Control of Cardiac Output Flashcards
What is the equation for cardiac out put?
CO= SV x HR
If you increase TPR what happens to arterial and venous pressure if CO does not compensate?
Arterial pressure rises
Venous pressure reduces
If TPR decreases and venous pressure thus increases what happens to venous return?
It increases.
What is pre-load?
Amount the ventricles stretch or fill in diastole. A function of EDV or central venous pressure.
What is total peripheral resistance?
Resistance to blood flow offered by all systemic vasculature.
The load the heart must eject blood against is known as?
The after load
Its related to aortic pressure
If CO increases but TPR is unchanged what happens to arterial and venous pressure?
Arterial pressure increases
Venous pressure decreases
Cardiac out put responds to changes in arterial blood pressure and central venous pressure by what mechanism types?
Intrinsic and extrinsic
If you start to exercise pre capillary sphincters to skeletal muscle will open and thus TPR will fall. If TPR fell and CO didn’t change the arterila pressure would drop and the venous pressure would rise, so how does the heart stop this?
Heart increases CO by increasing rate and contractility. This gives a higher SV and HR to maintain arterial pressure and avoid venous hypertension.
Whats a normal ejection fraction?
67%
How are venous pressure and EDV related?
The ventricles passively fill and stretch until the pressure in the ventricle equals that of the venous system
What is compliance?
Compliance is the left ventricle filling a bit without increasing the pressure. Disease can increase or decrease compliance.
What happens in ventricular filling in increased compliance?
Pressure doesn’t rise as it should
What is Frank Starlings law?
If you stretch a heart more it will contract harder giving a larger stroke volume
The higher the EDV the bigger the contraction, to a limit.
High preload means what for Stroke volume?
Increased CVP means increase preload which means higher EDV and so a greater SV.
What do length tension curved for cardiac muscle show?
If sarcomere are two short at the begining of contraction the levels of contraction is lower.
When cardiac muscle cells are streched they contract more- by which two mechanisms is this change brought about?
More stretch means more contraction by Frank Starlings law. (intrinsic mechanism)
Increase stretch means increased calcium sensitivity in cardiac muscle cells.
If the slope of a Frank Starling curve is altered what has changed?
Contractility
What are extrinsic factors affecting cardiac output?
Sympathetic stimulation from circulating adrenaline acting on Beta 1 receptors
Increase sympathetic innervation of the heart does what?
Positive inortopy
Positive chronotropy
What happens to stroke volume in increased TPR?
High TPR means high arterial pressure- so greater after load.
The venous pressure decreases so heart filling is lowered.
What effects how much the ventricles empty?
The contractility and the EDV
The after load
The parasympathetic nervous system innervates the heart by what nerve?
The Vagus nerve
Describe demand led pumping
Metabolism increases so tissue demand increases.
TPR falls to supply tissues.
Arterial pressure decreases and venous pressure increases.
Heart beats harder and faster to maintain arterial pressure. This happens by intrinsic and extrinsic mechanisms.
How does cardiac out put respond to TPR changes
The changes in cardiac out put act to oppose the TPR changes in terms of arterial and venous pressure effects
What happens when we stand up to arterial and venous pressure? (if we had no reflexes or compensatory mechanisms)
They both decrease. Venous pooling leads to reduced CO and thus lower arterial pressure.
What stops postural hypotension?
baroreceptor reflexes, autonimic nervous system and increase TPR
In exercise how is venous return increased?
Muscle pump activity
Lower TPR
Who’s law states higher EDV gives higher SV
Starlings
