Control of cardiac output Flashcards
Define cardiac output
- the amount of blood that is pumped through the circulatory system per minute
Define afterload
The load the heart must eject blood against
Define pre load
Amount the ventricles are stretched in diastole - related to end diastolic volume
Define total peripheral resistance
Resistance to blood flow offered by all the systemic vasculature
What blood vessels offer the greatest resistance ?
Arterioles because they play a crucial role in regulating blood pressure using their layer of smooth muscle.
Why is there a drop in pressure as blood flows through the arteries into arterioles ?
- the constriction of arterioles increases resistance , this would cause a reduction in the flow of blood to downstream capillaries and veins thus a decrease in blood pressure in capillaries and veins BUT will cause pressure on arterial side
If total resistance pressure increases, but cardiac output remains the same , what are the effects on venous and arterial pressure ?
1) arterial pressure would increase
2) venous pressure would decrease
This is because there is more resistance in the arteries so less blood would effectively flow out of the arteries in the veins so there is less blood in the veins,
If total peripheral resistance falls , and cardiac output remains unchanged , what are the effects on venous and arterial pressure?
- arterial pressure decreases
- venous pressure increases
This is because there is less resistance in the arteries , so flow of blood from the arteries in the veins increases. So there is less blood in the arteries hence the decrease in the pressure but more blood in the veins which causes an increase in venous pressure.
If cardiac output increases but TPR is unchanged , what are the effects on venous pressure and arterial ?
- arterial pressure increases
- but venous pressure decreases because you are emptying the heart more.
If a tissue requires more blood , how will the arterioles and precapillary sphincters accomadate to this ?
- 1) arterioles would dilate
2) pre capillary sphincters would also dilate - this would lead to peripheral resistance falling , which would cause arterial to also fall , the heart needs to pump more so that arterial pressure does not fall and venous pressure does not rise,
How to calculate stroke volume ?
End diastolic volume - end systolic volume
When does ventricular filling occur ?
During diastole
Define compliance
How easily a chamber of the heart fills with blood
- change in volume / change in pressure
When the ventricles fill with blood during diastole , what must the intraventrocular pressure equal to ?
Venous pressure - the ventricles stretch enough so that IV pressure is the same to venous pressure
What does an increased compliance mean ?
Dilated heart - stretched more which ,ends to lower left ventricle pressure
What does a decreased compliance mean ?
- heart has stiffened for example due to hypertrophy as muscular walls have thickened too much.
- this leads to an increased end diastolic pressure
What is frank-starling law of the heart
An increase in venous pressure would result in the heart filling more , the harder it contracts
- the harder it contracts , the bigger the stroke volume
The starling curve
- linear graph
- insert image
- x axis : left ventricular end diastolic pressure (mm hg)
- y axis : stroke volume (ml)
- increasing venous return would increase left ventricular end diastolic pressure which would cause an increase in stroke volume
What are the two mechanisms by which the volume of blood pumped out is regulated?
1) intrinsic control - heart is able to control the volume of blood ejected within itself.
2) extrinsic : autonomic nervous system control
Define contractility
The force of contraction for a given fibre length
What type of factors can increase contractility ?
Extrinsic factors such as sympathetic stimulation and circulating adrenaline
What do intrinsic control mechanism ensure ? According to frank sterling law of the heart
Ensures that the output of the left and right ventricles match
3=Factors determining cardiac output
1) stroke volume , heart rate
2) how hard it contracts - determined by contractility , EDV
3) how hard to eject blood ( aortic pressure increases decreases this ability)
How would the CV system respond by metabolism in the body increasing ?
1) TPR will fall by arteries dilating and precapillary sphincters. This would cause arterial pressure to decrease and an increase in venous pressure
- this results in the heart stretching more , so harder contractions and more blood pumped
How to measure jugular venous pulse ?
Measured in the right internal jugular vein
