Chapter 4
Flow measurement (cont)
Viet Dung Nguyen
Department of Electronic Technology and Biomedical Engineering, Hanoi University of Science and Tech
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4.3. TISSUE BLOW FLOW MEASUREMENTS
4.4. RESPIRATORY FLOW MEASUREMENTS
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4.3. TISSUE BLOOD FLOW MEASUREMENTS
4.3.1. Venous Occlusion Plethysmography
4.3.2. Clearance Technique
4.3.3. Indicator Dilution Method (self-reading)
4.3.4. Heat Transport Method
4.3.5. Laser-Doppler Flowmetry (self-reading)
4.3.6. Nuclear Magnetic Resonance (self-reading)
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4.3.1. Venous Occlusion Plethysmography
4.3.1.1. Principle
- Small pulsatile change of the
volume Is generally observed in
almost any tissue due to the arterial
pulsation →information about the
tissue blood flow can be obtained
by the plethysmographic
observation
- Mostly for limb tissue blood flow
measurement
- Principle:
Pressure of distal cuff > maximal
arterial pressure
Pressure of proximal cuff slightly
> minimal arterial pressure
Venous occlusion principle
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- Can be applied to the whole limb, or the extremity of the limb, and had
been widely used in physiological studies
- For normal subjects, the proximal cuff pressure is chosen around 6.7
kPa (50 mm Hg), and the distal cuff pressure is around 20 kPa (150
mmHg)
Applied time should be short: the maximum cuff pressures were reached
within 0.1 s
- It has been shown that as long as an appropriate cuff pressure is
applied, the venous flow can be completely obstructed while the arterial
pressure remains unchanged
- Many causes of error:
+ Local tissue deformation
+ Technique of volume recording