PowerPoint Presentation

Finger PulseDisplay ModuleAlex BodeEmmanuel CordovaMikel DualosChrista Hamilton Medical Instrumentation Spring 2011

OverviewClinical aspectsInterface design Electronic moduleVideo PresentationDesign Issues and ObservationsLessons Learned

Clinical AspectsMorphology of Pulse WaveformThe 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 AspectsMorphology of Pulse WaveformThe pressure causes the blood vessels to increase their radius.

The radius increases 6-8%.

Then bounce back to original size

Clinical AspectsFinger Tip Blood FlowCapillaries are the smallest blood vessels in the body.

Form part of microcirculation.

Thickness varies from 5-10 micro meters.

Clinical AspectsFinger Tip Blood FlowRed L.E.D projected through the finger tip.Production of 633-635 nm. Infrared L.E.D 850-950 nm (hemoglobin & H2O)Increase sensitivity by removing variability with change in O2 concentration.

Clinical AspectsOptical properties of HemoglobinHemoglobin makes up 97% of the blood dry weight.

35% wet weight however (H2O included).

Low absorption in water (300-600 nm).

Clinical AspectsOptical PlethysmographyUses light absorbance to generate waveform from pulse. Oxymeters & microprocessor to process input Output (L.E.D & Display)

Mechanical Interface DesignPhototransistorSemiconductor 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 DesignIR vs. Red LEDBoth 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

InfraredRed LED

Mechanical Interface DesignTransducer MountTwo Possible configurations for the LED and Phototransistor:

Configuration #1 : LED and Phototransistor 1cm apart with heads facing each other.

Configuration #2: LED Phototransistor 1cm apart heads facing the ceiling .

Configuration 1

Configuration 2Electronic ModuleDesign Schematic*tape to keep offset potentiometer in place

Band-Pass FiltersNormal resting Heart rate is 70 bpm=1.17 HzRange of 20 bpm to 200 bpm0.33 Hz to 3.33 HzHigh pass filter=0.33 HzLow 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 ohmsLP=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 ObservationsHand 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 No pressure should be applied onto skin from either transducer or LED, reduces capillary volume

10 bar LED display type depends on pin 9connection.

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