RESPIRATION AND ACIDOSIS 323 



The mask described above for use with infants may be very conveniently 

 used for the collection of alveolar air samples from dogs. The animal's nose is 

 inserted into the mask and the rubber tissue drawn closely around the muzzle. 

 The time of a collection need not exceed 25 seconds. 



Analysis of Sample. In analyzing a sample of air, about 2 or 3 c.c. of the 

 standard bicarbonate solution are poured into a clean test-tube of the same diameter 

 as the tubes containing standard phosphate solutions, but from 100 to 150 mm. 

 long. Air from the bag is then blown through the solution by means of a glass 

 tube drawn out to a fine capillary point, until the solution is saturated, as shown by 

 the fact that no further color change occurs. 1 The tube is stoppered and the 

 color immediately compared with that in the standard tubes. By interpolation, 

 one can readily read to millimeters. Color changes are not quite so sharp above 

 35 mm. as at the lower end of the scale, but here changes are of less significance. 

 In making the color comparisons the solution being compared is placed between the 

 two standards which it most nearly matches. When there is doubt as to whether 

 the color of the solution is higher or lower than one of the standards, changing 

 the order in which the tubes are placed in the comparison box will generally make 

 the relationship clear. 



The standard solutions described are so prepared as to give correct results 

 when the determination is carried out at a temperature of from 20 to 25C. (from 

 68 to 77F.). When the room temperature is considerably higher or lower than 

 these points it is advisable to immerse the tubes in water at approximately 25C. 

 during the blowing. They may be removed from the water for the color compari- 

 son, however, provided this is quickly made. The differences due to ranges of 

 temperature occurring under ordinary circumstances are practically negligible. 2 



Calculation. The standard tubes are marked to indicate the carbon dioxide 

 tension in millimeters of mercury, and the readings can be estimated to about 2 mm. 



Interpretation. In normal adults at rest the carbon dioxide tension in the 

 alveolar air, determined and described above, varies from 40 to 45 mm. Tensions 

 between 30 and 35 mm. are indicative of a mild degree of acidosis. When the ten- 

 sion is as low as 20 mm., the individual may be considered in imminent danger. 

 In coma, associated with acidosis, the tension may be as low as 8 or 10 mm. 

 In infants, the tension of carbon dioxide is from 3 to 5 mm. lower than in adults. 



Conditions other than acidosis may affect the carbon dioxide tension. Stimu- 

 lation of the respiratory center leads to increased pulmonary ventilation and a 

 consequent lowering of the alveolar carbon dioxide tension. Such stimulation 

 may be brought about by caffein 3 and possibly also by intracranial lesions. The 

 respiratory center may be depressed by morphin, and as the result of certain 8 

 infections. This leads to an increased carbon dioxide tension. Changes in the 

 excitability of the respiratory center, however, are but rarely great enough to affect 

 significantly the composition of the alveolar air. 



"Alveolar" air collected as described above is essentially air which has come 



1 If the operator first blows his own breath through the solution so as to bring it into 

 approximate equilibrium with alveolar air, saturation may be accomplished with as little 

 as 100 c.c. of air from the bag, blown through during 30 seconds. The same bicarbonate 

 solutions may be used for repeated determinations. 



2 No correction for barometric pressure is required as from the nature of the determina- 

 tion, barometric fluctuations are self-corrective. Variations in the temperature of the 

 subject are never great enough to affect the value as much as i mm. and therefore may 

 be neglected. 



3 Higgins and Means: Jour. Pharmacol. and Exper. Therap., 1915, vii, i. 



