1. The cardiac cycle
Objectives:
1) To list the phases of the cardiac cycle in consecutive order.
2) To recognize that pressure changes determine valve action
& direction of blood flow through the heart.
3) Explain the basis of the arterial pulse and heart sounds.
4)To relate an ECG & heart sounds to events of the cardiac
cycle.
3. Stages of card. Cycle :-
3
Ventricles are
relaxed
AV Valves are close
Atria are relaxed
Semilunar valves
are closed
1. Vent filling
a. rapidVent filling
AV Valves opened
4. Stages of card. Cycle :-
4
Ventricles are
relaxed
AV Valves are open
Atria are relaxed
Semilunar valves
are closed
b. diastasis
5. 20% of
ventricular
filling
Stages of cardiac Cycle :-
5
Ventricles are
relaxed
AV Valves are open
Contraction of Atria
Semilunar valves
are closed
c. Atrial systole.
6. Stages of cardiac Cycle :-
6
Contraction of
Ventricles
AV Valves are
closed
Semilunar valves
are closed
2. Isovolumic (isometric) ventricular contraction
7. Stages of cardiac Cycle :-
7
Contraction of
Ventricles
AV Valves are
closed
Semilunar valves
opened
3. Ejection phase
8. The volume of blood in the ventricle at the end of the
systole
EDV ESV SV
8
E.D.V.
E.S.V.
S.V
The volume of blood in the ventricle at the end of the
diastole (just before ventricular systole started)
End diastolic volume
End systolic volume
The volume of blood ejected per one beat
Stroke volume
↑EDV→↑SV
↓SV → ↑ ESV
Normally about 70 ml at rest
9. 9
E.F
It is the percentage of volume of blood which is ejected
from the E.D.V.
Ejection fraction
E.F= SV ×100%
EDV
What is the ejection fraction of a left ventricle with EDV of
150ml and SV of 75 ml
E.F= SV ×100%
EDV
= 75 ×100%= 50%
150
Normally about 65%
10. Stages of cardiac Cycle :-
10
Relaxation of
Ventricles
AV Valves are
closed
Semilunar valves
closed
4. Isovolumic (isometric) ventricular Relaxation
The cardiac events that occur from the beginning of one heartbeat to the beginning of the next are called the cardiac cycle.
The cardiac cycle consists of a period of relaxation called diastole, during which the heart fills with blood, followed by a period of contraction called systole.
Filling of the Ventricles.
Rapid ventricular filling: During ventricular systole, large amounts of blood accumulate in the right and left atria because of the closed A-V valves. Therefore, as soon as systole is over and the ventricular pressures fall, the moderately increased pressures that have developed in the atria during ventricular systole immediately push the A-V valves open and allow blood to flow rapidly into the ventricles. This is called the period of rapid filling of the ventricles. The period of rapid filling lasts for about the first third of diastole.
b. Diastasis : During the middle third of diastole only a small amount of blood normally flows into the ventricles; this is blood that continues to empty into the atria from the veins and passes through the atria directly into the ventricles.
c. Atrial systole: During the last third of diastole, the atria contract and give an additional thrust to the inflow of blood
into the ventricles; this accounts for about 20 per cent of the filling of the ventricles during each heart cycle
Isovolumic (isometric) ventricular contraction:
The ventricle will contract on the same volume of blood→↑Pr. In the ventricle. When the Pr. In the left ventricle exceeds the Pr. Of the aorta (80 mmHg ) and the Pr. Of the right ventricle exceeds the Pr. of pulmonary artery (10 mmHg) Ejection phase start
Ejection phase :
The blood will be ejected to the arteries. The Pr. in the aorta =120 mmHg and Pr. in the pulmonary artery= 25 mmHg
Isovolumic or isometric ventricular relaxation.
the ventricle is going to relax on constant volume <<<<<decreases Pr. In the ventricle
Isovolumetric relaxation ends when the ventricular pressure falls below the atrial pressure
and the AV valves open, permitting the ventricles to fill
Duration of systole &diastole
Period of diastole of ventricles = 0.62 sec .
Period of systole of ventricles = 0.3 sec.
Diastolic Period is longer ALLOWING :-
1. More time for filling of the ventricle.
2. More time for relaxation of the coronary arteries→ ↑ blood supply to the ventricular muscle
The pressure – volume loop
• It is the relation between ventricular volume and pressure
It is composed of 4 phases:
Phase I: Period of vent filling.
Phase I in the volume-pressure diagram begins at a ventricular volume of about 50 milliliters and a pressure of 2 to 3 mm Hg. The amount of blood that remains in the ventricle after the previous heartbeat, 50 milliliters, is called the end-systolic volume. As venous blood flows into the ventricle from the left atrium, the ventricular volume normally increases to about 120 milliliters, called the end-diastolic volume, an increase of 70 milliliters. Therefore, the volume-pressure diagram during phase I extends along the line from point A to point B with the volume increasing to 120 milliliters and the diastolic pressure rising to about 5 to 7 mm Hg.
Phase II: Period of isovolumic contraction.
During isovolumic contraction, the volume of the ventricle does not change because all valves are closed. However, the pressure inside the ventricle increases to equal the pressure in the aorta, at a pressure value of about 80 mm Hg (point C)
Phase III: Period of ejection.
During ejection, the systolic pressure rises even higher because of still more contraction of the ventricle. At the same time, the volume of the ventricle decreases because the aortic valve has now opened and blood flows out of the ventricle into the aorta.
Phase IV: Period of isovolumic relaxation.
At the end of the period of ejection (point D) the aortic valve closes and the ventricular pressure falls back without any change in volume. Thus, the ventricle volume returns to its starting point, with about 50 milliliters of blood left in the ventricle and at an atrial pressure of 2-3 mm Hg
