Cardiac Cycle Lecture Notes PDF

Cardiac cycle By Prof. Amr Medhat Abbas Professor of Medical Physiology  Learning outcomes: At the end of the lecture, you will be able to: 1. Explain the changes in ventricular pressure, aortic pressure and atrial pressure in all phases of the cardiac cycle. 2. Explain...

Cardiac cycle By Prof. Amr Medhat Abbas Professor of Medical Physiology  Learning outcomes: At the end of the lecture, you will be able to: 1. Explain the changes in ventricular pressure, aortic pressure and atrial pressure in all phases of the cardiac cycle. 2. Explain the changes in ventricular volume in all phases of the cardiac cycle. 3. Explain the changes in cardiac valves and heart sounds in all phases of the cardiac cycle.  Cardiac cycle Def: Cardiac events that occur from the beginning of one heart beat to the beginning of the next beat. Consists of: period of contraction (systole) & period of relaxation (diastole). Duration: 0.8 second (heart rate: 75/min). Systole Diastole Atria 0.1 sec 0.7 sec Ventricle 0.3 sec 0.5 sec Whole heart - 0.4 sec  Phases of the cardiac cycle The phases of cardiac cycle Ventricular systole Ventricular diastole are: 1- Atrial systole. Isometric contraction phase Isometric relaxation phase 2- Ventricular systole Maximum 3- protodiastolic phase. ejection phase Rapid filling phase 4- ventricular diastole. Reduced Reduced ejection ejection phase phase  Events in the cardiac cycle 1- Pressures: a. Atrial pressure. b. Ventricular pressure c. Aortic pressure 2- Ventricular volume. 3- Valves 4- Heart sounds.. 5- ECG 6- Duration  Atrial systole phase Atrial depolarization (P wave of ECG)  atrial contraction  atrial pressure   rush of blood into the ventricles through the open AV valves (semilunar valves are closed)  4th heart sound (not audible,) + slight  ventricular pressure & ventricular volume. Arterial pressure  because blood is going to the tissues.  Atrial systole 1. Duration: 0.1 sec. 2. Atrial P:  from 0 to 2 mmHg then  again. 3. Ventricular pressure:  slightly due to rush of blood from atria, then  again as the ventricles are still relaxed. 4. Ventricular volume:  due to entry of blood from atrium to ventricle. 5. Aortic pressure:  gradually due to continuous flow of blood into peripheral circulation. 6. Valves: A-V valves opened, S.L. valves closed 7. Heart sounds: S4 8. ECG: P wave.  Isometric contraction phase Ventricular depolarization  QRS wave of ECG  ventricular contraction   ventricular pressure more than the atrial pressure  sudden closure of the AV valves  1st heart sound and atrial pressure (due to ballooning of cusps of AV valves towards the atrium). All valves are closed  no change in the ventricular volume (isovolumetric, isometric)  aortic pressure still  (because blood is going to the tissues) (reach diastolic pressure; aortic pressure=80 mmHg).  Isometric contraction phase 1. Duration: 0.05 sec. 2. Atrial P: ↑ slightly due sudden closure of A-V valves  ballooning of cusps of AVV toward the atrium. 3. Ventricular pressure: ↑ from 0 to 80 mmHg and the ventricle is a closed chamber. 4. Aortic pressure:  to reaches its lowest value (diastolic bl.p.)= 80 mmHg due to continuous flow of blood into peripheral circulation. 5. Ventricular volume: kept constant. 6. Valves: A-V valves closed, S.L. valves closed 7. Heart sounds: early part of S1 8. ECG: QRS.  Maximum ejection phase Continuous ventricular contraction   ventricular volume rapidly  ↑ ventricular pressure  open the semilunar valves (AV valves remain closed)  rush of blood into the aorta  ↑arterial pressure (from diastolic value =80 mm Hg to systolic value 120 mmHg in the left side) and continued 1st heart sound. Atrial pressure:  (due to pulling down of the AV ring), then gradual  (due to blood coming from veins & Upward displacement of AV ring to its normal position). ECG: T wave (ventricular repolarization) starts at the end of this phase  Maximum ejection phase 1. Duration: 0.15 sec. 2. Atrial P:  with downward displacement of the AV ring then  due to upward displacement of the AV ring & accumulation of blood in atria. 3. Ventricular pressure:  to 130 mmHg in left ventricle, due to ventricular contraction. 4. Aortic pressure:  to reaches its highest value (systolic B.P.) = 120 mmHg due to opening of the aortic valve & ejection of blood from LV to aorta 5. Ventricular volume:  due to ejection of most of blood from LV into aorta. 6. Valves: A-V valves closed, S.L. valves opened 7. Heart sounds: late part of S1 due to continuous blood flow into aorta. 8. ECG: T wave starts at the late part of this phase.  Reduced ejection phase The ejection of blood continues but at a slower rate through the opened semilunar valves (AV valves still closed)  ventricular volume still   ventricular pressure slightly   arterial pressure slightly  (because blood leaving the arteries is more than that pumped into the arteries). Atrial pressure  due to continuous accumulation of blood from veins into the atria. ECG: Top of T wave No heart sound.  Reduced ejection phase 1. Duration: 0.1 sec. 2. Atrial P: slightly due to accumulation of venous return from veins into the atria. 3. Ventricular pressure:  slightly due to  force of contraction. 4. Aortic pressure:  slightly because blood escape to tissues is more than that pumped into aorta. 5. Ventricular volume: still . 6. Valves: A-V valves closed, S.L. valves opened 7. Heart sounds: no Sounds. 8. ECG: Top of T wave.  Protodiastole phase It is the period between end of ventricular systole & closure of semilunar valves. 1. Duration: 0.04 sec. 2. Atrial P: still  due to continuous accumulation of venous return from veins into the atria. 3. Ventricular pressure:  rapidly till it becomes just equal to aortic or pulmonary pressure. 4. Aortic pressure:  slightly to become equal to left ventricular pressure. 5. Ventricular volume: Remains constant. 6. Valves: A-V valves closed, S.L. valves opened 7. Heart sounds: no Sounds. 8. ECG: Descending limb of T wave.  Isometric relaxation phase Ventricular repolarization (end of T wave of ECG)  ventricular relaxation   ventricular pressure (falls to zero)  sudden closure of semilunar valves  2nd heart sound and initial  of aortic pressure (diacrotic notch) then  (due to elastic recoil) (diacrotic wave). All valves are closed  closed chamber  no change in ventricular volume (isometric relaxation) Atrial P: still  due to continuous accumulation of venous return from veins into the atria.  Isometric relaxation phase 1. Duration: 0.06 sec. 2. Atrial P:still  due to accumulation of venous return. 3. Ventricular pressure:  suddenly to 0 mmHg with closure of SL valves and the ventricle is a relaxed closed chamber. 4. Aortic pressure:  due to closure of the aortic valve (diacrotic notch) then  due to elastic recoil of the aorta (diacrotic wave). 5. Ventricular volume: constant. 6. Valves: A-V valves closed, S.L. valves closed. 7. Heart sounds: S2. 8. ECG: End of T wave.  Rapid filling phase At the beginning of this phase, atrial pressure is more than ventricular pr  opening of AV valve & rushing of blood by its weight into relaxed ventricle   atrial pressure +  ventricular volume + 3rd heart sound. Aortic pressure gradually  due to continuous escape of blood to peripheral circulation (semilunar valve is closed & no ejection of blood).  Rapid filling phase 1. Duration: 0.2 sec. 2. Atrial P: At the beginning of this phase, atrial pr is more than ventricular pr  opening of AV valve & rushing of bl by its weight into ventricle   atrial pressure. 3. Ventricular pressure: around 0. 4. Aortic pressure: Gradually  due to continuous escape of bl to peripheral circ. 5. Ventricular volume: Marked  due to rapid ventricular filling with blood from atria. 6. Valves: A-V valves opened , S.L. valves closed. 7. Heart sounds: S3. 8. ECG: U wave.  Reduced filling phase Because the atrial pressure is still more than ventricular pressure  blood continues to flow from atria into the relaxed ventricle but at a slower rate through the opened AV valves (semilunar valves are still closed)   ventricular volume + no heart sound. Aortic pressure gradually  due to continuous escape of blood to peripheral circulation (semilunar valve is closed & no ejection of blood). ECG: P wave (atrial depolarization) starts at end of this phase (for next cardiac cycle).  Reduced filling phase 1. Duration: 0.1 sec. 2. Atrial P: around 0 3. Ventricular pressure: around 0. 4. Aortic pressure: still  due to continuous escape of bl to peripheral circulation 5. Ventricular volume: . 6. Valves: A-V valves opened , S.L. valves closed. 7. Heart sounds: no sounds. 8. ECG: no change.  Important notes Ventricular filling: * 30% of blood passes actively during atrial systole. * 70% of blood passes passively during ventricular diastole (50% in rapid filling phase & 20% in Reduced filling phase). Pressures: Systolic pressure Diastolic pressure Left ventricle 130 0 Aorta 120 80 Right ventricle 35 0 Pulmonary artery 30 10  References 1. Costanzo, Linda S. "BRS Physiology (Board Review Series)." (2018). 2. Ganong, William F. "Review of medical physiology." (2020).