Multi-point sensor
Several medical sensors were combined into one device
Egor Length, N+1
American scientists have developed a wearable device capable of measuring several parameters simultaneously: blood pressure, pulse and the concentration of several biomarkers. It combines ultrasonic and electrochemical sensors that do not affect each other. The elastic polymer substrate makes it easy to fix the device on the skin without causing discomfort. Such devices will help to monitor the physiological parameters of patients with diabetes, cardiovascular and other diseases, and also help to monitor the condition of athletes during extreme loads.
The article is published in Nature Biomedical Engineering (Sempionatto et al., An epidermal patch for the simultaneous monitoring of haemodynamic and metabolic biomarkers).
Wearable sensors for measuring blood pressure, pulse, blood glucose and other physiological parameters may greatly facilitate some tasks of doctors in the future. Even now there are smart watches that measure pulse, blood pressure, and sometimes even the level of oxygen in the blood, which is especially important. Such devices do not cause discomfort, as they are small in size and use non-invasive methods. Despite the fact that many physiological parameters are well recorded separately, combined devices that can determine several parameters at once are of particular interest. Recent studies have made it possible to combine physical sensors with chemical ones: electrodes record an electrocardiogram and body temperature, and chemical sensors record the content of lactates and glucose. But to date, many relationships between the measured parameters and the content of biomarkers in the body remain unclear.
Figures from the article by Sempionatto et al.
Heart rate and blood pressure are the two most important parameters that characterize the state of the body. They are affected by mobility, nutrition, stress, alcohol consumption and many other factors. By itself, the measurement of pulse and pressure can already say a lot about the patient's condition. And together with measuring the concentrations of certain biomarkers, it is a very powerful tool for diagnosing and monitoring the patient's condition. Devices that simultaneously measure these parameters can be used in the prevention of diabetes, obesity and cardiovascular diseases. In addition, such devices can be used in neonatology for constant monitoring of newborns. Sports research also often requires small sensors to measure the body's response to loads.
Scientists led by Juliane Sempionatto from the University of California at San Diego have developed a combined elastic sensor that measures blood pressure, heart rate, as well as the levels of biomarkers: glucose, lactic acid, caffeine and alcohol. The device uses ultrasonic sensors to measure pressure and heart rate, and electrochemical sensors to measure the level of biomarkers. Due to its design, the device can measure all these parameters simultaneously, and the sensors do not distort each other's readings. At the same time, the substrate material consisting of a styrene-ethylene-butylene-styrene block copolymer is easy to manufacture. This greatly speeds up the manufacturing process of such devices and allows them to be used even with active physical exertion.
The pressure and pulse sensor is a chain of eight piezoelectrics. Electrical impulses are applied to it, which is why ultrasonic signals are created. The time of reflection of these signals from the walls of the artery gives information about pressure and heart rate. The chemical sensor analyzes sweat using electrophoresis. That is, two oppositely charged electrodes create an electric field in the liquid, due to which the charged molecules begin to move. Their mass-to-charge ratios are signals and differ for different molecules. At the same time, glucose was determined by scientists not in sweat, but in tissue fluid. Due to the fact that sweat mainly contains negatively charged molecules, they move to a positively charged electrode. At the same time, the tissue fluid and its glucose move towards a negative charge. This effect makes it possible to separate biomarker molecules and identify them separately.
The appearance of the device and the schematic diagram of the electrochemical sensor.
To prevent the sensors of the device from distorting each other's readings, they were separated from each other spatially. The authors placed the pressure and pulse sensor at a distance of one centimeter on each side of the electrochemical.
The generation of an ultrasonic signal requires high voltage and frequency electrical pulses, which can affect electrochemical measurements. To evaluate this effect, the authors switched on and off the electrochemical sensor every 30 seconds with the ultrasonic sensor constantly running. The same procedure was performed on the contrary: with the electrochemical sensor constantly working, the ultrasonic was turned on and off. The authors managed to find a distance at which their mutual influence is almost absent. At a smaller distance, the effect is noticeable: electrochemical readings become inaccurate and distorted.
Graphs of testing the mutual influence of sensors.
The authors tested the mechanical strength of the device by stretching it vertically and horizontally up to 20 percent along the corresponding axes. As a result, even after 200 cycles of such stretches, there were no significant changes in the sensor readings, and the results fell within the margin of error. Scientists achieved the stability of ultrasonic sensors on a polymer substrate by soldering piezoelectric elements into a polymer, moistening them with toluene, which dissolves the polymer. After evaporation of toluene, piezoelectric elements are fixed in the substrate material and it is much more difficult to displace or deform them. With various deformations already on the body, the sensor also maintains the stability of measurements.
Tests of the mechanical strength of the device.
To get the dependence of the measured parameters on physical activity, the authors asked volunteers to spin an exercise bike for 30 minutes, accompanied by five minutes of rest. The average pressure increases from 80 to 150 millimeters of mercury, from 60 to 80 beats per minute. The lactic acid level doubled at the same time. Alcohol consumption also significantly affects the measured parameters. The consumption of 200 milliliters of a drink with an alcohol content of 19 percent in an ordinary person who does not suffer from alcoholism caused an increase in the pulse from 69 to 85 beats per minute and an increase in pressure from 120 to 136 millimeters of mercury. The consumption of caffeine by the volunteer did not cause noticeable changes in blood pressure or pulse, expressed only in an increase in the concentration of caffeine in sweat. Small changes in the pulse are still observed when tested on a volunteer without regular caffeine consumption: from 75 to 88 beats per minute. The pressure remains at the same level.
It should be noted that a prototype of the future device is described here. Now it needs to be connected to an external power source and to a computer (the loop for this is shown in the figure in the UC San Diego New Skin Patch Brings Us Closer to Wearable, All-In-One Health Monitor). But the final version, which the team is already working on, will be autonomous and will be able to analyze a larger number of biomarkers – VM.
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