Ec 6001 medical electronics

EC6001- MEDICAL ELECTRONICS
Prepared by
Mr.P.Benesh Selva Nesan, AP/ECE
Rohini College of Engineering & Technology

AUTO ANALYZERS
 The autoanalyzer sequentially performs the
biochemical tests and displays the records. The
following figure shows the block diagram of a
typical autoanalyzer.
 Itconsists of
Sampler: Aspirates samples, standards, wash
solutions into the system.
Proportioning pump: Mixes samples with the
reagents so that proper chemical color reactions can
take place, which are then read by the colorimeter
2

AUTO ANALYZERS CONTD . . .
Dialyzer: separates interfacing substances from the
sample by permitting selective passage of sample
components through a semi permeablemembrane
Heating bath: Controls temperature (typically at
37°C), as temp is critical in color development.
Colorimeter: monitors the changes in optical density of
the fluid stream flowing through a tubular flow cell.
Color intensities proportional to the substance
concentrations are converted to equivalent
electrical voltages.
Recorder: Displays the output information in a graphical
form. 3

AUTO ANALYZERS CONTD . . .
 Points to be considered
 Sterilization is needed for samples and glass tubes
 Calibration is important.
5

BLOOD CELL COUNTERS
 The blood cells have important functions in our body. The
red blood cell is used for transport of oxygen and carbon-
di-oxide.
 When the haemoglobin in the blood decreses, anemia is
produced.
 The number of red blood cells can be counted using a
microscope, but the microscopic counting is time
consuming.
 Now-a-days automatic red blood cell counters are used.
 The blood cell counter count the number of RBC or WBC
per unit of volume of blood
6

AUTOMATIC RED BLOOD CELL COUNTER
 This method us based on the fact that red cells
have a higher electrical resistivity than the saline
solution in which they are suspended. Fig (1) shows
the automatic blood cell counter using electronic
circuitry.
7

AUTOMATIC RED BLOOD CELL COUNTER
8

OPERATION
 The threshold is first set to zero and the counter output is
given by the total number of particles (WBCs + RBCS +
platelets) per litre.
 Then the threshold is set to T1 and the counter gives the
total number RBCS and WBCS per litre.
 After that the threshold is set to T2 and the counter reads
the total number of WBC S per litre.
9

LASER BLOOD CELL COUNTER OPERATION
 This is a modern technique which gives the number of
RBCs, WBCs and Platelets, hematocrit and concentration
of haemoglobin.
 The basic Principle is that the angle of scattered light
intensity is different for different sized particles.
 The sample blood is heavily diluted to reduce the number
of particles counted to one at a time.
11

ELECTRICAL METHOD OR APERTURE IMPEDANCE
CHANGE BLOOD CELL COUNTING
 When blood is diluted in the proper type of solution, the
electrical resistivity of blood cells (ρc) is higher then the
resistivity of the surrounding fluid (ρf)
 By contriving a situation in which these resistivities can be
differentiated from each other,we can count cells.
12

BLOOD CELL SENSING
 The sensor consist of a two-chamber vessel in which the
dilute incoming blood is on one side of barrier, and the
waste blood to be discarded is on the other
 A hole with a small diameter (50μm) is placed in the
partition between the tow halves of the cell.
 Ohmmeter measure the change on the resistance when
the blood cell pass the aperture.
13

COULTER COUNTER
 Constant current source (CCS) and voltage amplifier
replace the ohmmeter
 RA is the resistance of the aperture and will be either
high or low, depending on whether or not the blood
cell is inside the aperture.
 Amplifier convert the current pulse to voltage pulse.
15

BLOCK DIAGRAM OF COULTER COUNTER
16

FLOW CYTOMETRY CELL COUNTERS
Optical flow cytometry sensing
– The optical cytometry sensor consists of a quartz
sensing sheath designed with a hydrodynamic
focusing region
– cell path region that passes only a single cell at
time.
– Focusing is done by decreasing the diameter of
the aperture.
Light source is (He-Ne) Laser
1.Two Photodetectors (photosensors)- Photodetector A
detects forward scatted light
2. Photodetector B detects orthogonal scatted light 17

OPTICAL METHOD OR FLOW CYTOMETRY
18

BLOOD FLOW METERS
 Blood flow meters are used to monitor the blood flow in
various blood vessels and to measure the cardiac output
 All blood flow meters are based on one of the following
physical principle.
 Electromagnetic induction
 Ultrasound transmission or reflection
 Thermal convection
 Radiographic principles
 Indicator (dye or thermal) dilution (Open &Closed
Circulation Methods)
20

BLOOD FLOW METERS TYPES
1. Magnetic Blood Flow Meter
2. Ultrasonic Blood Flow Meter
3. Thermal Convection Method
4. Radio Graphic Method
5. Indicator Dilution Metod ( Open& Closed Circulation
Methods)
21

 Electromagnetic blood flow meters measure blood flow
in blood vessels
 Consists of a probe connected to a flow sensor box
 They are based on the principle of magnetic induction.
When an electrical conductor is moved through a
magnetic field, a voltage is induced in the conductor
proportional to the velocity of its motion.
 The voltage inducted in the moving blood column is
measured with stationary electrodes located on opposite
sides of blood vessel and perpendicular to direction of
magnetic field.
24

 An Electromagnetic Flow Meter is a device capable of
measuring the mass flow of a fluid.
 This kind of flow meter use a magnet and two electrodes
to peek the voltage that appears across the fluid moving
in the magnetic field.
 The Neumann Law (or Lenz Law) states that if a
conductive wire is moving at right angle through a
magnetic field, a voltage E [Volts] will appear at the end of
the conductor.
E=B*L*V
Where B = Magnetic Induction( Weber/m2)
25

 L = Length of the portion of the wire 'wetted' by the
magnetic field [m]
 V = Velocity of the wire [m/sec]
26

ULTRASONIC FLOWMETERS- TRANSMIT TIME
ULTRASONIC FLOW METER DOPPLER TYPE
27

ULTRASONIC FLOWMETERS CONTD . . .
 The blood cells in the fluid scatter the Doppler signal
diffusively. In the recent years ultrasound contrast agents
have been used in order to increase the echoes. The
ultrasound beam is focused by a suitable transducer
geometry and a lens.
 In this, a beam of ultrasonic energy is used to measure the
velocity of flowing blood. The two different ways are:
28

BLOOD PRESSURE MEASUREMENT
 Pressure is defined as force per unit area p = F / A
P = pressure in pascal,
F= force,
A=Area
 Pressure is increased by increasing the applied force or
by decreasing the area.
 Hydrostatic Pressure: If the force in a system under
pressure is not varied then pressure is known as
Hydrostatic pressure.
 Hydrodynamic Pressure: If the force in a system under
pressure is varied then pressure is known as
Hydrodynamic pressure
30

CONTD . . .
Methods:
1. Indirect method using sphygmomanometer
2. Direct method
Indirect Method using Sphygmomanometer
 In this method Sphygmomanometer is used to measure
blood pressure indirectly. It consists of inflatable rubber
bladder which is known as cuff, rubber squeeze ball
pump & valve assembly. Pressure is measured using
manometer with mercury column.
 Procedure to use Sphygmomanometer: Cuff is
wrapped around the patient‘s upper arm at a point
midway between elbow & shoulder. Stethoscope is
placed over as artery distal to the off, because at this
place, brachial artery comes close to surface.
31

PREASURE MEASUREMENT WITH CUFF
PLACEMENT AND KOROTKOFF SOUNDS
32

PREASURE MEASUREMENT WITH CUFF
PLACEMENT AND KOROTKOFF SOUNDS
33

CONTD . . .
 Then doctor slowly reduces the pressure in the cuff & he
watches the mercury column when the systolic pressure
exceeds the cuff pressure. Then doctor can hear some
crashing, snapping sound through stethoscope. This
sound is known as korotkoff sound.
Advantages
 Method is very simple
 Painless techniques
 There is no hazardous surgical procedure involved.
Disadvantages
 Effective result depend on the fact how accurately doctor
read pressure values when koratkoff sound is heard. 34

DIRECT METHOD OF BP MEASUREMENT
35

 Direct method of blood pressure is used when
accurate blood pressure reading. If we want to
know blood pressure in deep region indirect method
is not useful.so direct method is used.
Probe used in Direct Blood Pressure
Measurement
 Catheter tip probe sensor mounted at the tip of the
probe. Pressure exerted on the tip is converted to
the corresponding electrical signal. In fluid filled
catheter type. Pressure exerted on the fluid filled
column is transmitted to external transducer. This
transducer converts pressure in to electrical signal.
36

DIRECT METHOD OF BLOOD PRESSURE
MEASUREMENT
 Here fluid filled cattheter is used. Before inserting
catheter into blood vessel, fluid filled system should be
completely flushed out. Usually sterile saline is used for
this purpose. Because blood clotting is avoided.
 Working:
 Blood taken from vessel using Cather tip probe. Pressure
exerted is transmitted to the pressure transducer. The
output of transducer is given to pressure monitor.
37

CIRCUIT DIAGRAM FOR MEASUREMENT OF
SYSTOLIC AND DIASTOLIC BLOOD PRESSURE
38

CONTD . . .
 Procedure for measurement of blood pressure:
(1) The cuff is wrapped around the patient’s upper arm (at a
point midway between
the elbow and shoulder). A stethoscope is placed over a
brachial artery distal (i.e.,
downstream) to the cuff.
(2) The cuff is inflated so that the cuff pressure becomes
slightly greater than the
anticipated systolic pressure. This pressure compresses the
artery against the
underlying bone. This causes “occlusion” that stops the
blood flow in the vessel.
(3)The cuff is then slowly deflated so that the cuff pressure
drops slowly.
39

CONTD. . .
(i) When the cuff pressure drops slightly below the systolic
pressure, a sudden rush of blood flow (through the
occlusion in the artery) takes place. This causes crashing and
snapping sounds called the “Korotkoff sounds” in the
stethoscope.
(ii) When the cuff pressure drops slightly below the
diastolic pressure, these sounds disappear. The
pressure indicated by the monometer on the onset of
these Korotkoff sounds is the systolic pressure and the
pressure indicated by the manometer on the
disappearance of these sounds is the diastolic pressure.
The onset of the Korotkoff sounds in the stethoscope
indicates the systolic pressure and the disappearance of
these sounds in the stethoscope indicates the diastolic
pressure.
40

INDIRECT METHOD: ULTRASONIC METHOD:
41

 The ultrasonic blood pressure measurement system
consists of
(i) an inflatable rubber bladder called the “cuff”
(ii) piezoelectric crystals for the transmission and reception
of ultrasonic waves
(iii) a pump and valve assembly to inflate and deflate the
cuff and
(iv) an electronic control system to coordinate all events.
 Piezoelectric crystals are placed between the patient’s
arm and the cuff.
 Generally 2 or 8MHz ultrasonic waves are used.
 The blood pressure is measured by measuring the
Doppler shift caused in the incident ultrasonic wave by a
moving wall of a brachial artery. 43

 Initially the cuff pressure is increased slightly above the
anticipated systolic pressure.
 Then the cuff is deflated slowly at a fixed rate.
 When the cuff pressure drops to the systolic pressure, high
frequency Doppler shifts corresponding to the opening
event from a heart beat are detected.
 At this point the reading on the systolic manometer is the
systolic pressure value.
 The valve v2 is closed to fix the manometer on this value.
 Low frequency Doppler shifts corresponding to the closing
event from the same heartbeat are not detected as they
overlap with the high frequency Doppler shifts at this point.
44

 When the cuff pressure drops further, the opening and
closing events from a heartbeat start to separate and
hence high and low frequency Doppler shifts detected
alternatively.
 When the cuff pressure drops to the diastolic pressure, the
closing event from a heartbeat coincides with the opening
event from the next heartbeat and hence once again only
the high frequency Doppler shifts are detected.
 At this point the reading on the diastolic manometer is the
diastolic pressure value.
 The valve v3 is closed to fix the manometer on this value
45

CO LORIMETERS - INTRODUCTION
 The colorimeter (filter-photometer) is an optical electronic
device that measures the color concentration of a substance in
a solution.
Principle:
 Light of a specific wavelength or color when passed through a
solution of a substance of certain concentration is absorbed by
an amount proportional to the length of the passage via the
solution and the concentration of the substance.
 The absorbance is defined as
A = log(I1/Io) = log(1/T)
 where A is absorbance, Io is initial light intensity, I1 is the light
intensity after attenuation and T is transmittance.
 The absorbance increases and the transmittance decreases as
the path length or the concentration increases. Hence, the
absorbance in terms of the path length and the concentration is
given by the Beer’s law
A = aCL
 where A is absorbance, a is absorbtivity, C is concentration of
absorbing substance and L is cuvette path length.
46

COLORIMETERS CONTD . . .
 In a basic colorimeter, the light from a light source is
passed through an optical filter, which filters out a particular
wavelength or color.
 This particular wavelength or color is focused by lenses on
to a reference cuvette with a solution containing a
substance of known (standard) concentration and
absorbance and onto a sample cuvette with the sample
solution.
 The light waves coming off the cuvettes fall on photo-
detectors, which convert their intensities into voltages.
 The difference between these two voltages is amplified by
a dc amplifier and applied to a meter, which has been
calibrated to yield this voltage difference directly in
transmittance or absorbance unit. 48

COLORIMETERS CONTD . . .
 The calibration procedure is as follows:
(1) Ground the amplifier input and adjust the
potentiometer (R4) for a zero reading on the meter.
(2) Fill both the cuvettes with the reference solution
and adjust the potentiometer (R1) for a zero reading on
the meter.
The measurement is made as follows:
(1) Fill the cuvette 1 with the same reference solution and
the cuvette 2 with the sample solution.
(2) Read the difference voltage on the meter, which has
been calibrated in transmittance or absorbance units. 49

CONCENTRATION VS ABSORBANCE
50

COLORIMETER CONTD . . .
 Transmittance
T= I1/I0 * 100%
Absorbance
A= - log I1/ I0
A=log 1/T
 If the path length or concentration increases, the
transmittance decreases and absorbance increases, a
phenomenon expressed by Beer’s Law.
 Absorbtivity related to the nature of the A=aCL
absorbing substance and optical wavelength (known for
a standard solutionconcentration).
C: Concentration
L: Cuvette path length 51

FILTER PHOTOMETER (COLORIMETER)
 It is used to measure transmittance. Light from a
halogen lamp is incident on a filter F. The divergent
transmitted light is converted into two parallel
beams by an optical arrangement.
52

FILTER PHOTOMETER CONTD . . .
 One beam falls on a reference selenium
photoelectric cell CR and other beam falls on a
sample selenium photoelectric cell Cs after passing
through sample in the cuvette. Without the sample,
outputs from photoelectric cells are the same
53

FLAME PHOTOMETER CONTD . . .
 A flame photometer is used to analyze urine or blood in
order to determine the concentration of K, Na, Ca, and
Li.
 Lithium is used as a calibration substance in analysis of
other three substances.
 A known amount of lithium is added to the sample and
the emitted light intensity is measured relative to that of
lithium.
 By this way, any error due to varying flame temperature
is eliminated.
 Using an atomizer, liquid sample is sprayed into fine
droplets by passing oxygen or air to it.
55

 Separate photo detector is used for each channel. The
photodetctor circuit consists of a reverse biased diode in
which current flow increases as the intensity of light
increases.
 Flame photometer has many advantages such as fast
response, high accuracy and lesser cost of equipment.
But its sensitivity is smaller than fluorometer.
56

 In this method, fine droplets of the sample is aspirated into
gas flame that burns in a chimney. A known amount of
lithium salt is added to the sample, as a reference.
 As a result, red light is emitted by the lithium and yellow
and violet beam are emitted due to sodium and potassium
respectively. These diffracted colours are made to incident
on photodiodes.
 The photo detector circuits consists of a reverse biased
diode in which the current flow increases as intensity of
incident light increases. A calibration potentiometer is used
in every channel.
 Since the lithium is used as a standard reference, the
output of sodium and potassium channel are calibrated
interms of differences with the known lithium. The output
can be compared with the spectral illustration. 57

CONTD . . .
 The principle of operation is based on absorb or emit EM
energy (light) at different wavelengths.
 Depending on the substance being measured, the wavelength
used is typically in the ultraviolet (200-400 nm), visible (400-
700nm) or infrared (700 to 800 nm) range.
 Spectrophotometer can be used to determine the entity of an
unknown substance, or the concentration of a number of
known substances.
 The type of source / filters used typically determines the type of
the spectrophotometer.
 Rays of light bend around sharp corners, where the amount of
bending depends on the wavelength. This results in separation
of light into a spectrum at each line.
 In spectrophotometer, selection filter of colorimeter is replaced
by a monochromator.
 Monochromatic uses a diffraction grating G to disperse light
from the lamp.
 Light falls through the slit S0 into its spectral components.
59

SPECTROPHOTOMETER CONTD . . .
 Slit S1 is used for selecting a narrow band of the spectrum
which is used to measure the absorption of a sample in the
cuvette.
 The light from the cuvette is given to photo detector. It
converts light into a electrical signal.
 This electrical signal is amplified by using an amplifier. The
output from the amplifier is given to meter which shows
absorbance.
 Light absorption is varied when the wavelength is varied.
 Mirror M is used to reduce the size of the instruments.
60

INTRODUCTION
 Cardiac output is the amount of blood delivered by the heart
to the Aorta per minute.
 For normal adult the cardiac output is 4-6 liters/min.
 The measurement of cardiac output is necessary to study
the various cardiac disorders.
 Decrease in cardiac output is due to low blood pressure,
Reduced tissue oxygenation, poor renal function shock and
acidosis.
 The Cardiac output is measured by 3 methods.
1. Ficks Method
2. Indicator Dilution method
3. Measurement of cardiac output by impedance change
method
63

FLICK’S METHOD
 This is based on the determination of cardiac output by
the analysis of gas-keeping of the organism.
 Cardiac output can be calculated by continuously
infusing oxygen into the blood or removing it from the
blood and measuring the amount of oxygen in the blood
before and after its passage.
I=CAQ - CVQ
64

INDICATOR DILUTION METHOD
 This is based on the principle that if we introduce an
indicator in the blood circulation and then measuring the
concentration of indicator with respect to time.
 We can estimate the volume flow of blood. Let M mg of an
indicator is injected into the right heart.
Dilution Curve
66

INDICATOR DILUTION METHOD CONTD . . .
 During the first circulation period, the indicator would mix
up with the blood in a small quantity.
 After that there is a rapid change of concentration.
 This is shows by rising portion of dilution curve.
 After reaching maximum, the concentration of indicator
decreased exponentially
67

THERMO DILUTION METHOD
 Now-a-days thermo dilution method is adapted to
measure cardiac output.
Thermo dilution system
68

THERMO DILUTION METHOD
 A linear relation between temperature and resistance of
the thermistor can be obtained by connected a parallel
resistor with it.
 Then the line arising amplifier works.
 Integrator delivers the value of integral of blood
temperature change over a given time.
 By feeding data about p, s, Q and thermal indicator, the
computer can deliver the cardiac output in lit/min.
69

MEASUREMENT OF CARDIAC OUTPUT BY
IMPEDANCE CHANGE
70

CONTD . . .
 By the impedance method, the cardiac output can
be determined electronically. L probes method is
adopted here.
 The electrode pair 1 & 4 is used as current
electrodes.
 The electrode pair 2 & 3 is used to pick up the
voltage across the thorax
Volume and flow measurement
 Flow – volume of a liquid/gas passing some point
over a given time
71

ADVANTAGES OF CARDIAC OUTPUT
MEASUREMENTS.
73

CONTD . . .
 Indicator dilution is more useful when there is no
severe heart defect. Here the diagnostic information
can be obtained from the changes in the shape.
 Fig (b) shows article output defect where blood
flows internally from left atrium to right atrium.
74

PH,PO2, PCO2 MEASUREMENT
 the partial pressure of oxygen (O2)  pO2
 carbon dioxide (CO2) gases and  pCO2
 the pH (hydrogen ion concentration).
76

REFERENCE ELECTRODE
 The reference electrode is used in the measurement of
pH and electrolyte parameters and is located in the
pH/Blood Gas module
77

PH ELECTRODE CONTD . . .
 The pH measurement is performed using two separate
electrodes:
 a pH-measuring electrode
 and a reference electrode
 The pH-sensitive glass membrane is located at the tip and
seals the inner buffer solution with a constant and known
pH.
 A saturated electrolyte solution (potassium chloride) in the
reference electrode and a leaky membrane permit current
flow from the reference electrode through the sample in the
measurement chamber to the measuring electrode.
 The potential difference is displayed on a voltmeter
calibrated in pH units. 80

PO2 ELECTRODE CONTD . . .
 Oxygen electrode measures the oxygen partial
pressure in a blood or gas sample.
 Cathode: platinum
 Anode: a silver/silver chloride
 Electrolyte: sodium chloride solution
Cathode and anode are placed in the electrolyte
 Applied voltage: 700 mV
83

PCO2 ELECTRODE CONTD . . .
 The pCO2 electrode is a combined pH and Ag/AgCl
reference electrode mounted in a plastic jacket, which is
filled with a bicarbonate electrolyte.
 The PCO2 electrode also contains a spacer (usually a
porous membrane of nylon) that acts as a support.
 As CO2 diffuses through the membrane and into the
support, the pH of the electrolyte changes
 The output of this modified pH electrode is proportional to
the PCO2 present in the sample. 85

PH MEASUREMENT
 The chemical balance in the body can be
determined by the ph value of blood and other
 body fluids.ph is defined as the hydrogen ion
concentration of a fluid. It is the logarithm of the
 reciprocal value of h+ concentration. The ph
equation is given as,
 Ph= - log10 [H+] = log10 1/[H+ ]
 pH is the measure of acid- base balance in a fluid,
A neutral solution has the ph value as 7.
 Solutions with pH value less than 7 are acidic and
above 7 are basic. Most of the body fluids are
 slightly basic in nature. 86

CONSTRUCTION AND WORKING
 The ph meter is made up of a thin glass membrane
and it allows only the hydrogen ions
 to pass through it. The glass electrode provides a
membrane interface for H+ ions. The glass bulb
 at the lower end of the ph meter contains a highly
acidic buffer solution. The glass tube consists
 of a sliver-sliver chloride (Ag/Agcl) electrode and
the reference electrode which is made up of
 calomel sliver-sliver chloride(Ag/Agcl) is tan placed
in the solution in which ph is being
 measured. 88

 The potential is measured across the two
electrodes. The electrochemical measurement,
 which should be obtained by each of the electrodes
called half- cell. The electrode potential is
 called as half-cell potential. Here the glass
electrode inside the tube constitutes one half –cell
and
 the calomel or reference electrode is considered as
the other half-cell.
89

 For easier ph measurement combination electrodes are
used. In this type both the active
 glass electrode and reference electrode are present in
the same meter. The glass electrodes are
 suitable only to measure ph values around 7. Since this
type of glass electrodes produce
 considerable errors during the measurement of high Ph
values, special type of Ph electrodes are
 used. After every measurement the pH meter is washed
with 20% ammonium biflouride solution,
 for accurate results. The Ph meter with hydroscopic
glass absorbs water readily and provides best
 pH value. 90

PO2 MEASUREMENT
 The term po2 is defined as the partial pressure of
oxygen respectively. The determination
 of po2 is one the most important physiological chemical
measurement. The effective functioning
 of both respiratory and cardiovascular system can be by
po2 measurement. The partial pressure of a gas is
proportional to the quantity of that gas present in the
blood.
 The platinum wire, which is an active electrode, is
embedded in glass for insulation and
 only its tip is exposed. It is kept in the electrolyte
solution in which the oxygen is allowed to
 diffuse. The reference electrode is made up of silver-
silver chloride (Ab/AgCl). 91

PO2 MEASUREMENT CONTD . . .
 A voltage of 0.7
 is applied between the platinum wire and the
reference electrode. The negative terminal is
 connected to the active electrode through a micro
ammeter and the positive terminal is given to
 the reference electrode.
92

PO2 MEASUREMENT CONTD . . .
 Due to the negative terminal, the oxygen reduction takes
place at the platinum cathode.
 Finally the oxidation reduction current proportional to the
partial pressure of oxygen diffused into
 the electrolyte can be measured in the micro ammeter.
The electrolyte is generally scaled in the
 electrode chamber by means of a membrane through
which the oxygen can diffuse from the
 blood or sample solution.
 There are two types of pO2 measurement. They are
 I) Vitro measurement
 II) Vivo measurement 94

VITRO MEASUREMENTS
 In case of dark electrode the platinum cathode and
the reference electrode is present in a single
 unit. This electrode is used for vitro and vivo meas
 In this method the blood sample is taken and the
measurement for oxygen saturation is
 made in the laboratory. The electrode is placed in
the sample blood solution and the pO2 value is
 determined.urements.
95

VIVO MEASUREMENTS
 In this method the oxygen saturation is determined while
the blood is flowing in the
 circulatory system. A micro version of the pO2 electrode
is placed at the tip of the catheter so that
 it can be inserted into various parts of the heart or
circulatory system.
 The pO2 measurement also has some disadvantages in
it. The reduction process in the
 platinum cathode removes a finite amount of the oxygen
from the cathode. And there is a gradual
 reduction of current with respect to time. However
careful design and proper procedures in
 modern pO2 electrodes reduce the errors. 96

PCO2 MEASUREMENT
 The term pco2 is defined as the partial pressure of carbon
dioxide respectively. The
 determination of pco2 is one the most important physiological
chemical measurement. The
 effective functioning of both respiratory and cardiovascular
system can be by pco2 measurement.
 The partial pressure of a gas is proportional to the quantity of
that gas present in the blood.
 The partial pressure of carbon dioxide can be measured with
the help of pCO2 electrodes.
 Since there is a linear relationship between the logarithm of
pCO2 and pH of a solution. The
 pCO2 measurement is made by surrounding a pH electrode
with a membrane selectively
 permeable to CO2. 97

PCO2 MEASUREMENT CONTD . . .
 The modern improved pCO2 electrode is called as
severinghous electrode. In this
 electrode the membrane permeable to CO2 is made up
of Teflon which is not permeable to other
 ions which affects the pH value. The space between the
Teflon and glass contains a matrix layer
 which allows only the CO2 gas molecules to diffuse
through it.
 One of the demerits in older CO2 electrode is, it requires
a length of time for the CO2
 molecules to diffuse through the membrane. The
modern CO2 electrode is designed in such a way
 to overcome this demerit. Here the CO2 molecules
diffuse rapidly through the membrane and the
 measurement can be done easily. 98

MEASUREMENT OF PHCO3
 Blood gas analyzers are used to measure the
content of pH, pCO and PO2 from the
 blood.
 Two gases of accurately known O2 and CO2
percentages are required for
 calibrating the analyzer in pO2 and pCO2 modes.
These gases are used with
 precision regulators for flow and pressure control.
99

MEASUREMENT OF PHCO3 CONTD . . .
 Two standard buffers of known pH are required for calibration
of the analyzer in
 the pH mode.
 Input signal to the calculator is obtained from the outputs of
the pH and pCO2
 amplifiers
 The outputs are adjusted by multiplying with a constant and
are given to an adder
 circuit
 The output of adder is passed to antilog generators circuit.
Then it is passed to
 A/D converter for display. Resistance R is used to adjust zero
at the output.
 Total CO2 is calculated by summing the output signals of the
calculators and the
 output of the pCO2 amplifier 100

CIRCUIT DIAGRAM OF COMPUTATION OF
BICARBONATE
101

MEASUREMENT OF PHCO3 CONTD . . .
The base excess calculator consists of three
stages.
 In the first stage, the output of pH amplifier is
inverted in an operational amplifier, whose gain is
controlled by a potentiometer.
 The output of HCO3 calculator is inverted in the
second stage.
 The third stage is a summing amplifier A3 whose
output is given to A/D converter, that gives a digital
read out.
102

Ec 6001 medical electronics

Empfohlen

Empfohlen

Weitere ähnliche Inhalte

Was ist angesagt?

Was ist angesagt? (20)

Ähnlich wie Ec 6001 medical electronics

Ähnlich wie Ec 6001 medical electronics (20)

Kürzlich hochgeladen

Kürzlich hochgeladen (20)

Ec 6001 medical electronics