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.

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    is soldered an ordinary %-inch three-way brass valve. Near this is soldered a small brass tap suitable for the attachment of small rubber tubing for taking samples of air. Over the top of the disk is stretched a woman’s rubber bathing-cap, held in place on the flange by a large rubber band. The subject, with his nose clamped, breathes through a mouthpiece which is attached by a short piece of wide-bore rubber tub¬ ing to the three-way tap in the bottom of the copper disk. The tap is at first turned so that the subject breathes to the outer air. It is then turned so that the subject breathes in and out of the bag for a given length of time. The tap is then turned again, the bag is closed and a sample of air taken from the bag for analysis. Porges begins with the bag empty, lets the subject take a deep inspiration, and at the height of the inspiration turns the tap so that the subject expires into the bag and then rebreathes. Experiments with this technic, however, show that the tension of the carbon dioxid in the bag varies considerably with the depth of the initial inspiration, and thus with the amount of air in the system of respiratory tract plus bag. In the following the time and number of respirations were constant: March 13; B.: Moderately deep initial inspiration: C02 =43.2 mm. Deeper initial inspiration: C02 = 41.5 mm. Very deep initial inspiration: C02 = 38.2 mm. Controls by Haldane method: Inspiration, C02 = 41.2 mm. Expiration, C02 = 41.2 mm. This source of error is to some degree at least avoided if one follows the suggestion of Higgins and fills the bag with a constant volume of air. The tap is then turned at the end of a normal expiration, and the patient begins by inspiring from the bag. This is the method which we have adopted, but instead of filling the bag with 600 c.c. of air (Hig¬ gins) we find it more satisfactory to fill with 1,000 c.c. of air, and thus allow the subject to take a deeper inspiration. The air is forced into the rubber bag through the small tap by water displacement from an ordinary flask. The time during which breathing takes place is of considerable importance. Porges4 states that after from twenty to thirty seconds there is very little change in the composition of the air. His experiments, however, show that practically there may be a considerable rise in the carbon dioxid tension if the same air is rebreathed for twenty- five-second periods after various intervals. We have performed a similar experiment and have found that after breathing from the bag four times in twenty seconds the carbon dioxid tension of the air in the bag was 39.5 mm. After an interval of three and one-half minutes the same air was rebreathed for two periods of twenty seconds each, the periods sepa-