Lecture 26 blood flow

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Lecture 26 blood flow
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Outline of class

• Visit to Neonatal ICU Dr Jack Dolcourt
• Next Thursday helicopter visit eye clinic
• Blood flow basic definition
• Gold Standard - Ficks Technique
• dye dilution thermal dilution
• Electromagnetic flow meter
• Ultrasound flow meter transit time
• Ultrasound flow meter doppler
• Plethysmography volume, impedance

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Blood Flow

• Chapter 8 Webster
• Flow Volume / Time
• Typical Cardiac output 5 liters/minute
• Cardiac output of heart is controlled by input
  pressure

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Ficks Law
Clinical measure uses Douglas bag and measure
oxygen concentration and consumption Integrating
Ficks equation gives bolus equation This is gold
standard and reference for other measures
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Ficks Method or Ficks Law

• derivations

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Dye dilution curve
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EM flow probe theory
V 2a B v /100 (uv) Vvoltage B magnetic flux
density (gauss) aradius in cm v fluid velocity
(cm/sec)
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Axial flow gives average velocity

• Given normal ranges of B and v, the V is very
  small (in uv)
• Flow in vessel is not uniform so equation must be
  intregrated
• If flow is axial (symmetric) around axis and the
  flow is laminar then v is the average flow. Which
  is what is desired

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EM Flow probes various designs
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EM flow probes
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Catheter type Electromagnetic Flow Probe
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System block diagram of EM Flow Meter
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EM Flow source of errorflow patterns

• Flow has circulating currents
• Voltage is highly dependent on hematocrit
• Thickness and conductivity of vessel changes
  sensitivity
• Fit of probe and serous fluid short out signal
• Excitation methods errors due to induced voltages
  from changing magnetic fields

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Sources of ErrorVessel walls
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EM Flow meter stimulation waveforms
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Ultrasound methods to measure flow

• Pulse transit method measure time it takes for
  pulse to transverse vessel and go back
• Doppler method change in reflected frequency
  due to movement of blood cells

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Ultrasound pulse transit time equations
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Transit time

• Assuming fluid velocity ltlt speed of sound
• T 2 D v cos theta / c 2
• Note that v is proportional to T
• Note, T is very small and hard to measure
  electronically

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Doppler - fundamentals
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Doppler - equations
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Doppler Equations
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Doppler Flow spectrum
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Ultrasound system block diagram
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Doppler comments

• Difference in frequency means velocity
• Larger difference means larger velocity
• Types of doppler
• Continuous wave
• Pulse
• Pulse range gate
• Quadrature analysis
• FFT methods
• Digital filtering methods

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Limb volume changes flow
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Impedance plethysmography

• 4 band method
• Measures breathing rates
• Possible 2D graphics