1. Solar Powered Blood Pressure Assist Device Laura Allen 1, James Berry 2, Casey Duckwall 2, David Harris 1 Advisor: Dr. Franz Baudenbacher 2 Department of Chemical and Biomolecular Engineering 1, Department of Biomedical Engineering 2, Vanderbilt University, Nashville, TN GE Novasensor’s NPC-100t will detect pressure variations arising from turbulent blood flow during the pressure regime between systole and diastole Range of operation Pressure: -30 – 300 mmHg Temperature: -13 – 158 o F Humidity: 10-90% The Problem Project Goals Results Device Design Acknowledgements The primary goal of this project is the development of an adjunct device to an existing blood pressure cuff that aids in the visual identification of systolic blood pressure. Dr. Franz Baudenbacher – VU Biomedical Engineering Dr. Paul King – VU Biomedical Engineering John Dunbar – VU Biomedical Engineering We would like the thank the Biomedical Engineering Department at Vanderbilt University for funding our project. Figure 6: The completed prototype on breadboard. Figure 5: Electronic schematic of the circuit controlling pressure transducer and LED outputs Device Theory Figure 2: Pressure response over the regime of physiological use; our device will identify systolic and diastolic with LED outputs Hypertension, or high blood pressure, kills more people worldwide than any other disease, and it is estimated that hypertension caused 7.6 million premature deaths worldwide in 2001. A recent estimate found that the prevalence of hypertension in SSA is just as high as many developed countries (approximately 30% ), but with lower detection and treatment. In a study published by Curb et al., only 75% of healthcare professionals passed a standardized measurement test after an extensive training session. This inaccuracy often stems from inability to use to Korotkoff sounds to identify systolic and diastolic pressure incorrect cuff placement incorrect arm positioning incorrect stethoscope placement Therefore, we have used Engineering World Health’s proposal and set out to design a blood pressure (BP) measurement device which can be used to accurately measure BP without formal training to identify Korotkoff sounds. Engineering World Health Vanderbilt University School of Engineering Table 1: Budget for the manufacture of a single device DescriptionCost Pressure Transducer$2.00 Solar Cells$6.00 Other Circuit Components$1.45 Housing and Other Supplies$1.82 Total$11.27 The device should be self-sustainable, reusable, portable, durable and have a long shelf-life. The device should cost less that approximately $10 when manufactured in bulk, and should be easy to assemble with the use of pictorial instructions. Minimally trained operators should able to use the device with the aid of pictorial instructions. Figure 1: Solar cell included in final design The NPC-100t has a 3/16” OD connection. This can be readily connected to numerous existing sphygmomanometers through the use of hosing and appropriately sized T-junctions Output from the sensor will pass through a differential amplifier of gain 10, to eliminate the linear voltage drop through the pressure range Two SCC2433B-MSE solar cells power the prototype; each generate approximately 3V indoors and 4.5V in sunlight Two red LEDs as well as the existing pressure gauge from the sphygmomanometer will be used to allow easy operation of the device: one as “power indicator” and one in response to oscillations. Figure 3: NPC-100T pressure transducer included in the final design Figure 4: Device circuit realized on breadboard Safety Considerations Conclusions Additional testing and calibration must be performed. Using simple circuit design powered by solar cells, we have created a rugged, cheap device that can be used in locations lacking a centralized power grid. Through simplistic design and inclusion of pictorial instructions, the device can be readily used by anyone, not solely trained medical personnel. Future work entails experimentally ascertaining blood pressure oscillation amplitudes in the arm. This will allow for proper circuit filtering to more accurately determine systolic pressure. In testing, the chosen solar cells produced approximately 1.5V in indirect sunlight inside the BME lab, conditions similar to those we expect to be encountered in the field. This voltage was very stable, with few oscillations to disturb our sensor output. After verifying the stability of the solar cell output, we assembled the circuit as described previously. Pumped up to physiological pressures, we simulated heart-beat oscillations by gently tapping the cuff. These oscillations are easily identified (see below). These oscillations will be used to light an LED that will indicate when the pressure is between systolic and diastolic. Figures 7 and 8: Sensor output recorded with blood pressure cuff inflated. Gentle tapping on the cuff band simulated oscillations that occur in blood pressure in the physiological range. Prototype Pictorial manual with minimal writing Allows use by operators of all education levels; warnings highlight risks such as over- inflation or entanglement Casing houses all electronic components other than face of solar cells to prevent accidental wire contact Maximum current capable from solar cells is only 18mA