Heart as a Pump - Cardiac Cycle, Pressure Volume Loops - PDF

Heart as a pump Cardiac cycle Pressure volume loops Wiggers diagram Factors that influence CO 2 Cardiac Cycle Ventricular Filling Period Relaxation of the myocardium Low pressure in ventricles causes the mitral valve to open and blood to...

Heart as a pump Cardiac cycle Pressure volume loops Wiggers diagram Factors that influence CO 2 Cardiac Cycle Ventricular Filling Period Relaxation of the myocardium Low pressure in ventricles causes the mitral valve to open and blood to passively flow in. Flow is enhanced by “ventricular suction” Passive flow is responsible for 70-80% Contraction of atrium results in the final 20-30% filling Cardiac Cycle Isovolumetric Contraction Period Following electrical stimulation of the ventricles, the ventricles contract Pressure within the ventricles increases but the volume remains the same, hence “isovolumetric”. 4  Cardiac Cycle Ventricular Ejection Period Period during which blood is pumped from the ventricles Ejection occurs when the pressure in the ventricles exceeds the pressure in the aorta and force the aortic valve open. Volume within the ventricles decreases until the pressure falls below the pressure in the aorta, forcing the aortic valve closed. This period determines stroke volume (end diastolic volume minus end systolic volume) 5 Cardiac Cycle Isovolumetric Relaxation Period Ventricles relax Pressure drops rapidly Since both sets of valves are now closed, there is no change in volume, hence “isovolumetric relaxation” This is a brief period as soon the pressure in the ventricles falls below that of the atria an the AV valves open which starts the entire cycle again. link to video regarding pressure-volume loops 6 http://www.cvphysiology.com/Cardiac%20Function/CF024.htm  Pressure volume loop 1) What is end diastolic volume? 2) What is end systolic volume? 3) What is SV? 4) Determine when the mitral and aortic valves are opening and closing. 7 8  Preload What is preload? How would pressure volume loop change with increased preload? How does that influence SV? 9 Afterload What is afterload? What would the pressure volume curve look like with: – hypertension (increased afterload) – hypotension (decreased afterload)? Why are people with heart disease on blood pressure medication? 10 Contractility What is contractility? What would the pressure volume curve look like with increased contractility? How does that influence SV? 11  Cardiac work Work = Force X distance The area within the pressure volume loop represents cardiac work – Volume X pressure What does this mean with regards to hypertension and blood pressure medication? 12  Pressure volume loop: rest and exercise During exercise all three factors change. – Increased preload – Increased contractility – Increased afterload. This leads to greater cardiac work but also greater SV. 13  How would the PV loop differ Right versus between the right and left ventricle? Left Ventricle 14  You should be able to explain this figure and identify the following: Wiggers Passive filling of ventricles, atrial contraction, Diagram: isovolumetric contraction, the point that identifies afterload, ventricular ejection, isovolumetric relaxation, end diastolic and end systolic volume 15  This illustration represents the left side of the heart (left atrium and ventricle). What Right side would be different if it represented the right versus left side side of the heart? 16  Atria do not contract prior to ventricular contraction? Explain how SV Ventricles do not contract following changes if: atrial contraction? 17 Factors that influence CO 18