Cardiovascular disease and diabetes mellitus are two of the most prevalent diseases in the modern world. Techniques for assessing the biological parameters associated with these conditions are therefore of great interest. During the last decade, noninvasive methods for assessing vital signs such as heart rate, blood pressure,1, 2 and blood glucose concentration3,4 have become increasingly popular as they not only reduce medical expenses but are often suitable for home use. However, these methods lack the required precision and repeatability to be clinically reliable, and most of them rely on undesirable contact with the patient's skin.
We have recently developed a novel optical technique that can be used to accurately record heart rate,5 blood pulse pressure,6 and blood glucose concentration,7 in addition to other biological processes such as the contraction of cardiomyocyte cells.8 Our optical sensor is noninvasive and functions at a distance from the subject, meaning there is no direct electrical exchange between the equipment and the human body. The technique relies on the fact that the movement of blood in the human body generates vibrations at the surface of the skin, which when illuminated by a laser beam create an optical pattern called a secondary speckle pattern. This is highly correlated to the blood flux, which itself depends on blood pulse pressure, blood viscosity (proportional to glucose concentration), and heart rate.
Figure 1. The setup of the sensing device used to capture secondary speckle patterns reflected from the wrist.
Figure 2. (a) A recording of heart rate demonstrates the clarity of individual heart beat measurements. (b) A graph of blood pulse pressure (green), calculated from measurements of systolic (black) and diastolic (pink) blood pressure using the sensor, shows a high level of accuracy compared to values obtained manually (blue). (c) Sensor measurement of blood glucose concentration (magenta) shows good correlation to data obtained using glucose meter (blue).
The setup of our sensing device is extremely simple. It consists of a laser to illuminate the subject and generate the secondary reflected speckle, and a specially designed imaging system to observe the pattern (see Figure 1). The camera is connected to a computer that tracks the trajectory of the reflected speckle pattern in 3D.
We tracked the temporal shifts and movements of the random speckle patterns reflected from the hand of a subject using a close-range demonstration model of our system. By adapting the optics of the imager and applying image-processing algorithms, we determined both the magnitude and the direction of the local surface displacement of the illuminated skin to nanometric accuracy. From this vibration profile we extracted parameters for the heart beat, blood pulse pressure, and blood glucose level that were in good agreement with conventional nonoptical measurement methods.
We generated a temporal signal from this optical measurement in which we observed almost constant peak values corresponding to individual heart beats of our subject: see Figure 2(a). We were also able to monitor blood pulse pressure in a similar way: see Figure 2(b). We calculated values of blood glucose concentration from our experiment and compared this with data obtained using a conventional Acuu-check glucose meter device: see Figure 2(c). The similarity of these recordings provides evidence of the accuracy of our sensor.
Our new technique represents an inexpensive method for remotely measuring important biological parameters. In our demonstration system, the distance from the laser to the subject's hand was about 50cm, but we also tested much larger distances of up to several hundred meters and were able to accurately record blood values. Measurement was not confined to the wrist, as we were also able to extract similar information from different regions of the body, including the chest and neck.
Further development of the technology we have presented will ultimately enable real-time monitoring of pulse, blood pressure, and other clinical values while allowing free movement of the subject. This will provide a powerful diagnostic tool for assessing some of the most life-threatening human diseases.
Zeev Zalevsky, Yevgeny Beiderman
Zeev Zalevsky received his PhD in electrical engineering in 1996. Since then he has published over 400 papers, five books, and 18 patents and has received several national and international awards in optics. He is currently a professor in the School of Engineering.
Vicente Micó, Javier Garcia
University of Valencia
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