Lecture 28 - Cardiovascular System: The Cardiac Cycle and Cardiac Output Flashcards
What does the cardiac cycle generate?
It generates pressure to produce cardiac output, causing blood flow into and through the blood vessels. This pressure drives blood out of the heart and into the systemic and pulmonary circuits
What is cardiac output and what is the formula to calculate it?
The volume of blood pumped into the aorta by the left ventricle each minute
CO = stroke volume (SV) x heart rate (HR) = mL/min
This describes the volume of blood (mL) moved through the heart into the systemic circuit given a time (min)
What is heart rate (HR)?
The number of cardiac cycles (beats) per minute (bpm)
What is stroke volume (SV)?
The volume of blood (mL) ejected into the artery during each cardiac cycle (mL/beat)
Describe Wiggers Diagram
It shows the relationship between time, pressures, and volumes across cardiac cycle
How does the cardiac cycle begin (and end)?
It begins and ends in ventricular (and atrial) diastole when passive filling of the ventricles occurs. During this time blood returning from the veins can flow through the atria and into the ventricles
State of the heart: all chambers are relaxed and the AV valves are open
What happens when the atrial systole completes the filling of the ventricles?
The heart reaches its End Diastolic Volume (EDV). During this time, blood is squeezed from atria to ventricles, and the ventricles achieve their maximum volume (EDV)
State of the heart: atria contracting, ventricles relaxed and the AV valves are open
Describe ventricular systole. What 2 components are associated with it?
It involves a brief period of isovolumetric contraction (occurs when pressure is rising, but both valves are still closed) and then a period of ventricular ejection (occurs as long as the semilunar valves are open), allowing the stroke volume to be squeezed into the artery
State of the heart: atria relaxes, ventricles contract. AV valves close and SL valves open
Describe ventricular diastole. What component is associated with it?
The semilunar valves close. The remaining blood in the ventricle is the End Systolic Volume (ESV). Isovolumetric relaxation occurs when pressure is decreasing with no change in volume (both valves closed)
State of the heart: ventricles relax, SL valves close, AV valves open
Describe venous return
When venous return increases, SV inc. When venous return decreases, SV dec.
It is the volume of blood that is delivered to the right atrium during the cardiac cycle. VR is affected by CO and by constriction of arteries or compression of veins
Describe preload
Preload is the amount of stretching of the heart wall due to blood volume within the ventricle (inc. EDV = inc. stretch). This affects the EDV by stretching the myocardium
Describe afterload
It is the amount of force the ventricle has to generate to open its semilunar valve (inc. aorta pressure = inc. afterload)
The greater the afterload, the lower the pumping efficiency of the heart, and the larger the ESV
What is EDV affected by?
Venous return and ventricular filling time
Describe filling time
The duration of ventricular diastole, which determines the time the AV valves are open. Filling time is a function of heart rate (inc. HR = dec. filling time)
How does the Frank-Starling Law affect EDV and how does this occur?
It describes how increasing EDV increases the stroke volume ejected during that cycle. This occurs through preload - stretching the cardiac myocytes of the myocardium increases the force (pressure) they produce when they contract
Therefore, incd. ventricular pressure increases the duration of SL valve opening, ventricular ejection, and thus the SV
