Oxygen and carbon dioxide permeability of subcutaneous pockets

¹ Naval Medical Research Institute, National Naval Medical Center, Bethesda, Maryland; and Department of Physiology, Harvard School of Public Health, Boston, Massachusetts

Uptake rate of a gas from a rat's subcutaneous gas pocket was divided by the surface area and by the apparent pocket-to-tissue tension difference to yield an exchange coefficient, K'. Values in (ml x 10^–4)/(min cm² atm) were O₂, 6.6; CO₂, 150; and N₂, 2. Blood flow in adjacent tissue appeared to have little influence on uptakes of O₂ and CO₂, since the K'co₂:K'o₂ ratio indicated that the uptakes were governed by diffusion alone, and drastic alteration of blood flow (death of the animal) decreased K'o₂ by only 10%. In contrast, blood flow apparently affected N₂ uptake. Because O₂ and CO₂ uptakes were not blood flow limited, K'o₂ and K'co₂ are estimates of true permeability coefficients; the calculated permeability coefficient for N₂ is 3.3 (ml x 10^–4)/(min cm² atm). Comparison shows the pocket surface to be 1/50–1/150 as effective for O₂ transfer as the lung. Finally, corrections are calculated for pocket-to-tissue pO₂ and pCO₂ differences in gas pockets used for tissue tonometry.