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Vanderbilt Senior Design 2010: Non-Electronic Blood Pressure Assist Device Members: Mentor: Laura Allen (ChBE) James Berry (BME) Casey Duckwall (BME) David Harris (ChBE) Prof. Baudenbacher Blood Pressure Assist Device • The Engineering World Health (EWH) Organization proposed the challenge: ▫ Can a mechanical adjunct for a sphygmomanometer be designed to amplify the oscillatory pressure signal? ▫ Can the design be used by minimally trained users to identify at least systolic pressure? (Ideally diastolic too) Developing World Usability • Self-sustainable ▫ Power supply from solar means • Low Cost: Less than $10 ▫ When produced in quantities of 5000+ • Mechanical adjunct to sphygmomanometer ▫ Eliminating the need for Korotkoff sound identification • Identify at least systolic • Pictorial instructions for all users Rationale • Cardiovascular diseases kill more people worldwide than any other disease1 ▫ Even a leading cause in developing nations, where AIDS and malaria receive greater attention • Hypertension is a primary risk factor for cardiovascular illnesses ▫ Managing blood pressure is vital for long-term health of cardiovascular disease patients2 ▫ Diagnosing hypertension can be challenging in developing countries Literature Review • Patent search did not reveal any useful information • Researched the science behind blood pressure • Investigated different methods of measurement • Identified a range for oscillation frequencies Preliminary Data Collection • Findings indicate that measuring blood pressure by observation of sphygmomanometer alone is unreliable Association for the Advancement of Medical Instrumentation and British Society of Hypertension Protocol [3] Results from Commercial BP Device • Commercially available electronic blood pressure devices in the range of $40 yielded extreme variations in blood pressure readings, going so far as to place some individuals in both stage 2 hypertension as well as hypotension. • Furthermore, these readings were extremely variable between measurements on the same individual, varying by more than 20mmHg for systolic. Project Budget Electronic blood pressure cuff Standard blood pressure cuff 4 solar cells Pressure transducer Batteries (AAA) Rubber tubing (8mm) T-junction Total Shipping $45 $20 $15 $40 $8 $10 $10 $148 $30 Circuit Specification • An electronic approach yields 5 new design elements ▫ ▫ ▫ ▫ ▫ Power Supply Filtering Amplification Readout Transducer Circuit Power Supply • Reusable ▫ Solar cell - $3.00 ▫ 4.5V • Sufficient voltage output ▫ ±3V operational amplifier rails ▫ ~1.8V LED • Charging capacitor ▫ Relatively large capacitor to charge device in sunlight as well as smooth voltage spikes Filtering and Amplification • Literature suggests frequency range of 20-75Hz • First-order active filtering using ▫ High-pass filter > 10Hz 50μF and 320Ω ▫ Low-pass filter < 80Hz 3.33nF and 640kΩ • Amplify signal to ~2.5V in passed range ▫ Gain of 2000 Output • Two red LEDs ▫ 1) Power light - Demonstrate sufficient power to the device ▫ 2) Indicator light – Light up during pass-band frequencies Transducer • Pressure Sensor: $2.00 in bulk ▫ NovaSensor NPC-100 ▫ Developed for usage in biomedical diagnostics ▫ Sensitivity ±1% 5µV/V/mmHg ▫ Linearity ±1% For physiological range ▫ Full range -30mmHg to 300mmHg ▫ Test operating resistance to compute peripheral resistor values Device Budget • Component pricing agrees with previously determined budget • Total price below $10.00 Cost $2.00 $0.95 $0.05 $3.00 $0.15 $0.15 $0.05 $0.05 $0.05 $0.05 Budget Quantity Description Total 1 Transducer $2.00 1 Op Amp $0.95 2 Red LEDs $0.10 2 Solar Cells $6.00 1 Hosing $0.15 1 T-Junction $0.15 Resistors 1 320Ω $0.05 1 640kΩ $0.05 Capacitors 3 1μF $0.15 3 10nF $0.15 Total: $9.75 References (1) WHO. “Fact Sheet: The Top Ten Causes of Death.” WHO. November 2008. Accessed October 28, 2009 http://www.who.int/mediacentre/factsheets/fs310_2008.pdf (2) Pickering TG. , Hall JE, Appel LJ, Falkner BE, Graves J, Hill MN, Jones DW, Kurtz T, Sheps SG, Roccella EJ; Subcommittee of Professional and Public Education of the American Heart Association Council on High Blood Pressure Research. Recommendations for blood pressure measurement in humans and experimental animals: Part 1: blood pressure measurement in humans: a statement for professionals from the Subcommittee of Professional and Public Education of the American Heart Association Council on High Blood Pressure Research. Hypertension. 2005 Jan;45(1):142-61. References (3) O’Brien E, Waeber B, Parati G, Staessen J, Myers MG. Blood pressure measuring devices: recommendations of the European Society of Hypertension. BMJ 2001; 322(7285): 531-6.