Applications of Gas Analysis

The analysis of 10 cc. of expired air to determine its percentage of oxygen and CO2 is not appreciably more difficult than the determination of the nitrogen in 10 cc. of urine by the Kjeldahl method. The nitrogen found in the sample multiplied by the total volume of t’he urine from which it was taken gives us the nitrogen metabolism of the body. In the same way the oxygen (deficit) and the CO2 found in the sample of expired air multiplied by the total volume of the air expired in a given time afford the oxygen and carbon metabolism, and, by indirebt calorimetry, the total energy exchange of the body. Certainly a knowledge of the oxygen, carbon, and energy exchanges is quite as important in a wide range of problems as is the nitrogen exchange. Each should be equally a matter of routine in every well equipped biochemical and clinical laboratory. In fact however the means and habit of determining nitrogen are universal, while determinations of the respiratory exchange are confined to a very few highly specialized laboratories. The reason for this anomaly lies in the fact that it is generally assumed that the elaborate and expensive apparatus of the “closed circuit” method used by Benedict, Lusk, and their collaborators is necessary. This is far from the truth. In fact, in a thorough comparative study and critique of ail available methods Carpenter (I), although he does not say so explicitly, has shown implicitly that the (Tissot) “open circuit” method of collecting the expired air in a graduated spirometer and analyzing a sample is equal in accuracy and superior in simplicity to the closed circuit method.