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Study: Optical cerebral blood flow monitoring may aid stroke care

Wednesday April 2, 2014
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Using a new device to continuously monitor cerebral blood flow in acute stroke patients, researchers found most patients’ blood flow was highest when the head of the bed was flat. However, about 25% actually showed the highest blood flow with their heads elevated, the study found.

Most patients admitted to the hospital with an acute stroke are kept flat for at least 24 hours to increase CBF in vulnerable brain regions around the damaged tissue. Findings from the study, published March 20 on the website of the journal Stroke, could lead to more personalized stroke care, according to the authors.

The research team from Penn Medicine and the University of Pennsylvania’s Department of Physics and Astronomy has been developing and testing a noninvasive optical device that continuously monitors CBF at the bedside. The device includes a noninvasive probe placed on the surface of the patient’s head measuring the fluctuations of near-infrared light that has travelled through the skull and into the brain, then back out to the tissue surface. These fluctuations are caused by moving red blood cells in tissue and have been shown to accurately track CBF in underlying brain tissue.

The novel optical technique, called diffuse correlation spectroscopy, proved to be more sensitive for detecting CBF changes with head of bed positioning than the transcranial Doppler ultrasound, which measures blood flow velocity of the large arteries supplying the brain.

“This study illustrates the potential of using advanced technology to make individualized treatment decisions in real time,” senior author John A. Detre, MD, professor of neurology and radiology in the university’s Perelman School of Medicine, said in a news release. “While, on average, our findings support current guidelines to lay patients flat following stroke, they also suggest that for some stroke patients, lying flat may be either unnecessary or even harmful. Future studies examining clinical outcomes after stroke and using optical CBF measurements to guide management will be needed to confirm this.”

Stroke is the leading cause of disability in industrialized nations and one of the leading causes of death so even subtle improvements in stroke outcomes can be expected to have a significant public heath impact.

A reduction in CBF causes stroke so most current interventions for stroke are intended to increase CBF. Yet, CBF is rarely measured in stroke patients and if CBF is measured it is usually a single measurement from a CT or MRI scan taken while the patient is lying flat. While CT and MRI are critical diagnostic tools used in stroke management, they are not well suited for assessing response to clinical interventions over time.

“We believe that these optical CBF measurements are detecting brain tissue blood flow of local microvasculature that might differ due to injury,” Arjun Yodh, PhD, a professor in the Department of Physics & Astronomy who has led the development of this new technology, said in the release.

For the study, 17 stroke patients were recruited from the Comprehensive Stroke Center at the Hospital of the University of Pennsylvania. All of the participants had unilateral acute ischemic stroke that affected large cortical areas in the anterior circulation. Researchers used diffuse correlation spectroscopy to measure frontal CBF while simultaneously using transcranial Doppler ultrasound to measure arterial flow velocity.

Averaged across all patients, blood flow to the brain hemisphere where the stroke damaged tissue was reduced by 9% when the head of bed was elevated 15 degrees, and 17% lower when elevated 30 degrees, researchers found. But in 29% of the patients, the optical method showed a “paradoxical” improvement in CBF when the bed was elevated. A past study also found almost the same proportion of “paradoxical” responders to elevated head-of-bed positioning.

Investigators found clinical features, stroke volume or distance to the optical probe did not explain the paradoxical response in some patients.

“Our study suggests that it would be impossible for stroke clinicians to know whether HOB flat is optimal without actually measuring the response,” Michael Mullen, MD, a Penn stroke neurologist involved in the study, said in the release.

This also may be true for other clinical interventions such as administration of fluids, withholding antihypertensive therapies or using medications to raise blood pressure, he added.

“The ability to measure cerebral blood flow continuously has tremendous potential and may one day allow clinicians to individualize therapy for each patient,” Mullen said in the release.

“We hope this technology will be able to guide management in advance of clinical symptoms,” Yodh said. While the optical CBF instrumentation used in the study required a team of physicists to acquire and analyze the data, newer versions can be operated by clinical personnel and provide a real-time CBF display.

The study was funded by grants from the National Institutes of Health’s National Institute of Neurological Disorders and Stroke, the Eunice Kennedy Shriver National Institute of Child Health and Human Development, the National Institute of Biomedical Imaging and Bioengineering, the Sao Paolo Research Foundation and Fundacio Cellex.

Study abstract: http://bit.ly/1lavuzX

To see what else is trending in Stroke, visit www.Nurse.com/Stroke.


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