Cardiac cycle Physiology

Mbbs Lecture

1. Cardiac cycle

2. Cardiac cycle Describing the sequence of events in one heart beat

3. CARDIAC CYCLE Cardiac events that occur from the beginning of one heart beat to the beginning of the next is called C Cycle. TIME OF ONE CYCLE : O.8 SECONDS So, 75 beats x 0.8 = 60 seconds or 1 mnt . MECHANICAL & ELECTRICAL EVENTS DIASTOLE SYSTOLE

4. Cardiac cycle

5. Cardiac cycle The 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. AP → Atria → A – V bundles → Ventricles. AV Delay - .1 sec Diastole: Period of relaxation – heart fills with blood. Systole: Period of contraction – heart pumps the blood.

6. Cardiac cycle Contraction of the myocardium generates pressure changes which result in the orderly movement of blood. Blood flows from an area of high pressure to an area of low pressure , unless flow is blocked by a valve. Events on the right and left sides of the heart are the same, but pressures are lower on the right.

7. Diastole systole Blood ejected to aorta and pulmonary trunk Blood comes to ventricles through AV valve from atria

8. Valves open passively & close actively due to pressure gradients AV valves open when P in atria > P in ventricles AV valves close when P in ventricles > P in atria Semilunar valves open when P in ventricles > P in arteries Semilunar valves close when P in arteries > P in ventricles

9. Cardiac cycle Normal average HR 75 bpm. Duration of each cardiac cycle is 60/75=0.8 sec Atrial cycle: Atrial systole – 0.1 sec Atrial diastole – 0.7 sec Ventricular cycle: Ventricular systole (0.3 sec) Isovolumic contraction – 0.05 sec Ventricular ejection: rapid ejection – 0.1 sec, slow ejection – 0.15 sec Ventricular diastole (0.5 sec) Protodiastole - 0.04 sec Isovolumic relaxation – 0.06 sec Rapid passive filling – 0.11 sec Reduced filling (diastasis) – 0.19 sec Last rapid filling – 0.1 sec

10. ATRIAL SYSTOLE The end of diastole

11. ATRIAL SYSTOLE - Heart Prior to atrial systole, blood has been flowing passively from the atrium into the ventricle through the open AV valve. Contraction of atria propels some additional blood into the ventricles. Atrial contraction is complete before the ventricle begins to contract.

12. ATRIAL SYSTOLE Pressures & Volumes The "a" wave occurs when the atrium contracts, increasing atrial pressure (yellow). Blood arriving at the heart cannot enter the atrium so it flows back up the jugular vein, causing the first discernible wave in the jugular venous pulse. Atrial pressure drops when the atria stop contracting.

13. ATRIAL SYSTOLE 1 Function of Atria as primer pumps : 80 % of Blood directly flows in 20 % of blood by Atrial Contraction ATRIAL PRESSURE ELEVATION WAVES a – wave c – wave v – wave a – wave = atrial contraction and the Pressure from 4 -6 goes up to 7-8 mmHg c- wave = ventricular contraction bulging of AV Valves. v – wave = end of ventricular contraction flow blood from veins to atria.

14. ISOVOLUMETRIC CONTRACTION The Beginning of systole

15. Ventricular systole Isovolumic contraction: Immediately after ventricular contraction begins, the ventricular pressure rises abruptly , causing the A-V valves to close . A n additional 0.02 to 0.03 second is required for the ventricle to build up sufficient pressure to push the semilunar valves open against the pressures in the aorta and pulmonary artery . Therefore , during this period , contraction is occurring in the ventricles , but there is no emptying. This is called the period of isovolumic or isometric contraction, meaning that tension is increasing in the muscle but little or no shortening of the muscle fibers is occurring.

16. 2 ISOVOLUMETRIC VENTRICULAR CONTRACTION ISOVOLUMIC + ISOMETRIC = ISOVOLUMETRIC Ventricular pressure rises abruptly causing AV VALVES closes. Then additional 0.02 -0.03 seconds Required for the ventricle to build Sufficient pressure to push aortic , pulmo . Valves. Therefore this period is called Iso Vol. contraction meaning –tension is building up with no shortening of muscle

17. Ventricular systole Ventricular Ejection: When the left ventricular pressure rises slightly above 80 mm Hg and the right ventricular pressure slightly above 8 mm Hg, the ventricular pressures push the semilunar valves open. Immediately, blood begins to pour out of the ventricles, with about 70 per cent of the blood emptying occurring during the first third of the period of ejection - and the period of rapid ejection. R emaining 30 per cent emptying during the next two thirds – the period of slow ejection.

18. 3 Ventricular pressure raises above to 8 and 80 mm Hg in RV & LV . PERIOD OF RAPID EJECTION PERIOD OF SLOW EJECTION VENTRICULAR EJECTION FIRST -- RAPID 1/3 - 70 % SECOND – SLOW 2/3 - 30 %

19. REDUCED EJECTION The end of systole

20. REDUCED EJECTION Heart At the end of this phase the semilunar (aortic and pulmonary) valves close.

21. REDUCED EJECTION Pressures & Volumes After the peak in ventricular and arterial pressures (red and green), blood flow out of the ventricles decreases and ventricular volume decreases more slowly (white). When the pressure in the ventricles falls below the pressure in the arteries, blood in the arteries begins to flow back toward the ventricles and causes the semilunar valves to close. This marks the end of ventricular systole mechanically.

22. Ventricular Diastole Protodiastole: Once the ventricular muscle is fully contracted, the already falling ventricular pressures drop more rapidly . The elevated pressures in the distended large arteries that have just been filled with blood from the contracted ventricles immediately push blood back toward the ventricles, which snaps the aortic and pulmonary valves closed. Isovolumic relaxation: At the end of systole , ventricular relaxation begins suddenly, allowing both the right and left intraventricular pressures to decrease rapidly. For another 0.03 to 0.06 second, the ventricular muscle continues to relax , even though the ventricular volume does not change , giving rise to the period of isovolumic or isometric relaxation . During this period, the intraventricular pressures decrease rapidly back to their low diastolic levels. Then the A-V valves open to begin a new cycle of ventricular pumping.

23. ISOVOLUMETRIC RELAXATION The beginning of Diastole

24. ISOVOLUMETRIC RELAXATION Heart At the beginning of this phase the AV valves are closed.

25. 4 ISOVOLUMETRIC VENTRICULAR RELAXATION DIASTOLE Intra ventricular pressure drops at the end Of the ventricular systole. Aorta, Pulm . Artery snaps back blood and Aortic, pulmonary valves closes . For about 0.03 to 0.06 seconds ventricular muscle relaxes even though ventricular volume does not change giving rise to Isovolumetric relaxation.

26. During this period intra ventricular pressure decreases rapidly back to their low diastolic levels. Then the AV Valves open to begin a new cycle of Ventricular pumping.

27. ISOVOLUMETRIC RELAXATION Pressures & Volumes Throughout this and the previous two phases, the atrium in diastole has been filling with blood on top of the closed AV valve, causing atrial pressure to rise gradually (yellow). The "v" wave is due to the back flow of blood after it hits the closed AV valve. It is the second discernible wave of the jugular venous pulse. The pressure in the ventricles (red) continues to drop. Ventricular volume (white) is at a minimum and is ready to be filled again with blood.

28. RAPID VENTRICULAR FILLING Heart Once the AV valves open, blood that has accumulated in the atria flows rapidly into the ventricles.

29. RAPID VENTRICULAR FILLING Pressures & Volumes Ventricular volume (white) increases rapidly as blood flows from the atria into the ventricles.

30. Ventricular volume (white) increases more slowly now. The ventricles continue to fill with blood until they are nearly full.

31. Ventricular Diastole Rapid passive 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 again, 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 - the rise of the left ventricular volume curve. (70% approx.) Reduced filling (diastasis ): During the middle third of diastole, only a small amount of blood normally flows into the ventricles that continues to empty into the atria from the veins and passes through the atria directly into the ventricles . (20% approx.) Last rapid filling: 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 10 per cent of the filling of the ventricles. (10% approx. - atrial kick)

32. Length Cardiac muscle has the unique property of contracting and repolarizing faster when the heart rate is high and the duration of systole decreases from 0.3 s at a heart rate of 65 to 0.16 s at a rate of 200 beats/min. T he duration of systole is much more fixed than that of diastole, and when the heart rate is increased, diastole is shortened to a much greater degree. This fact has important physiologic and clinical implications. It is during diastole that the heart muscle rests, and coronary blood flow to the subendocardial portions of the left ventricle occurs only during diastole. M ost of the ventricular filling occurs in diastole. At heart rates up to about 180, filling is adequate as long as there is sufficient venous return , and cardiac output per minute is increased by an increase in rate. However , at very high heart rates, filling may be compromised to such a degree that cardiac output per minute falls and symptoms of heart failure develop.

33. LEFT VENTRICULAR PRESSURE/VOLUME P/V LOOP LEFT VENTRICULAR PRESSURE (mmHg) LEFT VENTRICULAR VOLUME (ml) A B C D E F 100 150 50 120 40 80

34. 2 ） Pressure changes in the atria, the a , c , and v waves. a wave, the atrial contraction c wave, bulging of the A-V valves when the ventricles begin to contract

35. v wave, at the end of ventricle contraction, caused by the accumulated blood in the atria while the A-V valves are closed

36. The sounds heard over the cardiac region produced by the functioning of the heart. Heart Sounds

37. Heart Sounds S1- first sound Atrioventricular valves and surrounding fluid vibrations as valves close at beginning of ventricular systole

38. S2- second sound closure of aortic and pulmonary semilunar valves at beginning of ventricular diastole S3- third sound vibrations of the ventricular walls when suddenly distended by the rush of blood from the atria

39. CARDIAC CYCLE Atrial Systole Mitral Closes Isovolumic contract . Aortic opens S 1 Rapid Ejection Reduced Ejection Isovolumic Relax. Aortic closes Rapid Ventricular Filling Mitral opens S 2 Reduced Ventricular Filling Atrial Systole : >O : >D