PRESSURE IN THE AIR-PASSAGES DURING RESPIRATION. 223 



During loud speaking or singing the chest-wall vibrates vocal fremitus as 

 a consequence of the propagation throughout the bronchial tree of the vibrations 

 of the vocal bands. This vibration naturally is most pronounced in the region of 

 the trachea and the large bronchi. If the ear be applied to the chest-wall the 

 voice can be heard only as an unintelligible hum. If the pleural cavity contains 

 air or a large effusion, or if the bronchi are occluded by large quantities of mucus 

 the vocal fremitus is weakened or entirely absent. On the other hand all factors 

 that cause bronchial breathing will increase the vocal fremitus. Hence the latter 

 will be more marked also in those localities where bronchial breathing is heard 

 even under normal conditions. The ear under such circumstances will hear the 

 sounds conducted to the chest-wall with increased intensity. This is termed 

 bronckopkony. 



If a pleural effusion or a pulmonary inflammation causes a flattening of the 

 bronchi, the sound of the voice in the chest sometimes assumes a peculiar bleating 

 quality egopkony. 



Doubtless the gradations of increased or diminished fremitus could be readily 

 demonstrated by means of the sensitive flame (observed in a rotating mirror) or 

 by the use of the microphone. For the former there should be employed an appa- 

 ratus similar to the gas-sphygmoscope, with the lower part widened in the shape 

 of a funnel. 



PRESSURE IN THE AIR-PASSAGES DURING RESPIRATION. 



If a manometer be fastened in the trachea of an animal in such a manner 

 that respiration is not interfered with, the instrument will show a negative pressure 

 3 mm. of mercury) during inspiration, and a positive pressure during expira- 

 tion. Donders has modified this experiment for man by introducing a U-shaped 

 manometer-tube through one nostril, and instructing the subject to breathe quietly 

 through the other nostril with the mouth closed. He found that during each 

 quiet inspiration the mercury showed a negative pressure of i mm., and during 

 each expiration a positive pressure of 2 or 3 mm. Aron experimented with patients 

 having a tracheal fistula as the result of operation, and found during inspiration 

 a pressure of from 2 to 6.6 mm. of mercury, during expiration from +0.7 to 

 + 6.3 mm. of mercury. In speaking, the corresponding fluctuation was from 

 6 to + 7 , and when coughing from 6 to +46.1. 



As soon as the air is drawn in and expelled with greater force, the fluctuations 

 of pressure become more marked, especially in the acts of speech, singing, and 

 coughing. If forced respiration be practised with the mouth and one nostril 

 closed, so that the respiratory canal communicates only with the manometer, 

 the greatest inspiratory pressure is 57 mm. (between 36 and 74), and the greatest 

 expiratory pressure is +87 (between 82 and 100) mm. 



Notwithstanding the higher expiratory pressure, it must not be inferred that 

 the expiratory muscles are stronger than those of inspiration ; for during the latter 

 act a series of resisting forces must be overcome, leaving a much diminished 

 supply of force for the aspiration of the mercury. These resisting forces are: (i) 

 The elastic tension of the lungs, which amounts to 6 mm. during complete ex- 

 piration, but reaches 30 mm. during deepest inspiration. (2) The lifting of the 

 weight of the thorax. (3) The elastic torsion of the costal cartilages. (4) The 

 depression of the abdominal viscera and the elastic distention of the abdominal 

 walls. All these resisting forces aid the expiratory muscles during expiration. 

 With these facts in view, there is no doubt that the combined strength of the 

 inspiratory muscles is greater than that of the expiratory muscles. 



As the lungs, by reason of their elasticity, have a tendency to collapse, they 

 naturally exert a negative pressure within the thoracic cavity. In dogs this 

 amounts to from 7.1 to 7.5 mm. of mercury during inspiration, while in expiration 

 it is naturally less, namely only 4 mm. The analogous values obtained by different 

 investigators on the dead body vary; Hutchinson fixes them at 4.5 mm. and 3 mm. 



The greatest pressure during inspiration and expiration seems small when 

 compared to the blood-pressure in the large arteries. If, however, the pressure- 

 values obtained for the respired air be estimated for the entire superfices of the 

 thorax, considerable results are obtained. 



To measure the muscular respiratory power in case of illness, a U-shaped 

 mercurial manometer may be employed, provided with an attachment suitable for 

 introduction into a nostril or the mouth (Waldenburg's pnciimatomctcr} . The in- 

 spiratory pressure alone may be reduced (in the presence of almost all diseases 



