PRESSURE IN THE AIR-PASSAGES DURING RESPIRATION. l8l 



in doing so give rise to friction-sounds, which can be felt (often by the patient himself), and 

 can also be heard. The sound is comparable to the sound produced by bending new leather. 



(6) Pectoral Fremitus. When we speak or sing in a loud tone, the walls of the chest vibrate, 

 because the vibration of the vocal cords is propagated throughout the entire bronchial ramifica- 

 tions. The vibration is, of course, greatest near the trachea and large bronchi. The ear cannot 

 detect the sounds distinctly. If there be much exudation or air in the pleura, or great accumula- 

 tion of mucus in the bronchi, the pectoral fremitus is diminished or altogether absent. [In 

 health, when a person speaks, the vocal resonance over the trachea, although loud, maybe 

 inarticulate ; and on listening over the sternum the sound is diminished, and quite inarticulate ; 

 while over the chest-wall generally the sound, though distinct, is feeble. 



All conditions which cause bronchial breathing increase the pectoral fremitus. Under 

 normal circumstances, therefore, it is louder where bronchial breathing is heard normally. The 

 ear hears an intensified sound, called bronchophony, [which is a sound like that heard normally 

 over the trachea or bronchi, but audible over the vesicular lung-tissue. The conditions that 

 cause it are the same as those on which bronchial breathing depends, so that it is heard in 

 pneumonia and phthisis. If, through effusion into the pleura or inflammatory processes in the 

 lung-tissue, the bronchi are pressed flat, a peculiar bleating sound (segophony) may be heard.] 



118. PRESSURE IN THE AIR-PASSAGES DURING RESPIRATION. 



Respiratory Pressure. If a manometer be tied into the trachea of an animal, 

 so that the respiration goes on completely undisturbed, i.e., normal respiration, 

 during every inspiration there is a negative pressure (-3 mm. Hg) and during 

 expiration a positive pressure. Donders placed the (J -shaped manometer tube in 

 one nostril, closed his mouth, leaving the other nostril open, and respired quietly. 

 During every quiet inspiration the mercury showed a negative pressure of 1 mm., 

 and during expiration a positive pressure of 2-3 mm. (Hg). 



Forced Respiration. As soon as the air was inspired or expired with greater 

 force, the variations in pressure became very much greater, e.g., during speaking, 

 singing, and coughing. The inspiratory pressure was = - 57 mm. (36-74), the 

 greatest expiratory pressure + 87 (82-100) mm. Hg. The pressure of forced expira- 

 tion, therefore, is 30 mm. greater than the inspiratory pressure (Donders). 



Resistance to Inspiration. Notwithstanding this, we must not conclude that the 

 expiratory muscles act more powerfully than the inspiratory ; for during inspiration 

 a variety of resistances have to be overcome, so that after these have been met, there 

 is only a residue of the force for the aspiration of the mercury. The resistances to 

 be overcome by the inspiratory muscles are : (1) The elastic tension of the lungs, 

 which during the deepest expirations = 6 mm. ; during the deepest inspirations = 30 

 mm. Hg ( 107). (2) The raising of the weight of the chest. (3) The elastic 

 torsion of the costal cartilages. (4) The depression of the abdominal contents, and 

 the elastic distension of the abdominal walls. All these not inconsiderable resist- 

 ances, which the inspiratory muscles have to overcome, act during expiration, and 

 aid the expiratory muscles. The forces concerned in inspiration are decidedly much 

 greater than those of expiration. 



Intra-thoracic Pressure. As the lungs within the chest, in virtue of their elas- 

 ticity, continually strive to collapse, necessarily they must cause a negative pressure 

 within the chest. This amounts in dogs, during inspiration, to - 7*1 to - 7*5 mm. Hg, 

 and during expiration to 4 mm. Hg. The corresponding values for man have 

 been estimated at - 4*5 mm. Hg and - 3 mm. Hg, by Hutchinson. 



[We must distinguish between the respiratory pressure of the air within the respiratory passages, 

 and the intra-thoracic pressure. The former is the same as the atmospheric pressure when the 

 chest is passive, but less than it as the chest is being enlarged, and greater than it when it is 

 being diminished in size. The intra-thoracic pressure is the pressure within the chest, but 

 outside the lungs, i.e., in the pleura, mediastinum, &c. It is negative, i.e., less than the 

 atmospheric pressure, and must vary with the degree of distension of the lungs.] 



[Methods. A direct estimation was made by Adamkiewicz. and Jacobson. A trocar with its 

 stylette was forced into the fourth left intercostal space near the sternum and pushed into the 

 pericardium (sheep). The stylette was then withdrawn, and the trocar connected with a 

 manometer,, and the negative pressure of -3 to -5 mm. Hg was obtained. During severe 

 dyspnoea it was -9 mm. Hg. Rosenthal introduced an oesophageal sound with an elastic 



