Using a University of Pennsylvania-designed device to noninvasively and continuously monitor cerebral blood flow (CBF) in acute stroke patients, researchers from Penn Medicine and the Department of Physics and Astronomy in Penn Arts and Sciences are now learning how head of bed (HOB) positioning affects blood flow reaching the brain.

In research published in Stroke, Penn scientists found blood flow to the brain hemisphere where the stroke damaged tissue was reduced by 9 percent when the HOB was elevated 15 degrees, and 17 percent lower when elevated 30 degrees. But in 29 percent of the patients, the optical method showed a “paradoxical” improvement in CBF when the bed was elevated. A prior study found almost the same proportion of “paradoxical” responders to HOB positioning, and in the combined cohort no clinical or radiological differences predicted an expected versus a paradoxical response.

“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, M.D., a Penn stroke neurologist involved in the study, said in a statement accompanying the research's publication.

The Penn team has been developing and testing a new optical device that permits noninvasive and continuous monitoring of CBF at the patient’s bedside. The key technology development is a noninvasive probe placed on the surface of the head that measures the fluctuations of near-infrared light that has traveled 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 (DCS), proved to be more sensitive for detecting CBF changes with HOB positioning than the Transcranial Doppler (TCD), which uses acoustic waves to quantify blood flow velocity of the large arteries supplying the brain.

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