Lecture 10: Cardiac output Flashcards
What is cardiac output and how is it measured. What two main factors influence cardiac output
Cardiac output is the volume of blood ejected into the aorta per minute measured by (mL/min). CO= Heart Rate * Stroke volume
Explain the concept of demand and supply as it applies to the cardiovascular system
As the demand for oxygen, nutrients and waste removal increases with increased metabolism, the cardiovascular system is responsible for responding to that demand by increasing the supply-> ie the cardiac output. They do this by speeding up the pump or increasing the volume of blood
The cardiac system is a …. flow system. Why and What is the implication of that
High flow system because the whole blood volume passes through the heart nearly every minute. The implication of this is that when demand increases quickly, supply is also able to increase quickly
What is cardiac reserve and what is the general ratio of rest to exercise
The range between the maximum (at exercise) and minimum (at rest) cardiac output and shows how much demand you can cope with. This is generally a range of rest –4* rest
What is stroke volume
The amount of blood that exits the left ventricle of the heart in one cardiac cycle
What are the 3 factors that influence stroke volume
- Preload: this is intrinsic which is the degree of stretch on the myocardial fibres at the end of diastole because of the amount of blood returning to the heart, which is the pressure resulting from blood returning to the heart (mmHg)
- Contractility/ inotrophy (force of contraction) : this is extrinsic and the ability of the ANS to increase both SV and HR (especially through exercise). Different ions Ca2+, Na+ and K+ present in the plasma also help to regulate contractility by helping the cardiac AP.
- Afterload: The work the heart has to do to pump against the blood pressure in the aorta to pump blood out (arterial pressure with regards to LV in mmHG).
If you increase the volume of water in your blood (which sits in the veins) what happens to the filling pressure, end diastolic volume and stroke volume
The increase in volume of water in veins, increases filling pressure and therefore the end diastolic volume increases and therefore there is an increase in stroke volume.
What is Starlings Law
Whatever blood returns to the heart by venous circulation in the previous diastole is pumped out without excessive damming in the veins.
What does the pressure volume curve help to show (big picture)
It shows how the pressure of the ventricle against the volume of blood in the ventricle changes through the cardiac cycle.
What is stroke work
The work done by the ventricle of the heart each time it beats which is given by the area of pressure volume curve as it is a 3D system
Compare systolic and diastolic pressure (what and when)
Systolic is the max pressure when contracting at the peak of ejection phase whereas Diastolic is when the Aorta and ventricle pressure match - max arterial pressure when the Aortic valve opens.
Define contractility
The ability to increase stroke volume when positive inotropic agents are present. These agents usually promote inflow of Ca2+ for cardiac action potentials
