PRESSURE CONDITIONS IN LUNGS AND THORAX. 589 



to the mechanical changes in pressure during respiration and their 

 effect on the blood-flow, aided also by the fact that the heart beats 

 more rapidly during inspiration. This second general point of view 

 has been adopted in physiology, and to verify it numerous experi- 

 ments have been made upon lungs placed in an artificial thorax in 

 which the conditions of pressure could be varied at will.* As the out- 

 come of this work, the following results have been accepted in expla- 



Fig. 242. Respiratory waves of blood-pressure. Typical blood-pressure record as 

 taken with a mercury manometer: Bp the blood-pressure record, shows the separate 

 heart beats and the larger respiratory waves, each of which comprises six to seven heart 

 beats. 



nation of the occurrence of the respiratory waves of blood-pressure : 

 (1) During inspiration there is an increased flow of blood into the 

 right auricle (aspiratory action of inspiration). (2) During inspira- 

 tion the capacity of the blood-vessels in the lungs is increased and 

 also the velocity of the flow ; consequently there is an increased 



* For discussion and literature see de Jager, " Archiv f. die gesammte 

 Physiologic," 20, 426, 1879, and 27, 152, 1882; also "Journal of Physiology," 

 7, 130. 



