This document discusses various techniques for measuring blood flow, including electromagnetic methods, thermal methods using thermistors or hot wires, ultrasound using implantable CMUT arrays, and tracer dyes. It also describes designs for photoplethysmograph probes and analyzing blood flow using thermal modeling and heat transfer analysis. Finally, it mentions a biotelemetry system that was implanted in sturgeon to measure blood flow and temperature using an implantable Doppler flow meter and wireless data transmission to an external base station.

1. Perspectives in Blood Flow MeasurementBy SuhasDeshpandeProf. Druzgalski EE 506 (Fall 2009) P3

2. OutlineAbout Blood Flow measurementMeasurement techniquesElectromagnetic methodsThermal methodsTracer dyes for measurementUltrasound measurementPlethysmograph probe designBlood flow using thermal analysisBiotelemetry systemReferences

3. Blood flow measurementProvides vital info about the oxygen and nutrient supply to the various parts of bodyMore difficult and complicatedMost of the methods are invasive techniquesBlood flow ranges from 0.45 m/s in the arteries to 0.1 m/s in veinsBlood pressure measurement provides supplemental info which can be used

4. Measurement techniquesElectromagnetic methodsUltrasonic methodsThermal or using tracers methodsPeripheral or indirect methods

5. Electromagnetic methodsBlood being a conductive fluid adheres to the Faraday’s law of electromagnetic inductionFlow in a magnetic field results in a generation of electromagnetic force perpendicular to the magnetic field and flowAnother technique used is that of Nuclear magnetic resonance[2]

6. Thermal methodsA thermistor or a hot wire anemometer can be implanted inside the body.Blood acts as a coolant for a thermistor .By different designs and calculations based on fluid mechanics and heat transfer flow of blood can be estimated[5]

7. Tracer dyes for measurementThe injection of some tracers helps in imaging and analyzing the blood flowIndocyanine Green is a dye which causes fluorescence and images the blood flow [6]

8. Ultrasound measurementBlood flow measurement using implantable CMUT Array (Capacitive Micromachined Ultrasonic Transducer)CMUT consists of a SOC cmos electronics and transducer with cross section 40µm and shaft length 4-10mm[1]

9. Experimental operationUltrasonic pulse transmitted at frequency 1/T Echo is received at time t1 from position 1, t2 from positions 2The velocity is calculated as c(t2-t1)/2T cosѳ[1]

10. Photoplethysmograph probe design The probe detects the reflected light from the subject

11. The IR diode (OP240D Optek) and Phototransistor (LPT85A Siemens) were attached to an ellipsoid plastic sheet 0.5 cm apart

12. Probe attached to the skin using an ECG electrode[4]

13. Blood flow using thermal analysisArteriola and Venula connected by blood capillaries and AVABlood flow to capillaries controlled by AVATemperature regulation is based on blood flow in capillariesHeat transfer model analysis [7]

14. Blood flow in fingertip using heat transfer analysisNon Contact sensor placed below consists of an IR detector (Thermopile and resistance temperature sensor)Sensitivity enhanced by a Ge lensContact sensor consists of thermistor (0.25mm) to transmit the heat [7]

15. Blood flow in fingertip using heat transfer analysisFirst step ambient temperature measured (25s)Second step finger placed on the sensor initial temperature of skin surface measured (35s)Third step measure the thermal release characteristics for correction in second step (15s)Blood flow coefficient is calculated by using the temperature gradient in step 2[7]

16. Biotelemetry systemThe implant module (B) consists of a doppler flow meter µcontroller and a RF link communicatorThe base station (A) consists of RF link µcontroller and D-A Converter[8]