Cardiac cycle

CARDIAC CYCLE

Have a heart!!

Each of us has a pump inside ~To check the blood be on the right side…If its so you need not hide ~Just have a heart, full of pride …That it keeps the dirtiness outside ~And pumps the goodness all inside!!! (Dr.

Samina)

DEFINITION OF CARDIAC CYCLE:

THE CARDIAC EVENTS THAT OCCUR FROM THE BESINNING OF ONE HEART BEAT TO THE BEGINNING OF THE NEXT ARE CALLED CARDIAC CYCLE.

• Period between start of one beat to start of next.

• It consists of one complete heart beat.

• It consists of one systole & one diastole.

INITIATION OF CARDIAC CYCLE:

• Initiated by Cardiac Impulse, which originates from SA node.

EVENTS THAT OCCUR IN THE CARDIAC CHAMBERS

DURING CARDIAC CYCLE • Pressure Changes.

• Volume Changes.

• Production of Heart Sounds.

• Closure & Opening of Cardiac Valves.

• Electric Changes (ECG recording).

VENTRICULAR SYSTOLE 0.31 sec(Peak of R wave of QRS complex to the end of T wave)

ISO-VOLUMETRIC CONTRACTION 0.06 sec

MAXIMUM EJECTION (2/3) 0.11 sec

REDUCED EJECTION (1/3) 0.14 sec

VENTRICULAR DIASTOLE 0.52 sec(End of T wave to the peak of R wave of QRS complex)

PROTODIASTOLE 0.04 sec

ISO-VOLUMETRIC RELAXATION 0.06 sec

RAPID INFLOW 0.11 sec

SLOW INFLOW / DIASTASIS 0.2 sec

ATRIAL SYSTOLE (after P wave) 0.11 sec

8 Phases of CARDIAC CYCLE 0.8 sec

PRESSURE CHANGES:

Heart has 4 chambers:

A) Pressure changes in left ventricle

during cardiac cycle.

B) Pressure changes in right ventricle during cardiac cycle.

C) Pressure changes in atria.

Pressure changes in Left Ventricle (L.V)

during cardiac cycle:‘Phase 1’ of cardiac cycle / Iso-volumetric

contraction of ventricle:

At the start of ventricular systole L.V is full of blood (received from left atrium during previous diastole).

Pressure in L.V at this stage = 1-3 mm Hg. Now L.V begins to contract I.V.P (Intra-

ventricular pressure) begins to rise closure of mitral valve / Left AV Valve 1st phase starts: ISOMETRIC CONTRACTION PHASE OR ISOVOLUMETRIC CONTRACTION PHASE.

Pressure changes in Left Ventricle (L.V) during cardiac cycle:

• With closure of mitral valve ventricle is a closed chamber no change in blood volume ISO-VOLUMETRIC, as both valves are closed ISO-METRIC CONTRACTION (no change in length of muscle but rapid increase in I.V.P).

• When IVP rises just above 80 mm Hg opening of Aortic or Semi-lunar valve.

• Duration of I.V.C of Ventricle = 0.06 sec.

• With opening of Aortic valve, 2nd phase starts: MAXIMAL EJECTION PHASE.


‘Phase 2’ of cardiac cycle / Maximal Ejection Phase (M.E.P) / Rapid Ejection Phase (R.E.P):

Ventricle muscle is contracting powerfully with opening of Aortic valve.

Blood is ejected from ventricle (2/3 of stroke volume) Aorta (at maximum rate). 70% EMPTYING occurs in first 1/3 of ejection phase.

In this phase: I.V.P maximum = 120 mm Hg.

Duration of M.E.P = 0.11 sec.


• ‘Phase 3’ of cardiac cycle / Reduced Ejection Phase (R.E.P):

• Blood ejection (remaining 1/3 of stroke volume, 30% EMPTYING occurs in last 2/3 of ejection phase) from L.V Aorta, continues but at a reduced rate.

• I.V.P falls from maximum.

• This phase ends when I.V.P becomes equal to OR slightly less than AORTIC PRESSURE.

• Duration of R.E.P = 0.14 sec.

Duration of ventricular systole (3 phases):

Isovolumetric contraction = 0.06 sec

Maximum Ejection Phase = 0.11 sec

Reduced Ejection Phase = 0.14 sec

Ventricular Systole = 0.31 sec

• ‘Phase 4’ of cardiac cycle / Protodiastole:• A short phase = 0.04 sec.

• At the junction of systole & diastole, but included in diastole.

• At this stage, I.V.P = Aortic Pressure or I.V.P is slightly less than Aortic pressure, BUT SMALL

AMOUNT OF BLOOD CONTINUES TO OOZE, because of momentum.

• In protodiastole: THIS MOMENTUM IS OVERCOME due to further fall in I.V.P & there is some retrograde flow of Aortic blood in 1st part of Aorta closure of Aortic valve end of Protodiastole.

• ‘Phase 5’ of cardiac cycle / Isovolumetric Relaxation Phase (I.V.R):

• Starts with closure of Aortic valve.

• Why it is called ISOVOLUMETRIC RELAXATION?

ANSWER

• Ventricle relaxation without change in volume, because: BOTH VALVES ARE CLOSED no change in blood volume Rapid fall in I.V.P because of relaxation.

When (left ventricular pressure) < (left atrial pressure)Opening of left AV valve / mitral valve end

of I.V.R phase.• Duration of I.V.R = 0.06 sec.

Pressure changes in Left Ventricle (L.V)

during cardiac cycle:

• ‘Phase 6’ of cardiac cycle / Rapid Inflow Phase (R.I.P) / Rapid filling phase (R.F.P):

• Starts with opening of mitral valve.

• Blood from Left Atrium rapidly flows into Left Ventricle.

• 2/3 of ventricular filling occurs in this phase (during first 1/3 of ejection phase)

• Duration of R.I.P = 0.11 sec.

• ‘Phase 7’ of cardiac cycle / Slow Inflow Phase / Diastasis:

It appears that: No blood is flowing from Lt. Atrium Lt. Ventricle because:

• During last phase (R.I.P), most of blood Lt. Vent.

• Mitral valve is open Lt. atrium & Lt. Ventricle = common chamber whatever blood that returns in small amount from pulmonary veins Lt. Atrium Lt. Ventricle (through open valve) so it appears that no blood is flowing.

• Only slight (1/3) filling of Lt. Ventricle in this phase.

• Duration of diastasis / Slow Inflow Phase = 0.2 sec.

• THE LONGEST PHASE OF CARDIAC CYCLE.

• ‘Phase 8’ of cardiac cycle / Atrial Systole:

• Last phase of cardiac cycle

• Lt. Atrium contracts pushes the blood from its cavity Lt. Ventricle 20% ventricular filling by atrial contraction.

• Atria contract towards the end of ventricular diastole.

• With atrial contraction, ventricular filling is complete.

• Duration: 0.11 sec.

• Mechanism: AV nodal delay. It allows atria to contract before ventricles begin to contract, at the end of ventricular filling.

Duration of ventricular diastole (5 phases):

• Protodiastole = 0.04 sec

• Isovolumetric Relaxation = 0.06 sec

• Rapid Inflow Phase = 0.11 sec

• Slow Inflow Phase = 0.20 sec

• Atrial Systole = 0.11 sec

• Ventricular Diastole = 0.52 sec

Duration of Cardiac Cycle (8 phases):

= Duration of systole + diastole =

• (0.31) + (0.52) = [0.8 sec]

Pressure Changes in Right Ventricle:

• Same phases as for Lt. ventricle.

• Same duration as for Lt. ventricle.

• Only change in pressure levels & in names of valves.

• Aortic valve is replaced by pulmonary valve.

• Mitral valve is replaced by Tricuspid valve.


At the beginning of Rt. Vent. Systole:• Pressure = 0-1 mm Hg.

• During I.V.C Pressure increases on the right side just exceeds 8 mmHg opening of pulmonary valve (above 80 mmHg, there was opening of Aortic valve).

• Maximum increase in pressure in Rt. Vent systole = 25 mmHg (it was120 mm Hg in Lt. vent.)


• Right ventricle & Pulmonary artery is a low pressure system.

Pulmonary artery pressure variation:• 8 – 25 mm Hg

Aortic pressure variation:• 80 – 120 mm Hg

Duration of cardiac cycle & heart rate:

• Duration of cardiac cycle = 0.8 sec at heart rate = 70 beats / min.

• When heart rate increases duration of cardiac cycle decreases.

• Diastole is more affected as compared to systole with rapid heart rate.

• At heart rate = 180 / min, cardiac cycle duration = 0.33 sec: (systole = 0.18 sec, diastole = 0.15 sec).

QUESTION

• At a very rapid heart rate: Cardiac output decreases, Why???

ANSWER

• Because diastole becomes too short ventricular filling decreases decrease stroke volume & decrease in cardiac output, in spite of increase in heart rate.

Cardiac output:

• Output of heart per unit time = 5 L / min in a resting supine man.

• Cardiac output = stroke volume x heart rate

= 70 ml x 72 beats / min

nearly equal to 5 L / min

Stroke volume (S.V):• Difference between End Diastolic Volume (EDV)

& End Systolic Volume (ESV).• S.V = EDV - ESV• S.V = 120 – 50• = 70 ml

• When ventricular contraction is forceful ESV decreases (10-20 ml only). Normal is 50 ml.

• When venous return increases up to 200 ml or more EDV increases (normal = 120 ml)

EJECTION FRACTION:

• Fraction of EDV that is ejected in one systole or one stroke = Ejection Fraction.

• Value of Ejection Fraction = 60% (usually).

• 65% in some books.

• In Myocardial disease / heart failure Ejection Fraction decreases.

Pressure changes in Atria during the Cardiac Cycle:

• Atrial systole duration = 0.11 sec• Atrial diastole duration = 0.7 sec• Atrial systole + Atrial diastole = 0.8 sec = cardiac cycle.

• Atrial diastole > Atrial systole, because basic function of atria is to receive blood from large veins & it can receive blood only when it is relaxed.

3 waves can be recorded from atria which represent atrial pressure changes:

• a-wave, c-wave & v-wave (Seen as Jugular Venous Pulse, not a true pulse, but a reflection of pressure changes in right atrium.


a-wave: Due to increase in atrial pressure during atrial systole.


c-wave: Recorded at beginning of contraction of ventricle. During isovolumetric contraction, ventricular pressure increases Cusps of AV valves are pushed into atrial cavity pressure rises in atria ascent of c-wave.


The top of c-wave coincides with opening of semi-lunar valves (Aortic & Pulmonary).

With opening of semi-lunar valves, 2nd phase starts, which is maximum ejection phase.

It is later on followed by iso-volumetric relaxation

of ventricle muscle length increases now AV valve is pulled to ventricular cavity atrial cavity increases pressure falls in the atria descent of c-wave.

‘x’ Descent

• This occur when the ventricular systole results in pulling the tricuspid valve rings downwards along with the simultaneous relaxation of atrium.


• v-wave: Due to gradual increase in atrial pressure, resulting from venous filling of blood (from the venae cavae) into the atria, with closed AV valves ascent of v-wave.

• Top of v-wave coincides with opening of AV valves rapid inflow phase decrease pressure in atria descent of v-wave.

‘Y’ Descent

• It occurs when the tricuspid valve is opened and the right atrium empties, pressure within the right atrium falls and thus a negative venous pressure decent is recorded. A slow Y descent suggests an obstructions to right ventricular filling, as occur with tricuspid stenosis.

Right atrial pressure = Central Venous Pressure.

• During most of cardiac cycle, this pressure remains almost zero.

• During wave a, c & v pressure rises. Otherwise remains almost zero.

• 4-6 mm Hg Rt. Atrium (during a, c, v)

• 7-8 mm Hg Lt. Atrium (during a, c, v)

JUGULAR VENOUS PULSE:(a, c, v waves)

• Normally arteriolar pulse ends in arterioles & in veins no pulsation.

• But we can record pulsation in jugular vein, which is not a true pulse.

• It is just backward transmission of pressure changes in Rt. Atrium (a, c. v waves) transmitted in neck veins.

Significance of J.V.P:

• ac interval coincides with PR interval of ECG.

• ac interval increases in delayed AV conduction.

Significance of J.V.P:

• a waves are absent in: ATRIAL FIBRILLATION.

• (a wave) > (c wave) in COMPLETE AV BLOCK.

• ‘Giant a waves’ in TRICUSPID & PULMONARY STENOSIS.

• Pulsating Neck Veins in CCF (Congestive Cardiac Failure).

• The significance of a-c, c-v, v-y ,y-a, and v-c intervals gives the relationship b/w the intervals of the venous pulse with the respective phase of the cardiac cycle.

• INTERVAL SIGNIFICANCE• a-c approximately P-R

interval • c-v ventricular systole• v-y rapid filling ph of vent• y-a rapid filling ph of

ventrical.• v-c ventricular diastole

Volume changes in Ventricles during Cardiac Cycle:

Beginning of ventricular systole: Ejection Phases: (Maximum Ejection Phase & Reduced Ejection Phase)

Iso-volumic Relaxation Phase:

Rapid Inflow Phase:

Diastasis / Slow Inflow Phase:

Atrial Systole:

Beginning of ventricular systole:

• Ventricle is full of blood (collected during previous diastole, EDV = 120 ml) at the onset of ventricular systole.

• This much volume is there at the start of ventricular systole.

• With this volume onset of Isovolumic / Isometric Contraction, with no change in blood volume.

Ejection Phases: (Maximum Ejection Phase & Reduced Ejection Phase)

Maximum Ejection Phase:• 2/3 of Stroke Volume (total = 70 ml) is ejected

out.

Reduced Ejection Phase:• Remaining 1/3 is ejected out.

After ejection phases, the volume of blood left behind is ESV = 50 ml.

Iso-Volumic Relaxation Phase:

• No change in blood volume occurs.

Rapid Inflow Phase:

• 2/3 of ventricular filling.

Diastasis / Slow inflow phase:

• Only slight filling occurs.

Atrial Systole:

• Remaining 1/3 filling (30%). Now filling of ventricles is complete & EDV of 120 ml is left.

EJECTION FRACTION:

• Fraction of EDV that is ejected in one systole or one stroke = Ejection Fraction.

• Value of Ejection Fraction = 60% (usually).

• 65% in some books.

• In Myocardial disease / heart failure Ejection Fraction decreases.

Sequence of systole in chambers of heart:

RALA

RVLV

12

34

5

6

PULMONARYARTERY

AORTA PRESSURE

PRESSURE

Sequence of systole in chambers of heart:

• Right atrial systole begins earlier as compared to left atrial systole.

• Left ventricular systole begins earlier as compared to right ventricular systole.

• But blood ejection from right ventricle pulmonary artery, starts earlier as compared to ejection from left ventricle aorta, BECAUSE pressure in pulmonary artery < Aortic pressure.

Closure & Opening of Heart Valves:

AV VALVES:• Are closed at the beginning of Isovolumic contraction

Phase.

• Are open at the beginning of Rapid Inflow phase.

• AV valve closure is slow & soft & does not require backward flow of blood.

• Cusps of AV valves are soft & thin because they are not subjected to increase in pressure & rapid blood flow.

Closure & Opening of Heart Valves:

• SEMILUNAR VALVES:• Are closed at the beginning of Isovolumic

relaxation phase.

• Cusps of these valves are thick & heavier (as they are subjected to increased pressure & rapid blood flow).

• Their closure is rapid & requires backward flow of blood (incisura in case of Aortic valve).

Closure & Opening of both AV & Semilunar

Heart Valves:• Forward pressure gradient opening.• Backward pressure gradient closure.

• AV valves prevent, leakage of blood from ventricle atria, during ventricular systole (when pressure rises in ventricle).

• Semilunar valves prevent leakage of blood from large arteries ventricles, during ventricular diastole (when pressure falls in ventricle)

Heart Sounds:• During each cardiac cycle, 4 heart sounds are produced.

• These can be recorded in phonocardiogram.

• By auscultation we can hear / auscultate, 1st & 2nd heart sounds & sometimes 3rd as well.

• But 4th is Atrial heart sound, which is never auscultated normally.

• 1st & 2nd heart sounds are called as CLASSICAL HEART SOUNDS (as they are usually auscultated in normal subjects).

4 Auscultatory areas:

• Pulmonary Area: Left 2nd intercostal space, sternal border.

• Aortic Area: Right 2nd intercostal space, sternal border.

• Mitral Area: Apex.

• Tricuspid Area: 4th intercostal space.

4 basic factors affecting Heart Sounds:

• Acceleration of blood: Sudden flow.

• Deceleration: Sudden stoppage of blood flow.

• Turbulance.

• Thickness of chest wall effects.

1st Heart Sound:

Characteristics:

• Long, soft, low pitched. (heard as LUB)

• Frequency: 30 – 50 cycles / sec.

• Duration: 0.14 sec

CAUSES:• Vibrations due to closure of AV valves, at

the beginning of ventricular systole.

• Vibrations in ventricles & large vessels when ventricular muscle contracts.

• Vibrations when blood starts ejecting into large artery.

1st Heart Sound:

Physiological Splitting of 1st heart sound:

Mechanism:

• Tricuspid valve may close earlier than mitral.

Intensity of 1st heart sound:

Depends on:

• Force of ventricular systole.

• Rate of increase in ventricular pressure, during isovolumic contraction phase.

2nd Heart Sound:

Characteristics:

• Short, sharp, high pitched. (heard as DUBB)

• Frequency: 50 – 200 cycles / sec.

• Duration: 0.11 sec

• Increase in inspiration = 0.5 sec &

• Decrease in expiration = 0.02 sec.

2nd Heart Sound:

Minor causes:

• When blood flows from ventricle to large arteries, there may be turbulance.

Splitting of 2nd Heart Sound:• PHYSIOLOGICAL

• Increases or Widens during inspiration (0.5 sec) & decreases during expiration (0.02 sec or disappear).

Cause of splitting:

• During inspiration venous return increases more blood returns to right atrium right ventricle more ejection delayed closure of pulmonary valve.

• Reverse occurs in expiration.

• PATHOLOGICAL

• In bundle branch block, mainly right bundle branch block.

• Intensity of pulmonary component of 2nd heart sound is increased in pulmonary hypertension.

• Intensity of aortic component is increased in aortic hypertension

3rd Heart Sound:Prominent sometimes in children.Can be made prominent by increasing venous return: i) exercise. ii) lying position.

• Low frequency sound.

• Duration: 0.04 sec.

• Best heard at: Apex of heart, in 5th intercostal space (mid-clavicular line).

• Cause: Vibrations produced in ventricular wall during Rapid Inflow Phase.

4th Heart Sound:• Not normally auscultated but recorded in

phonocardiogram.

• Low frequency, low intensity sound.

• Produced just before 1st heart sound.

• Also called ATRIAL HEART SOUND.

Cause:• Vibrations of ventricular wall, due to impact of blood

pumped from the atrium ventricle, during Atrial Systole.

Diseases:• In CCF, 4th Heart Sound is auscultated.

MURMURS:

• Abnormal heart sounds.

Produced when:• Valvular stenosis.

• Valvular incompetence.

• Hyperdynamic circulation: Hyperthyroidism, severe anemia (hemic murmurs)

2 TYPES OF BLOOD FLOW:

• STREAM-LINE / LAMINAR FLOW &• TURBULENT FLOW• LAMINAR BLOOD FLOW: Blood flows in layers

or laminae.• A thin layer of blood in contact with vessel wall

does not move.• Next layer moves with a slow velocity & further

next with higher velocity.• At centre of vessel, maximum velocity.• Unidirectional & without noise or sound.

2 TYPES OF BLOOD FLOW:

• TURBULENT FLOW: Blood flows in different directions.

• Blood mixes within itself. There are edde currents (BHANWAR) in blood flow.

• This type of flow is accompanied by noise or sound.

• Normally in all vessels blood flow is streamlined, except ascending aorta & pulmonary trunk, where normally there is some turbulance.

• Turbulance can be determined & expressed in terms of REYNOLD’S NUMBER.

REYNOLD’S NUMBER• DEFINITION: It is the unit of turbulence.

• VALUE: Its value is between 2000-3000.

• It is directly proportional to the product of velocity, change in diameter & density.

• It is inversely proportional to the viscosity.

• Re = v.d.p• n

• When this no. is more than 3000, blood flow becomes turbulent.

• In hyperdynamic circulation, velocity increases Reynold’s no. increases (hyperthyroidism & severe anemia) HEMIC MURMURS.

• Turbulence occurs incase of: high velocity of blood flow, pulsatile nature of flow , sudden change in vessel diameter & large vessel diameter.

Examples of Hemic murmurs:1. Sound beyond the narrow vessel due to eddy currents.

2. Recording of B.P. Kortokoff sounds are heard. When brachial artery is occluded & blood flows through partially occluded artery, just beyond the cuff, sounds appear with sudden increase in diameter.

3. In valvular stenosis, just beyond the stenosed valve, diameter increases stenosed murmur.

• EXAMPLE OF CLASS ROOM DOOR.

• When viscosity of blood increases Re decreases no murmurs.• When viscosity of blood decreases Re increases murmurs.

Cardiac cycle

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