Bedside Monitoring of Brain Blood Flow in Stroke Victims

A new study describes the first successful demonstration of a noninvasive optical device to monitor cerebral blood flow in patients with acute stroke, a leading cause of disability and death.

Researchers at the University of Pennsylvania (Penn, Philadelphia, USA) have developed diffuse correlation spectroscopy (DCS), a technology for noninvasive transcranial measurement of cerebral blood flow (CBF) that can be hybridized with near-infrared spectroscopy (NIRS). As part of the development, the research then examined the utility of DCS and NIRS to measure the effects of head-of-bed (HOB) positioning of the patient on CBF at 30 degrees, 15 degrees, 0 degrees, -5 degrees, and 0 degrees angulations in patients with acute ischemic stroke affecting the frontal cortex, as well as in controls. HOB positioning was found to significantly alter CBF, oxy-hemoglobin (HbO2), and total-hemoglobin (THC) concentrations. Moreover, the researchers also found that the presence of an ipsilateral infarct was a significant effect for all parameters. The results were found to be consistent with the notion of impaired CBF autoregulation in the infarcted hemisphere. The study was published in the March 2009 issue of Optics Express.

"Our preliminary study demonstrates that blood flow changes can be reliably detected from stroke patients and also suggests that blood flow responses vary significantly from patient to patient," said lead author Turgut Durduran, Ph.D., of the High Energy group at the department of physics.

"Stroke is caused by a reduction in blood flow to the brain, yet brain blood flow is rarely if ever measured in stroke patients because most existing methods to measure blood flow require costly instrumentation that is not portable," said clinical collaborator John Detre, M.D., of the department of neurology in the School of Medicine. "The ability to quantify tissue hemodynamics at the bedside would provide new opportunities both to learn more about blood-flow changes in patients with acute stroke and to optimize interventions to increase blood flow for individual patients, potentially even allowing these interventions to be administered before the onset of new neurological symptoms."

The new noninvasive system uses embedded optical probes that are placed over major cortical blood vessels in each hemisphere of the brain. The probes use diffusing light to detect physiological changes such as blood flow, blood-oxygen saturation (SpO2), and hemoglobin concentration to inform clinicians about their treatments. The system uses lasers, photon-counting detectors, radio-frequency electronics, data processors, and a computer monitor to display user-friendly images of functional information to physicians and nurses.

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