Blood Pressure An Individuals blood pressure is a standard clinical measurement Is considered a good...
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Blood Pressure An Individuals blood pressure is a standard clinical measurement Is considered a good indicator of the status of the cardiovascular system
Blood Pressure An Individuals blood pressure is a standard
clinical measurement Is considered a good indicator of the status
of the cardiovascular system. Blood pressure values in the various
chambers of the heart and in the peripheral vascular system help
the physician determine the functional integrity of the cardio
vascular system.
Slide 2
Blood Pressure inside the heart chambers
Slide 3
Major Arteries & Veins of the Body
Slide 4
Cardiovascular system-typical values
Slide 5
Blood Pressure Measurement Direct (invasive) 1.Extravascular
Method The vascular pressure is coupled to an external sensor
element via a liquid filled catheter. [ Catheter is a long tube
introduced into the heart or a major vessel by way of a superficial
vein or artery. ] 2.Intravascular A sensor is placed into the tip
of a catheter that is placed in the vascular system. Indirect (non
invasive) Sphygmomanometer Consists of an inflatable pressure cuff
and a manometer to measure the pressure in the cuff.
Slide 6
Direct Measurement (Extravascular)
Slide 7
Disposable blood-pressure sensor with integral flush
device
Slide 8
Direct Measurement Extra Vascular The extra vascular sensor
system is made up of a catheter. The catheter is connected to a
three way stopcock and then to a pressure sensor It is filled with
a saline-heparin solution. It must be flushed with solution every
few minutes to prevent blood clotting at the tip.
Slide 9
Physician inserts the catheter Either by means of a surgical
cut-down, which exposes the artery or vein. or by means of
percutaneous insertion which involves the use of a special needle
or guide-wire technique. Blood pressure is transmitted via the
catheter column to the sensor and finally to the diaphragm which is
deflected. The displacement of the diaphragm is sensed
electronically. Direct Measurement Extra Vascular contd
Slide 10
Disadvantages The frequency response of the catheter-sensor
system is limited by the hydraulic properties of the system.
Creates time delay in detection of pressures when a pressure pulse
is transmitted. Direct Measurement Extra Vascular contd
Slide 11
The sensor is placed at the tip of the catheter. Enables the
physician to obtain a high frequency response in detection of
pressures at the tip of the catheter. Types of sensors
1.Strain-gage systems bonded onto a flexible diaphragm at the
catheter tip. 2.Fibre-optic device Measures the displacement of the
diaphragm optically by varying reflection of light from the back of
the deflecting diaphragm. Direct Measurement Intravascular
Slide 12
Bonded Strain Gage pressure transducer Consists of
strain-sensitive gages which are firmly bonded with an adhesive to
the membrane or diaphragm whose movement is to be recorded. Made by
taking a length of a very thin wire or foil which is formed into a
grid pattern and bonded to a backing material. Is then attached to
the diaphragm. Deflection of the diaphragm causes corresponding
strain in the wire gage. Causes a corresponding change in the
resistance which is proportional to the pressure.
Slide 13
Fiber optic type pressure transducer Measures the displacement
of the diaphragm optically by the varying reflection of light from
the back of the deflecting diaphragm. Inherently safer
electrically
Slide 14
Blood Pressure Waveforms
Slide 15
Harmonic Analysis of Blood Pressure Waveforms
Slide 16
Using Fourier Analysis techniques in the quantification of
pressure and flow. Blood pressure pulse can be divided into its
fundamental component (of the same frequency as the blood pressure
wave) and its significant harmonics. Analysis of the frequency
components of the pulse yield more information on arterial
properties.
Slide 17
Electrical Model of Catheter-Sensor system
Slide 18
Testing technique for measuring the transient response of the
catheter-sensor system
Slide 19
Transient response of the catheter-sensor system
Slide 20
Pressure-waveform distortion
Slide 21
Distortion during the recording of arterial pressure
Slide 22
For determining the function of Capillary bed Right side of the
heart The central venous pressure is measured in the central vein
or in the right atrium. It fluctuates above and below atmospheric
pressure as the subject breathes. The reference level for venous
pressure is at the right atrium. Central venous pressure is an
important indicator of myocardial performance Venous pressure
Slide 23
Monitored for assessing proper therapy for heart dysfunction
Shock Hypovolemic (Of or relating to a decrease in the volume of
circulating blood) or hypervolemic States Circulatory failure
Central venous pressure
Slide 24
Slide 25
Physicians usually measure steady state or mean venous pressure
by making a percutaneous venous puncture with a large bore needle,
inserting a catheter through the needle. Needle is then
removed.
Slide 26
Continuous dynamic measurements is made by connecting a high
sensitive pressure sensor to the venous catheter. Normal venous
pressure values range widely from 0 to 1.2 kPa with a mean pressure
of 0.5 kPa(0 12cm H2O). Central venous pressure
Slide 27
Heart Sounds Heart sounds are vibrations or sounds due to the
acceleration or deceleration of blood. Murmurs are vibrations or
sounds due to blood turbulence. The technique of listening to
sounds produced by the organs and vessels of the body is called
auscultation.
Slide 28
Heart Sounds
Slide 29
Slide 30
With each heartbeat, the normal heart produces two distinct
sounds that are audible in the stethoscope often described as
lub-dub The lub is caused by the closure of atrioventricular valves
and is called the first heart sound occurs approximately at the
time of QRS complex of the ECG and just before ventricular systole.
The dub part of the heart sounds is called the second heart sound
and is caused by the closing of the semilunar valves Which closes
at the end of the systole, just before the atrioventricular valve
opens. Occurs at the time of the end of the T wave of the ECG The
third heart sound attributed to the sudden termination of the rapid
filling phase of the ventricles from the atria and the associated
vibration of the ventricular muscle walls., which are relaxed.
Slide 31
Fourth or atrial heart sound not audible, can be recorded by
phonocardiogram, due to atria contract
Slide 32
Auscultation Techniques There are optimal recording sites for
the various heart sounds.
Slide 33
Auscultation Techniques Heart sounds and murmurs have extremely
small amplitudes with frequencies from 0.1 to 2000 Hz. Thus the
recording device must be carefully selected for wide band frequency
response characteristics. Specially designed acoustically quiet
environment is needed for noise free recording of heart
sounds.
Slide 34
Stethoscope Mechanical stethoscopes amplifies sound because of
Standing wave phenomenon. Firm application of the chest piece makes
the diaphragm taut with pressure thereby causing an attenuation of
low frequencies. Loose-fitting earpiece cause leakage which reduces
the coupling between the chest wall and the ear. Electronics
stethoscopes has selectable frequency response characteristics
ranging from ideal flat-response to selectable band- pass
response.
Slide 35
Stethoscope Frequency response
Slide 36
Phonocardiogram A Phonocardiogram is a recording of the heart
sounds and murmurs. Eliminates subjective interpretation of the
heart sounds Enables evaluation of the heart sounds and murmurs
with respect to the electric and mechanical events in the cardiac
cycle. Evaluation of the result is based on the basis of changes in
the wave shape and various timing parameters.
Slide 37
Phonocardiogram
Slide 38
Frequency spectrum of a typical Phonocardiogram
Slide 39
Cardiac Catheterization The process of introducing a catheter
into the heart for diagnosis. Used to asses hemodynamic
(circulation of the blood and the forces involved) function and
cardiovascular structure. Performed during most of the heart
surgeries. Performed in specialized laboratories outfitted with
x-ray equipment for visualizing heart structures and the position
of various pressure catheters.
Slide 40
Cardiac Catheterization A radiopaque die is injected into the
ventricles or aorta through the catheter for assessing the
ventricular or aortic function Pressures in all four chambers of
the heart and in the great vessels can be measured by positioning
the catheters in such a way to recognize the characteristics
pressure waveforms.
Slide 41
Cardiac Catheterization
Slide 42
Angiography Angiographic visualization is an essential tool
used to evaluate cardiac structure. Specially designed catheters
and power injectors are used in order that a bolus of contrast
material can be delivered rapidly into the appropriate vessel or
heart chamber. During catheterization cardiac catheterization
frequently occur. Clinics must have a functional defbrillaltor
Slide 43
Cardiac Catheterization & Angiogram
Slide 44
Angiogram
Slide 45
Angeography Types Left & Right ventricle ventriculography
Coronary arteries coronory angeography Pulmonary artery pulmonary
angeography Aorta- aortography
Slide 46
Slide 47
Angioplasty Surgical procedure to repair a damaged blood vessel
or unblock a coronary artery. PTCA Percuntaneous Transluenal
Coronary Angeoplasty
The pressure cuff on the upper arm is first inflated to a
pressure well above the systolic pressure. At this point no sound
can be heard through the stethoscope, which is placed over the
brachial artery, for that artery has been collapsed by the pressure
of the cuff. The pressure in the cuff is then gradually
reduced.
Slide 52
Sphygmomanometery When the systolic peaks are higher than the
occlusive pressure, the blood spurts under that cuff and causes a
palpable pulse in the wrist (Riva-Rocci Method) Audible sounds
(Korotkoff (named after Dr. Nikolai Korotkoff) sounds) generated by
the flow of blood and vibrations of the vessel under the cuff are
heard through the stethoscope.
Slide 53
Sphygmomanometery The pressure of the cuff that is indicated on
the manometer when the first Korotkoff sound is heard is recorded
as the systolic blood pressure. As the pressure in the cuff is
continues to drop, the Korotkoff sounds continue until the cuff
pressure is no longer sufficient to occlude the vessel during any
part of the cycle. Below this pressure the Korotkoff sounds
disappear, marking the value of the diastolic pressure.
Slide 54
Sphygmomanometery Auscultatory (based on the Korotkoff sounds)
technique is simpler and requires a minimum of equipment. Cannot be
used in noisy environments. Palpation (based on pulse on the blood
vessel) technique doesnt require a noise free environment. Normal
respiration and vasomotor waves modulate the normal blood-pressure
levels.
Slide 55
Automated Indirect Blood Pressure measurement techniques
Involves an automatic sphygmomanometer that inflates and deflates
an occlusive cuff at a predetermined rate. A sensitive detector is
used to measure the distal pulse or cuff pressure.
Slide 56
Automated Auscultatory device Microphone replaces the
stethoscope for sensing the Korotkoff sounds. The process begins
with a rapid (20-30mm Hg/s) inflation of the occlusive cuff to a
preset pressure about 30mm Hg higher that the suspected systolic
pressure. The flow of blood beneath the cuff is stopped by the
collapse of the vessel.
Slide 57
Automated Auscultatory device Cuff pressure is then reduced
slowly (2-3 mm Hg/s). The first Korotkoff sound is detected by the
microphone, at which time the level of the cuff pressure is
stored.
Slide 58
Automated Auscultatory device The muffling and silent period of
the Korotkoff sound is detected, and the value of the diastolic
pressure is also stored. After a few minutes the instrument
displays the systolic and diastolic pressure and recycles the
operation
Slide 59
Ultrasonic Based Blood Pressure Measurement Employs a
transcutaneous Doppler sensor that detects the motion of the
blood-vessel walls in the various states of occlusion. The Doppler
ultrasonic transducer is focused on the vessel wall and the blood.
The reflected signal (shifted in frequency) is detected by the
receiving crystal and decoded.
Slide 60
Ultrasonic Based Blood Pressure Measurement
Slide 61
The difference in frequency, in the range of 40 to 500 Hz,
between the transmitted and received signals is proportional to the
velocity of the wall motion and the blood velocity.
Slide 62
Ultrasonic Based Blood Pressure Measurement As the applied
pressure is further increased, the time between the opening and
closing decreases until they coincide. The reading at this point is
the systolic pressure. When the pressure is cuff is reduced, the
time between the opening and closing increases until the closing
signal from one pulse coincides with opening signal from the next.
The reading at this point is the diastolic pressure.
Slide 63
Ultrasonic Based Blood Pressure Measurement Advantages: Doesnt
require a noise free environment. Disadvantage: Movement of the
subjects body cause changes in ultrasonic path between the sensor
and the blood vessel.
Slide 64
Electromagnetic Blood Flow Meters Measures instantaneous
pulsatile flow of blood Works based on the principle of
electromagnetic induction The voltage induced in a conductor moving
in a magnetic field is proportional to the velocity of the
conductor The conductive blood is the moving conductor
Slide 65
Principle of Electromagnetic Blood Flow Meters
Slide 66
Principle of Electromagnetic Blood flow Measurement
Slide 67
Principle of Electromagnetic Blood Flow Meters A permanent
magnet or electromagnet positioned around the blood vessel
generates a magnetic field perpendicular to the direction of the
flow of the blood. Voltage induced in the moving blood column is
measured with stationary electrodes located on opposite sides of
the blood vessel and perpendicular to the direction of the magnetic
field.
Slide 68
Principle of Electromagnetic Blood Flow Meters The Induced emf
Where B = magnetic flux density, T L = length between electrodes, m
u = instantaneous velocity of blood, m/s
Slide 69
Principle of Electromagnetic Blood Flow Meters This method
requires that the blood vessel be exposed so that the flow head or
the measuring probe can be put across it.
Slide 70
Design of Flow Transducers The electromagnetic flow-transducer
is a tube of non-magnetic material to ensure that the magnetic flux
does not bypass the flowing liquid and go into the walls of the
tube. The tube is made of a conducting material and generally has
an insulating lining to prevent short circuiting of induced emf.
The induced emf is picked up by point electrodes made from
stainless steel or platinum.
Slide 71
Design of Flow Transducers The flow head contains a slot
through which the intact blood vessel can be inserted to make a
snug fit. Several probes of different sizes must therefore
accompany the flowmeter to match the full range of sizes of the
blood vessels which have various diameters. Flow heads having as
small as 1mm are available.
Slide 72
Slide 73
Types of Electromagnetic Blood Flow Meters DC Flow meters Use
DC Magnetic field. Cause electrode polarization and amplifier
drift. o/p same as ECG Poor SNR AC Flow meters Electromagnets are
driven by alternating currents. The transducer acts like a
Transformer and induces error voltages that often exceed the signal
levels by several orders of magnitude.
Slide 74
Electromagnetic AC flow meters Error recovery is achieved by
using several different waveforms for magnet current Sine, Square,
Trapezoidal. Suitable balancing circuits are used to balance out
the error voltage.
Slide 75
Sine wave Flowmeters The transformer induced voltage is 90 out
of phase and is eliminated by Injecting a voltage of equal strength
and opposite phase into the signal. Using a gated amplifier. Permit
the amplification of the signal only during the flow induced
voltages are maximum and the transformer induced voltages are
minimum.
Slide 76
Square wave Flowmeters The transformer induced voltage is only
a spike. Separation is easier as the amplifier can be gated only
for a very short period. Blanking is required only when the current
in the magnet is reversing its direction and the amplifier works
during the flat portion of the square wave.
Slide 77
Magnetic Flowmeter Block Diagram
Slide 78
The oscillator, which drives the magnet provides a control
signal for the gate, operates at a frequency of between 60 and 400
Hz. The frequency response is high enough to allow the recording of
the flow pulses. The mean or average flow can be derived by use of
a low-pass filter.
Slide 79
Ultrasonic Blood Flow Meters A beam of ultrasonic energy is
used to measure the velocity of flowing blood.. Lead zirconate
titanate is a crystal that has the highest conversion efficiency.
Two types: Transit time flow meters Doppler type.
Transit-Time Ultrasonic Flow Meters Where t - transit time D-
Distance between the transducers c - Sound velocity u - blood flow
velocity
Slide 82
Transit-Time Ultrasonic Flow Meters The pulsed beam is directed
through a blood vessel at a shallow angle and its transit time is
measured. The transit time is shortened when the blood flows in the
same direction as the transmitted energy The transit time is
lengthened otherwise.
Slide 83
Doppler Type Ultrasonic Flow Meters
Slide 84
Doppler type Ultrasonic Flow Meters Based on the Doppler
principle A transducer sends an ultrasonic beam with a frequency F
into the flowing blood. A small part of the transmitted energy is
scattered back and is received by a second transducer arranged
opposite the first one. The reflected signal has a different
frequency F + F D or F F D due to Doppler effect.
Slide 85
Doppler Frequency equation Where f d = Doppler frequency shift
f 0 = source frequency u = target velocity c = velocity of
sound
Slide 86
Doppler type Ultrasonic Flow Meters The Doppler component F D
is directly proportional to the velocity of the flowing blood. A
fraction of the transmitted ultrasonic energy reaches the second
transducer directly with the frequency being unchanged.
Slide 87
Doppler Type Ultrasonic Flow Meters
Slide 88
Doppler type Ultrasonic Flow Meters After amplification of the
composite signal, the Doppler frequency can be obtained at the
output of the detector as the difference between the direct and the
scattered signal components. For normal blood velocities, the
Doppler signal is typically in the low audio frequency range.
Slide 89
Indicator Dilution that uses continuous infusion (Indicator
Oxygen)- samples from artery & Pulmonary artery Indicator
Dilution method that uses rapid injection Dye dilution -indocyanine
green cardio green- dye injected to pulmonary artery samples from
artery Thermo Dilution cold saline- injected to RA- temp measured
in pulmonary artery
Slide 90
Indicator Dilution Method of Blood Flow Measurement An
Indicator I is mixed with the blood with a known injection rate.
The Concentration C of the indicator is measured after mixing. Then
the flow,
Slide 91
Indicator Dilution Method of Blood Flow Measurement
Slide 92
When a given quantity of m 0 of an indicator is added to a
volume V, the resulting concentration C of the indicator is given
by C = m 0 /V When an additional quantity m of indicator is then
added, the incremental increase in concentration is C = m/V
Slide 93
Indicator Dilution Method of Blood Flow Measurement When the
fluid volume in the measured space is continuously removed and
replaced, then in order to maintain a fixed change in
concentration, a fixed quantity of indicator per unit time must be
added continuously. C = (dm/dt) / (dV/dt) Then the Flow,
Slide 94
Fick Technique to measure blood flow from the heart Where F =
Blood flow, liters/min dm/dt = consumption of O 2, liters/min C a =
arterial concentration of O 2, liters/min C v = venous
concentration of O 2, liters/min
Slide 95
Fick Technique to measure blood flow from the heart
Slide 96
The blood returning to the heart from the upper half of the
body has a different concentration of O2 from the blood returning
fromthe lower half. The O 2 concentration measured by the
spirometer The arterial-venous concentration difference is measured
by drawing samples through catheters placed in an artery and in the
pulmonary artery.
Slide 97
Cv can be measure it in the pulmonary artery after it has been
mixed by the pumping action of the right ventricle. The clinician
can measure the concentration of the oxygenated blood Ca in any
artery.
Slide 98
Ficks Technique - Advantage The Fick technique is nontoxic,
because the indicator (O2) is a normal metabolite that is partially
removed as blood passes through the systemic capillaries. The
cardiac output must be constant over several minutes so that the
investigator can obtain the slope of the curve for O2 consumption.
The presence of the catheter causes a negligible change in cardiac
output.
Slide 99
Indicator Dilution Method that uses rapid injection
Slide 100
Rapid-injection indicator-dilution curve Bolus is injected at
time A There is a transportation delay before the concentration
begins rising at time B. After the peak is passed, the curve enters
an exponential decay region between C and D, which would continue
decaying along the dotted curve to t1 if there were no
recirculation. Recirculation causes a second peak at E before the
indicator becomes thoroughly mixed in the blood at F. The dashed
curve indicates the rapid recirculation that occurs when there is a
hole between the left and right sides of the heart.
Slide 101
An increment of blood of volume dV passes the sampling site in
time dt. quantity of indicator dm contained in dV is the
concentration C(t) times incremental volume. Hence dm =C(t) dV.
Dividing by dt, we obtain (dm/dt)= C(t) (dV/dt) dm= Fi C(t) dt
Slide 102
where t1 is the time at which all effects of the rst pass of
the bolus have died out (point E). The integrated quantity ( C(t)
dt) ) is equal to the shaded area in Figure we can obtain it by
counting squares or using a planimeter. If the initial
concentration of indicator is not zeroas may be the case when there
is residual indicator left over from previous injections( C(t) -
> C(t) )
DYE DILUTION A common method of clinically measuring cardiac
output is to use a colored dye, indocyanine green (cardiogreen). It
meets the necessary requirements for an indicator The dye is
available as a liquid that is diluted in isotonic saline and
injected directly through a catheter, usually into the pulmonary
artery. About 50% of the dye is excreted by the kidneys in the rst
10 min, so repeat determinations are possible.
Slide 106
The plot of the curve for concentration versus time is obtained
from a constant-ow pump, which draws blood from a catheter placed
in the femoral or brachial artery. Blood is drawn through a
colorimeter cuvette which continuously measures the concentration
of dye, using the principle of absorption photometry.
Slide 107
Thermo Dilution Injecting a bolus of cold saline as an
indicator. A special four-lumen catheter is oated through the
brachial vein into place in the pulmonary artery. 1- A syringe
forces a gas through one lumen; 2-The cooled saline indicator is
injected through the second lumen into the right atrium. 3- The
third lumen carries the thermistor wires. 4- Used for withdrawing
blood samples.
Slide 108
The gas inates a small, doughnut-shaped balloon at the tip. The
indicator is mixed with blood in the right ventricle. The resulting
drop in temperature of the blood is detected by a thermistor
located near the catheter tip in the pulmonary artery