CHAPTER XL 

 THE CONTROL OF RESPIRATION (Cont'd) 



VARIATIONS IN THE ALVEOLAR C0 2 AND THE ACID BASE 

 BALANCE IN HEALTH AND DISEASE 



At this stage and before we proceed to examine the respiratory dis- 

 turbances due to blood changes, it will be advantageous to review the 

 general nature of the adjustments which may occur in the body to com- 

 pensate for disturbances in the acid-base equilibrium, and to indicate the 

 type of symptoms which develop if these compensations are not promptly 

 effected. 



To understand the relationships it is most satisfactory to study a C0 2 

 absorption curve such as is shown in Fig. 128. As has already been 

 explained on page 50 this curve is obtained by finding the percentages of 

 C0 2 (ordinates) absorbed by blood exposed at 38 C. in a tonometer to 

 varying tensions of C0 2 (abscissae). Two such curves are shown in the 

 chart to represent the extreme limits which are found in normal blood. 

 The percentage of C0 2 going into simple solution in the blood is readily 

 calculated for each tension, by multiplying this by 0.0672, the coefficient 

 of solubility of C0 2 in blood (slanting straight line near the abscissa). 

 It is then an easy matter to calculate P H for the different parts of the 

 C0 2 curve (see equation on page 50). If this be done for curves of vary- 

 ing heights (e.g., blood of different individuals or blood of the same 

 individual under varying conditions) it has been found by Y. Henderson 

 and Haggard that lines joining the same P H 's all meet at the zero point. 

 By drawing such lines on the chart we can at a glance tell P H if we know 

 the total C0 2 absorbed and the partial pressure of C0 2 . Taking the 

 normal range of P H as 7.3-7.5 and of total C0 2 at 40 mm. C0 2 pressure, 

 43 and 55 vols. per cent, we can see from the chart the relationship of 

 these values to P H in various abnormal conditions. These may be classi- 

 fied as follows: 



Decrease in P H (increased H-ion concentration). 



1. Addition of C0 2 (I in diagram). The simplest form of this is where 

 atmospheres containing excess of C0 2 are respired. A true acidosis is 

 established and it is compensated for by greatly increased breathing (to 

 get rid of the C0 2 ), by excretion of excess of acid by the kidneys and by 

 an increase in the bases of the blood. The condition may occur in 



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