BIO–MEDICAL INSTRUMENTATION

Name: Mr. T.balasubramanian

Designation: Assistant Professor

Department: Electrical and Electronics Engineering

Subject code: EI 65

Year: IV

Unit: IIITitle: NON-ELECTRICAL PARAMETER MEASUREMENTS

NON-ELECTRICAL PARAMETER MEASUREMENTS

Measurement of blood pressure – Cardiac output – Heart rate – Heart sound – Pulmonary function measurements – spirometer – Photo Plethysmography, Body Plethysmography – Blood Gas analysers : pH of blood –measurement of blood pCO2, pO2, finger-tip oxymeter - ESR, GSR measurements .

Measurement of blood pressure

Blood pressure (BP) is the pressure (force per unit area) exerted by circulating blood on the walls of blood vessels, and constitutes one of the principal Vital signs. The pressure of the circulating blood decreases as it moves away from the heart through arteries and capillaries, and toward the heart through veins. When unqualified, the term blood pressure usually refers to brachial arterial pressure: that is, in the major blood vessel of the upper left or right arm that takes blood away from the heart. Blood pressure may, however, sometimes be measured at other sites in the body, for instance at the ankle. The ratio of the blood pressure measured in the main artery at the ankle to the brachial blood pressure gives the Ankle Brachial Pressure Index (ABPI).

Arterial pressure is most commonly measured via a sphygmomanometer, which historically used the height of a column of mercury to reflect the circulating pressure (see Noninvasive measurement). Today blood pressure values are still reported in millimetres of mercury (mmHg), though aneroid and electronic devices do not use mercury.

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For each heartbeat, blood pressure varies between systolic and diastolic pressures. Systolic pressure is peak pressure in the arteries, which occurs near the end of the cardiac cycle when the ventricles are contracting. Diastolic pressure is minimum pressure in the arteries, which occurs near the beginning of the cardiac cycle when the ventricles are filled with blood. An example of normal measured values for a resting, healthy adult human is 115 mmHg systolic and 75 mmHg diastolic (written as 115/75 mmHg, and spoken (in the US) as "one fifteen over seventy-five"). Pulse pressure is the difference between systolic and diastolic pressures.

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Systolic and diastolic arterial blood pressures are not static but undergo natural variations from one heartbeat to another and throughout the day (in a circadian rhythm). They also change in response to stress, nutritional factors, drugs, disease, exercise, and momentarily from standing up. Sometimes the variations are large. Hypertension refers to arterial pressure being abnormally high, as opposed to hypotension, when it is abnormally low. Along with body temperature, blood pressure measurements are the most commonly measured physiological parameters.

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Arterial pressures can be measured invasively (by penetrating the skin and measuring inside the blood vessels) or non-invasively. The former is usually restricted to a hospital setting.

The predominantly used unit for blood pressure measurement is mmHg (millimeter of mercury). For example, normal pressure can be stated as 120 over 80, where 120 is the systolic reading and 80 is the diastolic.

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Auscultatory method aneroid sphygmomanometer with stethoscope

Mercury manometer

Digital BP measurement equipment

The auscultatory method uses a stethoscope and a sphygmomanometer. This comprises an inflatable (Riva-Rocci) cuff placed around the upper arm at roughly the same vertical height as the heart, attached to a mercury or aneroid manometer. The mercury manometer, considered to be the gold standard for arterial pressure measurement measures the height of a column of mercury, giving an absolute result without need for calibration, and consequently not subject to the errors and drift of calibration which affect other methods. The use of mercury manometers is often required in clinical trials and for the clinical measurement of hypertension in high risk patients, such as pregnant women

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Classification of blood pressure for adults

Category systolic, mmHg diastolic, mmHg

Hypotension < 90 or < 60   

Normal  90 – 119 and 60 – 79   

Prehypertension 120 – 139 or 80 – 89

Stage 1 Hypertension 140 – 159 or 90 – 99

Stage 2 Hypertension ≥ 160 or ≥ 100 

Placement of Blood Pressure Cuff

Cardiac output

Cardiac output (Q) is the volume of blood being pumped by the heart, in particular by a ventricle in a minute. This is measured in dm3 min-1 (1 dm3 equals 1000 cm3 or 1 litre). An average cardiac output would be 5L.min-1 for a human male and 4.5L.min-1 for a female Measuring Cardiac Output

Cardiac output

Q can be calculated from these measurements:

VO2 consumption per minute using a spirometer (with the

subject re-breathing air) and a CO2 absorber.

the oxygen content of blood taken from the pulmonary artery (representing mixed venous blood) .the oxygen content of blood from a cannula in a peripheral artery (representing arterial blood).

From these values, we know that:VO2 = (Q x CA) - (Q x CV)where

CA = Oxygen content of arterial blood

CV = Oxygen content of venous blood.

This allows us to sayQ = (VO2/[CA - CV])*100

Cardiac rate

Heart rate (HR) is a measure of the number of heart beats per minute (bpm). The average resting human heart rate is about 70 bpm. Heart rate varies significantly between individuals based on fitness, age and genetics. Endurance athletes often have very low resting heart rates. Heart rate can be measured by monitoring one's pulse. Pulse measurement can be achieved using specialized medical devices, or by merely pressing one's fingers against an artery (typically on the wrist or the neck; note that this can be dangerous if done incorrectly or for too long).

Heart sound

The heart sounds are the noises (sound) generated by the beating heart and the resultant flow of blood through it, specifically the turbulence created when the heart valves snap shut. This is also called a heartbeat. In cardiac auscultation, an examiner uses a stethoscope to listen for these sounds, which provide important information about the condition of the heart.

In healthy adults, there are two normal heart sounds often described as a lub and a dub (or dup), that occur in sequence with each heart beat. These are the first heart sound (S1) and

second heart sound (S2), produced by the closing of the

tricuspid + mitral valves and aortic + pulmonic valves, respectively. In addition to these normal sounds, a variety of other sounds may be present including heart murmurs, adventitious sounds, and gallop rhythms S3 and S4.

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Heart murmurs are generated by turbulent flow of blood, which may occur inside or outside the heart. Murmurs may be physiological (benign) or pathological (abnormal). Abnormal murmurs can be caused by stenosis restricting the opening of a heart valve, resulting in turbulence as blood flows through it. Abnormal murmurs may also occur with valvular insufficiency (or regurgitation), which allows backflow of blood when the incompetent valve closes with only partial effectiveness. Different murmurs are audible in different parts of the cardiac cycle, depending on the cause of the murmur

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Respiratory rate

Respiratory rate (RR) (aka respiration rate, pulmonary ventilation rate or ventilation rate) is the number of breaths a living being, such as a human, takes within a certain amount of time (frequently given in breaths per minute).

The human respiration rate is usually measured when a person is at rest and simply involves counting the number of breaths for one minute by counting how many times the chest rises. Respiration rates may increase with fever, illness, OR other medical conditions. When checking respiration, it is important to also note whether a person has any difficulty breathing.

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General Control of Breathing

Breathing is controlled by the medulla of the brainstem. It repeatedly triggers contraction of the diaphragm initiating inspiration. The rate of breathing changes with activity level in response to carbon dioxide levels, and to a lesser extent, oxygen levels, in the blood. Carbon dioxide lowers the pH of the blood.

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Average respiratory rates, by age:

Newborns: Average 44 breaths per minute Infants: 20–40 breaths per minute Preschool children: 20–30 breaths per minute Older children: 16–25 breaths per minute Adults: 12–20 breaths per minute Adults during strenuous exercise 35–45 breaths per minute Athletes' peak 60–70 breaths per minute

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Gas volume – Flow rate of Co2, o2 in

exhaust air

Respiration refers to the mechanisms for obtaining oxygen from the air and delivering it to the tissues, while eliminating carbon dioxide from the body. It is related to cellular respiration, the biochemical processes that consume this oxygen and generate the carbon dioxide in the course of making adenosine triphosphate (ATP). Respiration in the former sense involves four processes: (1) breathing, or ventilation of the lungs (2) gas exchange between air and blood in the lungs (3) gas transport in the blood and (4) gas exchange between the blood and target tissues.

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Gas Transport

Blood leaving the lungs is therefore relatively high in O2

(oxygen in its diatomic form) and low in CO2. It travels via the

pulmonary veins to the left side of the heart, which pumps it out into the systemic circulation. This division of the circulatory system delivers it to every organ of the body.

Systemic Gas Exchange

When the blood reaches the systemic blood capillaries, gases undergo processes that are essentially the reverse of what occurs in the pulmonary alveoli. The blood unloads O2, which

diffuses into the tissue fluid and thus reaches the cells around the blood capillaries. At the same time, the CO2 generated by

the metabolism of those cells diffuses into the blood to be carried away to the lungs for disposal.

Blood typically contains 95 mmHg O2 upon arrival at the

systemic capillaries and 40 mmHg O2 upon leaving.

Conversely, the blood has 40 mmHg of CO2 on arrival at the

systemic capillaries and typically 46 mmHg CO2 when it

leaves. The blood does not, however, unload the same amount of O2 to all tissues or pick up the same amount of CO2. The

more active a tissue is, the warmer it is, the lower its O2 level

is, and the lower its pH is (because it generates more CO2 and

CO2 reduces the pH of body fluids). Heat, low O2, low pH, and

other factors enhance O2 unloading and CO2 loading, so tissues

that need the most oxygen and waste removal get more than less active tissues do. The biochemistry of hemoglobin is mainly responsible for this elegant adjustment of gas exchange to the individual needs of different tissues

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PH of blood

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GSR measurements

Galvanic skin response (GSR), also known as electrodermal response (EDR), psychogalvanic reflex (PGR), or skin conductance response (SCR), is a method of measuring the electrical resistance of the skin. There has been a long history of electrodermal activity research, most of it dealing with spontaneous fluctuations.

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One branch of GSR explanation interprets GSR as an image of activity in certain parts of the body. The mapping of skin areas to internal organs is usually based on acupuncture pointsA Galvanic Skin Response 60 second sample signal. The signal was acquired in the middle and ringer fingers. The source file was processed with scipy and exported with matplolib. The sampling rate was 256 Hz.

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The device measures electrical conductivity between 2 points, much like an ohmmeter. The two paths for current are along the surface of the skin and through the body. Active measuring involves sending a small amount of current through the body. Due to the sensitivity of the human body to electrical shock, sometimes more passive methods are used to determine the conductivity of the skin. When correctly calibrated, the GSR can measure these subtle differences.

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Plethysmography

A plethysmograph is an instrument for measuring changes in volume within an organ or whole body (usually resulting from fluctuations in the amount of blood or air it contains).

In a traditional plethysmograph, the test subject is placed inside a sealed chamber the size of a small telephone booth with a single mouthpiece. At the end of normal expiration, the mouthpiece is closed. The patient is then asked to make an inspiratory effort. As the patient tries to inhale (a maneuver which looks and feels like panting), the lungs expand, decreasing pressure within the lungs and increasing lung volume. This, in turn, increases the pressure within the box since it is a closed system and the volume of the body compartment has increased.

Plethysmography

There are two types of plethysmographs: flow and pressure. In flow plethysmography, airway resistance is measured by two maneuvers. The patient first pants while the mouth shutter is open to allow flow changes to be measured. Then, the mouth shutter closes at the patient's end expiratory or FRC level and the patient continues panting while maintaining an open glottis. This provides a measure of the driving pressure used to move air into the lungs.

  

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Pressure plethysmographs are usually measured at the end-expiratory level and are then equal to FRC. The patient sits in the box, which has the pressure transducer in the wall of the device, and breathes through a mouthpiece connected to a device that contains an electronic shutter and a differential pressure pneumotachometer. The mouth pressure and box pressure changes that are measured during tidal breathing and panting maneuvers which are performed during the test by the patient at the end of expiration are sent to a microprocessor unit that calculates thoracic gas volume.

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