CVS Session 8- Special Circulations Flashcards
What is ventricular fibrillation?
Uncoordinated contraction of the ventricles. They contract very fast and therefore CO plummets.
What does a longer P-R interval indicate?
A problem at the AV node causing delayed spread of electrical activity to the ventricles.
What are the two lung circulations and what do they do?
- bronchial- part of the systemic circulation and meets the metabolic requirements of the lungs
- pulmonary- provides blood supply to alveoli and is required for gas exchange.
What is the cardiac output at rest for a typical 70kg man?
5L/min
What is the max cardiac output?
20-25L/min
What has the pulmonary circulation got to be able to do?
Accommodate the entire cardiac output determined by the systemic circulation.
What is the main difference between the pulmonary and systemic circulation?
Pulmonary is supply driven where as systemic is demand led.
What is the mean arterial pressure in the pulmonary circulation?
12-15mmHg
What is the mean capillary pressure in the pulmonary circulation?
9-12mmHg
What is mean venous pressure in the pulmonary circulation?
5mmHg
What adaptations mean that resistance is low in the pulmonary circulation?
- short wide vessels,
- lots of capillaries,
- arterioles have little smooth muscle
What two adaptations means that the pulmonary circulation has efficient gas exchange?
- large surface area due to a high density of capillaries in alveolar walls
- short diffusion distance due to a thin tissue separating plasma and gas.
What is the optimum ventilation perfusion ratio?
0.8
How does hypoxia pulmonary vasoconstriction ensure that this ratio is maintained?
It causes vasoconstriction of poorly ventilated vessels, therefore they are less perfused and this blood is shunted to well ventilated alveoli.
What is the effect of gravity on lung vessels?
Apex vessels collapse during diastole
Middle vessels at heart level are patent
Base vessels are distended.
What 2 conditions cause pulmonary oedema due to high LA pressure?
Mitral valve stenosis
Let ventricular heart failure.
What is used to relieve symptoms of pulmonary oedema?
Diuretics
What is the result of lack of blood flow to the brain after:
- seconds
- minutes
- syncope
- death
How does the brain meet its high oxygen demand?(3)
- has a high capillary density and therefore a large surface area and short diffusion distance
- has a high basal flow rate
- high oxygen extraction
What 3 factors ensure a secure cerebral blood supply?
- anastomoses between basilar and internal carotid arteries
- Myogenic autoregulation
- metabolic regulation
What is the benefit of Myogenic autoregulation when blood pressure falls?
It causes vasodilation to increase blood flow to the brain despite this drop in blood pressure.
What is hypercapnia and what benefit does it have on cerebral blood flow?
It is a high partial pressure of carbon dioxide.
It causes vasodilation and therefore increases blood flow to the brain.
What happens due to Cushing’s reflex when intracranial pressure increases?
Cerebral blood flow decreases
What 2 factors increase intracranial pressure?
-cerebral tumour or haemorrhage
What pathway does decreased cerebral blood flow increase?
Sympathetic
Which molecules can diffuse freely across the blood brain barrier?
Lipid soluble ones e.g oxygen and carbon dioxide.
Where do the left and right coronary arteries arise from respectively?
The left and right aortic sinuses
When does blood flow in the coronary arteries mainly occur?
During diastole.
Why does coronary blood flow mainly occur during diastole?
Because during systole, the ventricular walls compress against the coronary vessels and therefore reduce their blood flow.
How is the oxygen demand met in the coronary circulation?(3)
- small fibre diameter therefore short diffusion distance
- high capillary density therefore efficient oxygen exchange
- nitric oxide production by coronary endothelium causes vasodilation and therefore an increased basal flow rate.
What is the normal state of capillaries and arterioles in skeletal muscle and why?
-arterioles have high vasomotor tone and are therefore constricted
-a lot of capillaries are shut off by pre-capillary sphincters
This allows recruitment of extra capillaries and dilatation of arterioles during exercise, in order to increase blood flow.
What are 5 vasodilators?
Increased potassium conc. increased osmolarity Inorganic phosphates Adenosine High H+ conc.
What does blood flow through in the cutaneous circulation?
Arterio-venous anastomoses
What do these anastomoses do when body temperature increases and why?
They dilate in order to increase heat dissipation .
Where are these anastomoses found?
In the peripheries- e.g fingers, toes, ears, nose etc.
What influences AVAs?
The sympathetic nervous system.
