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 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

•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 BudgetElectronic blood pressure cuff $45Standard blood pressure cuff $203 solar cells $15Pressure transducer $40Batteries (AAA) $8Rubber tubing (8mm) $10T-junction $10Total $148Shipping $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 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.