Observation and characterization of microvascular vasomotion using erythrocyte mediated ICG angiography (EM-ICG-A)

•Primate erythrocytes are isolated from blood, and ICG dye is sequestered in them.•High-speed ICG fluorescence angiograms are acquired for 12.5 seconds.•Numerous erythrocytes pause temporarily in capillaries due to pressure gradient reduction across the capillairies (vasomotion manifestation).•The angiogram images are softwawe analyzed to find each pausing erythrocyte and record the pausing duration.•These data plotted in an histogram, which characterizes the vasomotion state.

A clinical method for characterizing the state of micro-vasculature vasomotion is demonstrated, based on observing in capillaries the dynamics of autologously re-injected erythrocytes containing ICG dye. Since a manifestation of vasomotion is transient erythrocyte pausing, vasomotion state within a field of capillaries is characterized by an histogram plot of the number of paused erythrocytes as a function of pause duration during a fixed period of observation, then the ratio of long-pausing to short-pausing erythrocytes was calculated. The method was first applied to the posterior pole retinal vasculatures of anesthetized-monkey eyes, and normal vasomotion state during air-breathing was compared to the state induced by O2-breathing, known to cause mild arteriolar vasoconstriction in the mature eye. Subsequently, the effects of other antagonists to normal arteriolarvasotonia state (long-standing experimentally-induced ocular hypertension and branch-vein occlusion, as well as tissue edema) were similarly characterized and the results compared to those obtained during baseline air-breathing. The feasibility of applying the histogram characterization of vasomotion state to human eyes and skin was also preliminarily explored.