PHYSIOLOGY OF MOUTH-BREATHING APPLIANCES. 



183 



lungs each time and that the residual volume in the lungs and the 

 temperature conditions remain constant. Any alteration in the resid- 

 ual volume would alter the base of the respiration tracings on the 

 kymograph. This, of course, does occur occasionally in a deep inhala- 

 tion, but the low points of the tracings which mark the limits of expira- 

 tion are remarkably uniform after the first few respirations of the period, 

 and the rate at which these points rise give a very fair index of the rate 

 of oxygen consumption. The method, however, is intended merely 

 as an approximate comparison, for the volumes thus read are apparent 

 volumes and, like those for the pulmonary ventilation, are uncorrected 

 for temperature changes. 



The lower record (A) in figure 15 is the reproduction of a kymograph 

 tracing when the subject was standing and shows the rise in the curve 

 as the oxygen was absorbed from the ventilating circuit, without re- 

 newal. The upper record (B) in the same figure was obtained with 

 the subject walking, and indicates the points at which the main spirom- 

 eter was refilled from the duplicate spirometer. 



ini n mimtHh i un 1 1 m M ii H-HH 



-i r 



-t * i- 



FIG. 15. Reproduction of kymograph records in mouthpiece experiments, 



with intermittent renewal of oxygen. 

 A, subject standing without introduction of oxygen. B, subject walking on 



a 30 per cent grade, 50 meters per minute; intermittent renewal of oxygen. 



Time and pulmonary ventilation indicated by the horizontal tracings. 



