Home
Search
Study Topics
Glossary
|
|
|
|
|
|
Sponsored by: |
Medical University of Vienna |
---|---|
Information provided by: | Medical University of Vienna |
ClinicalTrials.gov Identifier: | NCT00814047 |
Blood flow autoregulation is defined as the ability of a tissue to maintain a relatively constant flow, despite moderate alterations in perfusion pressure. Similar to the cerebral, renal, coronary and skeletal muscle circulations, the ocular vascular bed shows the property of flow autoregulation. This homeostatic mechanism allows blood supply to the eye to match metabolic demand during daily activities, such as changes in posture, or in more critical conditions.
Autoregulation has been found to be a complex phenomenon, showing heterogeneity in its site and time course of action. Since metabolic, myogenic, neurogenic and possibly endothelium-related mechanisms may be involved, several factors may vary depending on the challenging stimulus, the vessel tone, or the degree of impairment of autoregulation.
To study the dynamics of ocular autoregulation, it is necessary to introduce a step disturbance (stimulus) in ocular perfusion pressure and to record the responses of ocular blood flow continuously before and after this step disturbance. The investigators have employed a mechanical noninvasive technique to induce an ocular perfusion pressure step disturbance without drugs or changes in the concentration of vasoactive substances in the blood by using the thigh cuff technique inducing a small step decrease in ocular perfusion pressure.
With this technique the investigators could show significant differences in the time response of blood velocities in the ophthalmic and middle cerebral artery. This clearly indicates different mechanisms to be responsible for autoregulatory mechanisms distal to the vessels.
Interestingly our results indicate that in the ophthalmic artery a late vasoconstriction occurs. Many previous investigations have demonstrated that sympathetic nerve stimulation causes vasoconstriction in the ocular circulation. Accordingly, the present study tests the hypothesis that α2-adrenoceptors are involved in the dynamic regulation of blood flow in the ophthalmic and middle cerebral artery after a step decrease in perfusion pressure.
Condition | Intervention | Phase |
---|---|---|
Blood Flow Velocity Autoregulation Ocular Physiology |
Drug: Yohimbine hydrochloride |
Phase IV |
Study Type: | Interventional |
Study Design: | Treatment, Randomized, Double-Blind, Placebo Control, Crossover Assignment, Safety/Efficacy Study |
Official Title: | The Effect of an α2-Adrenoceptor Antagonist (Yohimbine) on Dynamic Autoregulation in the Human Middle Cerebral Artery and Ophthalmic Artery |
Ages Eligible for Study: | 18 Years to 35 Years |
Genders Eligible for Study: | Male |
Accepts Healthy Volunteers: | Yes |
Inclusion Criteria:
Exclusion Criteria:
Austria | |
Department of Clinical Pharmacology, Medical University of Vienna | |
Vienna, Austria, 1090 |
Principal Investigator: | Gabriele Fuchsjäger-Mayrl, MD | Department of Clinical Pharmacology, Medical University of Vienna |
Responsible Party: | Department of Clinical Pharmacology, Medical University of Vienna ( Gabriele Fuchsjaeger-Mayrl, MD ) |
Study ID Numbers: | OPHT-280604 |
Study First Received: | December 22, 2008 |
Last Updated: | December 22, 2008 |
ClinicalTrials.gov Identifier: | NCT00814047 |
Health Authority: | Austria: Agency for Health and Food Safety |
ultrasonography |
Oculocerebrorenal Syndrome Yohimbine Oculocerebrorenal syndrome |
Neurotransmitter Agents Mydriatics Molecular Mechanisms of Pharmacological Action Adrenergic Agents Autonomic Agents |
Physiological Effects of Drugs Adrenergic Antagonists Peripheral Nervous System Agents Adrenergic alpha-Antagonists Pharmacologic Actions |