Vital Signs Monitoring Wearable Computer

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Vital Signs Monitoring Wearable Computer

• By
• Naresh Trilok
• Shreenath Laxman

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Abstract

• Acquire data continuously and provide a complete
  history of the patient and also provide real-time
  feedback as a warning of medical emergency.
• Equipped with special sensors and tools from
  signal processing to measure the vital
  physiological variables depending on the kind of
  patient.
• Communication with the central server using
  telemetry.
• Application software to manipulate acquired data
  and present in usable form to doctors and nurses.

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Vital physiological variables

• Pulse Rate.
• Blood Pressure.
• Temperature.
• Percentage of Oxygen Saturation in blood.
• Electro Cardio Graph.

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Block Diagram
Sensor Assembly
Signal Conditioning
Analog Signal
A/D Converter
TDM
Telemeter Transmitter
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Pulse Oximeter

• Measures Sa02.
• RBCs are responsible for transport of oxygen.
• Using light attenuation to determine saturation.
• Beers Law
• I Io e -(adc)
• a is the absorption coefficient
• d is distance
• c is concentration of absorbing substance.

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Light travels through your finger
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LED
Transimpedance Amplifier
Differential Amplifier
Photodetecter
Function Generator
Low Pass Filter
SOFTWARE
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Type of light
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System

• Trans impedance Amplifier.
• Differential Amplifier.
• Low Pass Filter.
• Using signal from hardware, output three things
• Ratio of Ratio
• Oxygen Saturation
• Heart Rate

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Ratio of Ratios

• Extension of Beers Law
• Low Ioexp(-?(?)d?A (?)?d)
• High Ioexp(-?(?)d)
• Simplify Expression by Taking ratio of Low to
  High
• Low/High exp(-?A (?)?d)
• Eliminates dependency on distance and reduces to
  standard equation for ratio of ratios
• Ratio (?A (?R))/ (?A (?IR)) Ln (RL/RH) /
  (ln(IRL/IRH))

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Oxygen Saturation

• SaO2 (?Hb(?R) - ?Hb(?IR)R) / (?Hb(?R) -
  ?HbO2(?R) ?HbO2(?IR) - ?Hb(?IR)R 100.
• Extinction Coefficients are known
• - HbR .81
• - HbO2R .08
• - HbIR .18
• - HbO2IR .29

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Heart Rate Determination

• Dependent on period of signal .
• Heart Rate (Sample Rate 60) / No. of
  samples per period.
• Software uses loop to find the index (location)
  of two consecutive peaks.
• Subtracts the two indexes from one another to
  determine No. of samples per period.
• Then determines heart rate.

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Temperature Telemeter
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Temperature Telemeter contd

• Oscillator circuit operates in the "blocking"
  mode.
• The circuit generates a 1 MHz. radio signal that
  pulses ON and OFF at a rate (blocking rate) set
  by a capacitor and the resistance sensor
  (Thermistor).
• The biotelemeter's signal can be picked up by a
  nearby AM broadcast band receiver.
• The clicking rate (i.e. clicks per minute)
  carries the measured temperature information as
  reflected in changes in the resistance sensor.
• It can be miniaturized.

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Server end
Telemeter Receiver
TDD
Application Software
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Server end