CIBA Foundation Symposium on Pulmonary Structure and Function

By A. V. S. De Reuck; Maeve O'Connor | Go to book overview

AS EXCHANGE PROCESSES IN THE PULMONARY CAPILLARIES*

R. E. FORSTER, MARGOT R. CRAW, H. P. CONSTANTINE and J. A. MORELLO Department of Physiology, Graduate School of Medicine, and Department of Anesthesiology, Schools of Medicine, University of Pennsylvania, Philadelphia

THE most important function of the lung is to promote the exchange of gases between alveolar air and pulmonary capillary blood. One normally assumes that the pulmonary structures of greatest importance in subserving this function are the capillaries because they present such a great surface area for exchange. However, present evidence indicates that the red cells themselves are of greater importance than the capillaries, or the pulmonary membrane, in limiting the speed with which equilibrating processes involving gases can take place in the lungs. Apparently the pulmonary vessels have subdivided into such small and thinwalled capillaries that the resistance to gas movement into the red cells themselves is often greater than that to gas movement from the alveoli into the blood.

A blood corpuscle is so small, approximating a disc 8.6 μ in diameter and 1.8 μ thick (Ponder, 1948), that it may seem unlikely that any gaseous diffusion processes between its interior and its environment would not be complete in a fraction of the time it remains in a tissue capillary, a time of the order of one second. However this intuition is not necessarily correct, owing in large part to the fact that in exchanging with the red cell, oxygen and

____________________
*
This work was supported in part by research grants from the Life Insurance Medical Research Fund and from the United States Public Health Service (H-4108).
Trainee of the United States Public Health Service (Grant H-5430).

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