Lecture 5- Control Of Cardiac Output Flashcards
What mechanical factor determines preload?
Venous pressure
What mechanical factor determines what happens during systole?
Afterload
What is starlings law?
Increase in venous pressure and end diastolic volume will lead to increase in stroke volume “more in more out”
What does a fall in peripheral resistance lead to?
Increased stroke volume as it is easier to eject blood. However blood pressure will be lowered whereas with a higher afterload stroke volume will decrease but pressure will be higher
Chemical effect of noradrenaline and adrenaline on the heart?
Provide a positive inotropic effect
Effect of total peripheral resistance on heart rate?
Low resistance will cause a decrease in blood pressure and so the heart will beat faster in order to compensate
What is afterload?
The load the heart must eject blood against, usually roughly equal to aortic pressure
What is preload?
Amount the ventricles are stretched in diastole and is released to the end diastolic volume or central venous pressure
What is total peripheral resistance?
Sometimes called systemic vascular resistance it is the resistance to blood flow offered by all the systemic vasculature
What happens if arterial resistance is increased?
Arterial pressure and total peripheral resistance will fall but venous pressure will increase
What happens if TPR increases and CO is unchanged
Arterial pressure increase and venous pressure fall
What happens if CO increases and TPR is unchanged
Arterial pressure increase venous pressure fall
What happens if CO decrease and TPR is unchanged?
Arterial pressure will fall and venous pressure will increase
What a problem associated with increased venous pressure?
Oedema
What causes total peripheral resistance to fall?
Dilation of arterioles and pre capillary sphincters
What causes increased heart rate in exercise?
Decrease in TPR to allow oxygen to tissues. This decrease arterial pressure and increases venous pressure so the heart combats this by increasing heart rate
Increased venous return through muscle pumps also
What is stroke volume?
SV=EDV-ESV average is 70ml
How can stroke volume be increased?
By increasing EDV eg mitral valve regurgitation or decreasing ESV
What is the ventricular compliance curve?
Describes the relationship between venous pressure and end diastolic pressure.
Increased compliance means that an increase in volume results in less pressure than in a normal heart while decreased compliance is the opposite
What factors determine how much the ventricles will fill?
Venous pressure and compliance
What is Frank-starling’s law of the heart?
The more the heart fills the harder it contracts (up to a point)
Intrinsic example of stroke volume control?
Increased stroke volume caused by increased filling of the heart ensures that both sides of the heart have the same output.
Effect of contractility?
Increased contractility will increase starling curve (higher stroke volume at a given end diastolic pressure) and decreased contractility will lower the starling curve
Effect of increased afterload?
Occurs when total peripheral resistance is increased. Results in lowered venous pressure which lowers the venous return to the heart
