4 o8 TEXT-BOOK OF PHYSIOLOGY 



5. Rise of intra-pulmonic air pressure above the atmospheric air 



pressure. 



6. Outflow of intra-pulmonic air, in consequence of its higher pres- 



sure, until the intra-pulmonic air pressure falls to that of the 

 atmosphere. 



Respiratory Movements of the Upper Air-passages. The resistance 

 to the entrance of air into and through the respiratory tract is much dimin- 

 ished by respiratory movements of the nares and larynx which are associated 

 and occur synchronously with the movement of the thorax. 



The nares at each inspiration are dilated by the outward movement of 

 their alae or wings, the result of muscle activity. At each expiration they 

 are diminished by the return of their cartilages through the play of elastic 

 forces. The larynx, as shown by observation with the laryngoscope, exhibits 

 corresponding movements of the vocal membranes. Their introduction at 

 this level naturally narrows the tract, and would interfere with both the 

 entrance and the exit of air were they not kept widely asunder during the 

 time they are not required for purposes of phonation. This is accomplished 

 by the tonic contraction of the posterior crico-arytenoid muscles, which are 

 entirely respiratory in function. 



It is not infrequently stated that these membranes exhibit considerable 

 oscillations, outward and inward, corresponding to the movements of 

 inspiration and expiration. The statements of the majority of laryngologists 

 do not favor this view. During tranquil breathing the membranes are 

 widely separated and almost stationary, seldom moving in either direction 

 more than a few millimeters. In labored respirations these movements are 

 naturally increased in extent. The irregular movements of the membranes 

 occasioned by the unskilful use of the laryngoscope, especially with nervous 

 patients, are not to be regarded as strictly physiologic. The respiratory 

 space in quiet breathing is an isosceles triangle, with a length of 20 mm. and 

 a width at the base of 15.5 mm. with an area of 155 square mm. 



Respiratory Types. Observation of the respiratory movements in the 

 two sexes shows that while the enlargement of the thoracic cavity is accom- 

 plished both by the descent of the diaphragm (as shown by the protrusion of 

 the abdomen) and the elevation of the thoracic walls, the former movement 

 preponderates in the male, the latter in the female, giving rise to what has been 

 termed in the one case the diaphragmatic or abdominal type and in the 

 other the thoracic or costal type of respiration. The cause of this greater 

 mobility and activity of the thorax in the female has been a subject of much 

 discussion. It has been attributed, on the one hand, to the necessity for a 

 physiologic adjustment between respiration and child-bearing, and therefore 

 a specific sex peculiarity; on the other hand, it has been attributed to per- 

 sistent constriction of the waist, in consequence of which the full play of the 

 diaphragm is prevented and the burden of inspiration is thrown on the thora- 

 cic muscles. It has been assumed that if inspiration were confined in women 

 to the diaphragm, there would arise in the latter stages of gestation such an 

 increase in intra-abdominal pressure that not only would respiratory ex- 

 changes be interfered with, but fetal life might be unfavorably influenced, 

 if not endangered. Modern investigations have not confirmed this assump- 

 tion, but, on the contrary, have corroborated the view that the preponderance 

 of thoracic movement is due to the influences of dress restrictions, for with 





