1 864 HUMAN ANATOMY. 



the lower border of the lung during the period preceding old age, which is more 

 rapid than the senile increase of the declination of the ribs. 



PRACTICAL CONSIDERATIONS : THE LUNGS AND PLEURA. 



The Lungs and Pleurae. — Many of the most important practical questions 

 arising in cases of injury or disease of the lungs and pleurae can be answered only 

 after a physical examination, the value of which will depend primarily upon com- 

 plete knowledge of the normal phenomena associated with respiration. Such 

 knowledge must be based upon acquaintance with the structural conditions that 

 influence the sounds caused by a current of air entering and leaving the normal air- 

 passages and with the chief modifications caused by disease. 



Only a few of even the most elementary facts bearing upon this subject can here 

 be mentioned, but their consideration at a time when the pulmonary system is being 

 studied can scarcely fail to be of practical value, and is necessary to an understanding 

 of those symptoms of pulmonary or pleural injury or disease which have the most 

 obvious anatomical bearing. 



Anatomical Basis for Varied Character of Breath- Sounds. — The normal sounds 

 of respiration vary with the situation of the air-passages examined. Their loudness 

 is in direct proportion to their nearness to the larynx, so that /ary?igea/, tracheal, 

 bronchial, and vesicular breathing sounds are here mentioned in the order that indi- 

 cates progressively increasing softness. 



These terms acquire pathological significance when breathing of one type is 

 heard in a portion of the chest where it should not be heard. The nearness of the 

 larynx to the surface and its inclusion of air, as if within a hollow box (West), 

 make laryngeal sounds loud and noisy on both expiration and inspiration. In the 

 trachea, part of which is deeper, and a portion of the walls of which is of soft 

 muscular and fibrous tissue, both these sounds, as heard over the suprasternal notch, 

 or over the lower cervical or upper dorsal vertebrae, while still loud, are softer and 

 are raised in tone. Over the bronchi, heard best between the scapulae (page 1842), 

 they are both audible and are harsh, but have still further diminished in loudness. 

 Over the pulmonary tissue inspiration has become soft and blowing and expiration 

 can scarcely be heard. The reasons for these differences are as follows. The sounds 

 of breathing are produced chiefly at or about the glottis, therefore distance from the 

 larynx accounts for the diminution in loudness. The decrease in the diameter of 

 the air-tubes accounts for the rise in pitch of the respiratory note. The entrance of 

 the air into compartments of various sizes within the pulmonary tissue breaks up the 

 air-column which carries the sound and distri^butes the vibrations, so that the sounds 

 are muffled and soft (West). 



If the bronchial tubes or tubules are obstructed, as from hyperaemia of the 

 mucosa, or the presence of viscid secretion, the exit of air will be interfered with, 

 and there will be ' ' prolonged expiration. ' ' 



In a broad way, it may be said that in cases in which vesicular breathing is dimin- 

 ished or absent the cause should be sought : (i) In obstruction (pseudo-membrane 

 or fibrinous exudate). (2) In compression (aneurism, glandular swellings, medias- 

 tinal tumors). (3) In immobilization of the chest-wall on the affected side (fracture 

 of rib, intercostal neuralgia, pleurisy or pleuritic adhesions). (4) In distention of 

 the pleura by liquids or air (pneumothorax, empyema). If as a result of disease 

 the vesicular structure is occupied by an exudate (as in pneumonia), the vibrations are 

 conveyed more directly to the ear, expiration becomes audible, and, as consolidation 

 increases, the sounds, first of the smaller bronchioles and then of the larger bronchi, 

 repla^ce the normal blowing sound, and " bronchial breathing" is established. If the 

 cavity of the pleura is distended with air ( p?ieumothorax), which separates the lung- 

 tissue from the thoracic wall and conducts sound vibrations much less effectively 

 than do solids, the breath-sounds will be feeble and distant or absent. If the 

 pleural cavity is so filled with either air or fluid {empyema) that the lung is collapsed 

 or compressed against the spine, the breath-sounds may be feeble or distant or entirely 

 wanting over the front and sides of the chest, but bronchial breathing can be heard 

 over the back. In exceptional cases of pleural eflfusion such breathing is also heard 



