The document summarizes the cardiac cycle, including: (1) It describes the four main events - atrial systole, ventricular systole, ventricular diastole, and atrial diastole. (2) It outlines the pressure and blood flow changes that occur in the heart chambers and valves during each phase of the cycle. (3) It examines the corresponding electrocardiogram changes and heart sounds that occur with each phase of the cardiac cycle.

1. Shama Praveen
Department of physiology
Cardiac Cycle

2. Definition
Events in Cardiac Cycle
(a) Atrial systole
(b) Ventricular systole
(c) Ventricular diastole
(d) Atrial diastole
Atrial pressure changes
during cardiac cycle- JVP
Record
ECG changes during cardiac
cycle
Objectives

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Definition
The sequence of changes in the pressure
and blood flow in the CVS in between the
two subsequent cardiac contractions is
known as cardiac cycle.
Duration of a cycle- 0.8 sec

4. Events in the cardiac cycle
 All 4 chambers are relaxed and filled with blood due to venous return.
 AV valves are open atrium and ventricle of each side are in continuity and the pressure in each
cavity is almost identical.
 Events :
 ATRIAL SYSTOLE,
 ATRIAL DIASTOLE,
 VENTRICULAR SYSTOLE &
 VENTRICULAR DIASTOLE.

5. Atrial Systole
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• Contraction phase (0.1 sec)
Contraction of atria propels some additional blood
into ventricles (approx. 30ml).
 its contraction narrows orifices of superior and
inferior vena cava and pulmonary veins and the
inertia of blood moving towards the heart tends to
keep blood in it.
Right atrial pressure-4-6 mmHg
Left atrial pressure- 7-8mmHg

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VENTRICULAR SYSTOLE
 2 major phases:
Isovolumetric ventricular contraction(0.05 sec):
 As the atrial contraction phase passes off, ventricular contraction begins and ventricular pressure
rises above atrial pressure very rapidly causing closure of the A-V valves with production of the first
heart sound (HS1)
 Intraventricular pressure rises sharply as the myocardium presses on the blood in the ventricle.
 0.05 sec until pressure in right and left ventricles exceeds the pressure in aorta (80mmHg) and
pulmonary artery (10mmHg) and get opened.
 During this phase, AV valves bulge into atria, causing a small but sharp rise in atrial pressure.
 During this phase, although contraction is occurring in the ventricles but there is no emptying;
therefore it is called isovolumetric ventricular contraction.

7.  Ventricular systole proper
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 Duration: 0.25.
 Associated with ejection of blood out of ventricles.
 Opening of semilunar valves occurs.
 This opening follows ejection phase. This phase is subdivided into 3 divisions:
 Initial phase: Rapid Ejection phase (0.1sec)
 The intraventricular pressure rises to maximum (LV:120mmHg, RV<25mmHg) causing rapid
increase in the output of ventricular volume.
 Approx.2/3 of the stroke volume is ejected.
 Summit : Curve is reached when aortic or pulmonary artery pressure actually
rises above ventricular pressure.
 Final phase: Slow ejection phase(0.15sec)
 The ventricular pressure decreases as the ventricular contraction begins to subside with slow
ejection.
 The AV valves pulled down by contractions of the ventricular muscle and atrial pressure drops.
 EDV – 130ml, at the end of systole ESV- 50ml
 Ejection fraction: Percentage of EDV that is ejected with each heartbeat is called ejection fraction.
Valuable measure of ventricular function.

8. ROWAN MURPHY ELIZABETH MOORE

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10. Ventricular diastole
PROTODIASTOLE: 0.04SEC
ISOVOLUMETRIC
VENTRICULAR RELAXATION
PHASE: 0.08SEC
VENTRICULAR DIASTOLE
PROPER; 0.28SEC
LAST RAPID FILLING PHASE
DUE TO ATRIAL SYSTOLE:
0.1SEC

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o The arterial pressure is better sustained
due to elastic recoil of the vessel wall and
immediately the arterial pressure
increases that in the ventricle. This results
in closure of semilunar valves, causing
sharp second heart sound
ISOVOLUMETRIC VENTRICULAR RELAXATION:
(0.08SEC)
o Begins with closure of semilunar valves.
o Intraventricular pressure continues to drop rapidly
without change in ventricular volume.
o it ends when ventricular pressure falls below the
atrial pressure resulting in the opening of AV
valves.
Protodiastole 0.04sec

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o Approx. 70% of ventricular filling occurs passively during this phase.
o It has 2 divisions:
 Initially rapid filling:
 By opening of AV valves and it occurs for 0.1-0.12sec.
 Pressure in ventricles remain low
 Finally, slow filling:
 Called diastasis
 It is due to continuous venous return filling both atrium and
ventricle.
o Due to atrial systole
 LAST RAPID FILLING PHASE
VENTRICULAR DIASTOLE PROPER
ATRIAL DIASTOLE (0.7sec)
 Atrial muscle relax n atrial pressure gradually increases due to continuous venous
return to drop to almost zero mmHg with the opening of AV valves.
 Pressure rises again during the phase of diastasis and follows ventricular pressure.

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Pressure-
volume loop of
the left
ventricles.

15. The pressure wave expands the arterial walls as blood travels
and the expansion is palpable as the pulse.
The strength of the pulse is determined by the pulse pressure
and bears
Little relation to the mean pressure.
The dicrotic notch, a small oscillation on the falling phase of the
pulse wave caused by vibrations set up when the aortic valve
snaps shut, is visible if the pressure wave is recorded but is not
palpable at the wrist.
The pulmonary artery pressure curve also has a dicrotic notch
produced by the closure of pulmonary valve.
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Arterial pulse

16. There is no valve at the junction of the superior vena cava
and the right atrium, therefore right atrial pressure are
transmitted to the jugular vein the neck, producing 3
characteristic waves
1. ‘a wave’ :due to atrial systole
2. ‘c wave’ : By bulging of tricuspid valve into right
atriumduring isovolumetric ventricular contraction phase.
3. ‘v wave’ : Due to rise in atrial pressure before tricuspid
valve opens during diastole
Absence of c wave indicate incompetent tricuspid valve.
Therefore, blood will flow from right ventricle into RA during
ventricular systole. This is associated with turbulence of
blood flow (called murmur).
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Jugular venous pressure record

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18. Record of electrical changes generated
with each heart beat.
 ‘p’ wave- due to atrial depolarization and
occurs before atrial systole.
 ‘Q’ ‘R’ & ‘S’ waves together constitute
the QRS complex and due to ventricular
depolarization. It occurs before
ventricular systole.
 ‘T’ wave is due to ventricular
repolarization . It co-exists with closure
of semilunar valves.
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ECG changes during cardiac cycle

19.  HS1: Due to closure of AV valves and marks onset of ventricular systole.
 Low pitch, frequency:30-40/sec, producing a loud sound. (LUBB)
 Best heard over mitral and tricuspid areas.
 It coexists with R wave of ECG
o HS2: Due to closure of semilunar valve and marks onset of ventricular diastole.
o High pitch, frequency: 150-200/sec, producing a sharp sound. (DUP)
o Best heard over pulmonary aortic areas.
o It co-exists with the end of T wave of ECG.
 HS3: Due to vibrations of the cardiac walls produced by the rapid filling phase of the ventricles
during ventricular diastole proper.
 HS4: Due to atrial systole, characterized by low frequency and low amplitude.
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Heart sounds

20. thank you