246 



ANATOMY FOR NURSES 



[Ch.\p. XII 1 



Reserve air is the amount of air in addition to the tidal air 

 one can expel from the lungs in a forced expiration. 



Residual air is the air remaining in the lungs after the most 

 powertul cxi)iration. 



The vital capacity is the sum of the tidal, complementary, 

 and reserve airs added together. It equals about 225 cubic 

 inches (3700 cc). 



It is not correct to think of the residual air in the lungs as 

 stationary, for the air is being constantly moved and renewed. 

 This movement is maintained by: (1) the alternate expansion and 

 collapse of the lungs in respiration, (2) the convection currents 

 due to the differences in temperature between the inspired air and 

 the residual air, (3) the pulsation of the arteries, and (4) the 

 difference in the proportion of carbon dioxide and ox^'gen in the 

 inspired air and residual air. This fourth factor is also responsible 

 for the interchange of gases between the air in the air-sacs and the 

 blood in the capillaries. The reason is that the blood contains 

 more carbon dioxide and less oxygen than the air in the alveoli, 

 and the tendency of gases is always to mix in uniform proportions. 



The effects of respiration upon the air outside the body. — AYith 

 every inspiration a well-grown man takes into his lungs about 

 30 cubic inches (500 cc.) of air. The air he takes in differs from 

 the air he gives out mainly in three particulars : — 



1. ^Vhatever the temperature of the external air, the expired 

 air is nearly as hot as the blood ; namely, of a temperature between 

 98° and 100° F. (36.7 and 37.8° C). 



2. However dry the external air may be, the expired air is 

 quite, or nearly, saturated with moisture. 



3. The air when breathed loses about one-fourth of its ox\'gen 

 and increases the carbon dioxide an hundred fold; the quantity 

 of nitrogen is changed little, if any. To be exact, the air loses 4.94 

 volumes of oxygen and gains 4.38 volumes of carbon dioxide. 

 Thus : — 



Inspired air 

 Expired air 



