VQ matching - not marked

Question 1

INTRO

what is lung ventilation

Answer 1

Lung ventilation is the flow of gas in and out of the lungs via inspiration and expiration to exchange gas between the inside of the body (that comes from blood) and outside in the atmosphere

Question 2

INTRO

what is lung perfusion

Answer 2

lung perfusion describes the flow of blood to the lungs via the alveolar capillaries of the pulmonary circulation

Question 3

INTRO

what is the ventilation perfusion ratio (V/Q)

Answer 3

The rate of lung ventilation to lung perfusion

the extent to which the two rates are equal, with the ideal lung having a ratio of 1 (as V=Q)

Question 4

INTRO

why is the ideal V/Q ratio 1?

Answer 4

a more efficient lung will match the rate of lung ventilation to the rate of lung perfusion to ensure that the blood is reaching areas of the lung where it can pick up the most oxygen, and the gas is being exchanged readily through ventilation

Question 5

INTRO

what is the V/Q of the average human lung?

Answer 5

average V/Q of a lung is 0.8

= this is because ventilation and blood perfusion are different in different parts of the lung

Question 6

EXPERIMENTAL

how do we measure lung perfusion?

Answer 6

1. inject Xenon-133 into peripheral veins of lung
2. patient takes first breath = xenon is taken up into alveoli in same proportion to blood flow = shows where blood flows
3. for the whole of the lung xenon is rebreathed until evenly distributed

Question 7

LUNG PERFUSION

what is the trend of lung perfusion?

Answer 7

blood flow increases towards the bottom of the lung in comparison to the top

Question 8

LUNG PERFUSION

why is perfusion of lungs greater at the bottom?

Answer 8

gravity = decreases hydrostatic pressure as you move up higher from the heart = decreased perfusion towards the top of the lung

Vascular tone = neural and circulating factors as well as oxygen concentration influence vascular tone of pulmonary circulation to regulate blood perfusion to parts of the lungs

Question 9

LUNG VENTILATION

what is the trend in lung ventilation?

Answer 9

lung ventilation decreases towards the base of the lung

Question 10

LUNG VENTILATION

why does lung ventilation decrease down the lung?

Answer 10

pleural pressure is increased at the base of lungs due to gravity = alveoli become more compliant and ventilation increases

but as the air flow comes in from the top of the lungs, these alveoli are best ventilated = bottom of the lung has poorly ventilated “dead space”

Question 11

ZONES OF LUNGS

why do we split the lung into 3 dynamic zones?

Answer 11

we split the lung into zones because of the differences in perfusion and gas flow throughout

Question 12

LUNG ZONES

what are the 3 zones

Answer 12

zone 1 = apex (top)

zone 2 = middle

zone 3 = base (bottom)

Question 13

LUNG ZONES

describe zone 1

Answer 13

ZONE 1 APEX

pulmonary artery pressure < alveolar pressure (alveoli close compliant vessels so pressure goes down)
= low blood flow
= high ventilation

Question 14

LUNG ZONES

describe zone 2

Answer 14

ZONE 2 MIDDLE

arterial > alveolar pressure
venous < alveolar pressure

blood only flows at arterial end where pressure exceeds alveolar that would normally constrict vessels

this is the point of dynamic equilibrium in ventilation perfusion matching

Question 15

LUNG ZONES

describe zone 3

Answer 15

ZONE 3 BASE

arterial > alveolar
venous > alveolar
= greatest blood flow
= blood flow is proportional to pressure difference between arterial and venous end of vessels

Question 16

V/Q MATCHING

why does the V/Q ratio vary throughout lung

Answer 16

because of the different rates of ventilation and blood flow in these zones

VQ decreasing from a value of 3 at the top of the lung to 0.6 at the bottom. When we take the average of the different V/Q ratios throughout the regions of the lung we see that the average is 0.8.

Question 17

V/Q MATCHING

how does V/Q matching occur

Answer 17

done by the pulmonary vessels using hypoxia to vasoconstrict.

Where there is a lack of ventilation, there is a lack of oxygen to that part of the lung = to keep the lung efficient by ensuring that blood goes where it can pick up the most oxygen, the lungs reduce perfusion to the area that has reduced ventilation

not like systemic where vasodilation occurs to meet metabolic needs during hypoxia

Question 18

V/Q mismatch

what diseases cause reduced V/Q

Answer 18

asthma where smooth muscles in the airways contract to reduce ventilation due to increased resistance

COPD where inflammation limits ventilation

partial pressure of oxygen in the capillaries drops, whilst that of carbon dioxide increases = cannot match the perfusion rate to the lowered ventilation = less efficient

Question 19

V/Q MISMATCH

what happens when V/Q is increased?

Answer 19

instead of the blood being closer to the composition of venous blood, it gets closer to the composition of inhaled air

Question 20

CLINICAL:

how can we treat V/Q mismatch?

Answer 20

usually leads to decreased oxygen = increasing proportion of oxygen inhaled will increase oxygen uptake into blood

breathing 100% ox = V/Q of 1 unless there is a total blockage of V or Q where the ratio is 0 = then altering oxygen has no impact