Haemodynamics

Question 1

What does a systolic BP greater than 140mmHg represent?

Answer 1

140-160mmHg indicates marginal hypertension, greater than 160mmHg indicates a definite intervention threshold for hypertension

Question 2

What does a diastolic BP greater than 90 mmHg represent?

Answer 2

90-100mmHg indicates marginal hypertension, greater than 100mmHg is the definite intervention threshold

Question 3

What is pulse pressure?

Answer 3

The difference between systole and diastole.

Question 4

What is prehypertension?

Answer 4

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

Question 5

How do you calculate mean arterial pressure?

Answer 5

MAP = DIASTOLIC + ⅓ (SYSTOLIC-DIASTOLIC/PULSE PRESSURE)

Question 6

Define cardiac output

Answer 6

Total blood flow out of the heart per unit time (litres/min)

Question 7

Define stroke volume

Answer 7

The amount of blood pumped out of the ventricles in one contraction

Question 8

How can you calculate cardiac output?

Answer 8

CO = HR X SV OR BP/TPR

Question 9

How does the cardiovascular system aid an increase in oxygen uptake during exercise?

Answer 9

Increase in pulmonary pressure to improve the perfusion of the lungs

Question 10

Why does the pulse pressure disappear in the small arteries?

Answer 10

Due to stretchiness/compliance

Question 11

What causes compliance of the blood vessels?

Answer 11

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.

Question 12

Why may compliance of arteries decline with age, and what can this cause?

Answer 12

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

Question 13

How can you calculate local flow?

Answer 13

Pressure/local resistance

Question 14

Why do we need a high and constant blood pressure to organs?

Answer 14

To ensure that local vasodilation is effective in increasing local blood flow

Question 15

What is Poiseuille’s law?

Answer 15

Flow = (RADIUS OF A VESSEL)4, therefore, if you keep the pressure constant but double the radius size, the flow will increase by 16x

Question 16

What determines the viscosity of the blood?

Answer 16

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

Question 17

Why don’t erythrocytes and epithelia ever touch?

Answer 17

They both have a negative charge so they repel each other

Question 18

What is polycythemia?

Answer 18

A disease state in which the haematocrit increases due to an excessive production of RBCs or decrease in the volume of blood plasma

Question 19

Describe the interaction of erythrocytes with polypeptide chains

Answer 19

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)

Question 20

What is Laplace’s law?

Answer 20

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

Question 21

How can the radius of a vessel affect the amount of pressure it can withstand?

Answer 21

The smaller the radius of the vessel, the greater the pressure that a given wall strength can withstrand

Question 22

What is an atheroma?

Answer 22

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

Question 23

How may an aneurysm present?

Answer 23

Discovered incidentally in MRI or angiography, rupture causing subarachnoid brain haemorrhage and symptoms of mass effect on neural structures.

Question 24

What is an aneurysm?

Answer 24

An excessive localized swelling of the wall of an artery