Events of Cardiac Cycle and Cardiac Output

Events of Cardiac Cycle and Cardiac OutputPresented by: Ananya Azad Hrisha

ContentsCardiac CycleDuration Of Cardiac CycleEvents & phases of Cardiac CycleCardiac OutputCardiac Output MeasurementRelationship of CO with BPSummary

Cardiac CycleRefers to a complete heartbeat from its generation to the beginning of the next beat.

Cardiac events that occur from

beginning of one heart beat to the beginning of the next are called the cardiac cycle.

Cardiac CycleInitiated by spontaneous generation of AP in SA node.Cardiac cycle has :A period of relaxation - Diastole - during which heart fills with blood.A period of contraction - Systole - during which blood is ejected.

Cardiac CycleSystolic Duration=0.3 sec Diastolic duration=0.5secDuring atrial systole, the ventricles are relaxed.During ventricular systole, the atria are relaxed.

Calculation For 72 beats time is 60 sec For 1 beat=60/72=0.8 sec Total duration of each cardiac cycle=0.8sec

Cardiac CycleSystole (0.3 s) includes: 1. Isovolumetric contraction. 2. Ejection. Diastole (0.5 s) includes: 3. Isovolumetric relaxation. 4. Rapid ventricular filling. 5. Slow ventricular filling (diastasis). 6. Atrial contraction.

Cardiac Cycle

EVENTS IN CARDIAC CYCLE (physiology) 'Lub-dub,' 'lub-dub' - This is the familiar sound of the heartbeat.The events in cardiac cycle includes Systole- term used to describe the contraction of the heart.Diastole -term used to describe the relaxation of the heart.

Atrial SystoleBlood normally flows continually from great veins into atria : 75% flows directly from atria into ventricle before the atria contracts.25% of filling of ventricles atrial contraction.

Atrial Systole (The end of diastole)Atrial contraction is complete before the ventricle begins to contract.

Atrial pressure drops when the atria stop contracting.

Beginning of Ven.Systole Isovolumetric ContractionAtrioventricular (AV) valves close at the beginning.Mechanically, its the interval between the closing of the AV valves and the opening of the semilunar valves (aortic and pulmonary valves). Electrically, it is the interval between the QRS complex and the end of the T wave (the Q-T interval).

Ven.Systole

The AV valves close when the pressure in the ventricles exceeds the pressure in the atria.As the ventricles contract isovolumetrically- their volume doesnt changethe pressure inside increases, approaching the pressure in the aorta and pulmonary arteries.

Ven. SystoleEjection

The Semilunar valves ( aortic , pulmonary ) open at the beginning of this phase.at first 2/3 rapid ejection (70%) & remaining 1/3 slow ejection (30%)ventricles continue to contract - pressure in ventricles exceed that of in aorta & pulmonary arteries & semilunar valves open-blood is pumped out of ventricles & volume decreases rapidly.

Ejection

Then, pressure in the ventricles falls below the pressure in the arteries.

blood in the arteries begins to flow back toward the ventricles.

At the end of ejection, the semilunar valves close.

Diastole Isovolumetric relaxationRelaxation of the heart.Is in this state of relaxation(diastole)-the pressure within the heart is low. The atrium in diastole has been filling with blood on top of the closed AV valve, causing atrial pressure to rise grad .

Diastole Rapid Inflow ( Rapid Ven. Filling)Pressure & volume of ventricle are low in this phase and This phase lasts for 0.06 sec.AV valves are open -blood accumulated in atria flows into the ventricle.Ventricular volume increases rapidly - blood flows from the atria into the ventricles.

DiastoleDiastasisPressure in atria and ventricles rises slowly as blood continues to return to the heart.This decreases the rate of blood flow from atria to ventriclescauses slow filling of ventricles called diastasis.

Diastole DiastasisAlso called reduced filling phase.During rapid filling and diastasis phase about 75% of blood passes from atria to ventricles.Then next cycles begins with atrial contraction.Then Atrial Diastole begins where the atria are relaxed after the contraction (period of atrial relaxation for rest of cardiac cycle) having duration of 0.7 sec.

Figure: Events of the Cardiac Cycle

Cardiac Cycle

Cardiac Output

Cardiac output (Q or or CO ) is the volume of blood being pumped by the heart, , in particular by a left or right ventricle in the time interval of one minute. The amount of blood the heart pumps through the circulatory system in a minute. A normal adult has a cardiac output of 4.7 liters (5 quarts) of blood per minute.

Cardiac OutputThe stroke volume output and the heart rate determine the cardiac output.Doctors think about cardiac output in terms of the following equation: Cardiac output = stroke volume heart rate (ml/min) (ml/beat) (beats/min)

Where,stroke volume = the amount of blood put out by the left ventricle of the heart in one contractionheart rate = number of times your heart beats per minute.

Cardiac OutputThe cardiac output is usually expressed in liters/minute. Someone weighing about 70 kg (154 lbs), the cardiac output at rest is about 5 liters/minute.In a resting male, CO = 70mL/beat x 75 beats/min = 5.25L/min. A number of clinical methods available for measurement of CO - having unique strengths and weaknesses & relative comparison.Is limited by the absence of a widely accepted "gold standard" measurement.

Cardiac OutputMeasuring cardiac output

1.The Fick principle2.Dilution methods3.Pulmonary artery thermodilution (trans-right-heart thermodilution)4.Doppler ultrasound method5.Impedance cardiography

Cardiac OutputRelationship With BPAs Cardiac output is made up of heart rate and stroke volume - at rest these are relatively constant.

With exercise the heart beats faster - more blood is pumped out with each beat contributing to a rise in BP.

Changes in the volume of blood within the cardiovascular system will also affect Bp.

Cardiac OutputRelationship With BP

A person was severely dehydrated or lost a large quantity of blood through a wound there would be less blood for the heart to pump, thereby reducing cardiac output and BP.For a typical, fit young person, the cardiac output might go up to about 20 liters/min at the peak of exercise. for a world-class athlete in an endurance sport, the maximum cardiac output might be around 35 liters/min.

SummaryCardiac Cycle :all events associated with one heartbeat, including diastole (relaxation phase) and systole (contraction phase) of both the atria and the ventricles.

During a cardiac cycle -Each heart chamber goes through systole and diastole.Correct pressure relationships are dependent on careful timing of contractions.

Summary

The sequence of events in one cardiac cycle is 1st is atrial systole,Followed by atrial diastole and ventricular systole,Finally, ventricular diastole.

SummaryAtrial systole (duration 0.1 sec) :Contraction of atria, increases pressure inside atria to 4-6 mmHg in right atrium and abt. 7-8mmHg in left atrium.Then there is a period of atrial relaxation for rest of cardiac cycle about duration 0.7 sec.Ventricular contraction (0.3 sec):Rising ventricular pressure exceeds the atrial pressure causing closure of AV valves(tricuspid & mitral valves) - responsible for generating 1st heart sound.Ventricular relaxation (0.5 sec) : called hearts state of relaxation, the pressure within the heart is low. blood passively flows through the atria and into the ventricles.

Summary

SummaryCardiac output:The cardiac output is simply the amount of blood pumped by the heart per minute. Necessarily, the cardiac output is the product of the heart rate, which is the number of beats per minute, and the stroke volume, which is amount pumped per beat.

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