Frequent measurement and study of changes in blood flow could be used to improve the ability of health care providers to diagnose and treat patients with vascular conditions, such as those associated with diabetes and high blood pressure.
An international collaboration between US and Chinese researchers that includes researchers from the National Institute of Biomedical Imaging and Bioengineering (NIBIB) and the National Heart, Lung, and Blood Institute, both parts of the National Institutes of Health, conducted a pilot study showing that an ultrathin, skin-conforming sensor that resembles a peel-off tattoo provides noninvasive, precise, and continuous monitoring of circulation, including blood flow within even the smallest vessels.
Their study, published in the journal, Science Advances, showed that the sensor can measure blood flow in both large and micro-sized blood vessels near the skin’s surface. The study also provided details about the design and operation of the device. The team of researchers assessed the sensor’s performance under various conditions, showing that the technology could be used for continuous blood-flow monitoring during daily activities as well as in a variety of clinical research and healthcare settings.
In addition to diabetes and chronic hypertension, other conditions that can affect the health of blood vessels and surrounding tissue include kidney disease, autoimmune and other inflammatory conditions, the effects of aging and smoking, and a class of cholesterol-related abnormalities called dyslipidemias. Continuous monitoring of variations in blood flow, they say, could also be valuable in assessing these conditions in clinical and research scenarios.
The pilot-tested device, which was codeveloped with researchers at Northwestern University, is among a variety of tools available to measure blood flow. Other devices, such as ones based on optical or acoustic methods, however, do not work as well when the body is in motion, and thus require a patient or study subject to remain still. But, movement does not pose a problem for this sensor because it adheres closely to the skin and does not accidentally dislodge.
How It Works
The soft, skin-conforming electronic device, which is applied directly onto the skin, uses thermal sensors to collect data on changes in temperature, including those caused by changes in blood flow. (See Figure 1)
The device can also apply a small amount of heat in order to test a subject’s responses. In this mode, a miniature pad in the device generates a heat impulse, while 14 surrounding thermal sensors detect the resulting heat flux. The signal is then sent to a computer to calculate the velocity of blood flow occurring within two millimeters of the skin surface.
In their study, the researchers placed the sensor on a study subject’s forearm, over a large, visible vein, and then applied pressure for 60 seconds at various positions near the vein. Each time, the device sensed corresponding reductions in blood flow. The researchers also used a thermal camera that measures infrared signals to confirm that the blood-flow sensor measurements were accurate, even when the subject moved around.
Next, they chose a placement on the forearm that was not near a large vein, so that the device would detect blood flow in micro-sized blood vessels within the underlying tissue. The researchers were able to detect changes in blood flow when the study subject took a deep breath. Members of the team at a collaborating institution performed a separate test that involved delivering a gentle slap to the skin near the electronic sensor, which caused a mild reddening reaction. The sensor registered the skin reaction as an increase of surface temperature, accompanied by a change in the direction of blood flow within two millimeters of the skin’s surface.
According to co-author Alexander Gorbach, PhD, head of NIBIB’s Infrared Imaging and Thermometry Unit, the tests performed with the thermal sensor helped to establish a number of guidelines for its use, such as optimal placement of the sensor, and how deeply under the skin’s surface the device can assess blood flow. At this stage, he says, the device shows promise as a low-cost, readily-fabricated sensor for use in ambulatory or hospital-based settings.
For more information, visit www.nibib.nih.gov/news-events .