THE AVERAGE TIME SPENT BY THE BLOOD IN THE HUMAN LUNG CAPILLARY AND ITS RELATION TO THE RATES OF CO UPTAKE AND ELIMINATION IN MAN

Abstract

The avg. time, tL) which the blood spends in passing through the lung capillaries is of interest, since it is only during this phase of the circulatory cycle that exchange of gases between the blood and air is possible. A knowledge of the value of tL. is therefore important in several kinetic problems of respiration. A theoretical method of calculating tL is described and its reliability critically discussed. Its accuracy in normal man is believed to be of the order of [plus or minus] 30%. The avg. value is 0.75 [plus or minus] 0.25 sec. for normal men; at rest, and 0.34 [plus or minus] 0.1 sec. in hard work. These values are of the order of magnitude to be expected from other physi-ological data. The total vol. of the blood in the patent lung capillaries is also calculated from tz. In normal men it; averages 60 ml. at rest and 95 ml. in hard work, thus indi-cating that no very extensive opening up of extra capillaries occurs in the lungs during exercise. Applications of, the new data to the kinetics of CO uptake and elimination in the lungs of man are discussed.