Session 6 Flashcards
If TPR is constant but cardiac output decreases what happens to the pressure in arteries and veins?
Arterial pressure decreases
Venous pressure increases
If TPR is constant but cardiac output increases what happens to the pressure in arteries and veins?
Arterial pressure increases
Venous pressure decreases
If cardiac output is constant but TPR increases what happens to the pressure in arteries and veins?
Arterial pressure increases
Venous pressure decreases
If cardiac output is constant but TPR decreases what happens to the pressure in arteries and veins?
Arterial pressure decreases
Venous pressure increases
What is the ventricular compliance curve?
Shows the relationship between the venous pressure and ventricular volume
What is starlings law of the heart?
If muscle is stretched before contracting, it contracts harder. More the heart fills up, the harder it contracts (within reason) therefore the bigger the stroke volume.
What is the starling curve?
Relates stroke volume to venous pressure. The slope represents contractility.
Define contractility
Ability of the heart fibres to contract
Contraction
Realisation of the ability to contract
What determines the end systolic volume?
How hard the hard contracts and how hard it is to eject the blood
What factors determine the force of contraction?
End diastolic volume and contractility
What is an aortic impedance?
Difficulty in ejecting blood from the left ventricle
What factors affect aortic impedance?
Depends mainly on TPR (if TPR increases then arterial pressure increases therefore its harder to push in).
What will the end systolic volume be if the arterial pressure is low?
Low. Systolic volume will be high.
Describe what would happen to the stroke volume if the venous pressure increased and if the arterial pressure increased
Venous - increase in stroke volume
Arterial - decrease in stroke volume
Where is the carotid sinus located?
Carotid bifurcation in carotid artery
What does a fall in arterial pressure do?
Increases heart rate by decreasing parasympathetic activity and increasing sympathetic activity. Increases contractility by increasing sympathetic activity.
What is the bainbridge reflex?
An increase in heart rate due to an increase in central venous pressure. Increased blood volume is detected by stretch receptors (baroreceptors) located in both atria at the venoatrial junctions.
What can contractility be affected by?
Neurotransmitters, hormones or drugs acting on myocardium
What are pre-load and after-load?
Pre-load - end diastolic stretch (venous pressure determines this)
After-load - when blood is expelled into arteries (force necessary to do this). Determines what happens during systole.
If heart rate increases with no other change then what would happen?
Initially CO rises, but TPR stays the same. Increase in CO, decrease in venous pressure therefore stroke volume falls and CO goes back to original value.
Describe the changes to blood supply to skeletal when exercising
Pre-capillary sphincters open up allowing huge amounts of blood to be available to them muscles (goes from a high TPR to low TPR). Veins surrounding the skeletal muscle become compressed.
When is there a risk of pulmonary oedema?
When the output from the RHS of the heart doesn’t match the output of the LHS.
How is overfilling of the ventricles prevented?
Increasing heart rate which occurs as exercise begins. Thus when venous pressure increases the heart rate is already high therefore keeping stroke volume down.
What happens when someone stands up?
Blood pools in the superficial veins of the legs due to gravity therefore central venous pressure decreases. Superficial veins are affected because they are surrounded by air which is less dense than the deep veins which are surrounded by water-logged tissues.
What is postural hypotension?
Decrease in blood pressure due to standing up. It occurs because of a compromise of the reflexes which keep blood pressure constant.
What does a long term increase in blood volume do?
Venous pressure increases, CO increases therefore arterial pressure increases. More blood goes to tissues. Autoregulation and increased TPR therefore arterial pressure increases more.
What is auto-transfusion?
Fluid tends to move from extra cellular space into circulation
What do diuretics do?
Alter sodium balance by interaction with hormonal control of kidney
