5th semester subject - medical electronics

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UNIT 5
Instrumentation for clinical
laboratory
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Respiratory Transducers and
Instruments

3. Respiration
It is responsible for bringing oxygen in to the body and
discharging waste particles from body.
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4. Respiratory System Measurements
1. Vital capacity
2. Functional residual capacity
3. Inspiratory capacity
4. Total Lung capacity
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5. Respiratory System Measurements
Tidal volume = volume of air inhaled during normal quiet
breathing.
Residual volume (RV) = volume of air in the lungs after
maximal expiration.
Functional residual capacity (FRC) = volume of air in the
lungs after exhalation during quiet breathing.
Inspiratory capacity = volume of air from FRC to maximal
inhalation.
Vital lung capacity from RV to maximal inhalation.
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6. Respiratory System Measurements
1. Pneumograph is used to detect respiration.
2. Spiro meters are used for the following measurements.
1. Tidal Volume (TV)
2. Inspiratory Reserve Volume (IRV)
3. Expiratory reserve volume (ERV)
4. Residual Volume (RV)
5. Minute Volume
3. Pulmonary Capacities are also calculated by respiratory
machine.
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Pneumograph

8. Pneumograph
A Pneumograph, also known as a pneumatograph or
spirograph, is a device for recording velocity and force of
chest movements during respiration.
There are various kinds of pneumographic devices, which have
different principles of operation.
1.In one mechanism, a flexible rubber vessel is attached to the
chest and the vessel is equipped with sensors.
2.Others are impedance based.
•In first case a very thin elastic tube filled with mercury is
stretched across patient chest.
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9. Pneumograph
Impedance pneumography is a commonly-used technique
to monitor a person ’s respiration rate, or breathing rate.
 The idea behind the Impedance pneumograph is that, the AC
impedance across the chest of a subject changes as
respiration occurs.
 It is mainly used in neonatal respiration monitors.
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10. Pneumograph
In second case it is implemented by either using two
electrodes or Four electrodes
The objective of this technique is to measure changes in the
electrical Impedance of the person ’s thorax caused by
respiration or breathing.
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11. Impedance Pneumograph
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12. Impedance Pneumograph Eqlt. Ckt.
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13. Pneumograph
• There are two type of pneumograph that uses piezoresistive
strain gauge transducers.
1. Mercury strainguage
2. Same wire foil or semiconductor piezoresistive devices.
• Thermistors are used as flow detectors in some
pneumographs.
• In one type a bed thermistor is placed just inside the
patients nostril.
• In another type thermistors are mounted on a patient who
is fitted with an endotracheal tube or is on a respirator or
ventillator.
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14. Thermistor airway Pneumograph
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15. Pneumograph
• In some transducer , the thermistor is placed with a thin
platinum wire stretched taut across a short section of
tubing.
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Spirometer

17. Spirometer
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18. Spirometer
• A bell or jar is suspended from top in a tank of water.
• An air hose leads from a mouthpiece to the space inside of
the bell above the water level.
• The weight maintains the bell at atmospheric pressure.
• When the patient exhales, the pressure inside the bell
increases above atmospheric pressure causing the bell to
rise.
• Similarly, When the patient inhales, the pressure inside the
bell decreases causing the bell to comes down.
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Bio Electric Amplifiers

20. Bio Electric Amplifiers
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21. Amplitudes and spectral ranges of some important bio-signals
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Instrumentation Amplifiers

23. Instrumentation Amplifier
An instrumentation (or instrumentational) amplifier is a type
of differential amplifier that has been outfitted with input
buffer amplifiers.
The input buffer eliminate the need for input impedance
matching and thus make the amplifier particularly suitable for
use in measurement and test equipment.
The gain of the circuit is given by
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24. Instrumentation Amplifier
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25. Instrumentation Amplifier
The two amplifiers on the left are the buffers.
The rightmost amplifier, along with the resistors is standard
differential amplifier circuit.
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Isolation Amplifiers

27. Isolation Amplifier
Isolation amplifiers are a form of differential amplifier that
allow measurement of small signals in the presence of a high
common mode voltage by providing electrical isolation and
an electrical safety barrier.
They protect data acquisition components from common
mode voltages, which are potential differences between
instrument ground and signal ground.
Isolation amplifiers are used in medical instruments to
ensure isolation of a patient from power supply leakage
current.
Amplifiers with internal transformers eliminate external
isolated power supply.
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28. Isolation Amplifier
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29. Symbol of Isolation Amplifier
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30. Isolation Amplifier
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31. Isolation Amplifier
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32. Isolation Amplifier
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33. Isolation Amplifier
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34. Isolation Amplifier
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35. Isolation Amplifier
The 3650 and 3652 are optically coupled integrated circuit
isolation amplifiers.
Compared to these earlier isolation amplifiers, the 3650 and
3652 have the advantage of smaller size, lower cost, wider
bandwidth and integrated circuit reliability.
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36. Isolation Amplifier
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Chopper Stabilized Amplifiers

38. Chopper Stabilized amplifiers
Chopper stabilization constantly corrects input offset voltage
errors, including both errors in the initial input offset voltage
and errors in input offset voltage due to time, temperature,
and common-mode input voltage.
A chopper-stabilized amplifier is actually two amplification
paths in parallel.
A high-accuracy, low-frequency path (A2) incorporates high
gain and chopping, while high-frequency signals are
amplified by the parallel wideband amplifier A1.
The outputs of both stages are subtracted in a summer
amplifier, whose output is fed back to the inputs of both
amplifiers through a feedback resistor.
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39. Chopper Stabilized Amplifiers
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40. Chopper Stabilized amplifiers
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41. Chopper Stabilized amplifiers
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42. Chopper Stabilized amplifiers
 Two problems arise when we tries to record low level bio-
potentials.
Noise
DC Drift
These are worse , if we are using high gain amplifiers to
amplify the weak bio-potentials.
Noises produced in amplifier circuit and human body makes
the problem worse.
Drift is the change in gain or dc offset caused by thermal
effects on amplifier components.
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43. Chopper Stabilized amplifiers
 Drift can be minimized with the use of negative feedback.
This can be avoid by convert a DC (or near dc, low frequency
analog) signal to an AC signal that will pass through the
amplifier.
The solution is to chop or sample the analog signal at a
frequency that will pass through the AC coupled amplifier.
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Input Guarding

45. Input Guarding
 Physiological signals are low amplitude signals.
In most cases physiological signals accompanied by large CM
signals.
 If Op Amps are used, both differential (E)and common mode
(Ecm) signals are present.
The op amp cannot distinguish artifact from real signal and
C.M signal.
To avoid these problem, input guarding is used.
Here , we are placing a shield at the CM signals.
Input cable is shielded to avoid CM signals.

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46. Input Guarding
 Technique for increase both the input impedance of the
amplifier of bio-potentials and the CMRR.
Instrumentation amplifier providing input guarding

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Driven-right-leg circuit
reducing common-mode
interference.

47. Input Guarding

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Flow volume Transducers

49. Flow volume Transducer
• It measures the flow volume in litres per minute.
• The transducer assembly consists of differential pressure
transducer and an airway containing a wire mesh
obstruction.
• The wire mesh produces a pressure drop when it placed in
an airway.
• This pressure drop is measured as a differential pressure
across the mesh.
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50. Flow volume Transducer
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Blood Cell counting

52. Blood Cell Counting
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53. Blood Cell Counting
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54. Blood Cell Counting
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55. Blood Cell Counting
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56. Blood Cell Counting
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57. Coulter Method: Blood Cell Counting
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58. Coulter Method: Blood Cell Counting
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59. Blood Cell Counting
Using this technology, cells are sized and counted by detecting
and measuring changes in electrical resistance when a particle
passes through a small aperture.
This is called the electrical impedance principle of counting
cells.
A blood sample is diluted in saline, a good conductor of
electrical current, and the cells are pulled through an aperture
by creating a vacuum.
Electrical resistance or impedance occurs as the cells pass
through the aperture causing a change in voltage.
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60. Blood Cell Counting
This change in voltage generates a pulse .
The number of pulses is proportional to the number of cells
counted.
The size of the voltage pulse is also directly proportional to the
volume or size of the cell.
This was the principal parameter used in earlier analyzers for
characterizing all cell types, but it is now used primarily for
counting and sizing red blood cells and platelets.
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61. Coulter Method: Blood Cell Counting
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62. Pico Cell Blood Cell Counting
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63. Pico Cell Blood Cell Counting
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64. Optical Blood Cell Counting
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65. Optical Blood Cell Counting
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66. Optical Blood Cell Counting
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Blood Flow Meter

68. Blood Flow Meter
• Blood flow is the continuous circulation of blood in the
cardiovascular system.
• The science dedicated to describe the physics of blood
flow is called hemodynamics.
• Usually the blood flow measurements are more invasive than
blood pressure measurements / ECG
The abnormal changes in the blood flow or blood velocity
gives rise to malformation of vessels.
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69. Blood Flow Meter
• Blood flow is nothing but the volume of blood per time
[ml/min].
Typical values for blood flow [cm/s]:
1. Aorta 100 – 250
2. Abdominal 100
3. Vena Cava 5 – 40
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EM Blood Flow Meter

71. EM Blood Flow Meter
• The commonly used instrument for blood flow is
Electromagnetic type.
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72. EM Blood Flow Meter
• The operation principle behind the electromagnetic blood
flow meters is Faraday’s law of electromagnetic induction
which states that if electrical current carrying conductor
moves at right angle through a magnetic field, an
electromotive force is induced in the conductor.
Electromagnetic blood flow meters can be classified in to
1. Sine wave electromagnetic blood flow meter
2. Square wave electromagnetic blood flow meters
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73. EM Blood Flow Meter
• The sine wave electromagnetic blood flow meter uses
wave alternating current to generate the required
magnetic field.
• The flow voltage (induced voltage) is also sinusoidal.
• Even if for lower frequency application, the circuit becomes
complex and high frequency application results a problem of
stray capacitance effect, it can’t be used for a wide range of
frequency values.
• In the square wave electromagnetic blood flow meter, the
excitation is square wave alternating current, and the
induced voltage is square wave too.
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74. EM Blood Flow Meter
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75. EM Blood Flow Meter
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76. EM Blood Flow Meter
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77. Types of EM Blood Flow Meter
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78. EM Blood Flow Meter
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79. EM Blood Flow Meter
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Ultrasonic Blood Flow Meter

81. Ultrasonic Blood Flow Meter
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82. Ultrasonic Blood Flow Meter
• An ultrasonic flow meter is a type of flow meter that
measures the velocity of a fluid with ultrasound to
calculate volume flow.
• The blood cells in the fluid reflects the ultrasound signal
with a shift in the ultrasonic frequency due to its
movement.
• Using ultrasonic transducers, the flow meter can measure the
average velocity along the path of an emitted beam of
ultrasound, by averaging the difference in measured
transit time between the pulses of ultrasound propagating
into and against the direction of the flow or by measuring
the frequency shift from the Doppler effect.
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83. Ultrasonic Blood Flow Meter
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84. Ultrasonic Blood Flow Meter
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85. Ultrasonic Blood Flow Meter
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86. Ultrasonic Blood Flow Meter
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87. Ultrasonic Blood Flow Meter
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88. Ultrasonic Blood Flow Meter
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89. Ultrasonic Blood Flow Meter
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90. Ultrasonic Blood Flow Meter
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91. Ultrasonic Blood Flow Meter
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92. Doppler Blood Flow Meter
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Blood pH Measurement

94. Blood pH Measurement
• In chemistry, pH is the negative log of the activity of the
hydrogen ion in an aqueous solution.
• Solutions with a pH less than 7 are said to be acidic and
solutions with a pH greater than 7 are basic or alkaline.
• Pure water has a pH of 7.
• Mathematically, pH is the negative logarithm of the activity
of the (solvated) hydronium ion, more often expressed as the
measure of the hydronium ion concentration
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95. Blood pH Measurement
• Blood pH is an important factor to determine the acid base
balance in the human body.
• Blood pH level plays an important role for your overall
health, because if your blood pH level is acidic, your cells
cannot function properly.
• One of the major contributors to acidosis is carbon dioxide, a
byproduct of metabolism.
• Carbon dioxide combines with water to form carbonic acid.
• The normal pH of blood is between 7.35-7.45.
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96. Blood pH Measurement
•The increase in hydrogen ion concentration causes the pH of
the body fluids to decrease.
•If the pH of the body fluids falls below 7.35, symptoms of
respiratory acidosis become apparent.
•Blood gas analyzers are used to measure pH, pCO2 and pO2
etc
•pH of biological fluids is measured using a glass electrode.
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97. Blood pH Measurement
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98. Blood pH Measurement
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99. Blood pH Measurement
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100. Blood pH Measurement
•A blood sample for measuring pH parameters is collected in
a glass syringe.
•The blood pH level can be determined by
1.Saliva pH test
2.Urine pH test
3.Blood pH test
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101. Saliva Blood pH Test
•Saliva pH test: It is one of the fastest and simplest tests for
measuring blood pH level.
•However, it is not the most accurate.
•Before taking the test, you should wait at least two hours
after eating.
•Depending on the food you eat, it can increase or decrease
your blood pH level.
•To do the saliva pH test, go buy the pH paper test strip at
your local drug stores and health food stores and follow the
directions on the package.
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102. Urine Blood pH Test
•This test works similar to the saliva pH test, but it tests urine
instead of saliva.
•The pH test strip for testing urine is the same as the saliva
pH test strip.
•Blood pH test
•This test is not as convenient as the saliva and urine pH test,
but it is usually more accurate.
•To do the blood pH test, you will need to visit your doctor
and get your blood drawn.
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103. Blood pH Measurement
•One of the best ways to bring your blood pH back to its
normal state is to eat mostly organic alkaline food. Another
way is to drink distilled water.
•Distilled water is very pure water, so if you want to reduce
your risk of acidosis, you will need to add some minerals to it.
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104. Blood pH Measurement
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105. Glass Electrode
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106. PH SENSITIVE FET
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107. Conductimetric PH Sensor
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108. Fiber Optic PH Sensor
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109. Fiber Optic PH Sensor
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