CARDIAC CYCLE

CARDIAC CYCLEDr. indrajeetDept. of prosthodontics

DEFINITIONThe cardiac events that occur from the beginning of one heartbeat to the beginning of the next are called the cardiac cycle.Each cycle is initiated by spontaneous generation of an action potential in the sinus node .

The heart is endowed with a special system for

(1) generating rhythmical electrical impulses to cause rhythmical contraction of the heart muscle

(2) conducting these impulses rapidly through the heart.

Division of cardiac cycle

Atrial systole & atrial diastole , ventricular systole & ventricular diastole7

Normal heart rate 72/minute

Duration of cardiac cycle -.8 sec

Duration of systole - .27 sec

Duration of diastole - .53 sec

ATRIAL SYSTOLE(LAST RAPID FILLING STAGE)Duration .11 secLast phase of ventricular diastole 10 % of blood is forced into ventricles

Atrial systole not essential during normal functioning helps during exercise.10

AV valves opened

Semilunarvalves closed

ISOMETRIC CONTRACTION PERIODDuration 0.05 secImmediately after atrial systoleA-v valves closed due to increased ventricular pressureSemilunar valves already closedContraction of ventricles without change in volume and length of muscle fibres

Significance explain to open semilunar valves12

AV valves closed

Semilunarvalves closed

EJECTION PERIODDuration is.22 secOpening of semilunar valvesEjection of blood from the ventriclesDivided into rapid ejection(0.13sec) & slow ejection(0.09sec)

AV valves closed

Semilunarvalves opened

PROTODIASTOLEDuration .04 secFirst stage of diastolePressure in aorta & pulmonary artery increases & in ventricles dropsSemilunar valves close

ISOMETRIC RELAXATION PERIODDuration - .08 secAll the valves are closedVentricles relax as closed cavitiesIntraventricular pressure fallsAV valves open

Significance explain opening of av valves17

Diastole: Period of isovolumic relaxation. Blood flowing back toward the relaxed ventricles causes the semilunar valves to close, which is the beginning of ventricular diastole. Note that the AV valves closed, also.

AV valves closed

Semilunarvalves closed

RAPID FILLINGDuration .11 secBlood collected in the atrium rapidly rushes into the ventriclesAbout 70 % of filling takes place

SLOW FILLINGDuration .19 sec Ventricular filling becomes slowThis slow filling is also called as diastasisAbout 20 % of filling occurs in this phase

AV valves opened

Semilunarvalves closed

INTRA ATRIAL PRESSURE CHANGES DURING CARDIAC CYCLEImportant for opening of AV valves & ventricular fillingLeft atrium 7-8 mm hgRight atrium 5-6 mm hg max0-2 mm hg - minimum

Intra Atrial pressure curveIt has three positive waves a,c,v

Three negative waves x,x1 ,y

a waveIt is the first positive wave and occurs during atrial systole

Pressure increases to 5 mm Hg in right atrium & 7 mm Hg in left atrium

x wave First negative wave & appears during the onset of atrial diastole

Pressure falls because of the relaxation of atriaAV valves close at the end of this wave

c wave Appears during isometric contractionRise in pressures is due to AV valve closureBulging of AV valves into atria

x1 waveAppears during ejection periodThe contraction of the ventricular musculature pulls the atrio ventricular ring towards the ventricles.

So fall in pressure28

v waveObtained during atrial diastole

Gradual increase in pressure due to filling of the atria

y waveApperas after opening of the AV valves Blood rushes to the ventriclesPressure in atria falls

Intraventricular pressure changes Maintenance of blood flow into systemic & pulmonary circulation depends upon the pressure at which the blood is pumped out of the ventricles.Right ventricle min 2-3 mm Hg max 25 mm Hg Left ventricle - min 5 mm Hg max- 120 mm Hg

Intra ventricular pressure curveA-B segmentB-C segmentC-D segmentD-E segmentE-F segmentF-G segmentG-A segment

Aortic pressure changesThe aortic pressure is responsible to maintain the blood flow through the circulating system.

PRESSURE SYSTEMIC AORTAPULMONARY ARTERYMAX PRESSURE 120 mm Hg 25 mm HgMIN PRESSURE 80 mm Hg 7-8 mm Hg

Volume of blood in right & left ventriclesMaximum volume of blood in each ventricle after filling is 150 ml .(End diastolic volume)

Minimum volume of blood after ejection period is about 70 ml . (End systolic volume)

ReferencesReview of medical physiology W.F Ganong 22nd editionText book of medical physiology guyton & hall 12th editionEssentials of medical physiology 2nd edition Sembulingam