The Effect of an α2-Adrenoceptor Antagonist (Yohimbine) on Dynamic Autoregulation in the Human Middle Cerebral Artery and Ophthalmic Artery

December 22, 2008 updated by: Medical University of Vienna

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.

Study Overview

Status

Completed

Conditions

Intervention / Treatment

Study Type

Interventional

Enrollment

18

Phase

  • Phase 4

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Locations

  • Austria
      • Vienna, Austria, 1090
        • Department of Clinical Pharmacology, Medical University of Vienna

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

18 years to 35 years (Adult)

Accepts Healthy Volunteers

Yes

Genders Eligible for Study

Male

Description

Inclusion Criteria:

  • Men aged between 18 and 35 years
  • Non-smokers
  • Normal findings in medical history and pre-study screening unless the investigator considers an abnormality to be clinically irrelevant
  • Normal laboratory values unless the investigator considers an abnormality to be clinically irrelevant
  • Normal ophthalmic findings, ametropia < 3 Dpt.

Exclusion Criteria:

  • Regular use of medication, abuse of alcoholic beverages, participation in a clinical trial in the 3 weeks preceding the study
  • Treatment in the previous 3 weeks with any drug
  • Symptoms of a clinically relevant illness in the 3 weeks before the first study day
  • History of hypersensitivity to the trial drug or to drugs with a similar chemical structure
  • History or presence of gastrointestinal, liver or kidney disease, or other conditions known to interfere with, distribution, metabolism or excretion of study drugs
  • Blood donation during the previous 3 weeks

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Treatment
  • Allocation: Randomized
  • Interventional Model: Crossover Assignment
  • Masking: Double

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Relation between blood pressure and local perfusion parameters.

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Medical University of Vienna

Investigators

  • Principal Investigator: Gabriele Fuchsjager-Mayrl, MD, Department of Clinical Pharmacology, Medical University of Vienna

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Registration Dates

First Submitted

December 22, 2008

First Submitted That Met QC Criteria

December 22, 2008

First Posted (Estimate)

December 23, 2008

Study Record Updates

Last Update Posted (Estimate)

December 23, 2008

Last Update Submitted That Met QC Criteria

December 22, 2008

Last Verified

December 1, 2008

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • OPHT-280604

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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