464 RESPIRATION 



means of the Rontgen rays that the vertical diameter of the chest is 

 increased by only 10 mm. in the central area of the diaphragm, and 

 while forced inspiration gives rise to a somewhat greater descent 

 (12 to 14 mm.), the real purpose of diaphragmatic respiration seems 

 to be to draw the inferior borders of the lungs into the complementary 

 space and to act upon the lower areas of these organs. Their upper 

 areas are also expanded, but in a much smaller measure. On this 

 account, pleuritic adhesions are more likely to form in the upper 

 recesses of the intrapleural space, and catarrhal and tuberculous 

 infiltrations are particularly liable to affect the more poorly ventilated 

 tips of these organs. 



As the diaphragm descends, it pushes the neighboring abdominal 

 viscera downward, ^ but their displacement is only made possible by 

 the outward bulging of the anterior and lateral abdominal walls. 

 In this way, the contracting diaphragm places the latter under a 

 certain elastic tension. In other words, its muscular energy is tempo- 

 rarily transformed into potential energy which is again made use of 

 during the succeeding expiration in forcing the abdominal viscera 

 and overlying diaphragm back into their original position. • It need 

 scarcely be emphasized that the direct mechanical effect of this move- 

 ment is far reaching, because it favors not only the venous return from 

 the posterior extremities and organs of the abdomen but also that 

 from the anterior parts of the body.^ In addition it exerts an im- 

 portant influence upon the flow of the lymph and bile. It should 

 also be remembered that the ^'aspiratory power of the thorax" which 

 is responsible for the negativity of the venous blood pressure, may in 

 large part be ascribed to the activity of the diaphragm. 



In lean persons the movements of this septum are frequently 

 indicated upon the external surface of the chest by a furrow-like 

 depression, the so-called linea diaphragmatica, which progresses 

 wave-like over the lower intercostal spaces. In as much as this 

 retraction follows in the wake of the contracting muscular brim of 

 the diaphragm, it is indicative of the strength of the aspiration and of 

 the force with which the atmospheric pressure tends to push the thoracic 

 wall of this region inward. This retraction may be made to appear 

 in almost any person by forcing the respiratory movements. It is 

 also of interest to note that the contractions of the diaphragm are 

 prolonged, simulating the " tetanic '^ contractions of striated muscle 

 tissue when subjected to a quickly interrupted current of brief dura- 

 tion.^ Clearly, this mode of contraction, which insures the fullest 



1 The earlier conception, that the pleural cavity is filled with air and that the 

 lungs contract actively, was proved to be erroneous by Haller, his evidence being 

 based upon observations of the movements of the diaphragm and adjoining 

 pulmonary tissue made through the thinned tissue of the lower intercostal space. 

 See: De diaphragmate, Gottingen, 1741. 



^ Burton -Opitz, Am. Jour, of Physiol., xxxvi, 1914, 64. 



3 Markwald, Zeitschr. fur Biol., xxiii, 1887, 149. 



