Douglas Bag, 1916

Douglas_Bag_1916

From: The respiratory exchange of animals and man by August Krogh, 1916, page 42.

“Regnard [1879] collected the expired air in a rubber bag from which it was afterwards delivered and measured through a meter, but his bags were probably not tight against diffusion and his technique very faulty.  This principal, however, is excellent for certain types of experiments, and it has recently been revived by Douglas who has worked out a method which is specially adapted for the study of the respiratory exchange during open-air exercise in circumstances where all other instruments would fail, but which also prove useful in a number of other cases, e.g. on bed-ridden patients (Fig. 17). The subject breathes during an introductory period through the mouthpiece and valves.  When it is desired to make an experiment the three-way tap is turned so as to connect with the bag and the expired air collected over a certain period.  With violent exercise a bag taking 60 liters will not hold the air expired during one minute, but is has been shown (Krogh [1913]) that experiments of even shorter duration are sufficient to give perfectly reliable results. The air collected in the bag is afterwards analysed and measured by connecting with a gas meter of suitable size and pressing the air slowly out of the bag. When a gas analysis is considered a thing to be avoided the contents of the bag can be taken through a Haldane set of vessels for absorbing water vapour and carbon dioxide and the total carbon dioxide determined by weighing.”

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.