218 



COMPARISONS OF RESPIRATORY EXCHANGE. 



A study of the results obtained for the ventilation of the lungs and 

 the volume per respiration shows that in practically all of the experi- 

 ments there was a larger ventilation of the lungs with the additional 

 dead space than with the normal breathing ; in other words, to have the 

 same amount of effective ventilation of the lungs, the subject was 

 obliged at each respiration to sweep out this increased dead space in 

 addition to that of the normal dead space of the apparatus and the 

 respiratory tract. The total ventilation of the lungs less that required 

 to sweep out the natural dead space of the respiratory tract of the 

 subject at each respiration may be designated as the alveolar ventila- 

 tion. If an assumption is made that the natural dead space is 100 c.c. 

 and the alveolar ventilation per minute is calculated by using this value, 



TABLE 40. Variations of average results obtained with dead space from those obtained withou 



dead space (spirometer unit). 



the total ventilation, and the respiration-rate per minute, it will be 

 found that in the periods with the additional dead space the value for 

 the alveolar ventilation is approximately equal to that in the normal 

 periods plus the product of the respiration-rate and the additional 

 dead space. These values have been calculated for all of the experi- 

 ments except those with an additional dead space of 45 c.c. ; in no case is 

 the alveolar ventilation thus calculated more than 0.2 liter per minute 

 higher in the periods with an additional dead space than in the normal 

 periods. The assumed value of 100 c.c for the natural dead space is 

 not accurate for all individuals, but it is immaterial what value is 

 assumed, as in this case only differences are to be calculated. 



