by enormous distension of the stomach or intestines with gas, by ab- dominal tumors, and by pregnancy. Under these circumstances ‘ome conside 24 ANATOMY AND PILYSIOLOGY, the thoracic muscles take on a supplementary activity, which is rendered sufficiently obvious by the increased movements of the thoracic walls. The breathing is then said to be thoracte or costal. On the other hand, the movements of the ribs are voluntarily re- pressed in consequence of the or in intercostal neuralgia, and they are mechanically limited by rigidity and ossification of the costal cartilages. The diaphragm, in this case, takes on an inereased action. ‘The breathing is then distinguished as diaphragmatic or abdominal, the latter term de- noting the fact that this supplementary activity is manifested by a corresponding increase in the visible rising and falling of the ab- dominal walls. The deviations from norma ain incident thereto in acute pleurisy, respiration known as thoracic ov costal, and diaphragmatic or abdominal, thus not only indicate the existence of disease, but point to its situation. By certain intra-thoracic affections the movements of the chest are diminished or suspended on one side, and, by way of compensation, abnormally increased on the other side. This obtains in cases of copions liquid effusion within one of the pleural sacs, Paralysis of the muscles of a lateral half of the body (hemiplegia) may also be attended by diminished thoracic movements of the affected side. Analysis of the movements of the thoracic walls develops other circumstances which are to be noted. The enlargement of the chest, exclusive of the diaphragm, in inspiration, is effected by the action of the thoracic muscles elevating the ribs, the latter, as has been con- seen, pursuing an obliqne direction and forming an angular nection with the costal cartil In proportion as the ribs are thus raised, the costal angles become more obtuse, and the ribs ap- proach to a horizontal direction, the ribs and cartilages together approximating to a continuous line. At the same time the sternum is raised upward and projected forward. The ribs, also, are rotated ° backward at their spinal junction, ‘The result is, the cavity of the chest becomes enlarged in every direction. Owing to the greater length of the lower trwe ribs as well as of their cartilages, and the less degree of obtuseness of the angle formed by the union of the former with the latter, these elevation and expansion movements, in the male, ave much more marked in the lower, than the upper t of the chest; and they are greater during the middle, than either at the beginning or the end of the inspiratory act. In ordi- nary breathing, the ribs at the summit of the male chest appear to have little or no part in the thoracic movements. Accurate measure- TIE THORACIC PARLETES. 25 ment shows that they do not remain quiescent, but the motion is usually so slight as seareely to be perecived. ‘The movements are mainly confined to the lower part of the chest and the abdomen, ring to be limited to the latter. This, it is to be borne in mind, is true of ordinary breathing in the male In rated or foreed breathi