Chapter 13 Blood Pressure Monitoring

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Chapter 13Blood Pressure Monitoring
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Circulation System
One of the oldest physiological measurements
Powerful risk factor for cardiovascular disease
Originates from the heart
Commonly refers to arterial blood pressure
Value depends on 3 factors cardiac output
diameter of arteries the quantity of blood
peripheral resistance
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Circulation System
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Blood Pressure
Definition ?? ??? ???? ???? ??? ? continuous
????? ??? ?? ??? ???? pumping?
?? ?? ?? ??? ?? ? ??? ????? ? Why do we need
BP? 1) ?? ???? ???? ???? ? ? ?? 2) cardiac
output? ??, ????? ??, ???? ? ???? ??? ??? ?? 3)
???? ??? ????? ?? ??? ?? 1) ??? ?? (systolic BP)
2) ??? ?? (diastolic BP) 3) ?? ?? (mean BP)
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Measurement of Blood Pressure

• Brachial artery is the most common measurement
  site
• Close to heart
• Convenient measurement

Other sites are forearm / radial artery wrist
(tends to give higher SP)
The most common indirect methods are Auscultation
and Oscillometric
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Measurement of Blood Pressure
Invasive (Direct) ???? brachial, carotid,
femoral ??? (CVP, central venous
pressure) ??? (RAP, right atrial
pressure) Catheter? ??? ?? as
short as possible as stiff as
possible Noninvasive (Indirect) Use of Korotkoff
sound Sphygmomanometer
(cuff, pressure
gage, pressure bulb, release valve)


sthethoscope
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Indirect Measurement
Use of Korotkoff sound 1906? Russian Physicist
Korotkoff 5 phase of korotkoff sound (400
500Hz) I - V first appearance of sound -
silence ?? safe (no side effect)
easy to measure ?? not accurate not
continuous difference between observers
instrument error (incorrect size of
cuff) Cuff size AHA (american heart
association) cuff width 40 of the arm
circumference bladder length should cover 80
of the arm circumference 3mmHg/sec of
slope thin cuff width high BP, wide cuff width
low BP
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Korotkoff Method
The frequency range of Korotkoff is 15500 Hz and
the accuracy is 2mmHg (SP) and 4mmHg (DP)

Korotkoff sounds are generated by the flow of
blood and vibrations of the vessel
The Korotkoff sounds are auscultated with a
stethoscope or microphone (automatic measurement)
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Oscillometric Method
The cuff pressure is deflated either linearly or
stepwise.
The intra-arterial pulsation is transmitted via
cuff to transducer
SP and DP are estimated from the amplitudes of
the oscillation by using a (proprietary)
empirical algorithm.
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Other Noninvasive Methods
Photoplethysmography (PPG)
Ultrasound
Tonometry
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Direct Measurement
Components 1) Catheter - semi rigid (filled
with saline) - ??? ???? ???? ??
(balloon tipped catheter) 2) Pressure
transducer 3) Monitor ?? continuous
observation, sampling blood ?? technical
problems (air bubble, infection)
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Direct Measurement
Extravascular sensor
Intravascular sensor
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Direct Measurement
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Catheter Model and Fluid Resistance
Flow of fluid in a catheter, , is
proportional to the pressure difference,
Resistance of the tube (friction between the
fluid and the inside surface of the tube)
viscosity of the fluid
length of the tube
radius of the tube
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Inertance and Compliance
Inertance (??? ??)
constant
Compliance (?? ??)
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Fluid-Electrical Analogy
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Catheter Equivalent Circuit
viscosity of the fluid
length of the tube
radius of the tube
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Frequency Response of a Catheter with a Diaphragm
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Example 1
Catheter length 2 meter Radius 0.46 mm Wall
with zero compliance Diaphragm compliance
(water)
Compliance of the water in the catheter,
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Example 2
Compute the transfer gain,
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Catheter with Pinch, Bubble, and Leak
Pinch
Assumption Pinch is a cylindrical
shape Compliance of the pinch is neglected as a
small quantity
Pressure difference inside and outside the
catheter
Leak
Bubble
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Example 3
Example 1 Pinch that reduces the radius by
one-half It has a length Calculate pinch
compliance, resistance, and frequency response,