Alex Bode Emmanuel Cordova Mikel Dualos Christa Hamilton Medical Instrumentation Spring 2011

Overview Clinical aspects Interface design Electronic module Video Presentation Design Issues and Observations Lessons Learned

Clinical Aspects Morphology of Pulse Waveform The wave originates as left ventricle contracts. Aortic valve opens. Rapid rise in pressure as the aortic valve opens and the blood is pushed out of the left ventricle into the aorta. Fall in pressure in left ventricle until the aortic valve closes when aortic pressure exceeds that of the ventricle.

Clinical Aspects Morphology of Pulse Waveform

Clinical Aspects Finger Tip Blood Flow

Clinical Aspects Finger Tip Blood Flow

Clinical Aspects Optical properties of Hemoglobin

Clinical Aspects Optical Plethysmography

Mechanical Interface Design Phototransistor Semiconductor device used to capture light. Converts light energy into electrical energy. When light from a source object falls on the unit, it is amplified and passed to the base collector diode. Works best around 800 nm.

Mechanical Interface Design IR vs. Red LED Both signals required much time and manipulation to produce Red LED took less time depending on the individual Red LED chosen since it passed trough skin easier/ wavelength not as high as Infrared Infrared Red LED

Mechanical Interface Design Transducer Mount Configuration 1 Configuration 2

Electronic Module Design Schematic *tape to keep offset potentiometer in place

Band-Pass Filters Normal resting Heart rate is 70 bpm=1.17 Hz Range of 20 bpm to 200 bpm 0.33 Hz to 3.33 Hz High pass filter=0.33 Hz Low pass filter=3.33 Hz

Frequency Response Curve Fc=1/(2*pi*R*C) R=resistor value (ohms) C=capacitance (Farads) HP=0.33 Hz when C=10 uF R=47k ohms LP=3.33 Hz when C=0.47 uF R=100k ohms

Band-Pass Filter The capacitive and resistive input components make up the high-pass filter. The capacitive and resistive feedback components make up the low-pass filter. Rf/Rx+1=Gain

Operational Amplifier Gain Output range for the LED bar graph display is.2 to 1.2 Volts. Signal peak to peak is 20 mV. (1.2-.2)/20m=50

Schematic

LED Bar Graph Display

Video Presentation

Design Issues and Observations Hand positing was very particular. Very time consuming to get a signal Since it was difficult to get a signal, using the EKG waveform allowed us to continue working on the other segments of the circuit during development Some noise was still visible in final output signal Use of infrared LED may have reduced noise

Lessons Learned O No pressure should be applied onto skin from either transducer or LED, reduces capillary volume O 10 bar LED display type depends on pin 9 connection. The collector voltage must be around 2.5 volts (half input voltage) in order for the photo transistor to properly transmit signal. (R1 = 10M  )

Lessons Learned When choosing resistor and capacitor values, it is important to take into account the time constant RC. this affects how long it takes for 10 bar LED to move past the transient phase where all bars are lit and slowly decline.

Group 6