Vanderbilt Senior Design 2010: Non-Electronic Blood Pressure Assist Device Members:Laura Allen (ChBE) James Berry (BME) Casey Duckwall (BME) David Harris (ChBE) Mentor: 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 mechanical or solar means Low Cost: Less than $10 ▫When produced in quantities of 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 disease 1 ▫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 patients 2 ▫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 Our final design should be within ±10mmHg per reading, taking into account that normal blood pressures vary by ±3mmHg with each beat

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$45 Standard blood pressure cuff$20 3 solar cells$15 Pressure transducer$40 Batteries (AAA)$8 Rubber tubing (8mm)$10 T-junction$10 Total$148 Shipping$30

Circuit Specification An electronic approach yields 5 new design elements ▫Power Supply ▫Filtering ▫Amplification ▫Readout ▫Transducer

Circuit

Power Supply Reusable ▫Solar cell - $3.45 in bulk ▫3.4V, 25mA Sufficient voltage output ▫±3V operational amplifier rails ▫~2V LED, 20mA

Filtering and Amplification Literature suggests frequency range of 20-80Hz First-order active filtering using ▫High-pass filter > 10Hz ▫Low-pass filter < 100Hz Amplify signal to approximately 2V in passed range

Output Two monochromatic LED ▫1) Power light - Demonstrate sufficient power to the device ▫2) Indicator light – Light up during pass-band frequencies

Transducer Pressure Sensor: $3.65 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

References (1)WHO. “Fact Sheet: The Top Ten Causes of Death.” WHO. November Accessed October 28, (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 Jan;45(1):