Control Of Cardiac Output Flashcards
What are the two factors which determine arterial pressure?
Cardiac output and total peripheral resistance
What determines venous pressure?
This is a balance between the rate at which blood enters the venous system and the rate at which it is pumped out of the heart.
What can be said about changes to arterial and venous pressure and how the other responds?
When arterial pressure increases, venous pressure decreases and vice versa.
What is the relationship between TPR and the body’s need for blood?
Inversely proportional, as the body’s need for blood increases, there needs to be vasodilation and so a decrease in TPR.
How do changes in metabolism cause changes at the heart?
Changes in metabolism cause changes in TPR which affects both arterial and venous pressure. These generates signals which lead to changes at the heart.
How can we calculate stroke volume?
End diastolic volume - end systolic volume.
What effect does higher venous pressure have in the ventricles?
Higher venous pressure leads to increased ventricular filling as there is an increased pressure gradient.
What is starlings law of the heart about stretching cardiac tissue?
The more the heart muscle is stretched, the more it pumps.
What is the relationship between venous pressure and Stroke volume?
Increased venous pressure leads to increased stroke volume.
What are alterations in contractility called?
This is called positive and negative inotropy.
What two factors determine force of contraction?
End diastolic volume and contractility
On a graph of stroke volume against end diastolic volume, what is the effect of altered contractility?
This leads to shifting of the curve left to right.
What is aortic impedance?
This is where there is high aortic pressure and so this makes it harder to eject blood.
What is preload?
This is the volume of blood in the ventricles at the end of diastole
Name some factors which can lead to increased preload.
Hypervolemia, regurgitation of cardiac valves, heart failure
What is afterload?
The resistance the LV must overcome to circulate blood
Under what circumstances will afterload be increased?
Hypertension and increased total peripheral resistance.
What detects arterial blood pressure?
Baroreceptors. These cause autonomic control over the heart.
When blood pressure decreases, how does the autonomic nervous system correct this?
There is an increase in sympathetic drive which increases heart rate and contractility, and a decrease in parasympathetic action on pulse.
What detects increase in venous pressure?
The bainbridge reflex, which results in a parasympathetic drive and an increase in heart rate.
Name the organs which always require a stable perfusion.
Heart, brain and kidneys.
How does blood flow change with intense exercise?
There is increased blood flow to the skeletal muscle and skin and decreased blood flow to the gut.
Why does cardiac fitness effect cardiac output?
If someone is more cardiac fit, then they will have a greater ventricular distensibility and contractility.
Where in the body are baroreceptors found?
Carotid sinus and aortic arch.
What blood vessels are responsible for TPR?
Arterioles
What vessels can control RA filling and therefore stroke volume?
The veins/ great veins which are reservoirs for blood with large volumes and low pressures.
What is the functional reserve in the CVS?
There are many capillary beds which are not perfused and so these serve as a functional reserve.
At what mean arterial blood pressure does perfusion become inadequate?
65mmHg.
What happens immediately in the CVS when a person stands up?
There is a drop in central venous pressure which leads to reduced atrial filling and therefore a drop in mean arterial blood pressure.
Hat is the orthostatic response to standing up?
Heart rate will increase and so will TPR to increase mean arterial blood pressure.
What is the importance of smooth muscle tone of the veins on standing up?
This means that there is less pooling of blood to the legs which increases CVP because more blood is pumped back to the heart.
When the body has a delayed CVS response to standing up, what happens?
When there is a delayed CVS response, this leads to dizziness and fainting which can result in syncope. This is due to inadequate cerebral blood flow.
What is the systemic effect of eating a large meal?
This causes an increase in action of the parasympathetic nervous system.
What is the effect on eating a large meal on TPR?
There is decreased TPR because there are more local dilators and autacoids and also an increased activity of the parasympathetic nervous system.
What two changes occur to the CVS as a result of eating a large meal?
There is an increase in cardiac output due to increased RA filling and there is also a decrease in arterial pressure.
What response do baroreceptors initiate to eating a large meal?
They detect the fall in MABP and so increase cardiac output which reduces CVP and increases arterial pressure.
What changes occur to the heart during strenuous exercise?
There is increased cardiac output due to an increase in pulse and Stroke volume.
What happens the instance exercise begins?
Vasodilation leads to an increased central venous pressure. This causes a fall in blood pressure.
In exercise, what is the benefit of muscle contraction?
Muscle contraction for the exercise also aids circulation.
What happens during haemorrhage?
This is stopped by clotting, and when there is blood loss this leads to hypovolaemia shock. Blood loss causes decreased CVP, Sv, CO and MABP.
What occurs in the tissue during haemorrhage which makes the situation worse?
Locally, there is metabolite build up and so this causes vasodilation which lowers TPR and causes a further drop in MABP
What is the major influence of baroreceptors in haemorrhage?
They increase sympathetic activity on the heart, particularly to increase pulse rate.
What can occur to major organs as a result of haemorrhage?
They can experience reduced perfusion which can lead to delayed death due to inability to maintain MABP.
Where in the brain does control of cardiac output occur?
In the medulla. Information from baroreceptors is sent here and then this coordinates the autonomic nervous system response.
