Title: Lecture 26 blood flow
1Lecture 26 blood flow
2Outline 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
3Blood Flow
- Chapter 8 Webster
- Flow Volume / Time
- Typical Cardiac output 5 liters/minute
- Cardiac output of heart is controlled by input
pressure
4Ficks 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
5Ficks Method or Ficks Law
6Dye dilution curve
7EM flow probe theory
V 2a B v /100 (uv) Vvoltage B magnetic flux
density (gauss) aradius in cm v fluid velocity
(cm/sec)
8Axial 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
9EM Flow probes various designs
10EM flow probes
11Catheter type Electromagnetic Flow Probe
12System block diagram of EM Flow Meter
13EM 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
14Sources of ErrorVessel walls
15EM Flow meter stimulation waveforms
16Ultrasound 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
17Ultrasound pulse transit time equations
18Transit 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
19Doppler - fundamentals
20Doppler - equations
21Doppler Equations
22Doppler Flow spectrum
23Ultrasound system block diagram
24Doppler 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
25Limb volume changes flow
26Impedance plethysmography
- 4 band method
- Measures breathing rates
- Possible 2D graphics