182 METABOLISM DURING WALKING. 



EFFECT OF MOUTHPIECE BREATHING UPON RESPIRATION-RATE, PULMONARY VENTILATION, 



AND RATE OF OXYGEN CONSUMPTION. 



The effect upon the respiration-rate and the pulmonary ventilation 

 of long-continued preliminary breathing through the mouthpiece was 

 also studied in these experiments, for it was conceivable that the mouth- 

 piece and nose-clip might cause a change in the ventilation which would 

 result in a pumping-out of carbon dioxide and a consequent change in 

 the respiratory quotient and the computed heat. As previously 

 stated, in ordinary experimenting it has been the practice to insert the 

 mouthpiece 2 or more minutes before the beginning of the period. If 

 there were any alteration in the respiration-rate and volume of venti- 

 lation under these conditions, it ought to be apparent in experiments 

 made with such wide variations in the length oi preliminary breathing 

 as comparison periods of 15 seconds and 15 minutes would give. If 

 this variation in conditions resulted in no material difference, it is safe 

 to say that the usual 2-minute period of preliminary breathing through 

 the mouthpiece was sufficient to insure uniformity. 



The respiration-rate and pulmonary ventilation were determined in 

 1-minute and ^4-imiiute intervals during the first 5 to 7 minutes of the 

 period by counting the respirations and measuring their excursion on 

 the kymograph, the time-intervals being marked in minutes by means 

 of a signal magnet in contact with a clock. The ventilation as thus 

 measured is the apparent ventilation, and the data have not been cor- 

 rected for temperature changes. 



At the time that these measurements of the ventilation were made, 

 advantage was taken of the opportunity to measure the rate of the 

 oxygen consumption during the first few minutes of the period. This 

 was done by the use of the double spirometer (see fig. 2, p. 22), and the 

 measurement of the kymograph record. During the regular experi- 

 ments it was the practice to admit the oxygen at such a rate as to 

 equalize the consumption, but in determining the rate in the mouth- 

 piece comparison experiments, no oxygen was admitted until the 

 spirometer-bell had reached a low level. The main spirometer was 

 then refilled from the duplicate spirometer by the method described 

 on page 21. Under these conditions, instead of a gradual alteration 

 in the relative positions of the kymograph tracings as a result of 

 the contractions in the volume of the ventilating circuit, the kymo- 

 graph record showed a slight rise with each respiration and a sud- 

 den fall when new oxygen was finally admitted from the duplicate 

 spirometer. By measuring the rise in the kymograph record due to 

 the fall of the spirometer-bell in a specified period of time, the rate of 

 oxygen consumption could be estimated for succeeding fractions of a 

 minute. 



There is a valid criticism against this method of measurement, for it 

 assumes that the subject exhales to the same point of deflation of the 



