I desire to record a phenomenon and to discuss its significance. The phenomenon is, the immediate reinspiration of a portion of our expired air. This occurs quite commonly — so commonly, in fact, that it is an accompaniment of respiration during the major part of the lives of many people, and during a large part of the lives of practically all.
The observation of this phenomenon is not new. Lehmann1 and Heymann2 have each reported a small group of experiments, in which they determined the carbon dioxid of the inspired air, compared this with the carbon dioxid of the surrounding air, and from the difference computed the proportion of the breath which was reinspired. The proportion varied greatly. It was sometimes more than 6 per cent.; it dropped to zero in the open air and in a breeze of 3 meters per second.
A few years ago
CROWDER TR. ON THE REINSPIRATION OF EXPIRED AIR. Arch Intern Med (Chic). 1913;XII(4):420-451. doi:10.1001/archinte.1913.00070040065005