Figure 5. Calculation of the mean vascular measurements correcting for cardiac pulsation.

In order to minimize the influence of cardiac pulsation on vascular measurements, the cardiac cycle was synchronized to the adaptive optics (AO) videos using pulsation data obtained through a pulse oximeter attached to the subjects’ earlobes. (a) The cardiac cycle was divided into 5 segments (0–0.2, 0.2–0.4, 0.4–0.6, 0.6–0.8, and 0.8–1.0), and each video frame was assigned to the corresponding segment. (b) The images on the same relative cardiac cycle were extracted from the AO videos. (c) The images of each corresponding segment were averaged, and the vascular caliber measurements were obtained for every 5 segments. Finally, the vascular measurements of 5 segments were averaged and used for analyses.