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Vital Signs Monitoring Wearable Computer. By Naresh Trilok Shreenath Laxman. Abstract. Acquire data continuously and provide a complete history of the patient and also provide real-time feedback as a warning of medical emergency.
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Vital Signs Monitoring Wearable Computer By Naresh Trilok Shreenath Laxman
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.
Vital physiological variables • Pulse Rate. • Blood Pressure. • Temperature. • Percentage of Oxygen Saturation in blood. • Electro Cardio Graph.
Block Diagram Sensor Assembly Signal Conditioning Analog Signal A/D Converter TDM Telemeter Transmitter
Pulse Oximeter • Measures Sa02. • RBC’s are responsible for transport of oxygen. • Using light attenuation to determine saturation. • Beer’s Law I = Io * e ^-(a*d*c) a is the absorption coefficient d is distance c is concentration of absorbing substance.
LED Transimpedance Amplifier Differential Amplifier Photodetecter Function Generator Low Pass Filter SOFTWARE
System • Trans impedance Amplifier. • Differential Amplifier. • Low Pass Filter. Using signal from hardware, output three things • Ratio of Ratio • Oxygen Saturation • Heart Rate
Ratio of Ratios • Extension of Beer’s Law: • Low = Io*exp(-()d+A ()d) • High = Io*exp(-()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))
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
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.
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.
Server end Telemeter Receiver Application Software TDD