Course module description:

Course module description:
This course gives an overview of Categories of Measurements, Calculation of Errors in electrical measurements, types of sensors and their uses in measuring systems Bridge circuits, application of measurement system in the Biomedical Devices, Active filters Course module objectives: The goals of the course are 1-Introduce students to know the fundamentals of electric measurements. 2- The student should be able to use the measuring devices, calculate the measuring errors, 3- be able to design and use simple measuring circuits 4- Understanding the main basics of different electric measurement processes especially during the use of biomedical equipments

Course/ module components
Books: Medical Instrumentation Application and Design, by Webster Introduction to biomedical Equipment Technology by J Car Electronic Instruments and Measurements, I.D. Jones and A.F. Chin Learning outcomes Knowledge and understanding 1-Understanding the basic system of units 2- Understanding different processes of measurements 3- Understanding the types of measuring processes and their basics specially in the medical equipments 4- Understanding the basic electric measuring circuits including filters and amplifiers

Cognitive skills (thinking and analysis).
ability to investigate the types of sensors in any measuring device ability to feel with the errors in the measurements Operate , maintain and use of the measuring instrumentation Communication skills (personal and academic). . Ability to work with medical team - Ability to work within a one team - Ability deal with the biomedical equipment Practical and subject specific skills (Transferable Skills). Medical Devices Troubleshooting and Maintenance Assessment instruments. Quizzes, Term Exam, Small team project Practical Exam, Oral Exam .

Allocation of Marks Mark Assessment 10%Quizzes 30%Med Term Exams
20%Practical Exam 40%Final Exam 100Total Expected workload: On average students need to spend 2 hours of study and preparation for each 50-minute lecture/tutorial. Attendance policy: Absence from lectures and/or tutorials shall not exceed 25%. Students who exceed the 25% limit without a medical or emergency excuse acceptable to and approved by the Dean shall not be allowed to take the final examination and shall receive a mark of zero for the course.

Biomedical Measurement Course Contents
Ch1 Introduction - Definition of Measuring Process - Measuring Types (Direct –Indirect, Null) - Measurement system components - Generalized medical instrumentation system Ch2 Errors in Measurements - Error definition - Accuracy , sensitivity, resolution - Types and sources of errors -Statistical analysis of error -Static characteristics of measuring system

Ch3 Sensing Element (Sensors) - Types of sensors - Resistive sensors - Resistive strain Gauges - Capacitive sensor- Inductive sensors - Temp Sensor - Piezo Electric sensor -Electrodes Ch4 Direct Current Bridge - Wheatstone bridge

Ch5 Blood Pressure and other Cardio Vascular Measurements - Important physiological definitions - Pressure measurements - Blood pressure measurements (direct – indirect ) - Blood flow measurement Ch6 Signal Conditioning - Op-amp and wave shaping - Filters

Lab 1- Units , Dimensions and some important definitions 2- Temperature Measurements 3- Blood Pressure measurements 4- Spiro meter 5- Pulse Oximeter 6-ECG (Electro cardio gram) Signal 7-Skin resistance 8-Time reaction 9- Strain gauge

Ch1 Introduction 1- Definition of Measuring Process:
Measurement is a process for comparing an unknown quantity with an accepted standard (calibrated) quantity. This process involves connecting a measuring instrument into the system and observing the response of instrument. Categories of measurements (Types) There are three main types of measurements Direct measurement Indirect measurement Null measurement

Direct measurement Direct measurements are made by holding the measurand (required quantity to be measured) up to some calibrated standard and comparing the two. A good example is the meter stick ruler used to measure and cut a piece of cable to the correct length

Indirect measurement Indirect measurements are made by measuring some thing other than the actual measurand The most common example of indirect measurement is the blood pressure measurements

Null measurement Null measurements are made by comparing a calibrated source to an unknown measurand and then adjust the reference until the difference between them become zero.

2- Electronic Measurement System
The block diagram of Electronic Measurement System is shown in Fig . I/P = Input O/P = Output Signal Conditioning Sensing Element Signal Processing Data Output I/P O/P

3- Generalized Medical (Measurement ) Instrumentation system

2- Sensors (Sensing Element)
1- Measurand (I/P) The physical quantity/ property that system measured is called measurand. Most medically important measurands can be grouped in the following categories: Bio-potential (ECG), Pressure, Flow, Dimension (imaging), displacement, Velocity, Force , Acceleration, Temperature and Chemical Concentration. 2- Sensors (Sensing Element) A sensor is defined as the device that converts a physical measurand to electric output. The sensor should be sensitive, Bio-compatible Many sensors have a primary sensing element such as diaphragm which converts the pressure to displacement A variable sensing conversion element such as the strain gauge that converts this displacement to volt. Strain Gauges Displacement mV Thermocouple T oC mV

3- Signal Conditioning 4- Output Display
Usually the sensors output can't be directly coupled to the display device Amplifier and filter are used to modify the signal 4- Output Display The measured value must be displayed in a form that the operator can analyze easily. The best form for display may be numerical or graphical. Example of simple Display

Example of simple Display

Example of simple instrument Thermometer
Example of simple Display Example of simple instrument Thermometer Scale Temp Hg Measurand is Temp Sensing Element is Mercury Signal Conditioning is (H) High of Mercury Data Presentation is scale

Load Cell using Strain Gauge
Example of simple instrument Load Cell using Strain Gauge Load Strain Gauge Body of Load Cell Wheatstone Bridge Amplifier and Filter I/P Sensing Element ∆Ω V Signal Conditioning PC A/D Display Signal Processing

Error = True (Expected) value – measured value
Ch2 Errors in Measurements Any measurement system is affected by many factors. Some of these factors are related to the instrument themselves and the other factor related to the person who using the instrument. 1- The deviation of the measured value from the true value is called the error in the instrument. Error = True (Expected) value – measured value True (Expected) Value of Measurement Measured Value Error

Percentage Error = 2- Accuracy Percentage Accuracy = 3- Sensitivity
The accuracy of measurement is the degree of closeness of the measured value to the true value. Percentage Accuracy = 3- Sensitivity Sensitivity is the ratio of output signal to the change in the input signal Sensitivity Output Signal Change in the Input

What is the output volt ,,,, say 1mv
For Example Thermocouple ,, the input is change in temp ,, the output is Volt If temp changes What is the output volt ,,,, say 1mv Then 4- Resolution Resolution is the minimum change in the measured value can be sensed by the instrument

2-Types of Errors Errors are generally categorized under the following three main types 2-1 Gross Error This error are generally the fault of the person using the instrument (error in reading, error in recording, incorrect use of the instrument) 2-2 Systemic Errors These errors due to the problem with the instrument environment effects and it can be classified to the following. Instrumentation Errors The source of these errors are the measuring device (internal error due to friction in the bearing of the meter movement, incorrect spring tension, improper calibration) The instrumentation errors can be reduced by good maintenance and use of the instrument Environmental Errors These errors are happened due to the change in the surrounded environment (Temp, Pressure and Humidity

2-3 Random Errors These errors is due to unknown causes and occur even when all gross and environmental errors have been reduced Systemic Errors 2-4 Limiting Error This error is due to the wrong choose of the measuring scale. For example the manufacturer of a certain voltmeter may specify the instrument to be accurate within ±2% of the full scale. This is the limiting error and means that a full scale reading will be within the limits of ±2% error. But if the measured value are less than the full scale, the limiting error will increase. So it is important to obtain the measurements as close as possible to the full scale of the used instrument.

For 120 volt this error become
Example (1) A 300 Volt voltmeter is specified to be accurate within ±2% at the full scale. Calculate the limiting error when the instrument is used to measure Volt and 2- a source of 220 volt Solution: Case 1 Limiting Error = For 120 volt this error become Case 2 For 220 volt this error become

Then Limiting Error for 80V reading become
Example (2) A voltmeter and Ammeter are used to determine the power dissipated in a resistor. Both instruments are guaranteed to be an accurate within ±1% at the full scale. If the voltammeter reads 80 Volt on its 150 Volt Range,, and the ammeter reads 70mA on its 100mA Full Scale. Calculate the limiting error for power calculation For Voltmeter Limiting Error = Then Limiting Error for 80V reading become For Ammeter Limiting Error = Limiting Error for 70mA become Then the limiting error for the power = sum of individual limiting errors = = 3.29%

Statistical Analysis of Error in Measurements
1- Arithmetic Mean If a measurement is repeated several times, at the same conditions, the reading may differ because of the founding of different errors causing If we have several values for one measurement At the same conditions The arithmetic mean= Average = 2- Deviation (d) If we have several readings for one measurement At the same conditions The deviation is the difference between each reading and the average

3- Standard Deviation (S) (Root Mean Square Value)
It is defined as the variance of the measured value about the mean value Example 3 The expected value of the voltage across a resistor is 50Volt, however measurement yields a value of 49Volt. Calculate 1-The absolute error 2-The percentage error 3-The percentage accuracy Solution 1-The absolute error = =50-49=1Volt 2-Percentage Error= 3-Percentage Accuracy=100%-e%=98%

Example 4 During measurements of the volt across battery the following readings are given at the same measuring conditions V1= V2= V3= and V4=50.2 Find 1-The Arithmetic mean The deviation of each value 3- The sum of deviations Standard deviation Solution 1- The arithmetic mean (Average) 2-Deviation of each value d1= = 0.2 V d2= = -0.2 V d3= = -0.3 V d4= = 0.3 V 3-Sum of Deviation= =0 S=0.295=0.3 4-Standard Deviation Reading become

Static Characteristics of Measuring Element
A- Range B- Span C- Ideal Straight Line D-Non-linearity E- Environmental Effects F- Wear and Aging A-Range It is specified by the minimum and maximum values of I/P and O/P (4-80)mV Pressure Transducer (10-104) Pa Min input =10Pa Min output 4mA Max input 104 Pa Max output 80mA B-Span Is the maximum variation in I/P and in the O/P Span of input =Imax-Imin Span of output =Omax-Omin

The relation between the input and the output should be straight line
C- Ideal Straight Line The relation between the input and the output should be straight line Output Input K = slope K = slope Output Input a Output = K input Output =K Input +a K is calibration factor (Slope)

The relation between the input and the output is non linear
D- Non-Linearity The relation between the input and the output is non linear Output Input K = slope Output Therortical Output Actual N N (non-linearity) = O actual – O Theoretical E-Environmental Effects Generally the output depends not only on the input but also on the environmental conditions Temp oC,,, Pressure =1Bar and Humidity =80% If these conditions changed the output also changed F-Wear and Aging Characteristics changes with time

Example1 During pressure measurement using a resistive strain gauge the following data are given Input (Pressure Pa) Output (mV) Find the calibration factor and write the relation between the input and output Example2 For the above example if the reading become as the following Input (Pressure Pa) Output (mV) Find the calibration factor and write the relation between the input and output

Types of Signals Signals can be categorized in several ways, but the most fundamental is according to time domain behaviour and the other major one according to the frequency domain If we assume that the signal of the form V=f (t). The time domain classes of signals include Static and Quasi-Static, Periodic, Repetitive, Transient and Random Static and Quasi-static Signal (a) Static signal is unchanged with the time (b) Quasi-Static is nearly unchanged with time ( C) Periodic ,, repeated its self on a regular basis (like square wave , sine, cosine wave) (d) Repetitive is quasi-periodic , the difference between periodic and repetitive is seen by comparing the signal f (t) and f (t +T) T is the period of signal This point may be not identical in in repetitive signal But it is identical in the periodic signal (d) Transient is a one time event Or periodical event in which T1< < < < < T2

Fourier Series All continuous periodical signals can be represented by a fundamental frequency sine wave and a collection of harmonics of that fundamental sine wave that are summarized linearly. These frequencies make up the Fourier series of the wave form

CH Sensing Elements 3-1 Sensing element is the first element in the measurement system that converts the measurand (Physical property) to electric signal Passive Active Electric Mechanical Sensors Inductive Resistive Capacitive Selection of transducer criteria 1- Operating Range 2-Sensitivity 3-Frequancy response 4- Environmental Compatibility 5-Accurcy Active sensors Required an external AC or DC source to power the device such as Strain Gauge. Passive Sensor Provide its own energy or derived its energy from the measured value such as thermocouple.

3-Displacement Measurements
The biomedical researches are interested in measuring the size and shape and position of the organs and tissue of the body. Variation in theses parameters are important to know the normal and abnormal function of the organs. The displacement sensor can be used to measure the change in the blood vessels diameter, diameter, volume, shape of cardiac chambers. 3-1 Resistive sensors The simplest form of potentiometer is the slide-wire resistor shown in fig. The sensor consists of a length L of resistive wire attached Across a voltage source Ein. A wiper moves along The length of the wire The relation between the output voltage Eo and measured distance X is

So We use High resistance wire wounded potentiometer
Wire has low resistance and this required excessive power for the input voltage to get sensible output voltage So We use High resistance wire wounded potentiometer 2- Angular potentiometer It is used to measure the change in angle Like Knee Elbow angles The angle is related to the input volt, output volt and total potentiometer angle as follow High Resistance wire wounded 2- Angular potentiometer

A displacement transducer with stroke length of 3 in is applied in the circuit shown in Fig. The total resistance of the potentiometer is 5KΩ and the applied volt VT= 5 V. when the wiper is 0.9 in from B what is the value of the output volt Vo Solution

3-Resistive Strain Gauge
Before discussing the strain gauge we should know the concept of stress, strain, elastic (Young’s) modulus and Poisson’s ratio

The Relation between length and resistance
When a fine wire is strained the wire resistance changes because of the changes in the length and wire diameter R is the total resistance of the wire in Ohm L is length in meter A is the wire cross sectional area in m2 Is the electric resistivity of the metal of wire (const for each material ) The strain gauge is used to measure the small displacement Load

R Vo Vi Strain Gauge in Electronic Measuring System (Gauge )R+dR
Body of Load Cell Wheatstone Bridge Amplifier and Filter I/P Sensing Element ∆Ω V Signal Conditioning PC A/D Display Signal Processing

Different Types of strain Gauge Bridges
R+dR Vi Vo Vi Vo R R+dR Quarter Bridge Half Bridge Vi Vo R+dR R-dR Full Bridge

A resistive strain gauge with a gauge factor of 2 is fastened to a steel bar with a diameter of 0.02m, and Young's modulus of 2x1010 Kg/m2 . This bar is subjected to load of 33Kg Find the change in resistance of the strain gauge if its initial resistance is 130 Ω . Solution

2-Capacitive Sensor The capacitive sensor consists of two parallel plates separated by insulation When charged, the plates carry equal charges of opposite sign.

w L L A-Type 1 Variable separation
The type of sensors used to measure the pressure between foot and shoe (variable distance between plates w L L Type 2-Variable Area Type 3-Variable dielectric

Capacitive Bridge C1 C2 C3 C4 Vo Vi

An electrode diaphragm pressure transducer has plates whose area is 5x10-3 and whose distance between plate is 1x10-3 m. Calculate its capacitance if it measures air pressure. The dielectric constant of air K=εr =1 Solution

Inductive Sensor تعتمد الحساسات الحثية على التغير فى الحث الناتج عن ملف نتيجة الإزاحة الحادثة على قلب هذا الملف Vi L=inductance, n=No. of turns, G=Factor depends on coil geometry, u=Permeability of the medium u air = 1.25x10-6 Henry /m The inductance changes due to external magnetic field. The device works on the principle that alternations in the self-inductance of a coil may be produced by changing the geometric form factor or the movement of a magnetic core within the coil

Linear Variable Deferential Transformer (LVDT)
c d Vout Linear Variable Deferential Transformer (LVDT) LVDT is widely used to measure displacement, pressure and force The LVDT is composed of a primary coil (a-b) and two secondary coils (c-e) and (d-e) connected in series. The coupling between these two coils is changed by the motion of high permeability alloy slug between them. The output volt Vcd=Vce-Vde When the slug is symmetrically placed (middle) the two secondary voltages are equal and the output=zero Materials cause the flux lines to move apart called diamagnetic Materials concentrate the flux called paramagnetic Vo الإزاحة الحساسية حوالى 2 ميللى فولت لكل 0.1 ميللى متر

Piezoelectric Transducers
Piezo electric sensor is used to measure displacement and record heart sound. Piezo electric material generate an electric potential when mechanically strained, and conversely and electric potential can cause physical deformation for the material مكبر Amplifier Crystal ++ V q=kf , q=surface charge coulomb f=force, (N) k=constant Coulomb/N

الدائرة المكافئة للبلورة المبسطة
The Piezo electric material can be act like parallel plate capacitor K=2.3x10-12 C/N for quartz K=140x10-12 C/N for barium Piezo electric materials have a high resistance The equivalent circuit of Piezo electric circuit as shown IR R C Vo الدائرة المكافئة للبلورة المبسطة Ia=0 IS Ic Charge generator

Thermocouple Temperature Transducer
There are 4 main types of common temperature transducers 1- Thermocouple 2- Thermistor (Thermal Resistor) 3- Radiation Thermometry 4- Solid state PN Junction (diode) Voltmeter Iron Copper T 1 , Hot junction (Measuring probe) Thermocouple A thermocouple consists of two dissimilar conductors or semiconductors joined together at one end. Due to the contact of different materials at junction , a potential will be generated when junction is heated. This potential changes linearly with temp

Temp 200 1600 V mv Type E Type J Type K Type W Type S 80 60 40 20 10
100 80 60 40 20 10 Temp V mv Type E Type J Type K Type W Type S

- Iron-(Copper Nickel) 0 to 750 5.268mv
Junction Material Temp Range Output Voltage J - Iron-(Copper Nickel) 0 to 750 5.268mv K (Nickel-Chrome)-(Nickel-Aluminum) -200 to 1250 4.095mv E (Nickel-Chrome)-(copper-Nickel) -200 to 900 6.317mv T Copper-(Copper-Nickel) -200 to 350 4.277mv S (Platinum10%-Rhodium)-Platinum 0 to 1450 0.645mv R (Platinum13%-Rhodium)-Platinum 0.647mv B (Platinum30%-Rhodium)-Platinum6%- Rhodium) 0 to 1700 0.033mv

Thermistor Radiation Thermometry
Thermistor is a semiconductor made of ceramic. The material react to temp changes. There are two types of Thermistor 1- Positive temp Coefficient (PTC) device where the resistance increase with temp. increase 2- Negative temp Coefficient (NTC) device where the resistance decrease with temp increase The resistivity of the Thermistor used in the biomedical applications ranges from 0.1 to 100 Ohm. The device is small in size Radiation Thermometry The basics of radiation thermometer is that there is a known relationship between surface temp and object radiation power. This principle makes it is possible to measure the skin temp without physical contact This method is also used to detect the breast cancer

Electrodes for Biophysical Sensing
1- Bioelectricity is a phenomenon that arises from the fact that the living organisms Are composed of ions at different quantities 2- Ionic conduction involves the migration of ions positively and negatively charged molecules through out a region. 3- Electric conduction involves the flow of electrons under the influence of an electric field 4- In an electrolytic solution, ions are easily available. Potential difference occur when concentration of ions is differ from point to point. 5- Bio-electrodes are class of sensors that transducer ionic conduction to electronic conduction so that the signal can be recorded easily 6- Bio-electrodes are used to detect the bioelectric signal such as Electro-cardiograph (ECG) Electro-miograph (EMG) Electro-encephalograph (EEG)

Electrodes Potentials
The skin and tissue of living organisms (human) are electrolytic and can be modeled as electrolytic solution Imagine a metallic electrode immersed in an electrolytic solution, then the electrode will begin to discharge some of metallic ions into the solution. Also at the same time some of ions in the solution start combining with the metallic electrode (Electro-plating – Anodizing) After a short time a potential difference or electric potential (Ve) or half cell potential has built

Then at the interface between electrode and electrolyte, ions migrate words one side of the electrode forming two parallel layers of ions of opposite charge. This layer is called the electrode double layer. This ionic difference is the source of half cell potential This means that if electrode (metal) is placed on the skin (Electrolyte ),, there will be a a value of volt (Ve) have cell potential,, depending on the metal of electrode and electrolyte solution at the region ( Region or position of electrode in the skin = electrolyte concentration) If we have 2 electrodes A ≠B ,, then we will have Vea and Veb Offset potential Vout = Vea-Veb If A=B and the same electrode ,, Vea = Veb and Vout = 0 If A=B and not the same electrolyte (another place in the body),, Vout = Value (Due to electrolyte effect only)

الأول هو الإلكترودات السطحية Body surface electrodes
The electrode must made of specific material because body fluids are are corrosive to metal Silver (Ag) –Silver Chloride (Ag Cl) electrode is the most common one the electrode consists of body silver coated with a thin layer of silver chloride . T he Ag Cl gives (Ag+) and Cl- which prevent the double layer forming. تستخدم الإلكترودات إما لقراءة إشارة من الجسم ، أو لإدخال إثارة Stimulation إلى الجسم تصنف إلى صنفين : الأول هو الإلكترودات السطحية Body surface electrodes الثانى هو الإلكترودات الداخلية Internal electrodes

1- إلكترودات السطح Body surface electrodes
كمية التيار التى يتم قياسها بالإلكترود تكون صغيرة جدا (ميكروأمبير) ، لذلك لابد من ملامسة سطح الإلكترود لسطح الجسم تماما . لابد من استخدام جيلا تين معين كوسط موصل بين سطح الإلكترود وسطح الجسم السلك الموصل بين الإلكترود والمكبر يجب أن يكون قصيرا ومعزولا (يستحسن أن يكون كابل محورى) بعض الإلكترودات الحديثة يكون المكبر صغير الحجم ويوضع مع الإلكترود مباشرة والبعض حتى يضع المحول الانسيابى الرقمى مع الإلكترود لتقليل تأثير هذه المسافة وتجنب الضوضاء بقدر الإمكان وبالذات الضوضاء الناتجة من خطوط القدرة (60/50 هرتز) . معظمها مصنع من شريحة من كلوريد الفضة معزولة بطريقة أو أخرى حسب شكل الإلكترود

توجد إلكترودات السطح فى أكثر من شكل
جيلا تين مادة صمغية قرص معدنى قرص معدنى يستخدم لمرة واحدة

أشكال أخرى

الإلكترودات الداخلية إبرة تحت الجلد الإلكترود
Hypodermic needle الإلكترود للقياسات البسيطة Acute measurements عازل قمة معدنية حادة قاعدة ماصة الإلكترود لقياس ضربات قلب الجنين عضلة للقياسات الدائمة Chronic recording

المايكروإلكترود Microelectrodes
تستخدم للقياسات من داخل الخلية ، يجب أن تكون أبعاده أقل من أبعاد الخلية حتى لا يسبب تخريب لها عند اختراقها ، ويجب أن يكون صلب بالرغم من هذا القطر الصغير . يتراوح قطرها من 0.05 حتى 10 ميكرومتر معدن عازل زجاج الرأس مايكروإلكترود معدنى Metal Microelectrode الرأس 1 ميكرون محلول ملحى KCl المايكروأنبوبة Micropipette أنبوبة شعرية زجاجية

The equivalent circuit for a biopotential electrode.
The circuit model of surface electrode contains Op-amp (difference) ,, so that the half cell potential of each electrode is cancelled

Wheatstone Bridge (Direct Current Bridge)
Ch4 Direct current bridge is an instrument that used to measure the resistance or change in resistance and converts it to output current This bridge circuit are also used in control circuit, when one arm of the bridge contains a resistive element that is sensitive to the physical parameters (Temp, Pressure , Load) Wheatstone Bridge It consists of 2 parallel resistance branches, each branch contains two series elements (Resistance) I 1 3 R 4 a b 2 I2 I1 + - R 1 2 3 4 a b I DC volt is used as a power source Null detector (Galvanometer) is connected to detect balance

Using the bridge to determine unknown resistance
1- Assume R4 is unknown ,, 2- Assume we can change one resistor in the bridge (say R1) till the balance condition 2 4 R 3 1 I a b At case of unbalance (reading= Va-Vb)

2 4 R 3 1 I a b

Example (1) Determine the value of unknown resistor Rx in Fig. assuming the balance condition Vo + - R 1 2 3 x a b I Solution At Balance Vo=0

Sensitivity of the bridge
When the bridge is in an unbalance, current flows through the galvanometer, causing deflection of the pointer. The sensitivity of the bridge = S Thevenin Theory for the bridge I 1 3 R 4 a b 2 I2 I1 E E + - R 1 2 3 4 a b I

Thevenin Theory for the bridge
2 R a 4 b R3 R1 R3 a b R2 R4 b a Vth + - a Load b

Example Calculate the current through the galvanometer shown in Fig + - R 1 2 3 4 a b I Rg Solution

تهيئة إشارة القنطرة لتوصيلها على الحاسب
R1 R2 + V1 + Vi Vo + R1 + V2 R2 Isolator (Buffer) Difference Amp.

Ch5 Blood Pressure and other Cardio Vascular Measurements
Firstly the blood pressure is measured in arteries There are two kind of arteries pressure 1-Systolic pressure It is the pressure in arteries at case of heart contraction ≈ 120 mmHg 2- Diastolic pressure It is the pressure in arteries in the case of heart relaxation ≈ 80 mmHg Pressure = F = Force in Newton A is the area in m2 1 Pa = N/m2

A small coin has a diameter of 1cm and a mass of 1.59 gram Find
(a) Gravitational force (Weight) (b) The pressure caused by the coin Solution (a ) Force = Mass. Acceleration

Pressure Measurements
The air on the surface of the earth has a pressure value called atmosphere (1 atom) = 760 mmHg ( zero pressure is reference) If the pressure is measured with respect to vacuum (0 atom) it is called absolute pressure ( zero pressure is reference) If the pressure is measured with respect to atmospheric pressure (1 atom) it is called gauge pressure (1 atom pressure (760mmHg) is reference ) Pressure in human circulatory system is measured with respect to atmospheric pressure (gauge pressure) Gauge pressure is usually given in mmHg above or below the atmospheric pressure Zero gauge pressure is 1 atom

Blood pressure measurement
There are many methods that can be used for blood pressure measurement 1- Direct measurements (Invasive) 2- Indirect measurements (Noninvasive) 1- Indirect Measurements This method is used for routine clinical measurements of blood pressure in human, a suitable technique without painful or hazard is required The instrument consists of an inflatable rubber bladder called cuff, rubber squeeze ball pump, assembly valve and manometer. The manometer might be a mercury column or dial gauge

The cuff is wrapped around the patient upper arm; the stethoscope is placed over the artery.
The cuff is inflated so that the pressure inside the cuff becomes greater than the expected systolic pressure. This pressure compresses the artery against the bone and shuts off the flow of the blood in the artery. 3-The pressure in the cuff then slowly released (using the valve) when the pressure of the cuff equal the systolic blood pressure the blood starts to flow and the operator can hear a crashing sound in the stethoscope. Then the systolic pressure can be watched on the dial gauge or in the mercury column. 4-The pressure of the cuff is lowered more and more and when the cuff pressure equals the diastolic pressure , the sound in the stethoscope is disappeared. Then the diastolic pressure can be watched

The Ultra-sound blood Pressure Measurements
The Ultra sound determination of blood pressure uses a Doppler sensor to detect the motion of blood vessel walls. The Fig. shows the placement of compression cuff over two small transmitting and receiving ultra sound crystals (8MHz) on the arm. The reflected signal (shifted in frequency) is detected with the receiving crystal. The difference in frequencies in the range from 40 t0 50 Hz, depends on the velocity of the wall motion and blood velocity.

As the cuff pressure increased above the diastolic pressure (80mmHg) but below the systolic pressure, the vessel opens and close with each heart beat, the opening and closing of vessel are detected by ultra sound system. As pressured increased as shown in Fig. the time between the opening and closing decreases until they coincide. The reading at this point in the manometer or dial gauge is the systolic pressure. Conversely, when the pressure in the cuff is reduced, the time between opening and closing increases until the closing signal on pulse coincide with opening signal of the next one. The reading in this case is the diastolic pressure. The advantages of the Ultra sound method can be used with infants can be used in high noise environment

(a) Give signal to stop the pump
Automatic Blood Pressure Measurements 1- The user adjusts the pressure of the system (by touching digital bottoms) this expected pressure above the expected systolic pressure 2- The pump triggers and gives a pressure to the cuff 3- The cuff pressure is measured using strain gauge system (calibrated) 4- The adjusted pressure from step 1 and the measured pressure by strain gauge and applied by the pump (step 2) are compared through a comparator 5- When the values of 2 pressures are equal, the comparator works in 2 ways (a) Give signal to stop the pump (b) Give signal to solenoid valve to start to release the cuff pressure gradually

6- The pressure is always measured by the strain gauges and recorded all the time using a memory system 7- The microphone (which placed under the cuff) detect the first sound when the cuff pressure equal the systolic pressure. This will trigger the memory and then store s the systolic value 8- The output of microphone is connected with a comparator with a minimum level of sound can be recorded 9- When the pressure reaches to the diastolic pressure the microphone output sound reaches to the value of minimum level of sound, then the comparator works and gives a signal to the memory to record the value of diastolic pressure ,, also it gives a signal to repeat the process again (a) Close the solenoid (b) Trigger the pump to be ready to work again

Invasive Blood Pressure Measurements
1-Extra Vascular measurement of blood pressure An electronic pressure transducer can be connected to the patient through a thin piece of tubing called a catheter is filled with a saline-heparin solution and inserted in the patient. The pressure transducer diaphragm is coupled to the patient’s blood stream; the diaphragm senses the pressure of the blood which transmuted through the fluid in the catheter The diaphragm is attached to strain gauge that converts the diaphragm displacement to electric current

2- The intravascular method
At this case the sensor is placed inside the blood stream in the body The optical pressure sensor is good example for invasive pressure sensor The sensor consists of 2 bundles of optical fibers which inserted into a thin catheter in the vessel. The first bundle is used to transmit light from source to the end of the catheter (the diaphragm). The other bundle is used to transmit the reflected light to the photo detector. At the end of the catheter, a very thin metal membrane (diaphragm) is attached. The inner surface of the membrane is polished to reflect the light. Due to the pressure of the blood, the metal membrane deflects with respect to the pressure value. The reflected light changes with the value of membrane deflection. This reflected light converted to current by the photo detector A calibration is needed to know the relation between reflected light (current) and blood pressure.

Blood Flow Measurement
The velocity of blood flow can be measured using many methods like (a) Electromagnetic flow meter (b) Ultra-sound flow meter (a) Electromagnetic flow meter The popularity of the magnetic flow meter results from the following factors 1- It measures volume flow rate independent of the velocity 2- It produces accuracy up to ± 5% 3- It can measures velocity in vessels from 1mm to 20mm diameter Theory We know from basic electrical theory that a voltage is created when moving a conductor cuts a magnetic flux. If that conductor is a blood carrying vessel of diameter EE’, the voltage generated will be

E is the resultant potential
Q is the volume flow rate m3/sec B is the magnetic flux in gauss (G) A is the vessel radius in (m) Example Find the potential generated if blood flowing in a vessel with a radius of 0.9cm cuts magnetic flux of 250G. Assuming a volume flow rate 175 cm3/sec. Solution If the blood flows in a magnetic field, an emf will be generated and picked by 2 electrodes. The electrodes must be small

The Ultra-sound Flow-meter
Ultra Sound waves are acoustical waves (like regular sound waves, 30Hz to 20 KHz) in the range above human hearing (more than 20 KHz). Like all acoustical waves, ultra sound waves are subjected to Doppler shift; this effect is a slight alteration of frequency (ΔF) when reflected from moving object. A transmitter piezoelectric crystal sends a sound wave with known frequency. These waves are reflected with different frequency and received by the receiver crystal. This difference in frequency corresponds to the velocity of the flow (blood). The ultra sound flow meter can be used to measure blood and gases flow rates in patient circuits because it’s known area.

Measurement of Gas Flow
The volume flow and volume flow rate are used to measure/estimate rate of changes of lung volume. The instrument used to measure the volume flow rate is called flow meter 1- The flow meter is a device that contains a calibrated tube to indicate gas flow in Litters/min and a valve to control the flow. The flow meter must be in upright position to obtain an accurate reading. The relation between shape and weight of floating ball pressure and flow rate are as follows Other different types of flow meters 1- Rotating Vane flow meters This type of sensor has a small turbine in the flow path. The rotation of the turbine can be related to the flow meter of gas by using a calibration technique. Interruption of a light beam by the turbine has also been sensed and converted to voltage potential to flow and / or its integral to be recorded or displayed continuously 2- Ultra sound flow meters 3- Thermal convection flow meters 4- Difference pressure flow meters

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