RESPIRATION 



145 



the cause of the natural increased depth may be, it is evident that 

 in the recumbent position the tendency to irregular distribution 

 of fresh air in the lung alveoli with any given depth of breathing 

 is much increased, so that anoxaemia from this cause, as shown 

 in normal persons by periodic breathing, is much more readily 

 produced. In my own case periodic breathing is rapidly produced 

 in the recumbent position when the breathing is kept at over 20 

 per minute by artificially limiting the depth by means of our 

 apparatus, whereas in the upright position there is no such effect. 

 The effect of the recumbent position is shown in Figure 48. 



We have thus a simple explanation of a phenomenon which 

 has been familiar to physicians since early times, but which has 

 hitherto never been satisfactorily explained. When patients are 



42 



41 

 40 

 39 



10 



fc 37 

 | 36 



! 



I 34 

 1.33 

 3*32 



V. 



I 31 

 *30 



29 



28 



800 700 600 500 400 

 Barometric Pressure m mm of mercury 



Figure 49. 



Effects of diminished barometric pressure on the 

 alveolar gas-pressures. The thick lines show the 

 alveolar CC>2 pressure, and the thin lines the alveolar 

 O 2 pressure. The dotted lines refer to the experiment 

 in which oxygen was added to the air. 



short of breath during illness they are often very uncomfortable 

 in the recumbent position, and may become dangerously worse 

 if not propped up in bed or in a chair. This condition is known as 



30Q 



