View clinical trials related to Regional Blood Flow.
Filter by:The aim of this project is to demonstrate that fluorescence-mediated photoplethysmography (FM-PPG) is capable of routinely acquiring the tissue perfusion data sufficient to detect and monitor skin tissue perfusion anomalies.
Autoregulation is the ability of a vascular bed to maintain blood flow despite changes in perfusion pressure. The existence of an effective autoregulation in the optic nerve circulation has been shown in animals and humans. The exact mechanism behind this autoregulation is still unknown. The motive for the investigation of optic nerve head (ONH) blood flow autoregulation is to enhance the understanding of pathologic eye conditions associated with ocular vascular disorders. To clarify the regulatory mechanisms of ONH microcirculation is of critical importance to understand the pathophysiology of glaucoma because there is evidence that glaucoma is associated with optic nerve head ischemia. Several studies indicate that a disturbed autoregulation might contribute to glaucomatous optic neuropathy. Previous findings suggest endothelial dysfunction in glaucomatous optic neuropathy, in particular alterations in endothelin- and nitric oxide- system, which both play an important role in local regulation of vascular tone. In the present study, changes in ocular perfusion pressure will be performed during administration of drugs, which may potentially alter the pressure-flow relationship. These drugs include endothelin-1 and the nitric oxide synthase inhibitor NG-monomethyl-L-arginine (L-NMMA).
The visual disorder of amblyopia affects 2% to 3% of the population. Amblyopia is a developmental condition that is characterized by reduced vision of the eye due to the presence of a sensory impediment during visual development, such as strabismus (ocular misalignment) or anisometropia (unequal refractive error), occurring early in life. Recent studies in humans and animals point towards a cortical locus for the processing deficit in amblyopia, revealing sensory deficits at the signal cell level that include reduced spatial resolution, reduced contrast sensitivity, and a reduced number of binocular neural cells. In the retina, however, no abnormalities have yet been reported. Like in the brain blood flow in the retina is coupled to neuronal activity. This phenomenon has been measured by different study groups with non invasive techniques in the brain and retina. We therefore use a Zeiss fundus camera for the assessment of retinal vessel diameters. This so called retinal vessel analyzer (RVA) is a combination of a fundus camera connected to a high resolution video camera equipped with a software based analyzing system. An unprecedented reproducibility and sensitivity of retinal vessel diameter measurements is attained with this system. In addition this system allows real time analysis of retinal vessels as well as off-line determinations from video tape. A special provocation test, which minimizes risk and discomfort to the subject under study is applied through the illumination pathway of the fundus camera: Diffuse luminance flicker is used as a stimulus to augment intrinsic mechanisms by which the retina can vary the vascular supply, in correspondence with local variations of functional activity. This system allows to study the flicker response of retinal vessels, which is within a magnitude of 6 to 8%. However, the exact mechanisms underlying this phenomenon are not fully understood. Especially in the eye it is not clear whether it is an exclusive metabolic effect within the retina and the surrounding blood vessels or dependent of central regulatory brain functions. The purpose of the current study is to improve our understanding of the mechanisms underlying flicker evoked responses of retinal blood vessels in humans. It is not clear whether the retina of amblyopic eyes can regulate retinal blood flow in response to increased metabolic demands as induced during flicking light stimulation. A detail understanding of the metabolic and functional processes within the retina of patients with amblyopia is a prerequisite for further research to prevent amblyopia.