FUNCTIONAL ANATOMY OF RESPIRATION AND CIRCULATION

- BY DR.S.RATNA DEEPIKA MDS PART 1

RESPIRATORY

SYSTEM

INTRODUCTION

• Respiratory system consists of

respiratory surfaces of lungs , and the air

passages provided by the nose, pharynx,

larynx and respiratory tree.

• Associated with the nasal cavities are

series of bony sacs, paranasal sinuses,

which are uncertain and included here

with respiratory tract

• Besides its primary respiratory role in gaseous exchange and

ventilation, a number of accessory activities are performed by

respiratory system as a whole

- Production of sound (phonation) by larynx and its

related structures.

- Odorant sampling by olfactory senses in the nasal

chambers.

- Mechanical stabilisation of thorax during

mechanical exertion.

- Biochemical functions such as conversion of

Angiotensin I to Angiotensin II

STRUCTURAL FEATURES OF RESPIRATORY SYSTEM

Respiratory surface:

• Very large as much as 200m2 .

• Forms very thin, moist barrier between air and blood capillaries

around perimeters of many millions of blind-ending sacs(alveoli),

constituting much of muscle mass.

• Because of their delicate structure these respiratory surfaces are

very vulnerable to mechanical damage from inhaled particles, and

also to infectious organisms.

Conducting passages:

• Protecting surface area from

dehydration, heat loss and abrasive

particles, conducting passages form

a series of moist, warm adhesive

channels between alveoli and the

pharynx.

• In addition, to the mucus secreted

on to these surfaces, these tubes are

lined by cilia which beat towards

the pharynx, so continually

removing most inhaled particles

from respiratory system(the

monocilliary clearance current).

• DURING INSPIRATION:

When volume of thorax increases

Intra thoracic pressure decreases

Air flows through the respiratory

passages

In to enlarging alveoli

• In expiration reverse process occurs.

DIVISIONS OF RESPIRATORY SYSTEM

Upper respiratory tract Lower respiratory tract

UPPER RESPIRATORY TRACT

• It can be defined as those parts of the air passages which lie above the inlet of larynx.

It includes‒ Nasal cavities‒ Nasopharynx‒ Oropharynx

LOWER RESPIRATORY TRACT

‒ Larynx‒ Trachea‒ Bronchi‒ Rest of respiratory tree and

respiratory surfaces of lungs

EXTERNAL NOSE

• Externally the nose is pyramidal in shape.

Upper angle or roof being

continuous with forehead.

And free tip forming the apex.

• Inferiorly are two ellipsoidal apertures,

the external nares or nostrils, separated

by nasal septum.

• The upper part of the nose is kept patent

by the nasal bones and the frontal

process by the maxillae below this

cartilage form the walls.

• The lateral surfaces end below in the rounded

alae nasi.

Cartilages:

• SEPTAL

• MAJOR ALAR

• LATERAL NASAL

BLOOD SUPPLY AND NERVE SUPPLYArteries:

Alar and septal branches of facial artery –

Alae and Lower septum,

Dorsal nasal branch of ophthalmic artery

and infraorbital branch of maxillary artery

–Lateral aspects and Dorsum of nose.

Veins:

Facial and Ophthalmic vein.

Nerves:

Buccal branches of facial nerve.

Ophthalmic nerve through infratrochlear

and external nasal branches of nasociliary

nerve.

Nasal branch of maxillary nerve.

NASAL CAVITY

• The nasal cavity is divided sagittally in to

right and left halves by the nasal septum.

• These two halves open on the face through the

nares and are continuous posteriorly with the

nasopharynx through the posterior nasal

apertures.

• The nasal cavity has a floor, roof, and a lateral

and medial wall.

• It is divisible in to three regions

-Nasal vestibule

-Respiratory region

-Olfactory area

• The respiratory regions constitutes majority of

the nasal cavity.

VESSELS AND NERVES OF THE NASAL CAVITY

ARTERIES:

The anterior and posterior

ethmoidal branches-Ethmoidal and

frontal sinus and nasal roof.

Sphenopalatine branch of maxillary

artery-Mucosa of conchae, meatus

and septum.

The septal branch of the superior

labial ramus of the facial artery

supplies the septum in the region of

the vestibule; anastomoses with

sphenopalatine artery; common site

of bleeding from nose(Epistaxis).

Veins:

These form a rich submucosal

cavernous plexus which is

especially dense in the lower

part of the septum and in the

middle and inferior conchae;

arteriovenous anastomoses also

occur(Harper 1947).

Venous drainage in to

- Sphenopalatine vein

- Facial vein

- Opthalmic vein

Innervation:

Anterior ethmoidal

branch of nasociliary

nerve.

Infraorbital nerve.

Anterior superior

alveolar nerve.

Lateral posterior superior

nasal and medial

posterior superior nasal

nerves.

Branches from nerve to

pterygoid canal.

PARANASAL SINUSES

Paranasal sinuses include bilaterally

paired -Frontal

-Ethmoidal

-Sphenoidal

-Maxillary All sinuses open into the lateral

wall of nasal cavity.

Most of the sinuses are rudimentary

or absent at birth; they enlarge

appreciably during the eruption of

permanent teeth and after puberty,

markedly altering the size and shape

of the face.

LARYNX

The larynx, which is an air passage, a

sphincteric device and an organ of

phonation, extends from the tongue to

the trachea.

It projects ventrally between the great

vessels of neck and is covered

anteriorly by skin, fasciae and the hyoid

depressor muscles.

Above-opens into laryngopharynx and

forms its anterior wall.

Below-opens into trachea.

It lies opposite to third to sixth cervical

vertebrae.

Laryngeal cartilages:

‒ Cricoid cartilage

‒ Thyroid cartilage

‒ Arytenoid cartilage

‒ Corniculate cartilage

‒ Cuneform cartilage

‒ Epiglottic cartilage

‒ Tritiate cartilage

LARYNGEAL VESSELS AND NERVES

Arteries:

Branches of superior and inferior

thyroid arteries.

Veins:

Superior thyroid vein opening into

internal jugular.

Inferior thyroid draining into left

brachiocephalic.

Nerve supply

External and internal branches of

superior laryngeal nerve.

Recurrent laryngeal nerve.

Sympathetic nerves.

TRACHEA

Trachea or windpipe is the

patent tube for the passage of

air from the lungs.

It is a wide tube lying more or

less in the midline, in the lower

part of the neck and in the

superior mediastinum.

Its upper end is continuous with

the lower end of the larynx.

At its lower end the trachea

ends by dividing into the right

and left principal bronchi.

Arterial Supply:

Inferior thyroid artery

Venous drainage:

Into the left

brachiocephalic vein

Nervous supply:

Parasympathetic: Nerves

through vagi and recurrent

laryngeal nerves.

Sympathetic: Fibres from

the middle cervical

ganglion reach it along the

inferior thyroid arteries.

BRONCHIAL TREE

The trachea divides at the level of

lower border of the fourth thoracic

vertebrae into two primary

principal bronchi, one for each

lung.

The right principal bronchus is

2.5cm long.

The left principal bronchus is 5cm,

longer, narrower and more oblique

than the right bronchus.

Angulation of the principal bronchi

with the tracheal bifurcation

-Right bronchus: 250

-Left bronchus: 450

Each principal bronchus enters the lungs through the hilium, and

divides into secondary lobar bronchi, one for each lobe of the lungs.

There are three lobar bronchi on the right side, and only two on the

left side.

Each lobar bronchus divides into tertiary or segmental bronchi, one

for each bronchopulmonary segment(10 on right and 10 on left).

The segmental bronchi divide repeatedly to form very small branches

called terminal bronchioles

Still smaller branches are called respiratory bronchioles.

Each respiratory bronchiole aerates a small part of lung

known as pulmonary unit.

The respiratory bronchioles ends in microscopic passages

which are termed as

Alveolar ducts Atria Air sacules Alveoli

• From functional point of view, therefore the whole trachea-

bronchial tree can be divided into two major zones:

1. Conducting zone:

-This includes the portion of air passage where no exchange of

gases is possible, called dead space.

-This extends from nose and mouth upto the terminal bronchioles.

-The total capacity of this zone is approximately 150ml.

2. Respiratory zone:

-This includes portion of air passage where gaseous exchange takes

place.

-This is made up of respiratory bronchioles, alveolar ducts and the

alveoli.

-Its volume is approx. 4 litres.

LUNGS

The lungs occupy the major portion

of the thoracic cavity.

Each lung is conical in shape

1. An apex at the upper end

2. A base resting on the diaphragm

3. Three borders, i.e. anterior, posterior

and inferior

4. Two surfaces, i.e. costal and medial

The medial surface is divided into

-Vertebral

-Mediastinal

Apex:

Is blunt and lies above the level

of the anterior end of the first

rib

It reaches nearly 2.5cms above

the medial one-third of the

clavicle, just medial to the

supraclavicular fossa.

It is covered by the cervical

pleura and the suprapleural

membrane

It is grooved by the subclavian

artery on the medial side and

anteriorly.

Base:

It is semilunar and concave.

It rests on the diaphragm which separates

the right lung from the right lobe of the

liver and the left lung from the left lobe of

the liver, the fundus of the stomach, and

the spleen.

Anterior border:

Thin, shorter than the posterior border.

On the right side, it is vertical and

corresponds to the anterior or

costomediastinal line of pleural reflection.

The anterior border of the left lung shows

a wide cardiac notch below the level of

the fourth costal cartilage.

Posterior border:

Thick and ill defined.

It corresponds to the medial margins of

the heads of the ribs.

It extends from the level of the seventh

cervical spine to the tenth thoracic

spine.

Inferior border:

Separates the base from the costal and

the medial surfaces.

Costal surface:

Large and convex.

It is in contact with the costal pleura

and the overlying thoracic wall.

Medial surface:

It is divided into a posterior or

vertebral part, and an anterior or

mediastinal part.

The vertebral part is related to

- Vertebral bodies

- Intervertebral discs

- Posterior intercostal vessels

- Splanchnic nerves

The mediastinal part is related to

the mediastinal septum, and shows

a cardiac impression, the hilium

and a number of impressions that

differ on the two sides.

BLOOD SUPPLY AND NERVE SUPPLY

Arterial supply:

On the right side, there is one bronchial

artery which arises from the third right

posterior intercostal artery.

On the left side, there are two bronchial

arteries both of which arise from the

descending thoracic aorta, the upper

opposite fifth thoracic vertebra and the

lower just below the left bronchus.

Deoxygenated blood is brought to the

lungs by the two pulmonary arteries and

oxygenated blood is returned to the heart

by the four pulmonary veins.

There are precapillary anastomoses

between the bronchial and pulmonary

arteries. These connections enlarge

when any one of them is obstructed in

disease.

Venous drainage:

There are two bronchial veins on each

side.

The right bronchial vein drains into the

Azygos vein.

The left bronchial veins drain into the

hemiazygous vein.

The greater part of the venous blood

from the lungs drained by the

pulmonary veins.

Nerve supply:

Parasympathetic nerves are

derived from the vagus.

The sympathetic nerves are

derived from second to fifth

sympathetic ganglia.

Auscultation of lung:

Upper lobe is auscultated

above 4th rib on both sides.

Lower lobes are best heard on

the back.

Middle lobe is auscultated

between 4th and 6th ribs on

right side.

THE RESPIRATORY MEMBRANE

The air in the alveoli is

separated from the blood in the

pulmonary capillaries by a wall

called alveolar-capillary

membrane or respiratory

membrane.

It has a thickness in the range

of 0.3 to 1 micro meter.

Due to its thinness, the gaseous

exchange between the alveoli

and the blood capillaries is

completed within fraction of

second.

PLEURAThe lungs are enveloped by pleura

which has two layers

1. Parietal

2. Visceral

Parietal pleura: It is adherent to

parieties i.e. inner side of the

chest wall and the thoracic side of

the diaphragm. Therefore, when

these structures move, the parietal

pleura has to move.

Visceral pleura: It is adherent to

the underlying viscus i.e. the

lungs itself. Therefore when the

lungs move, it has to follow the

viscus.

In between the two layers there is a

potential space, called pleural cavity.

This space is filled with a very small

amount (approx. 2ml) of serous

lubricating fluid, called pleural fluid.

The fluid is adhesive and non-

expansile and keeps the two pleurae

together, therefore, when one moves,

others follow.

That is why the lungs slide easily on

the chest wall but resist by being

pulled away from it.

Functions of pulmonary circulation:

1. Reservoir for left ventricle- If LV output becomes transiently

greater than systemic venous return, LV output can be maintained

for a few strokes by drawing out blood stored in pulmonary

circulation.

2. Fluid exchange and drug absorption:

I. Low pulmonary hydrostatic pressure tends to pull fluids from

alveoli into pulmonary capillaries and keeps the alveolar surface

free from liquids.

II. Drugs that rapidly pass through the alveolar-capillary barrier by

diffusion, rapidly enter the systemic circulation.

Therefore, these are administered by inhalation e.g.

-Anaesthetic gases

-Aerosol and other bronchodilators

Metabolic and endocrine functions of the lungs:

1. Substances synthesized and used in the lungs: surfactant.

2. Substances synthesized or stored and released into the blood: Prostaglandins

and histamine.

3. Substances removed from the blood: many vasoactive substances are

inactivated, altered or removed from the blood as they pass through the lungs.

For example,

-prostaglandins

-Bradykinin

-Adenine derivatives

-Seratonin

-Nor-epinephrine

-Acetyl-choline

4. Substances activated in the lungs e.g.

Angiotensin I Angiotensin II

Decapeptide Octapeptide

TRANSPORT OF GASES

Oxygen transport

Distribution of oxygen in the body:

pO2 (mmHg) O2 content

Inspired air 158 21 ml%

Expired air 116 16 ml%

Alveolar air 100-104 13-14 ml%

Arterial blood 98-100 19 ml%

Venous blood 40 14 ml%

For each 100 ml of inspired air – 5 ml of O2 is extracted by the

blood.

For each 100 ml of arterial blood – 5 ml of O2 is extracted by the

tissues.

Significance of alveolar pO2 :

pO2 difference across the alveolar capillary membrane

determines the diffusion of O2

It is practically kept constant, because air is continuously

going to the blood and coming from the inspired air.

It determines the pO2 and O2 content of the arterial blood.

Normal arterial pO2 is 98-100 mmHg.

Venous blood pO2 at rest is 40 mmHg. It varies according to

degree of body activity, since active tissue will utilize more O2

and pO2in venous blood decreases.

Carriage of oxygen in blood:

O2 is carried in 2 forms:

-Dissolved form

-In combination with haemoglobin

Dissolved form:

• Amount of O2 is 0.3 ml per 100 ml of blood per 100 mmHg of pO2

• Amount of dissolved O2 increases in linearity with arterial pO2 i.e. greater the

arterial pO2, more the amount in dissolve form.

Combined with haemoglobin:

• Each haemoglobin molecule has four heme groups which have an iron in

ferrous form.

• Fe2+ combines with 1 mole(2 atoms) of O2.

Therefore, 4 moles(8 atoms) of O2 combine with one mole of haemoglobin.

The reaction is rapid requiring

<0.01 sec.

The deoxygenation of Hb4O8 is

also very rapid.

The O2 carrying power of

haemoglobin is given by Oxygen

Haemoglobin Dissociation Curve

i.e. the curve relating percentage

O2 saturation of the haemoglobin

to the pO2 .

It has a characteristic sigmoid

shape.

Bohr Effect:

All the factors which shift the O2- haemoglobin dissociation curve to

right, decrease the affinity of haemoglobin for O2, therefore CO2 enters

the blood from tissues and helps unloading of O2 . This phenomenon is

called Bohr Effect i.e. decrease in O2 affinity of haemoglobin when pH

of blood falls.

CARRIAGE OF OXYGEN IN BODY:

A. In the tissues:

pO2 O2 content

Arterial blood 100 mmHg 19 ml % i. 0.3 ml% in

dissolved form

ii. 18.7 ml% bound to

haemoglobin

Venous blood 40 mmHg 14 ml% i. 0.12% in dissolved

form

ii. 13.88 ml% bound

to haemoglobin

B. In the Lungs:

Venous blood pO2 is 40 mmHg and alveolar air pO2 is 100 mmHg.

Thus, because of pressure gradient O2 rapidly diffuses from alveoli through

the thin pulmonary and capillary endothelium into plasma, therefore, arterial

blood finally leaves the lungs almost fully saturated with O2 at pO2 100

mmHg with O2 content of 19 ml% .

CARBON DIOXIDE TRANSPORT

Tissue activity produces CO2 which enters the blood

due to :

1. Difference in pCO2 between arterial blood and tissues.

Arterial blood pCO2 is 40 mmHg and tissues pCO2 is

46 mmHg.

2. CO2 has high diffusion coefficient, 20 times more

than O2 ; therefore, even this small pressure gradient

of 6 mmHg is sufficient for CO2 transport.

3. Decrease in O2 content, shifts “CO2 dissociation”

curve to left, causing further loading of CO2 from the

tissues to the blood.

HALDANE EFFECT:

When the haemoglobin

is oxygenated, the CO2

dissociation curve

shifts to right , i.e. the

blood begins to lose

some CO2 as it

becomes oxygenated.

This is called Haldane

effect.

HAMBURGER PHENOMENON:

Also known as Chloride shift.

It refers to the exchange of bicarbonate(HCO3-) and chloride (Cl-)

across the membrane of the red blood cells.

LUNG VOLUMES AND CAPACITIES

Tidal Volume: It is the volume of air breathed in or out of the

lungs during quiet respiration. Normal:500 ml.

Inspiratory Reserve Volume: It is the maximal volume of air

which can be inspired after completing a normal tidal

inspiration. Normal:2000-3200 ml.

Expiratory Reserve Volume: It is the maximal volume of air

which can be expired after a normal tidal expiration.

Normal:750-1000ml

Residual Volume: It is the volume of air which remains in the

lungs after a maximal expiration. Normal:1200 ml.

Inspiratory Capacity: It is the maximal volume of air which can

be inspired after completing tidal expiration. It can be computed

as: TV+IRV. Normal: 2500-3700 ml.

Expiratory Capacity: It is the maximal volume of air which can

be expired after completing tidal inspiration. It can be computed

as: TV+ERV. Normal: 1250-1500 ml.

Vital Capacity: It is the maximal volume of air which can be

expelled from the lungs by forceful effort following a maximal

inspiration. Normal: 4.8 litres in males and 3.2 litres in females.

VC=TV+IRV+ERV.

Functional Residual Capacity: It is the volume of air which is

contained in the lungs after completion of tidal expiration, It can

be computed as: RV+ERV. Normal: 2.5 litres.

CIRCULATORY

SYSTEM

INTRODUCTION

The human heart weighs about

300 gms and contains 4

chambers

i. Two thin walled atria

separated from each other by

an interatrial septum; and

ii. Two thick walled ventricles

separated from each other by

an interventricular septum.

Atria:

Serve a capacity function as well as that of

contraction.

Right atrium receives blood from the systemic

circulation via superior and inferior vena

cavae, while left atrium receives blood from

lungs via pulmonary veins.

Ventricles:

Serve as the pumps. They consist of two

separate pumps:

a. Right ventricle supplies the lung circuit via

pulmonary artery. Because of intrathoracic

location of pulmonary blood vessels,

pulmonary circuit offers less resistance to

blood flow.

b. Left ventricle supplies the systemic

circuit via aorta.

ii. As the systemic arteries offer greater

resistance to blood flow, ‘LV’ has to do

larger amount of work compared to ‘RV’.

The cavities of the cardiac chamber are

lined by the endothelial lining, called

Endocardium.

Muscles of the heart including the

pacemaking and conducting system

structures are called Myocardium.

The entire heart is enclosed by a double

layered structure, called Pericardium .

VALVES IN THE HEART

Atrio-ventricular valves:

Atria and ventricles are connected by a

fibrous A-V ring; on the right side by

the Tricuspid valve, and on the left

side by Mitral valve.

These A-V valves:

1. Prevent the backward flow of blood

from the ventricles to the atria during

ventricular systole

2. Close and open passively with the

pressure gradient forces

A-V valves consists of flaps which

are attached to the periphery of the

valve ring.

Chordae tendinae, the cord like

structures originate from the

papillary muscles arising from the

inner border of the ventricle, are

attached to the free edges of the

valve flaps.

The papillary muscles contract

when the ventricular walls contract,

but they do not help the valves to

close; instead prevent the bulging

of valve into the atria during

ventricular contraction

Semilunar valves:

They consists of three flaps of

half moon shaped appearance,

and are of two types:

i. Pulmonary valve situated at

pulmonary orifice which leads

from the ‘RV’ to the pulmonary

artery.

ii. Aortic valve situated at the

aortic orifice which leads from

the ‘LV’ to the aorta.

These valves also open and close

with passive gradient forces

Heart sounds:

Opening of valves is a slowly

developing process and does not

produce any noise; while closure

of valves is a sudden process

causing surrounding fluid to

vibrate producing noise.

1. Closure of A-V valves cause the

first heart sound; and

2. Closure of semilunar valves cause

the second heart sound.

PACEMAKER TISSUES OF THE HEART

Certain tissues in the heart, concerned

with the initiation and propagation of the

heart beat, are called pacemaker tissues.

They include

I. SINU-ATRIAL NODE:

• Location: posteriorly at the junction of the

superior venacava with right atrium.

• Dimensions: Length-15mm; Width-2mm;

Thickness-1mm.

• Cell outline ill defined; highly vascular;

rich in glycogen and mitochondria.

• They are called P-cells or Pacemaker

cells.

• These fibres can generate and

discharge impulses more rapidly

than any other pacemaker tissue

and their rate of discharge

determines the rate at which the

heart beats. That is why SAN is

called the Cardiac pacemaker .

II. ARTRIO VENTRICULAR

NODE:

• Location: Posteriorly on right

side of the interatrial septum.

• Structure: Same as that of

‘SAN’.

III. BUNDLE OF HIS:

• It takes origin from AVN and

then divides into a right and

left branch.

• The left branch divides into

anterior fascicle and a

posterior fascicle.

• The right branch passes down

the right side of the

interventricular septum.

• Both the branches divide

repeatedly to form a network

of fibres in the ventricles.

IV. PURKINJE FIBRES:

• Take a origin from the terminal

branches of the right and left branch of

the bundle of His to penetrate the

ventricular wall.

• These fibers are somewhat thicker and

larger than the cardiac muscle fibers.

• Thus, they transmit the impulse at a fast

velocity of 4mts/sec as compared to the

other conducting tissue.

CARDIAC CYCLE

The sequence of changes in the pressure

and flow in the heart chambers and blood

vessels in between the two subsequent

cardiac contractions is known as cardiac

cycle .

Normal duration: 0.8 sec at heart rate of

75/min.

Ventricular systole: 0.3 sec

Ventricular diastole: 0.5 sec

Atrial systole: 0.1 sec

Atrial diastole: 0.7 sec

EVENTS IN THE CARDIAC CYCLE

The parts of the heart normally beat in an orderly sequence:

• Atrial systole

• Ventricular systole

• Atrial diastole

• Ventricular diastole

ATRIAL SYSTOLE:

Duration: 0.1 sec.

It is seen following the impulse generation in the SAN.

Atrial muscle contracts and atrial pressure rises with ventricular pressure

following it.

Right atrial pressure rises 4 to 6 mmHg, whereas the left atrial pressure rises

approx. 7 to 8 mmHg.

It propels approx. 30% additional blood into ventricles.

VENTRICULAR SYSTOLE:

Duration: 0.3 sec.

It has 2 major phases:

1. Isovolumetric Ventricular Contraction:

• Duration: 0.05 sec

• As the atrial contraction phase passes off, the pressure in both atria and

ventricles falls.

• Ventricular contraction begins and ventricular pressure exceeds the atrial

pressure very rapidly causing closure of the AV valves with production of

First heart sound.

• Ventricles are now a closed chamber, and the pressure within them rises

promptly.

• During this phase, although contraction is occurring in the ventricles but

there is no emptying; therefore, this phase is called isovolumetric

ventricular contraction.

VENTRICULAR SYSTOLE PROPER:

Duration: 0.25 sec.

It is associated with ejection of blood out of

ventricles.

When the pressure in the ‘LV’ exceeds the

pressure in the aorta and the pressure in the ‘RV’

exceeds the pressure in the pulmonary artery,

opening of semilunar valves occurs.

With the opening of the semilunar valves there

follows of the ‘ejection phase’.

This phase is subdivided into 3 divisions:

1. Rapid ejection phase(0.1 sec)

2. The summit .i.e. peak

3. Slow ejection phase(0.15 sec)

The amount of blood ejected by each ventricle per stroke at rest is 70-80 ml.

This is called as Stroke Volume.

This is about 65% of the End-diastolic ventricular blood volume(120-140

ml) and leaves approx. 50 ml of blood in each ventricle at the end of systole,

called End-systolic ventricular blood volume.

VENTRICULAR DIASTOLE:

Duration: 0.5 sec

It comprises of 4 major phases:

1. Protodiastole:

• Duration: 0.04 sec

• At the end of the ventricular systole, ventricular pressure drops more rapidly.

• During this phase, the arterial pressure is better sustained due to elastic recoil

of the vessel wall and immediately the arterial pressure exceeds that in the

ventricle.

• This results in closure of semilunar valves, causing sharp second heart

sound.

2. Isovolumetric ventricular relaxation phase:

• It is the initial part of ventricular diastole.

• Duration: 0.08 sec

• It begins after the closure of the semilunar valves.

• The intraventricular pressures continues to drop rapidly, the ventricular

muscle continues to relax without change in the ventricular volume. That

is why, this phase is called isovolumetric ventricular relaxation phase.

• It ends when the ventricular pressure(practically to zero) below atrial

pressure resulting in opening of ‘A-V’ valves.

3. Ventricular diastole proper:

• Approx. 70% of the ventricular filling occurs passively during this phase.

• It has 2 divisions:

1. Initially rapid filling of the ventricles( opening of ‘A-V’ valves 0.1-0.12

sec).

2. Slow filling of the ventricles(Diastasis) 0.18-0.20 sec.

4. Last rapid filling phase:

• It is due to atrial systole.

• This terminates the cardiac cycle.

ATRIAL DIASTOLE:

Duration: 0.7 sec

During this phase, atrial muscles relax and

the atrial pressure gradually increases due to

continuous venous return tot drop to almost

zero mmHg with the opening of ‘A-V’

valves.

Then the pressure rises again during the

phase of diastasis and follows the

ventricular pressure.

ELECTROCARDIOGRAM

The record of electrical fluctuations

during cardiac cycle is called

Electrocardiogram.

ECG is recorded on a mm square

graph paper, moving at a speed of 25

mm/sec.

‘X-axis’ represents the time,

therefore, 1mm=0.04 sec(along X-

axis).

‘Y-axis’ represents the voltage, and,

1mm=0.1 mV( along Y-axis).

Any deflection of the record above the baseline is

regarded as positive deflection.

Any deflection below the baseline is regarded as the

negative deflection.

No deflection from the baseline means the isoelectric line

or isoelectric segment.

Spread of excitation wave i.e. depolarisation process

towards the electrode gives an upward deflection(positive

deflection).

Spread of excitation wave away from it causes a

downward deflection(negative).

WAVES ASSOCIATED WITH ECG

‘P wave’:

• 1st wave of ECG of duration of

0.1 sec; directed upwards and

rounded.

• It is due to atrial depolarisation

and represents the spread of

impulse from ‘SA’ node to atrial

muscles.

• Its peak represents the invasion of

‘AV Node’ by excitation process

• Its height is 0.5 mv, which

represents the functional activity

of atrial muscles.

P-R segment:

• Following the ‘p’ wave there is a

brief isoelectric period of 0.04 sec,

called ‘P-R segment’.

QRS Complex:

• It is due to the ventricular

depolarisation.

• It is completed just before the

opening of semilunar valves.

• Atrial repolarization activity

merges with the QRS complex.

‘Q’ wave:

• It is small negative deflection of height

less than 0.2 mV and duration less than

0.04sec.

• Beginning of ‘Q’ wave represents invasion

of mid-portion of the interventricular

septum by excitation process.

‘R’ wave:

• Prominent, positive wave.

• Its upstroke coincides with the onset of

ventricular systole.

• It represents excitation process suddenly

invading both ventricles.

• Its height is directly proportional to the

functional activity of ventricles.

‘S’ wave:

• Negative deflection which follows the

‘R’ wave.

• It represents the excitation of more

basal part of the ventricles.

Thus, the QRS complex extends from

the beginning of the ‘Q’ wave to the

end of ‘S’ wave with 0.08 to 0.12 sec

duration and height 1.5 to 2 mV.

S-T segment:

• Following QRS complex there is a

long isoelectric period which extends

from the end of ‘S’ wave to the

beginning of ‘T’ wave, called S-T

segment(0.04-0.08 sec).

‘T’ wave:

• Rounded positive deflection of duration

0.27 sec and 0.5 mV height.

• It represents ventricular repolarisation.

• End of ‘T’ wave coincides with the

closure of semilunar valves.

Isoelectric period:

• Following T-wave is a brief isoelectric

period of 0.04 sec.

‘U’ wave:

• Rarely seen, as positive small round

wave of 0.08 sec duration and 0.2 mV

height.

• It is due to slow repolarization of

papillary muscles.

PR Interval:• Interval from the beginning of

‘P’ wave to the beginning of Q

or R wave( if Q wave is absent).

• It represents the atrial

depolarization plus conduction

time of bundle of His.

• Normal duration 0.13 to 0.16

sec at a heart rate of 72/min;

duration decreases with increase

in HR.

QT Interval:

• Interval from the beginning of ‘Q’

wave to the end of T-wave; normal

duration 0.40 to 0.43 sec.

• It represents ventricular

depolarization and repolarization.

ST Interval:

• (QT-QRS complex) i.e. end of ‘S’

wave to end of ‘T’ wave; normal

duration 0.32 sec.

• It represents ventricular

repolarization.

TP Segment:

• Period from the end of ‘T’ wave to the

beginning of ‘P’ wave of next cardiac

cycle.

• It represents polarized state of whole

heart.

• Its duration is inversely related to H.R.

Normal is 0.2 sec @ H.R. 75/min.

J point:

• Point between ‘S’ wave and ST

segment.

• It is a point of no electrical activity.

HEART RATE

Foetal HR: 140-150bpm

At birth : 130-140bpm

At 12 years: up to 100bpm

Adults: 70-80bpm

Old age: up to 100bpm

Painful stimuli:

• Superficial pain via pressor area of ‘VMC’ causes sympathetic stimulation

producing tachycardia and rise in B.P.

• Pain arising from the deep body tissues via depressor area of ‘VMC’ causes

overall sympathetic inhibition producing bradycardia and fall in systemic B.P.

HR increases during inspiration and decreases during expiration, a

phenomenon called sinus arrhythmia.

Cardiac Output: The amount of blood pumped out by each

ventricle into the circulation per minute is called cardiac

output.

Stroke Volume: The amount of blood pumped by each

ventricle per beat is called stroke volume.

Cardiac Output = HR x Stroke Volume.

Cardiac Index: It is the ‘CO’ expressed as a function of

body surface area. Normal value: 3.2L/m2/min.

COMPONENTS OF SYSTEMIC

ARTERIAL BLOOD PRESSURE

REFERENCES

• Gray’s Anatomy : 35th edition R.WARWICK &P.L.WILLIAM

• B.D. Chaurasia Vol 3-Head and Neck

• Medical physiology – Guyton and Hall

THANK YOU