When stroke patients are brought to a hospital, one of the critical aspects of their care is to make sure there is adequate blood flow to their brains. A standard of that care has to been to keep patients resting totally flat for at least 24 hours, rather than with their heads elevated. 

The problem with this practice is that existing scanning technology makes it impossible to tell if it is truly beneficial for a given patient. Currently, accurate and detailed measurements of cerebral blood flow can only be performed with CT or MRI scans. This means that a patient’s cerebral blood flow can only be measured at a single point in time, if at all, and only while he or she is lying flat. The only technique able to continuously make these measurements—transcranial doppler, similar to an ultrasound machine—is not accurate enough to show blood flow at the parts of the brain damaged by a stroke. 

Without a way to continuously monitor cerebral blood flow, doctors have no way of determining if lying a stroke patient flat might actually be doing more harm than good.  

An interdisciplinary team of Penn researchers from the Perelman School of Medicine and the Department of Physics and Astronomy in Penn Arts & Sciences has shown a way out of this dilemma. In a paper recently published in the journal Stroke, they demonstrated the efficacy of a Penn-developed device that can non-invasively measure cerebral blood flow using infrared light.

“This study illustrates the potential of using advanced technology to make individualized treatment decisions in real time” says the study’s senior author, neurology and radiology professor John A. Detre. “While, on average, our findings support current guidelines to lay patients flat following a stroke, they also suggest that for some stroke patients, lying flat may be either unnecessary or even harmful.”

The device, designed by Arjun Yodh, a professor in the Department of Physics & Astronomy who contributed to the study, uses sensors that are placed on a patient’s head and can detect the fluctuations of infrared light caused by moving red blood cells in that patient’s brain.

The patients who saw improvements while elevated were a significant minority: The researchers found that 29 percent of the patients they studied had improved cerebral blood flow when their heads were elevated the standard 30 degrees.

“We believe that these optical [cerebral blood flow] measurements are detecting brain tissue blood flow of local microvasculature that might differ due to injury,” says Yodh.  

While a team of physicists were needed to acquire and analyze the data in this study, newer versions will be designed to be used by clinicians, making real-time monitoring of a stroke patient’s cerebral blood flow a more common part of their care.