Effect of Respiratory Gases Upon Choroidal Hemodynamics

Introduction  These experiments were performed to measure choroidal blood volume and blood flow in albino rabbits breathing room air; 100% oxygen; 10% carbon dioxide, 90% oxygen; and 10% carbon dioxide, 21% oxygen, 69% nitrogen gas. The simultaneous measurement of the orbital arterial blood pressure during the determination of blood flow allows comparison of the vasomotor tone of the choroidal bed as the respiratory gases were changed.Kety et al¹ devised the nitrous oxide technique to study changes in the average cerebral blood flow in human subjects. This work focused attention upon changes in regional blood flow with changes in the respiratory gas mixtures. In a group of normal human subjects breathing gases with elevated oxygen tensions, Kety demonstrated a decrease in the average cerebral blood flow from 52 to 45 ml/100 gm/min. This was accompanied by an increase in vascular resistance from 1.7 to 2.2 units. Further studies documented