A comparison of methods of obtaining alveolar air / Walter M. Boothby, M.D., and Francis W. Peabody, M.D. Boston.

  • Boothby, Walter M.
Date:
1914
Catalogue details

Licence: In copyright

Credit: A comparison of methods of obtaining alveolar air / Walter M. Boothby, M.D., and Francis W. Peabody, M.D. Boston. Source: Wellcome Collection.

    5/16 (page 3)
    The relative accuracy of the Haldane method with and without the valve is shown by the following observation: April 9, 9 a. m.; B.: With valve: Inspiration, C02 = 41.1 mm.; expiration, C02 = 41.3 mm. Without valve: Inspiration, C02=39.9 mm.; expiration, C02 — 40.1 mm. The Haldane method in one of its various modifications should be classed as the standard method of taking samples of alveolar air since it undoubtedly gives the most accurate values when used under proper conditions. Its clinical applicability is limited to patients who are in comparatively good health. To obtain satisfactory samples it is necessary not only that the expiration should be as complete as possible, but also that it be rapid and forcible. A slow prolonged expiration is not suffi¬ cient. Many sick patients are unable, on account of pain or dyspnea or weakness, to give an expiration of enough force and depth. In these and in patients of distinctly low intelligence the method is unreliable. We have found, moreover, that even among intelligent, healthy persons it frequently takes considerable training before satisfactory results are obtained. THE LINDHAKD METHOD Lindhard2 has recently described the following very ingenious way of obtaining alveolar air: The subject breathes through a Krogh glass valve with rubber flaps and dead space of from about 40 to 50 c.c. Through an opening directly opposite the mouth is passed a small flexible lead tube with an interior bore of about 1 mm. This lead tube passes back into the pharynx so far as possible for comfort. The samples of air are drawn with a sampling-tube in 3 or 4 c.c. amounts at the end of a nor¬ mal expiration. Accordingly to Krogh and Lindhard, this is reliable in subjects breathing 600 c.c. or over per respiration. The essential point in this method is the exact time at which the samples are taken, and this is somewhat difficult for the observer. If taken either just too early or too late alveolar air is not obtained. The movement of the rub¬ ber valve-flaps is an aid in timing. We have made an extensive trial of this method and have found it to check up with the Haldane method if the subject breathed deeply. In the ordinary person 300 or 400 c.c. is the normal expired air; therefore, we were obliged to have the subject exhale about double his usual amount on a given signal; we repeated these deep exhalations about every forty- five seconds. In order to determine more accurately the influence of the depth of expiration on this method of taking alveolar air, the valves were attached to a recording spirometer, and the volume measured of those expirations, at the end of which the samples were taken. 2. Linhard: Jour. Physiol., 1911, xlii, 337.