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.