Physiology, Ocular, Microcirculation, Regional Blood Flow, Autoregulation
Conditions
Brief summary
Autoregulation is the ability of a vascular bed to maintain blood flow despite changes in perfusion pressure. For a long time it had been assumed that the choroid is a strictly passive vascular bed, which shows no autoregulation. However, recently several groups have identified some autoregulatory capacity of the human choroid. In the brain and the retina the mechanism behind autoregulation is most likely linked to changes in transmural pressure. In this model arterioles change their vascular tone depending on the pressure inside the vessel and outside the vessel. In the choroid, several observations argue against a direct involvement of arterioles. However, the mechanism behind choroidal autoregulation remains unclear. In the present study autoregulation of the choroid will be investigated during a decrease in ocular perfusion pressure, which will be achieved by an increase in intraocular pressure. Pressure/flow relationships will be investigated in the absence or presence of a NO synthase inhibitor. As a control substance the alpha-receptor agonist phenylephrine will be used.
Interventions
PROCEDURESuction cup application
he IOP will be raised by a 11 mm diameter, standardized suction cup placed on the temporal sclera with the anterior edge at least 1 mm from the limbus.
PROCEDURELaser Doppler flowmetry
Measurement of choroidal blood flow
PROCEDUREMeasurement of intraocular pressure
Sponsors
Medical University of Vienna
Study design
Allocation
RANDOMIZED
Intervention model
CROSSOVER
Primary purpose
TREATMENT
Masking
TRIPLE (Subject, Investigator, Outcomes Assessor)
Eligibility
Sex/Gender
MALE
Age
19 Years to 35 Years
Healthy volunteers
Yes
Inclusion criteria
* Men aged between 19 and 35 years, nonsmokers * Body mass index between 15th and 85th percentile (Must et al. 1991) * Normal findings in the medical history and physical examination 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
Design outcomes
Primary
| Measure | Time frame |
|---|---|
| ocular perfusion pressure - choroidal blood flow relationship | — |
Countries
Austria
Outcome results
None listed