Introduction to Introduction to Cardiac Cycle and Cardiac Cycle and

Cardiac OutputCardiac Output

ObjectivesObjectives

Explain the ECG waves and correlate them with mechanical events.

Describe the phases of cardiac cycle. Identify the origin of heart sounds. Define heart rate, stroke volume, venous return

and cardiac output. Explain the Starling’s law of the heart. List the function of autonomic nervous system

on the heart.

Electrocardiogram ECG Electrocardiogram ECG (EKG)(EKG)

Electrocardiogram ECG Electrocardiogram ECG (EKG)(EKG)

Electrocardiogram ECG Electrocardiogram ECG (EKG)(EKG)

• Surface electrodes record electrical activity deep within Surface electrodes record electrical activity deep within body body

• Reflects electrical activity of whole heart not of single Reflects electrical activity of whole heart not of single cell!cell!

• EC fluid = “salt solution” (NaCl) EC fluid = “salt solution” (NaCl) good conductor of good conductor of electricity to skin surfaceelectricity to skin surface

ECG tracingECG tracing = = of all electrical potentials generated by of all electrical potentials generated by all cells of heart at any given momentall cells of heart at any given moment

Electrodes placed on arms and Electrodes placed on arms and legs (legs (limb leadslimb leads) + six ) + six positions on chest (positions on chest (chest chest leadsleads).).

Each lead records different Each lead records different electrical activity (each looks electrical activity (each looks at heart from a different at heart from a different position)position)

Electrocardiogram (ECG, Electrocardiogram (ECG, EKG)EKG)

3 waves appear with each heart beat:

P wave: represents atrial depolarization

QRS complex: represents ventricular depolarization

T wave: represents ventricular repolarization

Depolarization = signal for Depolarization = signal for contractioncontraction

Segments of ECG reflect mechanical heart eventsSegments of ECG reflect mechanical heart events

Since:Since:

Correlation of ECG waves with Atrial Correlation of ECG waves with Atrial and Ventricular Systoleand Ventricular Systole

ECG cont.ECG cont. Comparing records with one Comparing records with one

another & normal records, another & normal records, allows determination :allows determination : if if conductivityconductivity pathway is pathway is

normalnormal if the heart is if the heart is enlargedenlarged if certain regions of heart if certain regions of heart

are are damageddamaged

ECG time intervals or segments: P-Q interval S-T interval Q-T interval

ECG cont.ECG cont.

Cardiac CycleCardiac Cycle One cardiac cycle (CC): all events associated with one One cardiac cycle (CC): all events associated with one

heart beat.heart beat. (Systole and diastole of atria + systole and diastole of (Systole and diastole of atria + systole and diastole of

ventricles)ventricles)

At HR 75 beats /min, CC lasts 0.8 secs.At HR 75 beats /min, CC lasts 0.8 secs.

In each CC, atria & ventricles alternatively contract & relaxIn each CC, atria & ventricles alternatively contract & relax Force blood from areas of higher pressureForce blood from areas of higher pressure Areas of lower pressureAreas of lower pressure

Cardiac Cycle cont.Cardiac Cycle cont.Cardiac Cycle comprises the followingCardiac Cycle comprises the following

phases:phases: Atria systole:Atria systole:

atria contracting but Ventricles relaxing.atria contracting but Ventricles relaxing.

Lasts 0.1 secLasts 0.1 sec

Ventricular systole:Ventricular systole:

Ventricular Contracting while atria relaxVentricular Contracting while atria relax

(atrial diastole). Lasts 0.3 sec.(atrial diastole). Lasts 0.3 sec.

Relaxation PhaseRelaxation Phase (Complete cardiac diastole ), Both atria(Complete cardiac diastole ), Both atriaand ventricular relax. Lasts about 0.4 sec and ventricular relax. Lasts about 0.4 sec

Heart Sounds Heart Sounds Auscultation:Auscultation: act of listening to sounds within act of listening to sounds within

the body, usually done with a stethoscopethe body, usually done with a stethoscope

sounds are caused by vibrations set up within sounds are caused by vibrations set up within the walls of ventricles and major arteries the walls of ventricles and major arteries during valve closure.during valve closure.

During each CCDuring each CC4 heart sounds4 heart sounds

Only first & second (Only first & second (S1 &S2S1 &S2) heard in normal ) heard in normal heartheart

First heard sound (S1) lubb:First heard sound (S1) lubb:

- louder & longer than second- louder & longer than second

- caused by closure of A-V - caused by closure of A-V valvesvalves

(soon after beginning of (soon after beginning of ventricular systole)ventricular systole)

Second heart sound (S2) duppSecond heart sound (S2) dupp::

- shorter & not as loud as first- shorter & not as loud as first

- caused closure of SL valves - caused closure of SL valves

(beginning of ventricular (beginning of ventricular diastole)diastole)

S3 S3 is due to turbulance during is due to turbulance during ventric fillingventric filling

S4S4 is due to turbulance during is due to turbulance during atrial systoleatrial systole

Heart soundsHeart soundsS1 &S2 are S1 &S2 are best heard at best heard at the surface of the surface of chest in chest in specific specific locationslocations

Cardiac output (CO)Cardiac output (CO) COCO is the volume of blood ejected from the left ventricle is the volume of blood ejected from the left ventricle

(or the right ventricle) into the aorta (or pulmonary trunk) (or the right ventricle) into the aorta (or pulmonary trunk) each minute.each minute.

CO equals the stroke volume (SV) multiplied by heart rate CO equals the stroke volume (SV) multiplied by heart rate (HR)(HR)

CO = SV X HRCO = SV X HR SV volume of blood ejected by the ventricle during each SV volume of blood ejected by the ventricle during each

contractioncontraction HR number of heart beats per minute.HR number of heart beats per minute.

CO = SV X HR = 70 ml/beat X 75 beats/minute CO = SV X HR = 70 ml/beat X 75 beats/minute

= 5.25 L/min= 5.25 L/min

Cardiac Output cont.Cardiac Output cont. CO may CO may to meet demands to meet demands

During exercise CO can increase to 20-25 L/ minDuring exercise CO can increase to 20-25 L/ min

Cardiac reserve (CR):Cardiac reserve (CR): The difference between the The difference between the maximum CO and CO at rest.maximum CO and CO at rest.

Average CR: 4 -5 X resting value (20-25 L/m)Average CR: 4 -5 X resting value (20-25 L/m)

higher in athletes (35 L/m)higher in athletes (35 L/m)

little or no reserve in heart diseaselittle or no reserve in heart disease

Regulation of cardiac Regulation of cardiac outputoutput

CO= SV x HRCO= SV x HR

Depends on the regulation of Depends on the regulation of SV and HRSV and HR

Cardiac TerminologyCardiac Terminology End diastolic volume (EDV):End diastolic volume (EDV):

blood in the ventricles at the end of diastole.blood in the ventricles at the end of diastole.

Ejection fraction:Ejection fraction:fraction of EDV that is ejected (%), used to measure fraction of EDV that is ejected (%), used to measure heart efficiency.heart efficiency.

End systolic volume (ESV):End systolic volume (ESV):blood that remains in the blood at the end of systole.blood that remains in the blood at the end of systole.

Preload:Preload:the degree of stretch on the heart before it contracts.the degree of stretch on the heart before it contracts.

Afterload:Afterload:the pressure that must be exceeded before ejection of the pressure that must be exceeded before ejection of blood from the ventricles can occur.blood from the ventricles can occur.

Regulation of stroke Regulation of stroke volumevolumeTHREE factors regulate SV:THREE factors regulate SV:

1.1. Preload (EDV)Preload (EDV)

2.2. ContractilityContractility

3.3. AfterloadAfterload

1. Preload: effect of 1. Preload: effect of stretchingstretchingFrank-Starling (F-S) law of the Frank-Starling (F-S) law of the

heart:heart: Within limitsWithin limits, the more the , the more the

heart fills during diastole heart fills during diastole (preload – stretching), the (preload – stretching), the greater the force of contraction greater the force of contraction during systole.during systole.

the preload is proportional to the preload is proportional to EDV, the greater the EDV, the EDV, the greater the EDV, the more forcefull the next more forcefull the next contractioncontraction

“The heart will pump what it receives”- Starling’s law of the heart

Two factors determine EDV:Two factors determine EDV:

1.1. Duration of ventricular diastole (HR)Duration of ventricular diastole (HR)

Ventricular filling occur during diastoleVentricular filling occur during diastole

Tachycardia ( HR) diastole duration Tachycardia ( HR) diastole duration

ventricular filling end diastolic volumeventricular filling end diastolic volume

COCO

2.2. Venous return (volume of blood flowing back to the Venous return (volume of blood flowing back to the heart through systemic veins)heart through systemic veins)

Preload cont.Preload cont.

2. Contractility2. Contractility ContractilityContractility:: strength of contraction at any given preload strength of contraction at any given preload

+ve inotropism+ve inotropism: : contractility contractility

Include: - sympathetic stimulationInclude: - sympathetic stimulation - Hormones; adrenaline and noradrenaline- Hormones; adrenaline and noradrenaline

-ve inotropism:-ve inotropism: contractility contractility

May result from:May result from: - inhibition of the sympathetic system- inhibition of the sympathetic system - anoxia- anoxia - acidosis- acidosis

3. Afterload3. Afterload pressure in pulmonary tract is a bout 20 mm.Hg and in the aorta is

about 80 mm Hg. This pressure must be overcome before the semilunar valves open.

Depend on:

Elasticity of large arteries Peripheral resistance of arterioles

An in afterload SV more blood remains in ventricle at end of systole (ESV)

Conditions that afterload include: Hypertension Narrowing of arteries by atherosclerosis

Regulation of heart rateRegulation of heart rate

Several factors, the most important areSeveral factors, the most important are

1. Nervous factors1. Nervous factors

2. Chemical factors2. Chemical factors

3. Others3. Others

Autonomic regulation of Autonomic regulation of HRHR

Chemical regulation of Chemical regulation of HRHR

1. Hormones1. Hormones:: Adrenaline and noradrenaline (adrenal medulla)Adrenaline and noradrenaline (adrenal medulla) HR & HR &

contractilitycontractility

Adrenal medulla stimulated by: Adrenal medulla stimulated by: exercise exercise stressstressexcitementexcitement

Thyroid hormones Thyroid hormones HR & HR & ContractilityContractility

Hyperthyroidism Hyperthyroidism tachycardia tachycardia

2. Cations2. Cations Na+ & K+ Na+ & K+ HR & Contractility HR & Contractility Ca2+ Ca2+ HR & HR & ContractilityContractility

Other factors in HR Other factors in HR regulationregulation

Age:Age: Newborn HR ~120 beats/min Newborn HR ~120 beats/min Old people may also develop Old people may also develop HR HR

Gender:Gender: Adult females Adult females higher HR than higher HR than malesmales

Exercise:Exercise: Athletic bradycardia (60 or Athletic bradycardia (60 or under) (more efficient heart)under) (more efficient heart)

Body temperature (BT):Body temperature (BT): BT (fever or exercise) BT (fever or exercise) HR HR BTBT HR & contractility HR & contractility