Flashcards in Haemodynamics Deck (24)
What does a systolic BP greater than 140mmHg represent?
140-160mmHg indicates marginal hypertension, greater than 160mmHg indicates a definite intervention threshold for hypertension
What does a diastolic BP greater than 90 mmHg represent?
90-100mmHg indicates marginal hypertension, greater than 100mmHg is the definite intervention threshold
What is pulse pressure?
The difference between systole and diastole.
What is prehypertension?
Blood pressure readings with a systolic pressure of 120-139 mmHg or a diastolic pressure from 80-89 =mmHg, where they do not currently require medication, but should be monitored for future interventions that may be required
How do you calculate mean arterial pressure?
MAP = DIASTOLIC + ⅓ (SYSTOLIC-DIASTOLIC/PULSE PRESSURE)
Define cardiac output
Total blood flow out of the heart per unit time (litres/min)
Define stroke volume
The amount of blood pumped out of the ventricles in one contraction
How can you calculate cardiac output?
CO = HR X SV OR BP/TPR
How does the cardiovascular system aid an increase in oxygen uptake during exercise?
Increase in pulmonary pressure to improve the perfusion of the lungs
Why does the pulse pressure disappear in the small arteries?
Due to stretchiness/compliance
What causes compliance of the blood vessels?
Compliance is due to elastin in the arterial walls so compliance is good with high elasticity as this stretchiness reduces the work of the heart in pumping the blood as some of the blood is stored in the large arteries by them stretching and increasing their volume.
Why may compliance of arteries decline with age, and what can this cause?
The arteries lose some of their elastin which is subsequently replaced by collagen which causes a loss of elasticity and ‘harden’ which means the systolic pressure is increased as the aorta cannot stretch to accommodate the stroke volume
How can you calculate local flow?
Why do we need a high and constant blood pressure to organs?
To ensure that local vasodilation is effective in increasing local blood flow
What is Poiseuille's law?
Flow = (RADIUS OF A VESSEL)4, therefore, if you keep the pressure constant but double the radius size, the flow will increase by 16x
What determines the viscosity of the blood?
Depends mainly on haematocrit (proportion of red cells in the blood); if this is too high, the blood is too viscous and the heart has to work harder. Other factors include; red cell deformability, red cell aggregation and plasma viscosity
Why don't erythrocytes and epithelia ever touch?
They both have a negative charge so they repel each other
What is polycythemia?
A disease state in which the haematocrit increases due to an excessive production of RBCs or decrease in the volume of blood plasma
Describe the interaction of erythrocytes with polypeptide chains
Edges of erythrocytes interact with polypeptide chain which protrude into the capillary lumen from the endothelium --> deflection caused by erythrocytes passing through --> allows calcium into the endothelium and triggers NO formation --> relaxation and dilatation of the walls (anticoagulant)
What is Laplace's law?
The pressure that an elastic vessel can withstand is dependent on the tension produced in the walls by their elasticity, divided by the vessel radius
How can the radius of a vessel affect the amount of pressure it can withstand?
The smaller the radius of the vessel, the greater the pressure that a given wall strength can withstrand
What is an atheroma?
A fatty deposit on the inside of an artery, but due to Poiseuille’s law even a small atheroma can dramatically decrease blood flow and render tissue hypoxic
How may an aneurysm present?
Discovered incidentally in MRI or angiography, rupture causing subarachnoid brain haemorrhage and symptoms of mass effect on neural structures.