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Bruce I. Gaynes, Pang-Yu Teng, Justin M. Wanek, Mahnaz Shahidi; Hemorheologic and Hemodynamic Response of Conjunctival Microcirculation to Acute Hypotension in Rabbits. Invest. Ophthalmol. Vis. Sci. 2012;53(14):6834.
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Understanding microcirculatory pathophysiology as result of disease and/or drug or surgical treatment is an important yet relatively underappreciated facet of clinical patient management. Quantification of conjunctival microvascular hemodynamics and hemorheologics may provide valuable insight into perturbation of microcirculation perfusion as a consequence of vascular compromise. In this study, the feasibility of quantifying the conjunctival hemodynamic response to acute hypotension was evaluated.
Image sequences of the conjunctival microvasculature of anesthetized rabbits were captured using a previously developed slit lamp biomicroscope imaging system. Hemodynamic parameters consisting of venous diameter (D), blood velocity (V), blood flow (Q), and wall shear stress (WSS) were derived by image analysis. The reproducibility and validity of hemodynamic parameters were established by obtaining repeated measurements in venules and measuring changes after topical administration of phenylephrine. Conjunctival hemodynamic and hemorheologic responses to acute hypotension were evaluated by intravenous administration of esmolol.
Venous D and V measurements ranged from 9 to 34 microns (19 ± 7 microns, mean ± SD, N = 16) and 0.13 to 0.99 mm/s (0.37 ± 0.27 mm/s), respectively. Calculated values of Q and WSS ranged from 14 to 307 pL/s (102 ± 80 pL/s) and 0.8 to 29.2 dynes/cm2 (5.5 ± 7.6 dynes/cm2), respectively. The coefficient of variations of D, V, Q, and WSS measurements were on average 7%, 21%, 25%, and 27%, respectively. With phenylephrine administration, venous diameter was reduced on average by 21%. With esmolol administration, a marked reduction in blood pressure was noted with a concomitant decrease in V, Q, and WSS, with increased D. Venous V, Q, and WSS were positively correlated (R > 0.92; p < 0.002; N≥ 7) and D was negatively correlated (R < -0.73; p < 0.035; N ≥ 7) with blood pressure.
Alterations in microvascular hemodynamics due to experimental hypotension can be readily measured in the bulbar conjunctiva thereby providing an accessible and potentially exploitable approach to effectively evaluate microcirculatory hemorheologic and hemodynamic parameters related to cardiovascular disease and its treatment.
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