Cardiac Cycle Genesis and Events 2023 PDF

Genesis and events of the Cardiac cycle K Thaxter Nesbeth Physiology Section Basic Medical Sciences  Objectives: You will Know about phases of cardiac cycle Understand the volume and pressure changes during the cardiac cycle  Ca...

Genesis and events of the Cardiac cycle K Thaxter Nesbeth Physiology Section Basic Medical Sciences  Objectives: You will Know about phases of cardiac cycle Understand the volume and pressure changes during the cardiac cycle  Cardiac cycle ❑ Two phases: ❑ Systole (contraction/emptying)& diastole(relaxation /filling ) ❑ Contraction results from spread of excitation across the heart ❑ Relaxation follows subsequent repolarisation of cardiac musculature.  CARDIAC CYCLE Cardiac cycle time : 0.8 second when heart rate is 75 beats per minute. Atria and Ventricle go through separate cycles of systole and diastole. When we use the term Systole and Diastole, we refer to ventricles, until unless specified for atria.  Atrial Systole Semilunar valves closed AV valves opened ❑ Caused by atrial depolarization ❑ Ventricles are relaxed ❑ AV valves are open because pressure in atria is greater then ventricular pressure  Atrial Systole Semilunar valves closed AV valves opened ❑ Ventricles were passively filling with blood prior to atrial systole ❑ Atrial systole causes further increase in ventricular volume (final 10-30% of blood volume in ventricle) ❑ Through out atrial contraction atrial pressure exceeds ventricular pressure so AV valves remain open  Atrial Systole Semilunar valves closed AV valves opened ❑ Ends with ventricles maximally filled with blood ❑ = End diastolic volume = 120ml ❑ Atrial pressures fall after systole ❑ May produce heart sound S4 during atrial contraction as it causes the ventricular wall to vibrate if ventricle is ‘stiff’  Isovolumetric ventricular contraction Initiated by QRS complex = ventricular depolarisation ❑Myocytes contract, causing rapid increase in ventricular pressure ❑Causes closure of mitral and tricuspid valves ❑cause heart sound (S1) ❑S1 may be split as closure of mitral preceded closure of tricuspid ❑Papillary muscles contract and pull chordae tendinae, keeping AV valves closed  Isovolumetric ventricular contraction Myocyte contraction leads to rapid rise in pressure No change in ventricular volume as all valves are closed  Ventricular Systole: rapid ejection Aortic and pulmonary Aortic and valves closed pulmonary valves open Mitral and tricuspid valves AV valves closed closed Pressures in ventricles exceed aortic and pulmonary artery pressures Blood flows into arteries rapidly, then with reduced velocity Ventricular volumes decreased  Isovolumetric ventricular relaxation ❑ Ventricles begin to relax after rapid ejection phase ❑ Intraventricular pressures Semilunar fall to below aortic and valves pulmonary artery pressures closed ❑ Aortic and pulmonary AV valves valves close closed ❑ = Second heart sound (S2)  Isovolumetric ventricular relaxation – when semilunar valves closes AV valves is not yet open because pressure in ventricles still exceeds that of atria. Semilunar valves – All valves again closed for closed short period of time when ventricles are relaxing AV – Constant ventricular valves volume closed – End systolic volume = vol. of blood remaining in a ventricle – = 50ml in left ventricle  Rapid ventricular filling ❑ Ventricles continue to relax (after repolarisation) ❑ Ventricular pressures fall below atrial and pulmonary artery pressures ❑ Atria maximally filled Semilunar valves (passively via venous return) closed ❑ Mitral and tricuspid valves open AV ❑ Rapid inflow of blood valves opened ❑ May hear heart sound S3  Reduced filling of ventricles Corresponds with atrial systole (contributes to 20-30% of ventricular filling) Intraventricular Semilunar pressures rise with valves volume increase closed Aortic and pulmonary AV artery pressures fall as valves blood moves further opened into circulation Cycle continues  Movie time! http://www.wiley.com/college/interactions /Distribution/content/Distribution/cardio2 a/frameset2.htm  Part 2: Pressure and Volume changes during the cardiac cycle Wiggers Diagram  Cardiac Pressures Pressures on right side of heart much lower than left Aids blood flow Rt- Atrium = 0-8mm Hg. Lt- Atrium = 2-10 mm Hg. Rt – Ventricle = 25 / 6(2-8) mm Hg. Lt – ventricle = 120 / 8(2-10) mm Hg. Aorta = 120 / 80 mm Hg. Pul. Artery = 25 / 10 mm Hg. Pressure changes during cardiac cycle 19 Atrial pressure waves  a wave: Atrial contraction c wave: Ventricular contraction/systole causes the A-V valve to bulge upward and increases intra-atrial pressure v wave: peak of passive filling of the atria – (very full atria) opening of the AV valve leads to the fall in pressure after the v-wave peak  Ventricular pressures LV end-diastolic pressure = 8-12 mmHg RV end-diastolic pressure = 3-6 mmHg Aortic pressure  Volume changes: Important terms and definitions Stroke Volume: Volume of blood pumped out by each ventricle per beat. It is about 70 - 80 ml. Stroke volume (SV) = EDV – ESV End Diastolic Volume: Volume of blood in each ventricle at the end of diastole. It is about 120 – 130 ml. End Systolic Volume: Volume of blood in each ventricle at the end of Systole. It is about 50 to 60 ml  Ejection fraction (EF) is the percentage of ventricular end diastolic volume (EDV) which is ejected with each stroke. SV EF = X 100 EDV 75 X 100 = 62.5% 120 Normal ejection fraction is about 60 – 65 %. Ejection fraction is good index of ventricular function.  Tachycardia, Effect on Cardiac Cycle During tachycardia, when heart rate is increased, both systole and diastole time decreases. Diastole length (time) is shortened much more than systole length reduces the time for ventricular relaxation and filling  HEART SOUNDS First : Closing of the mitral and tricuspid valves. Second : Closing of the aortic and pulmonary valves Third : Rapid filling of the ventricles (audible in children) Fourth : Atrial systole (normally not audible)  THE 3RD HEART SOUND Heard during rapid diastolic filling EARLY DIASTOLE heard in early diastole Best heard with bell KENTUCKY - (CADENCE) < 40 years old: may be normal Possible CONGESTIVE HEART FAILURE OR VALVULAR DISEASE  THE 4TH HEART SOUND Heard in late diastole Sign of ‘stiff’, fibrotic or thickened ventricle BELL TENNESSEE - (CADENCE) Vibration of ventricular wall as atria contract May be normal finding in children May be sign of AORTIC STENOSIS, HYPERTROPHIC CARDIOMYOPATHY, HYPERTENSION  https://www.youtube.com/watch?v=btN2pOS gBE4 https://www.youtube.com/watch?v=9TRYM7I dnDY https://www.youtube.com/watch?v=IS9TD9fH Fv0