Physiology and biochemistry in modern medicine . 40 THE RESPIRATION the method by which the tensions of these Liases in alveolar air can be determined. The simplest and until recently the most accurate methodis that of Haldane and This consists in having an individual,with his nostrils clamped, breathe quietly through a piece of hose pipeabout a meter long, which has at the mouth end a short side-tube lead-ing to an evacuated gas-sampling bulb of about 50 capacity.* Afterthe subject has become accustomed to breathing through the tube, heis asked to make a forced expiration an
Physiology and biochemistry in modern medicine . 40 THE RESPIRATION the method by which the tensions of these Liases in alveolar air can be determined. The simplest and until recently the most accurate methodis that of Haldane and This consists in having an individual,with his nostrils clamped, breathe quietly through a piece of hose pipeabout a meter long, which has at the mouth end a short side-tube lead-ing to an evacuated gas-sampling bulb of about 50 capacity.* Afterthe subject has become accustomed to breathing through the tube, heis asked to make a forced expiration and at the end of it to close themouthpiece with his tongue. At this moment the operator opens thetap of the sampling tube, allowing the air from the tubing throughwhich the individual has made the forced expiration to rush in and fillit. This sample represents the air from the alveoli (see page 302), andis analyzed for percentages of (()., and 02. Since each normal inspira-tion dilutes the alveolar air somewhat, it is necessary, for constant re-. Fig. 124.—Apparatus for collection of a sample of alveolar air by Ilalrlanes method. It isbetter to use a mouthpiece than a mask. suits, to make two analyses of alveolar air from each subject, one takenat the end of a normal inspiration and the other at the end of normalexpiration. The average of the two results is taken as the compositionof the alveolar air. On account of the difficulty in securing intelligent cooperation in theapplication of this method, particularly with children, others have beendeviled. One of the simplest is that of Fridericia, which is a modification of the Haldane-Priestley method, the apparatus for which is shownin the figure (Fig. 125), and the manipulation of which is outlined inthe legend. Another is to take a mixed sample of the very last portionof several normal expirations. On account of the extended use which isbeing made of measurements of alveolar air composition, both in lab- *In place of the gas sa
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