Department Of ECEInstitute of Engineering & Technology, Bhaddal

Assignment

“Cardiovascular System”

The HEART and Cardiovascular System

The heart is a muscular organ responsible for pumping blood through the blood vessels by repeated, rhythmic contractions, or a similar structure in the annelids, mollusks, and arthropods. The term cardiac (as in cardiology) means "related to the heart" and comes from the Greek καρδία, kardia, for "heart." The heart is composed of cardiac muscle, an involuntary muscle tissue which is found only within this organ. The average human heart beating at 72 BPM, will beat approximately 2.5 billion times during a lifetime spanning 66 years.

The function of the right side of the heart (see right heart) is to collect de-oxygenated blood, in the right atrium, from the body and pump it, via the right ventricle, into the lungs (pulmonary circulation) so that carbon dioxide can be dropped off and oxygen picked up (gas exchange). This happens through the passive process of diffusion. The left side (see left heart) collects oxygenated blood from the lungs into the left atrium. From the left atrium the blood moves to the left ventricle which pumps it out to the body. On both sides, the lower ventricles are thicker and stronger than the upper atria. The muscle wall surrounding the left ventricle is thicker than the wall surrounding the right ventricle due to the higher force needed to pump the blood through the systemic circulation.Starting in the right atrium, the blood flows through the tricuspid valve to the right ventricle. Here it is pumped out the pulmonary semilunar valve and travels through the pulmonary artery to the lungs. From there, blood flows back through the pulmonary vein to the left atrium. It then travels through the mitral valve to the left ventricle, from where it is pumped through the aortic semilunar valve to the aorta. The aorta forks, and the blood is divided between major arteries which supply the upper and lower body. The blood travels in the arteries to the smaller arterioles, then finally to the tiny capillaries which feed each cell. The (relatively) deoxygenated blood then travels to the venules, which coalesce into veins, then to the inferior and superior venae cavae and finally back to the right atrium where the process began.The heart is effectively a syncytium, a meshwork of cardiac muscle cells interconnected by contiguous cytoplasmic bridges. This relates to electrical stimulation of one cell spreading to neighboring cells.

Cardiovascular System

The circulatory system (or cardiovascular system) is an organ system that moves nutrients, gases, and wastes to and from cells, helps fight diseases and helps stabilize body temperature and pH to maintain homeostasis. While humans, as well as other vertebrates, have a closed circulatory system (meaning that the blood never leaves the network of arteries, veins and capillaries), some invertebrate groups have open circulatory system. The most primitive animal phyla lack circulatory systems.

The Circulation is Constructed from Pumps, Tubing and Valves Pumps:

Circulatory pumps (hearts) are vessels filled with the circulatory fluid or blood

When muscles around the container contract they exert pressure on the blood, causing it to flow

Heart type: pump produces a high pressure which causes blood to flow out through arteries

Muscle pump: muscle contraction squeezes veins, causing blood to flow toward heart

Tubing or pipes = arteries, capillaries, veins Carry blood toward delivery site Sometimes deliver within a few microns of site (capillaries in

tissue) Blood vessels may be elastic (which helps keep the pressure

high between heartbeats) Vessels may constrict and dilate (which gives control over the

flow) Valves give direction to the flow

Blood vessels (including hearts & veins) have flap valves that open in only one direction

Example: when pressure increases in veins this opens valves toward the heart and closes those in the other direction -> blood flows toward heart

The purposes of circulation: To deliver food materials and oxygen to the tissues To remove waste products and heat These things can be done by diffusion in a small animal, but in

a large animal a circulation is necessary.

The Mammalian Heart is Really 2 Hearts in Series Right heart:

Pumps to lungs: nearly 100% of the flow goes through the lungs

Low pressure side: 25 mm Hg systolic pressure in humans Right ventricle has thin walls

Left heart: Pumps to rest of body High pressure side: 120 mm Hg systolic pressure in humans Left ventricle has thick walls

Right & and left atria:

Help fill the ventricles Very low pressure Thin walls

Pumping of the right & lift sides occurs together Must be accurately balanced, otherwise fluid may accumulate

in the lungs (pulmonary edema) The muscle pump helps return blood to the heart

When muscles contract the veins passing through them are squeezed

This causes blood to flow toward the heart Valves prevent flow away from the heart

The Entire Blood Supply Passes Through the Heart About Once Every Minute

Your body has approximately 5 liters of blood (large people have a little more, small people a little less)

The heart's pumping rate is called the cardiac output: at rest its value is about 5 liters/min

Comparing the volume with the cardiac output you can see that the entire blood volume passes through the heart on the average once every minute

All of the output from the right heart goes through the lungs (5 liters/min)

The output from the left heart splits and goes through different organs General outline of the circulation:

Electrocardiogram

An electrocardiogram (ECG or EKG, abbreviated from the German Elektrokardiogramm) is a graphic produced by an electrocardiograph, which records the electrical activity of the heart over time. Its name is made of different parts: electro, because it is related to electronics, cardio, Greek for heart, gram, a Greek root meaning "to write".

Electrical waves cause the heart muscle to pump. These waves pass through the body and can be measured at electrodes (electrical contacts) attached to the skin. Electrodes on different sides of the heart measure the activity of different parts of the heart muscle. An ECG displays the voltage between pairs of these electrodes, and the muscle activity that they measure, from different directions. This display indicates the overall rhythm of the heart, and weaknesses in different parts of the heart muscle. It is the best way to measure and diagnose abnormal rhythms of the heart[1], particularly abnormal rhythms caused by damage to the conductive tissue that carries electrical signals, or abnormal rhythms caused by levels of salts, such as potassium, that are too high or low.[2] In myocardial infarction (MI), the ECG can identify damaged heart muscle. But it can only identify damage to muscle in certain areas, so it can't rule out damage in other areas. [3] The ECG cannot reliably measure the pumping ability of the heart; ultrasound is used for that.

ECG graph paper

A typical electrocardiograph runs at a paper speed of 25 mm/s, although faster paper speeds are occasionally used. Each small block of ECG paper is 1 mm². At a paper speed of 25 mm/s, one small block of ECG paper translates into 0.04 s (or 40 ms). Five small blocks make up 1 large block, which translates into 0.20 s (or 200 ms). Hence, there are 5 large blocks per second. A diagnostic quality 12 lead ECG is calibrated at 10 mm/mV, so 1 mm translates into 0.1 mV. A "Calibration" signal should be included with every record. A standard signal of 1 mV must move the stylus vertically 1 cm, that is two large squares on ECG paper.

Leads

The word lead has two meanings in electrocardiography: it refers to either the wire that connects an electrode to the electrocardiograph, or (more commonly) to a combination of electrodes that form an imaginary line in the body along which the electrical signals are measured. Thus, the term loose lead artifact uses the former meaning, while the term 12 lead ECG uses the latter. In fact, a 12 lead electrocardiograph usually only uses 10 wires/electrodes. The latter definition of lead is the one used here.

An electrocardiogram is obtained by measuring electrical potential between various points of the body using a biomedical instrumentation amplifier. A lead records the electrical signals of the heart from a particular combination of recording electrodes which are placed at specific points on the patient's body.

When a depolarization wavefront (or mean electrical vector) moves toward a positive electrode, it creates a positive deflection on the ECG in the corresponding lead.

When a depolarization wavefront (or mean electrical vector) moves away from a positive electrode, it creates a negative deflection on the ECG in the corresponding lead.

When a depolarization wavefront (or mean electrical vector) moves perpendicular to a positive electrode, it creates an equiphasic (or isoelectric) complex on the ECG. It will be positive as the depolarization wavefront (or mean electrical vector) approaches (A), and then become negative as it passes by (B).

There are two types of leads—unipolar and bipolar. The former have an indifferent electrode at the center of the Einthoven’s triangle (which can be likened to a ‘neutral’ of the wall socket) at zero potential. The direction of these leads is from the “center” of the heart radially outward and includes the precordial (chest) leads and limb leads— VL, VR, & VF. The latter, in contrast, have both the electrodes at some potential and the direction of the corresponding electrode is from the electrode at lower potential to the one at higher potential, e.g., in limb lead I, the direction is from left to right. These include the limb leads--I, II, and III.

Waves and Intervals

A typical ECG tracing of a normal heartbeat (or cardiac cycle) consists of a P wave, a QRT complex and a T wave. A small U wave is normally visible in 50 to 75% of ECGs. The baseline voltage of the electrocardiogram is known as the isoelectric line. Typically the isoelectric line is measured as the portion of the tracing following the T wave and preceding the next P wave.

P wave

During normal atrial depolarization, the main electrical vector is directed from the SA node towards the AV node, and spreads from the right atrium to the left atrium. This turns into the P wave on the ECG, which is upright in II,

III, and aVF (since the general electrical activity is going toward the positive electrode in those leads), and inverted in aVR (since it is going away from the positive electrode for that lead). A P wave must be upright in leads II and aVF and inverted in lead aVR to designate a cardiac rhythm as Sinus Rhythm.

The relationship between P waves and QRT complexes helps distinguish various cardiac arrhythmias.

The shape and duration of the P waves may indicate atrial enlargement.

PR interval

The PR interval is measured from the beginning of the P wave to the beginning of the QRT complex. It is usually 120 to 200 ms long. On an ECG tracing, this corresponds to 3 to 5 small boxes.

A PR interval of over 200 ms may indicate a first degree heart block. A short PR interval may indicate a pre-excitation syndrome via an

accessory pathway that leads to early activation of the ventricles, such as seen in Wolff-Parkinson-White syndrome.

A variable PR interval may indicate other types of heart block. PR segment depression may indicate atrial injury or pericarditis. Variable morphologies of P waves in a single ECG lead is suggestive

of an ectopic pacemaker rhythm such as wandering pacemaker or multifocal atrial tachycardia hi

QRT complex

The QRT complex is a structure on the ECG that corresponds to the depolarization of the ventricles. Because the ventricles contain more muscle mass than the atria, the QRT complex is larger than the P wave. In addition, because the His/Purkinje system coordinates the depolarization of the ventricles, the QRT complex tends to look "spiked" rather than rounded due to the increase in conduction velocity. A normal QRT complex is 0.06 to 0.10 sec (60 to 100 ms) in duration represented by three small squares or less, but any abnormality of conduction takes longer, and causes widened QRS complexes.Not every QRT complex contains a Q wave, an R wave, and an T wave. By convention, any combination of these waves can be referred to as a QRS

complex. However, correct interpretation of difficult ECGs requires exact labeling of the various waves. Some authors use lowercase and capital letters, depending on the relative size of each wave. For example, an Rt complex would be positively deflected, while a rS complex would be negatively deflected. If both complexes were labeled RT, it would be impossible to appreciate this distinction without viewing the actual ECG.

The duration, amplitude, and morphology of the QRT complex is useful in diagnosing cardiac arrhythmias, conduction abnormalities, ventricular hypertrophy, myocardial infarction, electrolyte derangements, and other disease states.

Q waves can be normal (physiological) or pathological. Normal Q waves, when present, represent depolarization of the interventricular septum. For this reason, they are referred to as septal Q waves, and can be appreciated in the lateral leads I, aVL, V5 and V6.

Q waves greater than 1/3 the height of the R wave, greater than 0.04 sec (40 ms) in duration, or in the right precordial leads are considered to be abnormal, and may represent myocardial infarction.

RT segment

The RT segment connects the QRT complex and the T wave and has a duration of 0.08 to 0.12 sec (80 to 120 ms). It starts at the J point (junction between the QRT complex and RT segment) and ends at the beginning of the T wave. However, since it is usually difficult to determine exactly where the ST segment ends and the T wave begins, the relationship between the RT segment and T wave should be examined together. The typical RT segment duration is usually around 0.08 sec (80 ms). It should be essentially level with the PR and TP segment.

The normal RT segment has a slight upward concavity. Flat, downsloping, or depressed ST segments may indicate coronary

ischemia. ST segment elevation may indicate myocardial infarction. An

elevation of >1mm and longer than 80 milliseconds following the J-point. This measure has a false positive rate of 15-20% (which is slightly higher in women than men) and a false negative rate of 20-30%.[11]

T wave

The T wave represents the repolarization (or recovery) of the ventricles. The interval from the beginning of the QRS complex to the apex of the T wave is referred to as the absolute refractory period. The last half of the T wave is referred to as the relative refractory period (or vulnerable period).In most leads, the T wave is positive. However, a negative T wave is normal in lead aVR. Lead V1 may have a positive, negative, or biphasic T wave. In addition, it is not uncommon to have an isolated negative T wave in lead III, aVL, or aVF.

Inverted (or negative) T waves can be a sign of coronary ischemia, Wellens' syndrome, left ventricular hypertrophy, or CNS disorder.

Tall or "tented" symmetrical T waves may indicate hyperkalemia. Flat T waves may indicate coronary ischemia or hypokalemia.

The earliest electrocardiographic finding of acute myocardial infarction is sometimes the hyperacute T wave, which can be distinguished from hyperkalemia by the broad base and slight asymmetry.

When a conduction abnormality (e.g., bundle branch block, paced rhythm) is present, the T wave should be deflected opposite the terminal deflection of the QRS complex. This is known as appropriate T wave discordance.

QT interval

The QT interval is measured from the beginning of the QRS complex to the end of the T wave. Normal values for the QT interval are between 0.30 and 0.44 (0.45 for women) seconds.[citation needed] The QT interval as well as the corrected QT interval are important in the diagnosis of long QT syndrome and short QT syndrome. The QT interval varies based on the heart rate, and various correction factors have been developed to correct the QT interval for the heart rate. The QT interval represents on an ECG the total time needed for the the ventricles to depolarize and repolarize.The most commonly used method for correcting the QT interval for rate is the one formulated by Bazett and published in 1920.

U wave

The U wave is not always seen. It is typically small, and, by definition, follows the T wave. U waves are thought to represent repolarization of the papillary muscles or Purkinje fibers. Prominent U waves are most often seen in hypokalemia, but may be present in hypercalcemia, thyrotoxicosis, or exposure to digitalis, epinephrine, and Class 1A and 3 antiarrhythmics, as well as in congenital long QT syndrome and in the setting of intracranial hemorrhage. An inverted U wave may represent myocardial ischemia or left ventricular volume overload.

Blood Pressure Measurement

Blood pressure (strictly speaking: vascular pressure) refers to the force 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 blood moves through arteries, arterioles, capillaries, and veins; the term blood pressure generally refers to arterial pressure, i.e., the pressure in the larger arteries, arteries being the blood vessels which take blood away from the heart. Arterial pressure is most commonly measured via a sphygmomanometer, which uses the height of a column of mercury to reflect the circulating pressure (see Non-invasive measurement). Although many modern vascular pressure devices no longer use mercury, vascular pressure values are still universally reported in millimetres of mercury (mmHg).The systolic arterial pressure is defined as the peak pressure in the arteries, which occurs near the beginning of the cardiac cycle; the diastolic arterial pressure is the lowest pressure (at the resting phase of the cardiac cycle). The average pressure throughout the cardiac cycle is reported as mean arterial pressure; the pulse pressure reflects the difference between the maximum and minimum pressures measured.Typical values for a resting, healthy adult human are approximately 120 mmHg (16 kPa) systolic and 80 mmHg (11 kPa) diastolic (written as 120/80 mmHg, and spoken as "one twenty over eighty") with large individual variations. These measures of arterial pressure 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, or disease. 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.

Indirect Measurement

A sphygmomanometer (often condensed to sphygmometer[1]) or blood pressure meter is a device used to measure blood pressure, comprising an inflatable cuff to restrict blood flow, and a mercury or mechanical manometer to measure the pressure. It is always used in conjunction with a means to determine at what pressure blood flow is just starting, and at what pressure it is unimpeded. Manual sphygmomanometers are used in conjunction with a stethoscope.The word comes from the Greek sphygmós (pulse), plus the scientific term manometer (pressure meter). The device was invented by Samuel Siegfried Karl Ritter von Basch. Scipione Riva-Rocci, an Italian physician, introduced a more easily used version in 1896. Harvey Cushing discovered this device in 1901 and popularised it.

A sphygmomanometer usually consists of an inflatable cuff, a measuring unit (the mercury manometer), a tube to connect the two, and (in models that don't inflate automatically) an inflation bulb also connected by a tube to the cuff. The inflation bulb contains a one-way valve to prevent inadvertent leak of pressure while there is an adjustable screw valve for the operator to allow the pressure in the system to drop in a controlled manner.

The cuff is normally placed around the upper left arm, at roughly the same vertical height as the heart while the subject is in an upright position. The cuff is inflated until the artery is completely occluded. Listening with a stethoscope to the brachial artery at the elbow, the examiner slowly releases the pressure in the cuff. As the pressure in the cuffs falls, a "whooshing" or pounding sound is heard (see Korotkoff sounds) when bloodflow first starts again in the artery. The pressure at which this sound began is noted and recorded as the systolic blood pressure. The cuff pressure is further released until the sound can no longer be heard and this is recorded as the diastolic blood pressure.

Direct Measurement

Cardiac catheterization (heart cath) is the insertion of a catheter into a chamber or vessel of the heart. This is done for both investigational and interventional purposes. Coronary catheterization is a subset of this technique, involving the catheterization of the coronary arteries.A small puncture is made in a vessel in the groin, the inner bend of the elbow, or neck area (the femoral vessels or the carotid/jugular vessels), then a guidewire is inserted into the incision and threaded through the vessel into the area of the heart that requires treatment, visualized by fluoroscopy or echocardiogram, and a catheter is then threaded over the guidewire. If X-ray fluoroscopy is used, a radiocontrast agent will be administered to the patient during the procedure. When the necessary procedures are complete, the catheter is removed. Firm pressure is applied to the site to prevent bleeding. This may be done by hand or with a mechanical device. Other closure techniques include an internal suture. If the femoral artery was used, the patient will probably be asked to lie flat for several hours to prevent bleeding or the development of a hematoma. Cardiac interventions such as the insertion of a stent prolong both the procedure itself as well as the post-catheterization time spent in allowing the wound to clot.

A cardiac catheterization is a general term for a group of procedures that are performed using this method, such as coronary angiography. Once the catheter is in place, it can be used to perform a number of procedures including angioplasty, angiography, and balloon septostomy.

Blood Flow

Blood flow is the flow of blood in the cardiovascular system. The discovery that blood flows is attributed to William Harvey.Mathematically, blood flow is described by Darcy's law (which can be viewed as the fluid equivalent of Ohm's law) and approximately by Hagen-Poiseuille's law. Blood is an inhomogeneous medium consisting mainly of plasma and a suspension of red blood cells. White cells, or leukocytes, and platelets while present in smaller concentrations, play an important role in biochemical processes, such as immune response, inflammation, and coagulation. Red cells tend to coagulate when the flow shear rates are low, while increasing shear rates break these formations apart, thus reducing blood viscosity.This results in two non-Newtonian blood properties, shear thinning and yield stress. In healthy large arteries blood can be successfully approximated as a homogeneous, Newtonian fluid since the vessel size is much greater than the size of particles and shear rates are sufficiently high that particle interactions may have a negligible effect on the flow. In smaller vessels, however, non-Newtonian blood behavior should be taken into

account. The flow in healthy vessels is generally laminar, however in diseased (e.g. atherosclerotic) arteries the flow may be transitional or turbulent.

This is important in angioplasty, as it enables the increase of blood flow with balloon catheter to the deprived organ significantly with only a small increase in radius of a vessel.

Measurement of Blood Flow

1. Blood flow electromagneticBlood flow electromagnetic methods make use of the principle that movement of a charged particle through an electromagnetic field produces an emf. Essentially two electrodes are attached along the length of a vessel, and an electromagnetic field is applied at approximately 90o to the flow. The emf between the two electrodes can be measured and gives a continuous result proportional to the flow velocity. The response is governed by uBL, where u is the velocity (typically 10mm/s), B the magnetic field strength (typically 0.1T), and L the length between electrodes (10mm). Smaller vessels will have a lower u, and will be unable to have such a great L, reducing the signal. Typical voltage signals are in the region of 0.01mV, which is in the region of the electrode contact potential (which poses a great problem to the S/N ratio), and interferes with the ECG signal. These problems however can be reduced by using a 400MHz A.C. signal. The spatial and depth resolution are better than both previous measurements, and once the angle of field to flow has been allowed for, it is potentially an accurate and continuous measurement. The disadvantage of this is that it is by no means non-invasive, unlike the previous two methods, needing exposure of a given length of vessel for electrode fitting. This however makes it suitable for measurements during surgical procedures, especially coronary bypass or plastic cosmetic surgery.

An electromagnetic blood flow probe for measuring blood flow having at least two separable and connectable coil segments cooperatively connected to an appropriate switching device selectively movable from a first position where the segments are connected to form a single coil having a given polarity to a second position where the segments are connected separately with opposite polarities so that the coil segments may be energized to

eliminate or reorient the flux field and reflect an electrical zero without physically terminating blood flow in a vessel.

2. Ultrasonic (Doppler, Transit Time) flow meters

Ultrasonic flow meters measure the difference of the transit time of ultrasonic pulses propagating in and against flow direction. This time difference is a measure for the average velocity of the fluid along the path of the ultrasonic beam. By using the absolute transit times both the averaged fluid velocity and the speed of sound can be calculated.

Measurement of the doppler shift resulting in reflecting an ultrasonic beam off the flowing fluid is another recent innovation made possible by electronics. By passing an ultrasonic beam through the tissues, bouncing it off of a reflective plate then reversing the direction of the beam and repeating the measurement the volume of blood flow can be estimated. The speed of transmission is affected by the movement of blood in the vessel and by comparing the time taken to complete the cycle upstream versus downstream the flow of blood through the vessel can be measured. The difference between the two speeds is a measure of true volume flow. A wide-beam sensor can also be used to measure flow independent of the cross-sectional area of the blood vessel.For the Doppler principal to work in a flowmeter it is mandatory that the flow stream contains sonically reflective materials, such as solid particles or entrained air bubbles.

3. 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).

Use for lungs

Pulmonary plethysmographs are commonly used to measure the functional residual capacity (FRC) of the lungs -- the volume in the lungs when the muscles of respiration are relaxed -- and total lung capacity. A typical human has an FRC of 25mL/kg.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 glottis is closed and 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.Boyle's Law is used to calculate the unknown volume within the lungs. First, the change in volume of the chest is computed. The initial pressure and volume of the box are set equal to the known pressure after expansion times the unknown new volume. Once the new volume is found, the new volume minus the original volume is the change in volume in the box and also the change in volume in the chest. With this information, Boyle's Law is used again to determine the original volume of gas: the initial volume (unknown) times the initial pressure is equal to the final volume times the final pressure.The difference between full and empty lungs can be used to assess diseases and airway passage restrictions. An obstructive disease will show increased FRC because some airways do not empty normally, while a restrictive disease will show decreased FRC. Body plethysmography is particularly appropriate for patients who have air spaces which do not communicate with the bronchial tree; in such patients gas dilution would give an incorrectly low reading.Newer lung plethysmograph devices have an option which does not require enclosure in a chamber.

Use for limbs

Some plethysmograph devices are attached to arms, legs or other extremities and used to determine circulatory capacity. Impedance plethysmography is a non-invasive method used to detect venous thrombosis in these areas of the body.

How to measure high blood pressure? Principles5.1 - The most reliable method: to place a probe measuring the pressure directly in the artery5.2 - The most useful method: The measure of the blood pressure using a sphygmomanometer with a cuffMeasurement of the blood pressure5.3 - At rest at the doctors5.4 - At rest at home, using a self-measurement device 5.5 - During a physical exercise5.6 - Measurement by an ambulatory monitoring of the blood pressure during 24 hoursDescription of the device5.7 - The cuff5.8 - Method for the measurement of the blood pressure5.9 - The sphygmomanometer

5.8 - Method for the measurement of the blood pressure: listening (microphonic), oscillometric or much more rarely photoplethysmographic.

Once the cuff is inflated, the artery of the arm is compressed and the passage of the blood is stopped. Then, the cuff is gradually deflated, at on average 2 to 3 millimetres of mercury per second.

During this phase, two phenomena occur:

- Auscultatory method

The noise emitted by the artery changes: when the artery is compressed, the physician listening with his stethoscope or the microphone which «replaces the ears» hears no noise. Then, when the pressure decreases in the cuff, the artery starts to emit a noise: the pressure then measured on the device defines the maximal blood pressure or systolic blood pressure.

Then, the noise continues to be heard during the decrease of the pressure in the cuff, until the noise disappears: the pressure then read on the device defines the minimal blood pressure or diastolic blood pressure.

This method of measurement of the blood pressure is the auscultatory method. It is used by the physician, but also by an automatic measurement of the blood pressure device.

Auscultatory method

- Oscillometric method

The pulsations induced by the artery are different: when the artery is compressed, no pulsation is perceived by the device, then when the pressure decreases in the cuff, the artery starts to emit pulsations: the pressure then measured on the device defines the maximal blood pressure or systolic blood pressure.

During the pressure decrease in the cuff, the oscillations will become increasingly significant, until a maximum amplitude of these oscillations defines the average blood pressure.

Then, the oscillations can still be seen during the decrease of the pressure in the cuff, until they disappear: the pressure then read on the device defines the minimal blood pressure or diastolic blood pressure.

This method of measurement of the blood pressure is the oscillometric method. It is very often used in the automatic device for the measurement of the blood pressure because of its excellent reliability. On the other hand, it is less precise than the microphonic or auscultatory method. Many devices and in particular the automatic devices measuring the blood pressure during 24 hours, use the two measurement techniques.

Oscillometric method

- Photoplethysmographic method

This technique measures the blood pressure at the level of the arteries of the fingers. A small cuff is inflated around the finger, and the pressure is maintained constant in the small cuff. Any variation of pressure on the level of the finger will involve a modification of the pressure in the cuff, which thus translates it into blood pressure

5.9 - The sphygmomanometer

The pressure existing in the cuff will be transmitted by hollow pipes to a system which will give a legible blood pressure value. Several devices are currently available: those that use a mercury column, and those that use a metal membrane.

- Sphygmomanometer with mercury

It consists in a mercury column, which can allow the reading of the blood pressure.This technique is the oldest and it is for this reason that the blood pressure unit is the millimetre of mercury. Up to now, this technique has been the basic method for measuring blood pressure. The results obtained are highly reliable in a long run, but the use of mercury will soon be prohibited within the European Community. It will thus be necessary to think of solutions for replacement, and to change the unit of measurement of the blood pressure (millimetre of mercury

replaced by the kilopascal?).

This type of sphygmomanometer is exclusively reserved for the measurement of the blood pressure at the level of the arm.

- aneroid sphygmomanometer

This type of device does not contain mercury. A metal membrane located in a case translates the blood pressure transmitted by the cuff. This type of device is very practical to use and is generally reliable if it is regularly controlled.

This method constitutes a good alternative to the sphygmomanometer with mercury, which will be abandoned in a few years.

This device can produce blood pressure at the level of the arm, but also at the level of the wrist or the finger.

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 1000cm3).

Cardiac output is equal to the stroke volume (SV) multiplied by the heart rate (HR). SV is the volume pumped per beat and the HR is the number of beats per minute. Therefore, if there are 70 beats per minute, and 70 ml blood is ejected with each beat, (SV), the cardiac output (Q) is 4900 ml/minute. This value is typical for an average adult at rest, although Q may reach up to 31.97865 litres/minute during extreme exercise by elite athletes.

Measurement of Cardiac Output

Circulation is a critical and variable function of human physiology and disease. An accurate and non-invasive measurement of Q is the holy grail of cardiovascular assessment. This would allow continuous monitoring of central circulation and provide improved insights into normal physiology, pathophysiology and treatments for disease. Invasive methods are well accepted, but there is increasing evidence that these methods are neither accurate nor effective in guiding therapy, so there is an increasing focus on development of non-invasive methods. There are a number of clinical methods for measurement of Q ranging from direct intracardiac catheterisation to non-invasive measurement of the arterial pulse. Each method has unique strengths and weaknesses and relative comparison is limited by the absence of a widely accepted “gold

standard” measurement. Q can also be affected by the phase of respiration with intra-thoracic pressure changes influencing diastolic filling and therefore Q. This is important especially during mechanical ventilation, and Q should therefore be measured at a defined phase of the respiratory cycle (typically end-expiration).

The Fick Principle

The Fick principle was first described by Adolph Fick in 1870 and assumes that the rate at which oxygen is consumed is a function of the rate of blood flows and the rate of oxygen pick up by the red blood cells. The Fick principle involves calculating the oxygen consumed over a given period of time from measurement of the oxygen concentration of the venous blood and the arterial blood. 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)cheers life

From these values, we know that:VO2 = (Q x CA) - (Q x CV)where CA = Oxygen concentration of arterial blood and CV = Oxygen concentration of venous blood. This allows us to sayQ = (VO2/CA - CV)*100and therefore calculate Q. While considered to be the most accurate method for Q measurement Fick is invasive and requires time for the sample analysis, and accurate oxygen consumption samples are difficult to acquire. There have also been modifications to the Fick method where respiratory oxygen content is measured as part of a closed system and the consumed Oxygen calculated using an assumed oxygen consumption index which is then used to calculate Q. Other modifications use inert gas as tracers and measure the change in inspired and expired gas concentrations to calculate Q.

Dilution Method

This method was initially described using an indicator dye and assumes that the rate at which the indicator is diluted reflects the Q. The method measures the concentration of a dye at different points in the circulation, usually from an intravenous injection and then at a downstream sampling site, usually in a systemic artery. More specifically, the Q is equal to the quantity of indicator dye injected divided by the area under the dilution curve measured downstream.

Pulmonary Artery Thermodilution (Trans-right-heart Thermodilution)

The indicator method was further developed with replacement of the indicator dye by heated or cooled fluid and temperature change measured at different sites in the circulation rather than dye concentration; this method is known as thermodilution. The pulmonary artery catheter (PAC), also known as the Swan-Ganz catheter, was introduced to clinical practice in 1970 and provides direct access to the right heart for thermodilution measurements.The PAC is balloon tipped and is inflated to occlude the pulmonary artery. The PAC thermodilution method involves injection of a small mount (10ml) of cold saline at a known temperature into the pulmonary artery and measuring the temperature a know distance away (6-10cm).The Q can be calculated from the measured temperature curve (The “thermodilution curve”). High Q will change the temperature rapidly, and low Q will change the temperature slowly. Usually three or four repeated measures are averaged to improve accuracy. However it is complex to perform and there are many sources of inaccuracy in the method. Modern catheters are fitted with a heating filament which intermittently heats and measures the thermodilution curve providing serial Q measurement.PAC use is complicated by infection, Pulmonary artery rupture, cardiac tamponade, and air embolism. Recent studies suggest use of the PAC is both dangerous and expensive, and it may not improve patient survival or treatment. PAC use is in decline as clinicians move to less invasive, more effective technologies for monitoring haemodynamics.

Doppler Ultrasound Method

This method uses ultrasound and the Doppler effect to measure Q. The blood velocity through the heart causes a 'Doppler shift' in the frequency of

the returning ultrasound waves. This Doppler shift can then be used to calculate flow velocity and volume and effectively Q using the following equations:

Q = SV x HR SV = vti x CSA

where: CSA = flow cross sectional area from πd²/4 d = valve diameter vti = the velocity time integral of the trace of the Doppler flow profile

Doppler ultrasound is non-invasive, accurate and inexpensive and is a routine part of clinical ultrasound with high levels of reliability and reproducibility having been in clinical use since the 1960s.

Echocardiography

Echocardiography uses a conventional ultrasound machine and a combined two dimensional (2D) and Doppler approach to measure Q. 2D measurement of the diameter (d) of the aortic annulus allows calculation of the flow CSA which is then multiplied by the vti of the Doppler flow profile across the aortic valve to determine the flow volume or SV. Multiplying SV by HR produces Q. Echocardiographic measurement of flow volume is clinically well established and of proven accuracy but requires training and skill, and may be time consuming to perform effectively. The 2D measurement of the aortic valve diameter is challenging and associated with significant error, while measurement of the pulmonary valve to calculate right sided Q is even more difficult.

Transcutaneous Doppler: USCOM

An Ultrasonic Cardiac Output Monitor (USCOM) (Uscom Ltd, Sydney, Australia) uses Continuous Wave Doppler (CW) to measure the Doppler flow profile vti, as in echocardiography, but uses anthropometry to calculate aortic and pulmonary valve diameters so both the right and left sided Q can be measured. Real time Automatic tracing of the Doppler flow profile allows for beat to beat right and left sided Q measurement. Importantly this single method can be used in neonates, children and adults for low and high Q measurement.

Transoesophageal Doppler: TOD

Transoesophageal Doppler (TOD), also known as esophageal Doppler monitor (EDM), supports a CW sensor on the end of a probe which can be introduced via the mouth or nose and positioned in the oesophagus so the Doppler beam aligns with the descending thoracic aorta (DTA) at a known angle. Because the transducer is close to the blood flow the signal is clear, however the alignment, and thus reliable signal, can often be difficult to maintain during respiration and patient movement. This method has good validation, particularly for measuring changes in blood flow, but is limited in that it only measures the DTA flow and not true Q and is therefore influenced by non-linear changes in Q and SVR. Additionally this method requires patient sedation and is accepted for use only in adults and large children.

Pulse Pressure Methods

Pulse Pressure (PP) methods measure the pressure in the arteries over time to derive a waveform and use this information to calculate cardiac performance. The problem is that any measure from the artery includes the changes in pressure associated with changes in arterial function.Physiologic or therapeutic changes in vessel diameter will be assumed to reflect changes in Q. Put simply PP methods measure the combined performance of the heart and the vessels thus limiting the application of PP methods for measurement of Q. This can be partially compensated for by intermittent calibration of the waveform to another Q measurement method and then monitoring the PP waveform. Ideally the PP waveform should be calibrated beat to beat.There are invasive and non-invasive methods of measuring PP:

Non-invasive PP – Sphygmomanometer and Tonometry

The sphygmomanometer or cuff blood pressure device was introduced to clinical practice in 1903 allowing non-invasive measurements of blood pressure and providing the common PP waveform values of peak systolic and diastolic pressure which can be used to calculate mean arterial pressure (MAP). The pressure in the arteries, measured by sphygmomanometry, is often used as a guide to the function of the heart. Put simply, the pressure in

the heart is conducted to the arteries, so the arterial pressure approximately reflects the function of the heart or the Q.

The pressure in the heart rises as blood is forced into the aorta The more stretched the aorta, the greater the pulse pressure (PP) In healthy young subjects, each additional 2 ml of blood results in a 1

mmHg rise in pressure Therefore:

SV = 2 ml × Pulse Pressure

Q = 2 ml × Pulse Pressure × HR

By resting a more sophisticated pressure sensing device, a tonometer, against the skin surface and sensing the pulsatile artery, continuous PP wave forms can be acquired non-invasively and analysis made of these pressure signals. Unfortunately the heart and vessels can function independently and sometimes paradoxically so that changes in the PP may both reflect and mask changes in Q. So these measures represent combined cardiac and vascular function only. Another similar system that uses the arterial pulse is the pressure recording analytical method (PRAM).

Invasive PP

Invasive PP involves inserting a manometer (pressure sensor) into an artery, usually the radial or femoral artery and continuously measuring the PP waveform. This is usually done by connecting the catheter to a signal processing and display device. The PP waveform can then be analyzed to provide measurements of cardiovascular performance. Changes in vascular function or the position of the catheter tip will affect the accuracy of the readings. Invasive PP measurements can be calibrated or uncalibrated.

Impedance cardiography

Impedance cardiography (ICG) is a method which calculates Q from the measurement of changes in impedance across the chest over the cardiac cycle. Lower impedance indicates greater the intrathoracic fluid volume, and as the only fluid volume which changes beat to beat within the thorax is the blood, the change in impedance can be used to calculate the SV and, combined with HR, the Q. This technique has progressed clinically (often called BioZ, i.e. biologic impedance, as promoted by the leading

manufacturer in the US) and allows non-invasive estimations of Q and total peripheral resistance using only 4 paired skin electrodes.While the method is desirably non-invasive and inexpensive, it has not achieved the reliability and reproducibility required of a useful clinical tool, and the evolution of algorithms to convert impedance signals to Q across a variety of outputs and in a variety of diseases continues.

Magnetic Resonance Imaging

Velocity encoded phase contrast Magnetic Resonance Imaging (MRI) is the most accurate technique for measuring flow in large vessels in mammals. MRI flow measurements have been shown to be highly accurate compared to measurements with a beaker and timer and less variable than both the Fick principle and thermodilution. Velocity encoded MRI is based on detection of changes in the phase of proton precession. These changes are proportional to the velocity of the movement of those protons through a magnetic field with a known gradient. When using velocity encoded MRI, the result of the MRI scan is two sets of images for each time point in the cardiac cycle. One is an anatomical image and the other is an image where the signal intensity in each pixel is directly proportional to the through-plane velocity. The average velocity in a vessel, i.e. the aorta or the pulmonary artery, is hence quantified by measuring the average signal intensity of the pixels in the cross section of the vessel, and then multiplying by a known constant. The flow is calculated by multiplying the mean velocity by the cross-sectional area of the vessel. This flow data can be used to graph flow versus time. The area under the flow versus time curve for one cardiac cycle is the stroke volume. The length of the cardiac cycle is known and determines heart rate, and thereby Q can be calculated as the product of stroke volume and heart rate. MRI is typically used to quantify the flow over one cardiac cycle as the average of several heart beats, but it is also possible quantify the stroke volume in real time on a beat-for-beat basis.While MRI is an important research tool for accurately measuring Q, it is currently not clinically used for hemodynamic monitoring in the emergency or intensive care setting. Cardiac output measurement by MRI is currently routinely used as a part of clinical cardiac MRI examinations.

Measurement of HEART Sound

1. Stethoscope

The stethoscope is an acoustic medical device for auscultation, or listening to, internal sounds in a human or animal body. It is most often used to listen to heart sounds and breathing. It is also used to listen to intestines and blood flow in arteries and veins. Less commonly, "mechanic's stethoscopes" are used to listen to internal sounds made by machines, such as diagnosing a malfunctioning automobile engine by listening to the sounds of its internal parts. It can also be used to leak check vacuum chambers for scientific purposes.

Types of stethoscopesAcoustic Acoustic stethoscopes are familiar to most people, and operate on the transmission of sound from the chestpiece, via air-filled hollow tubes, to the listener's ears. The chestpiece usually consists of two sides that can be placed against the patient for sensing sound — a diaphragm (plastic disc) or bell (hollow cup). If the diaphragm is placed on the patient, body sounds vibrate the diaphragm, creating acoustic pressure waves which

travel up the tubing to the listener's ears. If the bell is placed on the patient, the vibrations of the skin directly produce acoustic pressure waves traveling up to the listener's ears. The bell transmits low frequency sounds, while the diaphragm transmits higher frequency sounds. This 2-sided stethoscope was invented by Rappaport and Sprague in the early part of the 20th century. One problem with acoustic stethoscopes was that the sound level is extremely low. This problem was surmounted in 1999 with the invention of the stratified continuous (inner) lumen, and the kinetic acoustic mechanism in 2002. Acoustic stethoscopes are the most commonly used.

Electronic

An electronic stethoscope (or stethophone) overcomes the low sound levels by electronically amplifying body sounds. However, amplification of stethoscope contact artifacts, and component cutoffs (frequency response thresholds of electronic stethoscope microphones, pre-amps, amps, and speakers) limit electronically amplified stethoscopes' overall utility by amplifying mid-range sounds, while simultaneously attenuating high- and low- frequency range sounds. Currently, a number of companies offer electronic stethoscopes, and it can be expected that within a few years, the electronic stethoscope will have eclipsed acoustic devices.Electronic stethoscopes require conversion of acoustic sound waves to electrical signals which can then be amplified and processed for optimal listening. Unlike acoustic stethoscopes, which are all based on the same physics, transducers in electronic stethoscopes vary widely. The simplest and least effective method of sound detection is achieved by placing a microphone in the chestpiece. This method suffers from ambient noise interference and has fallen out of favor. Another method, used in Welch-Allyn's Meditron stethoscope, comprises placement of a piezoelectric crystal at the head of a metal shaft, the bottom of the shaft making contact with a diaphragm. 3M also uses a piezo-electric crystal placed within foam behind a thick rubber-like diaphragm. Thinklabs' Rhythm 32 inventor, Clive Smith uses a stethoscope diaphragm with an electrically conductive inner surface to form a capacitive sensor. This diaphragm responds to sound waves identically to a conventional acoustic stethoscope, with changes in an electric field replacing changes in air pressure. This preserves the sound of an acoustic stethoscope with the benefits of amplification.Because the sounds are transmitted electronically, an electronic stethoscope can be a wireless device, can be a recording device, and can provide noise reduction, signal enhancement, and both visual and audio output. Around 2001, Stethographics introduced PC-based software which enabled a phonocardiograph, graphic representation of cardiologic and pulmonologic sounds to be generated, and interpreted according to related algorithms. All of these features are helpful for purposes of teaching.

Noise reduction

More recently, ambient noise filtering has become available in some electronic stethoscopes, with 3M's Littmann 3000 and Thinklabs ds32a offering methods for eliminating ambient noise. In acoustic stethoscopes ambient noise filtering is available in DRG (R. Deslauriers) external noise

reducting models, and Magna Fortis (M. Werblud) acoustic noise canceling stethoscope models.

Recording stethoscopes

Some electronic stethoscopes feature direct audio output that can be used with an external recording device, such as a laptop or MP3 recorder. The same connection can be used to listen to the previously-recorded auscultation through the stethoscope headphones, allowing for more detailed study for general research as well as evaluation and consultation regarding a particular patient's condition and telemedicine, or remote diagnosis. .

2. Phonocardiogram

Graphical representation of heart sound obtained by a machine called phonocardiogram. A record of the heart sounds made by means of a phonocardiograph. Phonocardiogram, of the sounds and murmurs produced by the contracting heart, including its valves and associated great vessels. The phonocardiogram is obtained either with a chest microphone or with a miniature sensor in the tip of a small tubular instrument that is introduced via the blood vessels.

3. Auscultation

Auscultation is the act of listening, with a stethoscope, to sounds made by the heart, lungs, and blood. It is performed as one of the initial and very important steps in cardiac diagnosis.

Aortic phenomena include 'sounds,' which are brief vibrations caused by momentary events, and 'murmurs,' which are the sound of turbulence as blood flows through some narrow orifice or tube. The two sounds heard in everyone are the first sound (S1 or 'lub,' in lub-dub) caused by closing of the mitral and tricuspid valve as the ventricles begin to contract and pump blood into the aorta and pulmonary artery. The second sound (S2 or 'dub') is caused when the ventricles finish ejecting, begin to relax, and allow the aortic and the pulmonary valves to close.

One approach for analyzing heart sounds is to record them using a microphone and to then display the electrical signals graphically. This is called a phonocardiogram, in which the x-axis represents time and the y-axis voltage (which is a measure of the intensity of sound). The picture below shows a simple phonocardiogram of four heartbeats. The first and second sounds of the first heartbeat are labeled. In our laboratory exercises, this type

of display is used to help you identify problems associated with abnormal heart sounds.