[Physiological mechanism of stabilization of O2 pressure in capillary blood]

The pattern of changes in pO2 in the blood of arterioles (5-100 microns in diameter) and capillaries (3-5 microns in diameter) of the rabbit pia mater was examined in the course of pO2 fluctuations in femoral arterial blood (paO2) within the range of 160-150 mm Hg. Observations over paO2 fluctuations demonstrated that the lesser the diameter of arterioles the less noticeable the changes in pO2 of arteriolar blood. The magnitudes of the blood pO2 in the venous area of the capillaries were, within the range indicated, actually independent of the paO2 changes. Stabilization of the pO2 magnitudes in the capillary blood was determined by O2 diffusion through the arteriolar wall and by the shape of the hemoglobin dissociation curve.