LASER-DOPPLER FLOWMETRY MEASUREMENT OF CHANGES IN HUMAN OPTIC-NERVE HEAD BLOOD-FLOW IN RESPONSE TO BLOOD-GAS PERTURBATIONS

Purpose: The objective of this study was to establish the ability of l aser Doppler flowmetry to detect relative changes in human optic nerve head hemodynamics caused by physiologic blood gas perturbations. Meth ods: Laser Doppler flowmetry permits the noninvasive assessment of rel ative blood velocity, volume, and flow (flux) in a sample volume of th e nerve head. Such measurements were performed in two groups of health y subjects. The first group (n = 11) was tested during normal room air breathing and then while breathing 100% oxygen (isocapnic hyperoxia). The second group (n = 10) was also tested under normal conditions as well as during isoxic hypercapnia (+15% end-tidal carbon dioxide). Res ults were analyzed by paired t tests. Results: Hyperoxia created a sig nificant 255 (p = 0.002) decrease in optic nerve head blood flow, with blood volume decreased by 9% (p = 0.095) and blood velocity reduced b y 13% (p = 0.154) compared to the room air condition. During hypercapn ia, optic volume increased by 22% (p = 0.017) and blood velocity incre ased by 9% (p = 0.218) as compared to the normal room air condition. C onclusion: Blood flow in the optic nerve head capillaries changes in r esponse to hyperoxia and hypercapnia as demonstrated in the brain and retina. Laser Doppler flowmetry permits the noninvasive assessment of these responses in humans under conditions within the physiologic rang e.