Cardiac Cycle Lecture 06 PDF

Cardiac Cycle Lecture 06 Richard Klabunde, PhD Professor of Physiology MU-WCOM 1 Learning topics & objectives 1. Accurately draw and describe the time sequence of cardiac contraction and relaxation, including valve opening and closing, chamber volum...

Cardiac Cycle Lecture 06 Richard Klabunde, PhD Professor of Physiology MU-WCOM 1 Learning topics & objectives 1. Accurately draw and describe the time sequence of cardiac contraction and relaxation, including valve opening and closing, chamber volumes and pressures, and pulmonary artery and aortic pressures 2. Describe how cardiac valves normally open and close 3. Recall normal values for: LVEDV, LVESV, EF, right and left atrial pressures, pulmonary and aortic pressures 4. Identify the cardiac cycle phases associated with ventricular and atrial systole and diastole 5. Identify on a cardiac cycle diagram the location of S 1, S2, S3 and S4 heart sounds, and describe the origin of these sounds 6. Accurately draw and label cardiac cycle components using ventricular pressure- volume loops 7. Describe how pulmonary capillary wedge pressure is measured and its significance 2 Recommended resources Klabunde, cvphysiology.com (see links in slides) Klabunde, Cardiovascular Physiology Concepts, Wolters Kluwer: 3e, Ch 4: 64-71 3 Cardiac chambers and valves Abbreviations: IVC & SVC - inferior & superior vena cavae RA - right atrium T - tricuspid valve RV - right ventricle P - pulmonary valve PA - pulmonary artery LA - left atrium M - mitral valve LV - left ventricle A - aortic valve Ao - aorta 4 Basic phases of the cardiac cycle (click links at bottom of page for each phase) Systole Begins with ventricular contraction Ends when ejection ceases (Note: relaxation occurs before the end of ejection) Diastole Begins when ejection ceases as ventricles relax Ventricular filling begins after sufficient relaxation 5 Atrial systole (contraction) (Phase 1) Atrial contraction occurs near the end of ventricular diastole Initiated by atrial depolarization (P wave of ECG) Atrial pressure transiently increases (a wave), forcing additional blood into ventricles Accounts for ~10% of ventricular filling at resting HR (up to 40% during exercise) Klabunde, Cardiovascular Physiology Concepts, 3e 6 Ventricular systole (Phases 2 – 4) Isovolumetric Contraction (#2) Filled volume is the end-diastolic volume (EDV) Initiated by ventricular depolarization (QRS) LVP increases Mitral valve closes Systole is initially isovolumetric (LVP increases, but LV volume does not change) Maximal rate of pressure development occurs (LV dP/dtmax) Klabunde, Cardiovascular Physiology Concepts, 3e 7 Ventricular systole (Phases 2 – 4) Ejection (Rapid & Reduced, #3, 4) Aortic outflow valve opens; maximal ejection velocity occurs early in Phase 3 (dV/dtmax) Repolarization (T wave) initiates relaxation, causing ejection rate to rapidly decline (Phase 4) Residual volume after ejection is end- systolic volume (ESV) Klabunde, Cardiovascular Physiology Concepts, 3e 8 All heart valves passively open and close in response to pressure gradients across the valve Aortic valve ○ Opens when LVP > AP ○ Closes when LVP < AP Mitral valve ○ Opens when LAP > LVP ○ Closes when LAP < LVP 9 Papillary muscle contraction exerts tension on chordae tendineae, which prevents AV valve leaflets from bulging backwards into the atria and becoming incompetent Klabunde, Cardiovascular Physiology Concepts, 3e 10 Ventricular diastole (Phases 5 – 7) Isovolumetric Relaxation (#5) Decreasing ventricular pressure leads to aortic valve closure (diastole begins) Diastole is initially isovolumetric (LVP decreases at constant LVV) Klabunde, Cardiovascular Physiology Concepts, 3e 11 Ventricular diastole (Phases 5 – 7) Passive Filling (Rapid & Reduced, #6 & 7) Mitral valve opens when ventricular pressure < atrial pressure Most ventricular filling (~90% at rest) occurs before atrial contraction How does ↑HR affect passive filling? Klabunde, Cardiovascular Physiology Concepts, 3e 12 During isovolumetric contraction and relaxation, all valves are normally closed 13 Ventricular stroke volume is the difference between ventricular end-diastolic (EDV) and end-systolic volumes (ESV) In a normal heart, EDV-ESV is SV the same volume of blood as ejected into the aorta during each systole 14 Ventricular ejection fraction (EF) is the fraction of blood ejected from the ventricle relative to the end- diastolic (EDV) EF is a clinical index of LV systolic function In a normal heart, the EF is about 55-60% In a weakened (failing) heart, the EF is < 50% and may be as low as 10% 15 In pathological conditions, a portion of the SV may be ejected into the left atrium (e.g., mitral regurgitation – see figure) Therefore, SV is not necessarily the volume ejected from LV into the aorta https://cvphysiology.com/Heart%20Disease/HD005 16 Atrial diastole (filling) (Phases 2–7) Occurs throughout ventricular systole and diastole until P wave Blood continuously enters the atria, except when transiently y descent impeded during atrial systole (a wave) AV valves suddenly open when ventricular pressure falls below atrial pressure, creating the v wave followed by y descent 17 Right atrial and ventricular pressure and volume changes during the cardiac cycle The timing of events on the right side of the heart are almost identical to left-sided events, with the main difference being slightly different timing for right-sided valve opening and closing Right-sided pressures are lower ○ Right atrial and right ventricular end-diastolic pressures are about one-half of those pressures found on the left side ○ Right ventricular peak systolic pressure is about 1/5 of the left ventricular peak systolic pressure Right-side and left-sided volume changes are virtually identical over time, although they vary beat-to-beat largely because of respiratory effects on systemic and pulmonary venous return 18 Average, normal intracardiac and vascular pressures (mmHg) Note: RAP < LAP RAP ≅ RVEDP RVESP ≅ PASP LAP ≅ LVEDP LVESP ≅ AoSP Klabunde, Cardiovascular Physiology Concepts, 3e Click here for a 3-minute YouTube video 19 Basic heart sounds S1: Closure of mitral and tricuspid valves Follows QRS and occurs at the onset of isovolumetric contraction Mitral precedes tricuspid S2: Closure of aortic and pulmonic valves Follows T wave and occurs at onset of isovolumetric relaxation Aortic precedes pulmonic, producing a split sound 20 Basic heart sounds cont. S3: Found in highly compliant LVs Caused by rapid expansion of ventricle during early, rapid filling phase Normal in children Pathologic in adults; associated with dilated ventricles S4: Found in stiff LVs Caused by atrial contraction forcing blood into stiff ventricle Heard in hypertrophied hearts and hearts of older people 21 Analysis of the Cardiac Cycle using Left Ventricular Pressure-Volume Loops 22 Ventricular pressure-volume loops 23 Animated pressure-volume loops 24 Pulmonary Capillary Wedge Pressure 25 Pulmonary capillary wedge pressure Indirect measure of left atrial pressure Measured by right-sided cardiac catheterization ○ Balloon-tipped, Swan-Ganz catheter is inserted into a branch of the pulmonary artery via a peripheral vein ○ Balloon is inflated to stop flow in the pulmonary artery branch ○ Pressure measured at the tip of the catheter several seconds after balloon inflation represents left atrial pressure 26 Swan-Ganz catheter Balloon inflated 27 Intracardiac pressure measurements https://www.cvphysiology.com/Heart%20Failure/HF008 28 Summary of major concepts The cardiac cycle is divided into systole and diastole, determined by events occurring at specific points in time Systole is initiated by ventricular depolarization, which results in isovolumetric ventricular pressure generation, mitral valve closure, aortic valve opening, and ejection of blood into the aorta Ventricular repolarization results in ventricular relaxation beginning late in systole, which reduces pressure generation and ejection Ejection ends and diastole begins with closure of the aortic valve Ventricular filling begins with opening of the mitral valve following isovolumetric relaxation Ventricular pressure-volume loops are an important tool for analyzing ventricular function 29 END 30 QUESTIONS 31 Q1: Why does the mitral valve close when the left ventricle (LV) begins to contract? A. Atria rapidly relax B. LV pressure exceeds left atrial pressure C. Mitral valve contracts D. Papillary muscles contract and close the valve 32 Q2: During the phase between the QRS complex and the upstroke of the aortic pressure A. All valves are closed B. Only the aortic and pulmonic valves are closed C. Peak ventricular pressure is attained D. Ventricular volume rapidly decreases E. Ventricular muscle is relaxed 33 Q3: At the end of ventricular diastole A. all valves are open B. left ventricular pressure is higher than pulmonary artery pressure C. the ventricles are at their maximal, filled volume for that filling cycle D. left atrial pressure lower than right atrial pressure 34 Answers to questions Q1: B Valves open and close in response to pressure gradients across the valve. When the LV pressure is greater than LA pressure, the mitral valve closes. This valve opens when LA pressure is greater than LV pressure. Q2: A Between the QRS and aortic valve opening, the ventricle is contracting isovolumetrically because both the mitral and aortic valves are closed. Q3: C The volume of blood at the end of diastole (filling) is the maximal filled volume (end-diastolic volume) produced by both passive filling and atrial contraction 35