Unit 4 biomedical

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UNIT 5

Instrumentation for clinical laboratory

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Respiratory Transducers and Instruments

RespirationIt is responsible for bringing oxygen in to the body and discharging waste particles from body.

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Respiratory System Measurements1. Vital capacity

2. Functional residual capacity

3. Inspiratory capacity

4. Total Lung capacity

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Respiratory System MeasurementsTidal 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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Respiratory System Measurements1. 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

PneumographA 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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PneumographImpedance 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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PneumographIn 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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Impedance Pneumograph

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Impedance Pneumograph Eqlt. Ckt.

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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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Thermistor airway Pneumograph

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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

Spirometer

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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

Bio Electric Amplifiers

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Amplitudes and spectral ranges of some important bio-signals

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Instrumentation Amplifiers

Instrumentation AmplifierAn 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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Instrumentation Amplifier

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Instrumentation AmplifierThe 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

Isolation AmplifierIsolation 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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Isolation Amplifier

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Symbol of Isolation Amplifier

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Isolation Amplifier

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Isolation Amplifier

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Isolation Amplifier

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Isolation Amplifier

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Isolation Amplifier

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Isolation AmplifierThe 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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Isolation Amplifier

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Chopper Stabilized Amplifiers

Chopper Stabilized amplifiersChopper 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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Chopper Stabilized Amplifiers

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Chopper Stabilized amplifiers

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Chopper Stabilized amplifiers

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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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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

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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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.

Input Guarding

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Flow volume Transducers

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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Flow volume Transducer

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Blood Cell counting

Blood Cell Counting

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Blood Cell Counting

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Blood Cell Counting

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Blood Cell Counting

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Blood Cell Counting

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Coulter Method: Blood Cell Counting

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Blood Cell CountingUsing 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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Blood Cell CountingThis 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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Pico Cell Blood Cell Counting

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Pico Cell Blood Cell Counting

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Optical Blood Cell Counting

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Blood Flow Meter

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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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 – 2502. Abdominal 1003. Vena Cava 5 – 40

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EM Blood Flow Meter

EM Blood Flow Meter• The commonly used instrument for blood flow is

Electromagnetic type.

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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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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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EM Blood Flow Meter

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EM Blood Flow Meter

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EM Blood Flow Meter

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Types of EM Blood Flow Meter

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EM Blood Flow Meter

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EM Blood Flow Meter

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Ultrasonic Blood Flow Meter


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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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Doppler Blood Flow Meter

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Blood pH Measurement

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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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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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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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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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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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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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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Glass Electrode

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PH SENSITIVE FET

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Conductimetric PH Sensor

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Fiber Optic PH Sensor

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Fiber Optic PH Sensor

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Engineering

Unit 4 biomedical