Cardiac Cycle and Cardiac Output PDF

Paul W. Craig, PhD, MS, CPT, CNC The Cardiovascular System - Continued Module Organization/Outline Anatomy of the Cardiovascular System: o The Heart o The Blood and Blood Vessels o Blood Flow/Circulation o Cardiac Cells o Cardiac Electrophysiology Cardiac Function o Cardiac Cycle...

Paul W. Craig, PhD, MS, CPT, CNC The Cardiovascular System - Continued Module Organization/Outline Anatomy of the Cardiovascular System: o The Heart o The Blood and Blood Vessels o Blood Flow/Circulation o Cardiac Cells o Cardiac Electrophysiology Cardiac Function o Cardiac Cycle o Cardiac Output Cardiovascular Pathology Cardiac Function: Cardiac Cycle So, how does blood move from one chamber of the heart to another? It's all about Pressure. Blood flows from areas of high pressure to low pressure. When one chamber of the heart contracts, it creates high pressure, while another chamber relaxes, causing low pressure. Think of the contraction as squeezing and the relaxation as remaining unchanged. Cardiac Function: Cardiac Cycle The cardiac cycle is the coordination of the filling and emptying of blood by electrical signals that cause the heart muscles to contract and relax. In each cardiac cycle, the heart o contracts (systole) and o relaxes (diastole) Cardiac Function: Cardiac Cycle Periods of contraction (systole) in heart chambers must alternate with periods of relaxation (diastole) in order for the heart to function properly During systole, a contracting chamber will eject blood During diastole, a relaxed chamber will fill with blood Incomplete filling or ejection can lead to inadequate pumping of blood to tissues Cardiac Function: Cardiac Cycle The Cardiac Cycle is the summary of all the mechanical activities within the heart during a single heartbeat Intrinsic Conduction System Cardiac Muscle Contraction  Cardiac Function: Cardiac Cycle Events during Cardiac Cycle o Atrial muscle contraction/relaxation o Ventricle muscle contraction/relaxation o AV Valve actions o SL Valve actions o Blood volume in heart o Blood pressure in heart o Heart Sounds  Cardiac Function: Cardiac Cycle The Cardiac Cycle: o 1. Mid to Late Ventricula r Diastole o 2. Ventricula r Systole o 3. Early Ventricula  Cardiac Function: Cardiac Cycle: Mid to Late Diastole The Cardiac Cycle: Always begins at MID to LATE DIASTOLE: (or when the ventricles are filling) Two components: Ventricular Filling/Atrial Contraction o Atria relaxed and filling with blood o Ventricles relaxed and filling with blood o AV valves are open o SL valves are closed o IN LATE DIASTOLE: The Atria’s Contract o The maximum filling, END  Cardiac Function: Cardiac Cycle: Mid to Late Diastole Ventricles are Filling! o Ventricles are relaxed (intraventricular pressure is low) o Most Ventricular filling is passive Passive blood flow from the atria into the ventricles accounts for about 70-80 % of filling  Cardiac Function: Cardiac Cycle: Mid to Late Diastole Atrial Contraction! o Atria contract following SA node depolarization  Cardiac Function: Cardiac Cycle: Mid to Late Diastole Atrial Contraction! o Atria contract and compress blood in the atria Last volume of blood into ventricles (20%) Slight rise in atrial pressure  Cardiac Function: Cardiac Cycle: Ventricular Systole Next, Ventricular Systole is triggered Two components: Isovolumetric Contraction/Ventricular Ejection o Atria relaxed o Ventricles contract o AV valves close (prevent backflow) o SL valves closed initially causing ISOVOLUMETRIC CONTRACTION Both valves are closed, no volume changes, just pressure increasing o SL valves open when pressure is high enough, blood is ejected o Volume of blood ejected is the Stroke Volume (SV) o Volume of blood at the end is, END Systolic VOLUME (ESV)  Cardiac Function: Cardiac Cycle: Ventricular Systole Isovolumetric Contraction! o All four heart valves are momentarily closed! When pressure in ventricles exceeds atrial pressure, the AV valves close The semilunar valves remain closed until the ventricular pressure exceeds the pressure in the  Cardiac Function: Cardiac Cycle: Ventricular Systole Ventricular Ejection! o Once the ventricular pressure exceeds the pressure in the pulmonary trunk and aorta, the semilunar valves open o Blood is ejected from the ventricles  Cardiac Function: Cardiac Cycle: Ventricular Systole Ventricular Ejection! o Blood is pumped out of the ventricles into the pulmonary trunk and aorta o Ventricular volume decreases  Cardiac Function: Cardiac Cycle: Ventricular Diastole Finally, Ventricular Diastole Begins Two components: Isovolumetric Relaxation/Ventricular Filling phase o Atria relaxed o Ventricles relaxed o AV valves close (prevent backflow) o SL valves closed initially causing ISOVOLUMETRIC RELAXATION Both valves are closed, no volume changes in the ventricles AV valves open when enough PRESSURE or enough blood fills the atria Then back to mid-late diastole  Cardiac Function: Cardiac Cycle: Ventricular Diastole Isovolumetric Relaxation! o Begins with ventricular relaxation Semilunar Valves close During this time Atria have been in diastole o Filling with blood and o Increasing atrial pressure  Cardiac Function: Cardiac Cycle: Ventricular Diastole Ventricular Filling! o In early diastole, the atrial blood pressure begins to exceed the pressure in the ventricles The AV valves open Blood flows form the atria into the ventricles  The Cardiac Cycle Atrial Systole 1.Atrial systole o Atrial contraction begins o Right and left AV valves are open 2.Atria eject blood into ventricles o Filling ventricles 3.Atrial systole ends o AV valves close o Ventricles contain maximum blood volume o Known as end-diastolic volume (EDV)  The Cardiac Cycle Ventricular Systole 4. Ventricles contract and build pressure o AV valves close cause isovolumetric contraction 5. Ventricular ejection o Ventricular pressure exceeds vessel pressure opening the semilunar valves and allowing blood to leave the ventricle o Amount of blood ejected is called the stroke volume (SV) 6. Ventricular pressure falls o Semilunar valves close o Ventricles contain end-systolic volume (ESV), about 40% of end-diastolic volume  The Cardiac Cycle Ventricular Diastole 7.Ventricular diastole o Ventricular pressure is higher than atrial pressure o All heart valves are closed o Ventricles relax (isovolumetric relaxation) 8.Atrial pressure is higher than ventricular pressure o AV valves open o Passive atrial filling o Passive ventricular filling Start 0 800 msec 100 msec msec Cardiac cycle 370 msec  Atrial systole begins: Start Atrial contraction forces a small amount of additional blood into relaxed ventricles. 0 800 msec msec 100 msec Cardiac cycle  Atrial systole ends, atrial diastole begins 100 msec Cardiac cycle