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- 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.
- 2. Cardiac cycle: 2 period of relaxation period of contraction Cardiac cycle diastole systole
- 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
- 11. Diastole: 11 Isovolumic (isometric) ventricular relaxation Rapid vent. Filling Diastasis Atrial Contraction
- 13. 13 diastole 0.62 sec systole 0.3 sec More time for filling of the ventricle More time for relaxation of the coronary arteries
- 14. 14 pressure(mmHg) Volume (ml) 120 80 0 50 120 40 Diastolic filling IVC Ejection IVR SV Mitral v open Aortic v open Aortic v close Mitral v close The pressure – volume loop EDV ESV A B C D
Notas del editor
- 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