Session 8

Question 0

How does the pulmonary circulation work?

Answer 0

With low pressure and low resistance

Question 1

Describe the blood flow to the lungs

Answer 1

Brachial - part of systemic circulation, meets metabolic requirement of the lungs
Pulmonary - blood supply to the alveoli, required for gaseous exchange

Question 2

What is the pressure in the RA?

Answer 2

0-8 mmHg

Question 3

What is the pressure in the LA?

Answer 3

1-10 mmHg

Question 4

What is the pressure in the aorta?

Answer 4

100-140mmHg

Question 5

What is the mean arterial pressure?

Answer 5

12-15mmHg

Question 6

What is the mean pressure in pulmonary capillaries?

Answer 6

9-12mmHg

Question 7

What is the mean venous pressure?

Answer 7

5mmHg

Question 8

What is the ventilation-perfusion ratio?

Answer 8

Ratio of the amount of air reaching the alveoli to the amount of blood reaching the alveoli.

Question 9

What is the optimal V/Q ratio?

Answer 9

0.8

Question 10

How is V/Q ratio maintained?

Answer 10

By diverting blood from the alveoli that aren’t well ventilated

Question 11

What is hypoxic pulmonary vasoconstriction?

Answer 11

Ensures optimal ventilation perfusion ratio by constricting the pulmonary arteries. Poorly ventilated alveoli are less well perfused therefore gaseous exchange is optimised.

Question 12

What happens in chronic hypoxic vasoconstriction?

Answer 12

RV failure. Can occur at high altitudes or as a consequence of lung disease –> chronic pulmonary hypertension. High after load on RV leading to RV failure.

Question 13

What is transit time?

Answer 13

The time it takes RBCs to flow through capillary

Question 14

How does tissue fluid form?

Answer 14

Hydrostatic pressure of blood within capillaries pushes fluid out
Oncotic pressure (colloid osmotic pressure) draws fluid into the capillary

Question 15

What influences capillary hydrostatic pressure?

Answer 15

Venous pressure in systemic circulation fluid tends to move out at the arterial end

Question 16

How does oedema form?

Answer 16

Increased capillary pressure causes more fluid to filter out

Question 17

How do you treat pulmonary oedema?

Answer 17

Give the patient diuretics to decrease blood volume which therefore decreases hydrostatic pressure.

Question 18

What causes pulmonary oedema?

Answer 18

High capillary pressure (if it exceeds 20-25mmHg)

Question 19

How much of the cardiac output does the brain use?

How much of the oxygen consumption of the body is attributed to the brain?

Answer 19

15% of CO

Grey matter consumes 20% of the oxygen of the body at rest

Question 20

How is the brain supplied well?

Answer 20

High capillary density (large SA, decreased diffusion distance)
High basal flow rate
High oxygen extraction
Structure - anastomoses between basilar and internal carotid arteries

Question 21

How can blood vessels respond to fluctuations in blood pressure?

Answer 21

Myogenic autoregulation - increase in BP leads to vasoconstriction, decrease in BP leads to vasodilation

Question 22

What is hypercapnia?

What is hypocapnia?

Answer 22

Hyper - increased PCO2 leading to vasodilation
Hypo - decreased PCO2 leading to vasoconstriction
Panic/hyperventilation can cause hypocapnia and cerebral vasoconstriction leading to dizziness/fainting

Question 23

What is cushing’s reflex?

Answer 23

A physiological nervous system response to increased intracranial pressure (ICP) that results in Cushing’s triad (increased blood pressure, irregular breathing, and a reduction of the heart rate). There is increased sympathetic vasomotor activity.

Question 24

What forms the blood brain barrier?

Answer 24

Cerebral capillaries form a tight BBB.

Question 25

What is the diffusion distance for myocardium?

Answer 25

9 micro metres