Matching ventilation and perfusion

Question 1

How much blood does the lung receive per minute?

Answer 1

5l/min (cardiac output)

Question 2

How much air does the lung receive per minute?

Answer 2

5l/min

Question 3

Why does the intra-pleural pressure cary along the lung?

Answer 3

Due to gravity on the base

Question 4

Is the intra-pleural pressure positive or negative?

Answer 4

Negative

Question 5

Does the base or the apex of lung have the least negative pressure and why?

Answer 5

The base because it is more compressed due to gravity

Question 6

Why does the base expand better on inspiration than the apex?

Answer 6

Because it has a less negative intra-pleural pressure and is more compressed due to gravity (under its own weight)

Question 7

Why do the lungs and chest cavity pull away from each other?

Answer 7

Intra-pleural pressure is more negative than the atmospheric pressure

Question 8

Does posture effect the efficiency of ventilation?

Answer 8

Yes

Question 9

What happens to the apex of the lung due to the higher pressure at the base?

Answer 9

The apex becomes distended (swollen)

Question 10

When the diaphragm contracts it expands the bottom part of the thoracic cavity. Why is this more efficient that expanding the apex?

Answer 10

Because the base is easier to expand than the apex due to it being more compressed (less negative pressure)

Question 11

How much does the pulmonary circulation accept?

Answer 11

The entire cardiac output always

Question 12

Why is vascular resistance less than systemic resistance?

Answer 12

Vascular circulation is at a lower pressure

Question 13

Why does perfusion occur easier in pulmonary circulation?

Answer 13

It has a lower resistance than systemic

Question 14

At the base is ventilation and perfusion efficient or not?

Answer 14

Efficient

Question 15

At the apex is ventilation and perfusion efficient or not?

Answer 15

Not

Question 16

When is the apex well perfused?

Answer 16

When blood pressure increases

This increases the number of capillaries and alveoli that are used and causes the apex to be well perfused

Question 17

The proportion of which molecules are monitored to change levels of perfusion/ventilation?

Answer 17

Oxygen and CO2

Question 18

How is ventilation/perfusion changed?

Answer 18

affecting smooth muscles of bronchioles and capillaries

Question 19

What happens in the lungs when there is a high ventilation perfusion ratio and what does high V/Q mean?

Answer 19

Means there is a high alveolar oxygen concentration and a low alveolar CO2 concentration.
Causes vasodilation and broncho constriction

Question 20

What is the effect of vasodilation on blood concentration?

Answer 20

Increases blood flow so more CO2 and be moved into the lungs and more O2 can be moved out

Question 21

What is the effect of broncho-constriction on gas composition?

Answer 21

More O2 can leave the alveoli. Constriction will increase resistance, decreasing the amount of air coming into a space that is not well perfused. More oxygen leaves the well perfused alveoli

Question 22

What happens in the lungs when there is a low ventilation effusions ratio and what does low V/Q mean?

Answer 22

Means there is a low alveolar oxygen concentration and high alveolar CO2 concentration
Causes vasoconstriction dn broncho-dilation

Question 23

What is the effect of vasoconstriction on blood concentration?

Answer 23

Decrease in blood flow so more CO2 can leave the alveoli and more O2 can enter

Question 24

What happen in systemic circulation when there is a low V/Q?

Answer 24

Leads to arterial vasodilation

Question 25

When does hypoxic vasoconstriction occur?

Answer 25

When V/Q is low

Question 26

What is hypoxic vasoconstriction?

Answer 26

Drop in oxygen saturation causes constriction of the pulmonary capillaries causing blood supply to be reduced in the hypoxic region and diverted to the well ventilated areas of the lung where V/Q will be matched

Question 27

Why can hypoxic vasoconstriction be harmful to someone with pulmonary disease?

Answer 27

In the hypoxic area hypoxic vasoconstriction will occur and this will increase resistance in that area. This will increase pulmonary BP and so induce right ventricle heart failure.
As BP rises more blood is pressed into capillaries and causes pulmonary oedema

Question 28

Why is partial pressure of oxygen lower in the arteries than alveoli?

Answer 28

Anatomical shunt. Bronchiole arteries to pulmonary vein - bypass gas exchange, so oxygenated blood goes straight back to the lung.

Question 29

What is anatomical shunt?

Answer 29

Bronchiole arteries drain straight into pulmonary veins

Miss gas exchange

Question 30

What is pulmonary shunt?

Answer 30

Ventilation/perfusion ratio is 0

alveoli are perfused but no ventilation to that area

Question 31

How doe left ventricle heart failure impact V/Q?

Answer 31

Lv heart failure leads to an increase in pulmonary pressure.
This disturbs the hydrostatic/oncotic pressure balance
Causes H2O to be trapped in the lung causing pulmonary oedema

Question 32

Why is giving a hypoxic patient oxygen dangerous?

Answer 32

Increased oxygen reduces ventilation and causes less CO2 to be released so CO2 concentrations increase and H2CO3 forms this decreases pH.
This will mean less CO2 will enter the alveoli so when the O2 leaves the alveoli will collapse