Regulation of ocular blood flow during increases of arterial blood pressure.

Abstract

The blood flow in the uvea in cats and monkeys during acute increases of arterial blood pressure is well controlied by a sympathetic mechanism protecting the eye from overperfusion. Ocular macrocirculation (ophthalmic artery) and ocular microcirculation (iris) were examined in 22 healthy subjects during acute increases of arterial blood pressure induced by physical exercise (125 W). With a data aquisition and storage software in real time mode several parameters of ocular perfusion and systemic functions were measured simultaneously. Blood flow parameters were measured in the ophthalmic artery by pulsed Doppler sonography and in the iris by laser Doppler flowmetry. Systolic, diastolic, and mean velocities of the ophthalmic artery peak velocity pulse curve, the ophthalmic artery mean velocity pulse curve, and the iris velocity pulse curve were estimated off line. The ophthalmic artery mean velocity pulse curve resembles the integrated velocity of ali erythrocytes in the vessel including the slowly running celis near the vessel wail. The iris velocity pulse curve was calculated by a special statistic procedure (ALDF). After exercise there was a significant increase in systolic and diastolic blood pressure and heart rate. The pulse curve of the ophthalmic artery showed significantly increased systolic and decreased diastolic velocities. The vascular resistance of the branches of the ophthalmic artery increased significantly. The iridal vasculature showed no significant change in blood celi velocity but an increased vascular resistance.It was observed that the elevated perfusion pressure was associated with an increased vascular resistance and a constant mean blood velocity in the ophthalmic artery and iridal vessels. The paraliel elevation of vascular resistance and blood pressure during exercise may be the reason for a constant blood flow in the ophthalmic artery and the iris. This may be accounted for by a sympathetic mechanism for protecting the eye from overperfusion. (BrJ3 Ophthalmol 1994; 78: 461-465) Several authors observed in rabbits, cats, and monkeys, a good regulation of the ocular blood flow during increased perfusion pressures. In these observations sympathetic stimulation reduced the blood flow in all parts of the uvea in these animals. The

Comportamento da pressão intra-ocular segundo os efeitos cardiorrespiratórios e hemodinâmicos induzidos pela anestesia com desflurano, em cães submetidos à hipovolemia experimental

“…Em humanos observou-se que a PAM elevada não alterava a Po, pois ocorria aumento na resistência vascular e a velocidade média de fluxo sangüíneo permanecia constante na arté-ria oftálmica e nas artérias ciliares (19) . Em suínos relata-se que a hipotensão arterial induzida por drogas não alterava a Po (20) .…”

Retinal Blood Flow Autoregulation after Dynamic Exercise in Healthy Young Subjects

“…Many studies have shown that choroid flow did not change during exercise because of autoregulation [1,2,3,4,5,6]. In particular the dynamic exercise should increase the flow velocity due to the increase in heart rate and systemic pressure, but theoretically local regulation could keep ocular flow at the same level or decrease the choroid and retinal capillary flow during exercise.…”

“…The parallel changes of vascular resistance and blood pressure during exercise might be the reason for a constant blood flow in the ophthalmic artery [6]. Some studies have analyzed ocular blood flow after dynamic exercise to understand ocular autoregulation.…”

“…This response could be due to a kind of valve system able to regulate retinal blood flow under some stressed condition. The autoregulation might be accounted for by a sympathetic mechanism for protecting the eye from overperfusion [6] together with the IOP reduction.…”

“…Different types of regulatory factors such as metabolic, myogenic and neurogenic factors can act on vascular tone systems. Although many factors such as age, heart, blood pressure, intraocular pressure (IOP) and psychic stress can influence the retinal blood flow, only few studies have examined the effect of physical exercise on orbital blood flow velocities of different ocular tissues [1,2,3,4,5,6]. …”