PSL301H – Lecture 3: Cardiac Cycle PDF

PSL301H – Lecture 3: The cardiac cycle How do electrical signals initiate contraction and cause blood movement? What is the cardiac cycle? Silverthorn 7th ed: 461-466 Silverthorn 8th ed: 459-464 Cardiac action potential to Aortic Flow: Summary 1. Electrical signals originate in the SA node, and...

PSL301H – Lecture 3: The cardiac cycle How do electrical signals initiate contraction and cause blood movement? What is the cardiac cycle? Silverthorn 7th ed: 461-466 Silverthorn 8th ed: 459-464 Cardiac action potential to Aortic Flow: Summary 1. Electrical signals originate in the SA node, and propagate through the heart. Can be regulated. 2. electrical signals are converted by contractile cells to generate force and pump blood. 3. requires ordered electrical and contractile mechanism 4. We can monitor these signals and sounds to accurately assess cardiac function. 5. Systems need to work at near 100% effectiveness What is the cardiac cycle? Sequence of events that occur when the heart beats. There are two phases of this cycle: 1. Diastole - Ventricles are relaxed. 2. Systole - Ventricles contract. Overall Aim: Understand and integrate electrical activity, contraction, and blood flow in/out of the heart Cardiac cycle 3 General Principles: 1) The heart is a biological pump ! Contraction-relaxation cycle generates pressure gradients ! Directs the orderly movement of blood through the circulation. 2) Blood flows high pressure ! low pressure 3) Events on the right and left sides of the heart are the same, but pressures are lower on the right. Mechanical events of the cardiac cycle 1 Late diastole—both sets of chambers are relaxed and ventricles fill passively. START 5 Isovolumic ventricular relaxation—as ventricles Atrial systole—atrial contraction 2 relax, pressure in ventricles forces a small amount of falls, blood flows back into additional blood into ventricles. cusps of semilunar valves and snaps them closed. S1 S2 3 Isovolumic ventricular 4 Ventricular ejection— contraction—first phase of as ventricular pressure ventricular contraction pushes AV rises and exceeds pressure valves closed but does not create in the arteries, the semilunar enough pressure to open semilunar valves open and blood is valves. ejected. Pressures in aorta, ventricle, atrium Time (msec) 0 100 200 300 400 500 600 700 800 120 B 90 Aorta Dicrotic notch Pressure A (mm Hg) Left 60 venticular pressure Left atrial 30 pressure D 0 C S1 S2 Heart sounds Atrial Ventricular Ventricular Atrial systole systole diastole systole Atrial Isovolumic Ventricular Early Late Atrial systole ventricular systole ventricular ventricular systole contraction diastole diastole Ventricular pressure and volume Time (msec) 0 100 200 300 400 500 600 700 800 120 90 Pressure (mm Hg) Left 60 venticular pressure 30 0 135 S2 S1 E Left ventricular volume (mL) 65 F Atrial Ventricular Ventricular Atrial systole systole diastole systole Atrial Isovolumic Ventricular Early Late Atrial systole ventricular systole ventricular ventricular systole contraction diastole diastole Ventricular pressure and volume Time (msec) 0 100 200 300 400 500 600 700 800 120 90 Pressure (mm Hg) Left 60 venticular pressure 30 0 135 S2 S1 E Left ventricular volume (mL) 65 F Atrial Ventricular Ventricular Atrial systole systole diastole systole Atrial Isovolumic Ventricular Early Late Atrial systole ventricular systole ventricular ventricular systole contraction diastole diastole Wiggers Diagram: overview Time (msec) 0 100 200 300 400 500 600 700 800 QRS QRS Electro- complex cardiogram complex (ECG) P T P 120 For the Wigger’s diagram shown at left, match the letters in boxes B 90 Aorta Dicrotic notch with the following events of the Pressure A cardiac cycle: (mm Hg) Left 60 venticular pressure 1. End-diastolic Volume 2. Aortic valve opens 30 Left atrial pressure D 3. Mitral valve opens 4. Aortic valve closes 0 C 5. Mitral valve closes S1 S2 6. End-systolic volume Heart sounds 135 E Left ventricular volume (mL) 65 F Atrial Ventricular Ventricular Atrial systole systole diastole systole Atrial Isovolumic Ventricular Early Late Atrial systole ventricular systole ventricular ventricular systole contraction diastole diastole Heart Sounds First heart sound Vibrations following closure of the AV valves “Lub” Second heart sound Vibrations created by closing of semilunar valve “Dup” Auscultation is listening to the heart through the chest wall through a stethoscope What are some further applications of this knowledge? What ways are there to diagnose this?? Pressure Volume Loop: Ventricular filling 120 KEY Left ventricular pressure (mm Hg) EDV = End-diastoilc volume ESV = End-systolic volume 80 40 START A A¢ 0 65 100 135 Left ventricular volume (mL) Pressure Volume Loop: End Diastolic Volume 120 KEY Left ventricular pressure (mm Hg) EDV = End-diastoilc volume ESV = End-systolic volume 80 40 START EDV B A A¢ 0 65 100 135 Left ventricular volume (mL) Pressure Volume Loop: Isovolumetric Contraction 120 KEY Left ventricular pressure (mm Hg) EDV = End-diastoilc volume ESV = End-systolic volume 80 C 40 START EDV B A A¢ 0 65 100 135 Left ventricular volume (mL) Pressure Volume Loop: Blood Ejection Phase Stroke volume 120 D KEY ESV Left ventricular pressure (mm Hg) EDV = End-diastoilc volume ESV = End-systolic volume 80 C 40 START EDV B A A¢ 0 65 100 135 Left ventricular volume (mL) Pressure Volume Loop: Isovolumetric Relaxation Stroke volume 120 D KEY ESV Left ventricular pressure (mm Hg) EDV = End-diastoilc volume ESV = End-systolic volume 80 C 40 START EDV B A A¢ 0 65 100 135 Left ventricular volume (mL) What information can PV Loops provide? 1) Stroke Volume 2) Atrial Filling Pressure (preload) 3) Aortic Pressure (afterload)