Physics of Heart

8/9/2019 Physics of Heart

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Physics Of HeartKhurram Shahzad, Dr Farzana Perveen,Imran Khan

Hazara University Department of PhysicsBS(1V)

ABSTRACT:

The goal of our research is to study the human heart structure, functions and its cardiac

cycle. Its also discussed the relationship of the study of heart to physics. This study is

made to confirm the presence, extent and contributors of total heart volume and pressure

variation during the cardiac cycle in atria and ventricle. But then its major purpose is to

concentrate on the characteristics of the individual cardiac chambers, little is known

about total heart volume and pressure variation during the cardiac cycle and the

respective contributors to this variation. This will allow the opportunity to explore total

heart volume variation and pressure from a structural (planimetry) and functional (flow)

perspective.

KEYWORDS:

Cardiac cycle, volume, pressure, atria, ventricle

INTRODUCTION:

The heart is one of the most important organs in the entire human body and has a cone

shaped, muscular and powerful organ and is about the size of a fist and has a mass of

between 250 and 350 grams. It is located slightly left of middle in the chest between two

lungs, anterior to the vertebral column and posterior to the sternum. It is really nothing

more than a pump, composed of muscle which pumps blood throughout the body,

beating approximately 72 times per minute of our lives. On average each day human


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heart beats about 100,000 times andpumps around 7,571 liters of blood. The heart

pumps the blood, which carries all the vital materials which help our bodies function and

removes the waste products that we do not need. For example, the brain requires oxygen

and glucose, which, if not received continuously, will cause it to loose consciousness.

Muscles need oxygen, glucose and amino acids, as well as the proper ratio of sodium,

calcium and potassium salts in order to contract normally. The glands need sufficient

supplies of raw materials from which to manufacture the specific secretions. If the heart

ever ceases to pump blood the body begins to shut down and after a very short period of

time will die.

EXPLANATION:

Heart is enclosed in a double-walled sac called the pericardium. The superficial part of

this sac is called the fibrous pericardium. This sac protects the heart,and prevents

overfilling of the heart with blood. The outer wall of the human heart is composed of

three layers. The outer layer is called the epicardium, or visceral pericardium since it is

also the inner wall of the pericardium. The middle layer is called themyocardium and is

composed of muscle which contracts. The inner layer is called the endocardium and is in

contact with the blood that the heart pumps. Also, it merges with the inner lining

(endothelium) of blood vessels and covers heart valves.

The human heart is composed of four chambers, each separated from the others. The left

side of the heart has two connected chambers, the left atrium and the left ventricle the

right side of the heart also has two connected chambers, the right atrium and the right

ventricle. These two sides, or pumps, of the heart are not directly connected with one

another. Oxygenated blood from the lungs travels through larger vessels called the
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pulmonary veins and enters the left side of the heart, emptying directly into the left

atrium, the pulmonary veins are unusual in that they carry oxygenated blood; other veins,

because they carry blood back to the heart form the body tissue, carry deoxygenated

blood. From the left atrium, Blood through a one way value, called the left

atrioventricular valve that is also known as bicuspid valve, into the left ventricle. Most of

this flow roughly 70 percent occurs while the heart is relaxed. The atrium then contracts,

filling the remaining 30 percent of the ventricle with its blood. After a slight delay, the

ventricle contracts. The contraction forces the blood to exit into an opening that leads to

the largest artery in the body the aorta. The atrioventricular value closes and prevents the

backflow of blood into the atrium. The aorta is closed off from the left ventricle by a one

way value, the aortic semi lunar value. It is oriented to permit the flow of the blood out

of the ventricle, but it snaps shut in response to backflow. Many arteries branch from the

aorta, carrying oxygen rich blood to all parts of the body. The pathway of blood vessels

to the body regions and organs other than the lungs is called the systemic circulation. The

systemic circulation brings blood to the neck and head and to organs in the rest of the

body. The systemic circulation gives up oxygen to the body tissues and receives carbon

dioxide. The blood that flows into the arterial system eventually returns to the heart after

flowing through the capillaries. As it returns, blood passes through a series of veins,

eventually entering the right side of the heart. Two large veins collect blood form the

systemic circulation. The superior vena cava drains the upper body, and the inferior vena

cava drains the lower body. These veins dump deoxygenated blood into the right atrium.

Blood passes from the right atrium into the right ventricle through a one way valve, the

right atrioventricular valve that is also known as tricuspid value. Blood passes out of the


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contracting right ventricle through a second valve, the pulmonary semi lunar value, into a

single pulmonary artery, sometimes called the pulmonary trunk, which subsequently

branches into arteries that carry deoxygenated blood to the lungs, replenished with

oxygen and cleared of much to its load of carbon dioxide.

The pumping of the heart is a repeated cardiac cycle of relaxation and contraction of the

atria and ventricles. Cardiac cycle is the term referring to all or any of the events related

to the flow orblood pressure that occurs from the beginning of one heartbeat to the

beginning of the next. The frequency of the cardiac cycle is theheart rate. Each beat of

the heart involves five major stages: The first, "late diastole", is when the semilunar

valves close, the atrioventricular (AV) valves open, and the whole heart is relaxed. The

second, "atrial systole", is when the atrium contracts, the AV valves open, and blood

flows from atrium to the ventricle. The third, "isovolumic ventricular contraction", is

when the ventricles begin to contract, the AV and semilunar valves close, and there is no

change in volume. The fourth, "ventricular ejection", is when the ventricles are empty

and contracting, and the semilunar valves are open. During the fifth stage, "Isovolumic

ventricular relaxation", pressure decreases, no blood enters the ventricles, the ventricles

stop contracting and begin to relax, and the semilunar valves close due to the pressure of

blood in the aorta. Throughout the cardiac cycle,blood pressure increases and decreases.

The cardiac cycle is coordinated by a series of electrical impulses that are produced by

specialized heart cells found within the sino-atrial node and the atrioventricular node.

The cardiac muscle is composed ofmyocytes which initiate their own contraction

without help of external nerves (with the exception of modifying the heart rate due to
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metabolic demand). Under normal circumstances, each cycle takes approximately one

second.

The cardiac cycle diagram shown to the right depicts changes in aortic pressure (AP), left

ventricular pressure (LVP), left atrial pressure (LAP), left ventricular volume (LV Vol),

and heart sounds during a single cycle of cardiac contraction and relaxation. These

changes are related in time to the electrocardiogram. Aortic pressure is measured by

inserting a pressure

catheter into the aorta

from a peripheral

artery, and the left

ventricular pressure is

obtained by placing a

pressure catheter inside

the left ventricle and

measuring changes in

intraventricular pressure as the heart beats. Left atrial pressure is not usually measured

directly, except in investigational procedures. Ventricular volume changes can be

assessed in real time using echocardiography or radionuclide imaging, or by using a

special volume conductance catheter placed within the ventricle.

A single cycle of cardiac activity can be divided into two basic stages. The first stage

is diastole, which represents ventricular filling and a brief period just prior to filling at

which time the ventricles are relaxing. The second stage issystole, which represents the

time of contraction and ejection of blood from the ventricles.


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To analyze these two stages in more detail, the cardiac cycle is usually divided into seven

phases. The first phase begins with the P wave of theelectrocardiogram, which

represents atrial depolarization. The last phase of the cardiac cycle ends with the

appearance of the next P wave. In order to understand the events of the cardiac cycle,

the reader should first review basic cardiac anatomy.

The entire cardiac cycle diagram, which contains information on aortic, left ventricular

and left atrial pressures, along with ventricular volume, heart sounds and the

electrocardiogram, is shown above.

This is the first phase of the cardiac cycle because it is initiated by the p

wave of the electrocardiogram (ECG), which represents electrical

depolarization of the atria. Atrial depolarization then causes contraction of

the atrial musculature. As the atria contract, the pressure within the atrial

chambers increases, which forces more blood flow across the open

atrioventricular (AV) valves, leading to a rapid flow of blood into the

ventricles. Blood does not flow back into the vena cava because of inertial

effects of the venous return and because the wave of contraction through the

atria moves toward the AV valve thereby having a "milking effect."

However, atrial contraction does produce a small increase in venous pressure

that can be noted as the "a-wave" of the left atrial pressure (LAP). Just

following the peak of the a wave is the x-descent.

Atrial contraction normally accounts for about 10% of left ventricular

filling when a person is at rest because most of ventricular filling occurs
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prior to atrial contraction as blood passively flows from the pulmonary veins,

into the left atrium, then into the left ventricle through the open mitral valve.

At high heart rates, however, the atrial contraction may account for up to

40% of ventricular filling. This is sometimes referred to as the "atrial

kick." The atrial contribution to ventricular filling varies inversely with

duration of ventricular diastole and directly with atrial contractility.

After atrial contraction is complete, the atrial pressure begins to fall

causing a pressure gradient reversal across the AV valves. This causes the

valves to float upward (pre-position) before closure. At this time, the

ventricular volumes are maximal, which is termed the end-diastolic

volume (EDV). The left ventricular EDV (LVEDV), which is typically

about 120 ml, represents the ventricularpreload and is associated with end-

diastolic pressures of 8-12 mmHg and 3-6 mmHg in the left and right

ventricles, respectively.

A heart soundis sometimes noted during atrial contraction (fourth heart

sound, S4). This sound is caused by vibration of the ventricular wall during

atrial contraction. Generally, it is noted when the ventricle compliance is

reduced ("stiff" ventricle) as occurs in ventricular hypertrophy and in many

older individuals.

This phase of the cardiac cycle begins with the appearance of the QRS

complex of the ECG, which represents ventricular depolarization. This

triggersexcitation-contraction coupling, myocyte contraction and a rapid
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increase in intraventricular pressure. Early in this phase, the rate of pressure

development becomes maximal. This is referred to as maximal dP/dt.

The AV valves to close as intraventricular pressure exceeds atrial

pressure. Ventricular contraction also triggers contraction of the papillary

muscles with their attached chordae tendineae that prevent the AV valve

leaflets from bulging back into the atria and becoming incompetent (i.e.,

leaky). Closure of the AV valves results in the first heart sound (S1). This

sound is normally split (~0.04 sec) because mitral valve closure precedes

tricuspid closure.

During the time period between the closure of the AV valves and the

opening of the aortic and pulmonic valves, ventricular pressure rises rapidly

without a change in ventricular volume (i.e., no ejection occurs). Ventricular

volume does not change because all valves are closed during this phase.

Contraction, therefore, is said to be "isovolumic" or "isovolumetric."

Individual myocyte contraction, however, is not necessarily isometric

because individual myocyte are undergoing length changes. Individual

fibers contract isotonically (i.e., concentric, shortening contraction), while

others contract isometrically (i.e., no change in length) or eccentrically (i.e.,

lengthening contraction). Therefore, ventricular chamber geometry changes

considerably as the heart becomes more spheroid in shape; circumference

increases and atrial base-to-apex length decreases.


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The rate of pressure increase in the ventricles is determined by the rate of

contraction of the muscle fibers, which is determine by mechanisms

governingexcitation-contraction coupling.

The "c-wave" noted in the LAP may be due to bulging of mitral valve

leaflets back into left atrium. Just after the peak of the c wave is the x'-

descent.

RESULT:

This section was about to discuss the most important and reliable member of cardiac

cycle. It has been shown experimently that the right depicts changes in aortic pressure

(AP), left ventricular pressure (LVP), left atrial pressure (LAP), left ventricular volume

(LV Vol), and heart sounds during a single cycle of cardiac contraction and relaxation.

These changes are related in time to the electrocardiogram.

REFERENCE:

1. Campbell, Reece-Biology, 7th Ed. p.873,874

2. Guyton, A.C. & Hall, J.E. (2006) Textbook of Medical Physiology (11th

ed.) Philadelphia: Elsevier SaunderISBN 0-7216-0240-1

3. "Eating for a healthy heart". MedicineWeb. Retrieved 2009-03-31.

4. Advanced Biology for You - Gareth Williams

5. Cardiovascular Physiology Concepts by Richard E. Klabunde, Ph.D.: Cardiac

Cycle - Reduced Ejection (Phase 4)

6. Plethysmograph
http://www.cvphysiology.com/Cardiac%20Function/CF022.htmhttp://en.wikipedia.org/wiki/Special:BookSources/0721602401http://www.medicineweb.com/nutrition-/eating-for-a-healthy-hearthttp://www.cvphysiology.com/Heart%20Disease/HD002d.htmhttp://www.cvphysiology.com/Heart%20Disease/HD002d.htmhttp://facstaff.elon.edu/shouse/physiology/frog/plethys/frogplethys.htmlhttp://www.cvphysiology.com/Cardiac%20Function/CF022.htmhttp://en.wikipedia.org/wiki/Special:BookSources/0721602401http://www.medicineweb.com/nutrition-/eating-for-a-healthy-hearthttp://www.cvphysiology.com/Heart%20Disease/HD002d.htmhttp://www.cvphysiology.com/Heart%20Disease/HD002d.htmhttp://facstaff.elon.edu/shouse/physiology/frog/plethys/frogplethys.html


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7. The Heart

8. Human Cardiopulmonary Physiology
http://faculty.ucc.edu/biology-potter/heart.htmhttp://www.susqu.edu/facstaff/r/richard/ECGlab.htmlhttp://faculty.ucc.edu/biology-potter/heart.htmhttp://www.susqu.edu/facstaff/r/richard/ECGlab.html

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