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Yuhua Zhang, Xiaolin Wang, Boyu Gu; High-order hemodynamic properties of erythrocyte flow in human retinal capillaries. Invest. Ophthalmol. Vis. Sci. 2021;62(8):1764.
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Purpose: To characterize retinal hemodynamics and identify sensitive biomarkers for quantifying age-related changes in retinal microcirculation, we investigate high-order dynamic characteristics relating to the time derivatives of the velocity of erythrocyte flow in human retinal capillaries, using high speed adaptive optics ophthalmoscopy.
Erythrocyte flows in retinal capillaries were imaged in human subjects with normal healthy retinae using an adaptive optics near-confocal ophthalmoscope (AONCO) at a frame rate of 800 Hz. Continuous pulsatile velocity of the erythrocytes flowing in the capillary was measured from the consecutive frames. In addition to conventional measures of the velocity (Figure 1), such as the maximum (Vmax), the minimum (Vmin), the mean velocity (Vm), the amplitude (Vd), and the pulsatility index (PI), we proposed new metrics, including the maximum acceleration (Amax), the acceleration time index (Tp), the rising rate (Rr). We further introduced the acceleration change index (AI) of the second order derivative of the velocity for estimating the acceleration change. This metric has been used to assess age-related vascular stiffness in photoplethysmography. Hemodynamic characteristics were measured in human subjects in normal physical health in 2 age groups: 24-25 years old (n = 8) and 50-60 years old (n = 4).
Conventional measures pertaining to the velocity (Vmax, Vmin, Vm, Vd, and PI) showed no difference between the 2 age groups. In contrast, high-order characteristics disclosed significant differences (Figure 2). The prolonged Tp for cells to reach peak velocity in one cardiac cycle may indicate that the capillary or the erythrocytes have higher rigidness that increases the friction between the cell and the capillary, thereby delaying the time to reach the maximum velocity. Likewise, increased stiffness may increase the Rr and reduced Amax as well as AI.
High-order hemodynamic characteristics of the erythrocyte flow in the retinal capillary provide new and sensitive biomarkers for assessing age-related changes in the retinal microcirculation that cannot be differentiated by conventional metrics. These metrics may reflect the mechanical properties of the erythrocyte-capillary system.
This is a 2021 ARVO Annual Meeting abstract.
Hemodynamic characteristics of the pulsatile erythrocyte velocity
Retinal hemodynamic characteristics measured in subjects in normal health with different ages
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