The Cardiac Cycle Lecture Notes PDF

The Cardiac cycle Dr Hala Bagabir Dr. Ali Kabli Learning Outcomes After this lecture you should be able to: 1. Describe the cardiac cycle in terms of systole and diastole of the atria and ventricles. 2. Recognize all phases of the cardiac cycle. 3. Memorize the pressure, volume, f...

The Cardiac cycle Dr Hala Bagabir Dr. Ali Kabli Learning Outcomes After this lecture you should be able to: 1. Describe the cardiac cycle in terms of systole and diastole of the atria and ventricles. 2. Recognize all phases of the cardiac cycle. 3. Memorize the pressure, volume, flow changes and state of cardiac valves that occur during the cardiac cycle. 4. Justify phases of the cardiac cycle in relation to the ECG. 5. Predict the causes of first & second heart sounds. 6. Describe the jugular pulse curve & its relation to the phases of cardiac cycle. 7. Analyze the arterial pulse curve and the causes of dicrotic notch & wave. What is cardiac cycle? The period of time during which the heart completes one contraction (systole) and relaxation (diastole) At average HR (75 BPM) cardiac cycle is 60/75=0.8 sec Let’s make a deal Chamber 1 Chamber 2 Atrial systole (late diastole) ↑P S4 10% EDV=120 ml Atrial systole (late Isovolumetric cont. diastole) ↑P S4 S1 10% EDV=120 ↑ ↑ ↑P ml Atrial systole (late Isovolumetric cont. Rapid ejection diastole) ↑P S4 S1 10% EDV=120 ↑ ↑ ↑P ml Atrial systole (late Isovolumetric cont. Rapid ejection diastole) ↑P S4 S1 10% EDV=120 Reduced ejection ↑ ↑ ↑P ml Atrial systole (late Isovolumetric cont. Rapid ejection diastole) ↑P S4 S1 10% EDV=120 Reduced ejection ↑ ↑ ↑P ml 60 % of EDV is ejected SV=EDV-ESV EF= SV/EDV x100 70/120 x 100= 55 % S2 ↓P ESV=50 ml Isovolumetric relaxation Atrial systole (late Isovolumetric cont. Rapid ejection diastole) ↑P S4 S1 10% EDV=120 Reduced ejection ↑ ↑ ↑P ml S3 S2 ↓P ↓↓P ESV=50 ml Rapid Ventricular filling Isovolumetric relaxation  Atrial systole (late Isovolumetric cont. Rapid ejection diastole) ↑P S4 S1 10% EDV=120 Reduced ejection ↑ ↑ ↑P ml S3 S2 ESV=50 ml Reduced Ventricular filling (Ventricular Rapid Ventricular fillingIsovolumetric relaxation Diastasis)  Ventricular diastole Ventricular systole 1. Isovolumetric relaxation 1. Isovolumetric contraction 2. Rapid filling 2. Rapid ejection 3. Reduced filling 3. Reduced ejection 4. ??  0.0 sec Atrial 0.8 systole sec 0. c 1 se Atrial Ventricul Diastole ar Systole Ventricul ar Diastole 0.4 Changes in heart rate HR 75 BPM HR 200 BPM Duration of cardiac cycle 0.8 0.3 Duration of ventricular 0.3 0.15 systole Duration of ventricular 0.5 0.15 diastole Duration of cardiac cycle ↓ with ↑ HR. ↑ HR affects diastole more than the systole. The cardiac cycle (diagram) The physiological parameters of the cardiac cycle 1. Duration of each phase 2. ECG waves 3. State of cardiac valves 4. Heart sounds 5. Ventricular volume 6. Ventricular pressure 7. Atrial pressure 8. Arterial pressure  Phase 1: Atrial Systole Atrial pressure> ventricular pressure. Opening A-V valves. Incerase of ventricular volume P wave on ECG.  Phase 2: Isovolumetric contraction Ventricular pressure rise abruptly. Closure of A-V valves. 1st Heart sound. Ventricular Contraction start but no emptying occur. QRS complex on ECG.  Phase 3: Rapid ejection Ventricular pressure rise abruptly. Opening of of semilunar valves. Rapid ejection of blood (60%). Decrease of ventricular volume.  Phase 4: Reduced ejection Longer ejection period (two third of ejection time). Emptying of the remaining 30 %. Decrease of ventricular volume. T wave on ECG.  Phase 5: Isovolumetric relaxation Rapid decrease in intraventricular pressure. Increase arterial pressure (closure of semilunar valves). 2nd Heart sound. No change in venticular volume.  Phase 6: Rapid filling Atrial pressure> ventricular pressure. Opening A-V valves. Increase in ventricular volume.  Phase 7: Reduced filling Last two third of diastole period. Responsible for 10-20% of venticular filling by The atrial contraction Intracardiac pressure Ventricular pressure-volume relationship Right Atrial Pressure Curve and Jugular Venous Pulse (JVP) a: atrial contraction c: bulged tricuspid valve during isovolumetric contraction x: downward pull of the AV ring during rapid ejection phase Aortic pressure curve Systolic arterial BP Diastolic arterial BP Dicrotic notch: sharp drop of pressure and sudden closure of the aortic valve Dicrotic wave: bouncing up of the blood against the closed aortic valve Test you understanding True or false: Atria and ventricles contract at the same time. All valves are closed in the isovolumic relaxation phase. In the rapid ejection phase, ventricular pressure exceeds aortic pressure. Ventricular repolarization (T- wave) occur in the reduced ejection phase. Ventricular volume decreased rapidly during the rapid filling phase. a wave of atrial pressure is due to venous return. References 1. Cardiovascular Physiology Concepts, second edition, Richard E. Klabunde.