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Chapter 5 Part Three

Chapter 5 Part Three. Blood Pressure and flow by Ibrhim AlMohimeed. Blood Flow. Blood flow helps to understand basic physiological processes and e.g. the dissolution of a medicine into the body .

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Chapter 5 Part Three

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  1. Chapter 5Part Three Blood Pressure and flow by IbrhimAlMohimeed BMTS 353

  2. Blood Flow • Blood flow helps to understand basic physiological processes and e.g. the dissolution of a medicine into the body. • Blood flow and changes in blood volume, are usually correlated with concentration of nutrients and other substance in the blood. • Also, Blood Flow measurement reflects the concentration of O2. BMTS 353

  3. Cont. Blood Flow Normal blood flow velocity 0,5 m/s 1 m/s (Systolic, large vessel) BMTS 353

  4. Blood Flow Measurement Blood Pressure 1 Non-invasive (Indirect) Method of Blood Flow Measurement BMTS 353

  5. Ultrasonic Doppler Method Blood Pressure • The blood cells in the fluid reflects the ultrasound signal with a shift in the ultrasonic frequency due to its movement. • In the recent years ultrasound contrast agents have been used in order to increase the echoes. f = 2 – 10 MHz c f = 1,3 – 13 kHz d c = 1500 - 1600 m/s (1540 m/s) BMTS 353

  6. Cont. Ultrasonic Doppler Method Blood Pressure The ultrasound Doppler device can be either a continuous wave or a pulsed Doppler CW DOPPLER PULSED DOPPLER No minimum range Accuracy No minimum flow Simpler hardware Range ambiguity Minimum range Low flow cannot be detected (Maximum flow) x (range) = limited BMTS 353

  7. Laser Doppler Flowmetry Blood Pressure • The principle of measurement is the same as with ultrasound Doppler. • The laser parameter may have e.g. the following properties: • 5 mW • He-Ne-laser • 632,8 nm wavelength • The method is used for capillary (microvascular) blood flow measurements. BMTS 353

  8. PlethysmographyMethod (Strain Gage) Plethysmography means the methods for recording volume changes of an organ or a body part. Blood Pressure • Strain gage is made of silicone rubber tubes, which are filled with conductive liquid (e.g. mercury) whose impedance changes with volume. • Venous occlusion cuff is inflated to 40 – 50 mmHg. In this way there will be the arterial inflow into the limb but no venous outflow. BMTS 353

  9. PlethysmographyMethod(Electric-Impedance) Blood Pressure • Different tissues in a body have a different resistivity. Blood is one of the best conductors in a body. • A constant current is applied via skin electrodes. • The change in the impedance is measured. • The accuracy is often poor. BMTS 353

  10. Plethysmography Method (Photoelectric) Blood Pressure • A beam of IR-light is directed to the part of the tissue which is to be measured for blood flow (e.g. a finger or ear lobe). A B • The blood flow modulates the attenuated / reflected light which is recorded. • The light that is transmitted / reflected is collected with a photo detector. Method is simple Heart rate is clearly seen Poor measure for changes in volume Very sensitive to motion artefacts BMTS 353

  11. Blood Flow Measurement Blood Pressure 2 Invasive (direct) Method of Blood Flow Measurement BMTS 353

  12. Indicator Dilution Methods (Dye Dilution) Blood Pressure • A bolus of indicator, a colored dye (indocyanine green), is rapidly injected in to the vessel. • The concentration is measured in the downstream • The blood is drawn through a colorimetric cuvette and the concentration is measured using the principle of absorption photometry. BMTS 353

  13. Indicator Dilution Methods (Thermal Dilution) Blood Pressure • A bolus of chilled saline solution is injected into the blood circulation system (right atrium). • This causes decrease in the artery temperature. • Catheter-tip probes are used to measure the change in tempreture. BMTS 353

  14. End of the Chapter BMTS 353

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