CHAPTER LXIV 



A CLINICAL METHOD FOR DETERMINING THE RESPIRATORY 



EXCHANGE IN MAN* 



(Contributed by R. G. PEARCE) 



Principle. Since the determination of the respiratory exchange in 

 man is of some importance in the study of certain diseases of the respira- 

 tion, circulation and metabolism, and also because directions for carry- 

 ing out the necessary procedures are not generally available, we have 

 thought it might be of assistance to include here brief directions for the 

 Tissot and the Douglas methods. These methods have been found to 

 compare favorably in accuracy with others in use at present,! and be- 

 cause of their adaptability and simplicity they are specially suited for 

 clinical work. 



By these methods the energy metabolism of the body is calculated from 

 oxygen consumption or carbon dioxide excretion per minute (indirect 

 calorimetry) (page 580), the figures for which are determined from the 

 volume and percentile gaseous composition of the expired air. 



The subject breathes through valves which automatically partition the 

 inspired and expired air. The expirations from a number of respirations 

 are collected in a spirometer or bag, and the volume of the respirations 

 per minute is determined. The gaseous composition of the expired air 

 is determined by gas analysis, and the oxygen consumption and energy 

 output of the body are calculated from the data obtained. 



Description and Use of Parts of the Apparatus: 1. THE MOUTHPIECE AND VALVES. 

 The mouthpiece is made of soft pure gum rubber, and consists of an elliptical rub- 

 ber flange having a hole in the center 2 cm. in diameter. The flange is attached on 

 one side to a short rubber tube. On the other side at right angles to the rubber flange, 

 are attached two rubber lugs. The rubber flange is placed between the lips, and the 

 lugs are held by the teeth. The rubber tube of the mouthpiece is connected to the 

 tube carrying the valves. The nose must be tightly closed if mouth breathing is used. 

 This is accomplished by a nose clip, which consists of a V-shaped metal spring, the 

 ends of which are provided with felt pads. A toothed rachet is attached to the ends of 

 the spring, and serves to hold the spring tightly clamped on the nostrils in the proper 

 position (see Fig. 177). 



Some individuals experience great distress when made to breathe through the mouth. 



*This chapter is added for the convenience of workers in this subject. 

 tCarpenter: Carnegie Institution of Washington Reports, No. 216, 1915. 



589 



