Pulse Transit Time Measuring Device Team: Jonathan Baran, Karen Chen, William Stanford, Mark Yarmarkovich University of Wisconsin-Madison BME 200/300 October 20, 2006

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Department of Pedatrics Client: Dr. Christopher Green Department of Pedatrics Advisor: Wally Block Associate Professor Department of Biomedical Engineering

Client Motivation Effects of sleep apnea on children Sleep apnea is a disorder where a patient’s tongue will fall into the back of their mouth Can cause blocked airway Epinephrine affects pulse transit time Conducting tests in sleep centers are not economically feasible A more feasible option is desired http://www.focusonhealthyaging.com/images/sleep_apnia.gif

Pulse Transit Time ECG Pulse caused by the pressure wave travels down to the fingertip (takes about 250-280 ms) PPT is the difference between the peak of the R wave and the peak of the pressure wave (Plethysmogram)

Problem Statement Current instruments used in the measurement of pulse transit time are inefficient for home use. An existing product with working ECG and pulse wave circuits along with software to analyze the data has been provided. The primary goal will be to optimize the existing setup for use at home. This will be performed by miniaturizing the circuit, improving the signal to noise ratio, and improving of the already existing software. These tasks will attempt to be rectified by numerous design additions.

Specifications Finger probe (uses LED 805nm) Circuits to magnify detected voltages Power supply to run for up to 10 hours Peak detection of ECG (QRS complex) and plethsymograph waves (finger tip) Reduced wires Small, portable device http://www.susquemicro.com/image/probes/smi_refurb.jpg

Plethysmogram Circuit Existing Device Setup Labview Program ECG Circuit Laptop Computer DAQ Plethysmogram Circuit User Display

Existing Setup: Pros/Cons Data stored directly on computer Analyzed immediately after collection Cons Bulky Restricts patient movement in sleep Cords detach during sleep High noise levels Imperfect software

Existing System Circuits ECG Circuit Buffer Stage Provides a clean signal Amplify the signal Differential Amplification Minimize interference Bandpass Filter Cuts of certain frequencies

Existing System Plethysmogram Pressure wave circuit Bandpass filter High pass filter Amplification Low pass filter

Software - LabVIEW ECG template Eliminates low frequencies in ECG and plethysmograph signals Threshold detection to determine times of QRS complex and plethysmograph peak Difference of QRS complex and peak is calculated = PTT

Proposed Setup Transfer to computer when needed Improved ECG Circuit Memory Plethysmogram Circuit Improved Labview Program

Proposed Setup: Pros/Cons Memory Addition Pros Small and wearable Eliminates bedside computer No restriction of movement Cons No immediate permanent data storage No immediate analysis

Microcontroller/Memory Addition Specifications Needs A/D converter 10-bit microcontroller will handle data best Minimum of 100Mb of data to safely store all data Input from two leads recorded 30 times per second for up to ten hours Memory interface EasyPSoC3 allows for all of these features in a developmental environment EasyPSoC3 $199.00

Pros of Additional Modifications Improved ECG circuit Reduce noise in the circuit Miniaturize circuit How will this be done? Addition of an instrumentation amplifier Reduces noise by combining many parts of the circuit into one Improved LabVIEW software Allow for more accurate measurements How will this be done? Programming of the software to account for skipped beats

Cost List for Improved Setup EasyPSoC3 $199.00 Memory Chip 512MB $35.99 Analog Devices AD624AD Instrumentation Amplifier $23.50 Total= $258.49

Future Work Incorporate flash memory Obtain Microprocessor unit Program processor Incorporate flash memory Rework Circuit Improve LabView program Edit out skipped beats

References http://www.sciam.com/article.cfm?articleID=000C74E4-5172-1C74-9B81809EC588EF21&pageNumber=1&catID=2 http://www.focusonhealthyaging.com/images/sleep_apnia.gif http://www.susquemicro.com/image/probes/smi_refurb.jpg www.wikipedia.com

Questions?