Ventilation/perfusion relationship

Question 1

What does ‘ventilation’ refer to?

Answer 1

ventilation refers to the air that reaches the alveoli - the mechanical act of moving air in and out of lungs

Question 2

what is ‘pulmonary ventilation’?

Answer 2

minute ventilation = voulme of air breathed in and out in one minute =

Question 3

what is more important? Pulmonary or alveolar ventilation?

Answer 3

alveolar = becuase it takes out the ‘dead space’ that is in the upper airway that doesn’t exchange gas

Question 4

How do you determine alveolar ventilation?

Answer 4

Question 5

what is ‘perfusion’?

Answer 5

The blood that reaches the alveoli

• The process by which CO2 from tissues is brought to lungs for removal
• The process by which deoxygenated blood passes through the lung and becomes oxygenated.

Question 6

what are the waste products of respiration?

Answer 6

water, CO2, nitrogen?

Question 7

what type of epithelial cells make up the alveolus?

Answer 7

type 1 alveolar cells

Question 8

what is the only barrier between gas and blood?

Answer 8

the structual matrix

*when people have cystic fibrosis, they feel breathless b/c this region has increased in thickness therefore they are not properly exhanging

Question 9

how do RBCs pass through the capillary component>?

Answer 9

single file

Question 10

how does gas exchange occur in the lungs?

Answer 10

by simple diffusion from high to low concentration

Question 11

what makes up the partial pressure of the gas leaving your lungs?

Answer 11

N2, O2 and CO2 (and H2O)

Question 12

does the oxygen content in the alveoli fluctuate?

Answer 12

no, O2 arriving in alveoli replaces O2 diffusing out of alveoli to pulmonary capillaries - it doesn’t accumulate but remains the same

Question 13

GAS DIFFUSES FROM HIGH TO LOW CONCENTRATIONS

Question 14

how many alveoli are in the lungs?

Answer 14

•The lungs contain around 300-500 million alveoli and have a surface area of around 70 square metres (half a tennis court)

•

Major function : Gas Exchange

•The Lungs are ideally structured for gas exchange

Question 15

what is the law of gas exchange?

Answer 15

Ficks Law of diffusion

The greater the surface area

and the shorter the distance ;

the greater the rate of diffusion

Question 16

what occurs during rest and exercise to our gas exchange?

Answer 16

• During exercise the area available for exchange can be physiologically increased. decreasing the ‘thickness’ of membrane and allowing more gas exchange
• During rest ; some pulmonary capillaries closed

–Low pressure pulmonary circulation

•Increased cardiac output ; opening of capillaries.

Question 17

pulmonary oedema reduces gas exchange how?

Answer 17

it increases the thickness of the barrier between capillaries and the alveoli - therefore you have a decreased gas exchange

the same thing happens in pulmonary fibrosis - but there is scar tissue etc between alveoli and the capillaries

Question 18

what is the ventilation/perfusion ratio?

Answer 18

•The ratio of the amount of air reaching the alveoli (V)

–To the amount of blood reaching the alveoli (Q)

This ratio is very important - but the numbers themselves are useless

• 1L Air contains approx 200ml O2
• 1L Blood can hold approx 200ml O2
• our bodies have managed to take in as much oxygen as our blood can absorb
• Efficiency and Adequacy

Question 19

if your V/Q is high what happens?

Answer 19

you’re taking in more oxygen than you’re absorbing and you’ll be saturated with oxygen

(high Pressure O2, low pressure CO2)

Question 20

what is the cause of hypoxemia in cardiopulmonary disease?

Answer 20

the mismatch of the ration between V and Q is the most frequent cause of hypoxemia (reduced blood PO2 and low V/Q ratio)

Question 21

does normal V/Q relationship indicate that ventilation and perfusion is normal?

Answer 21

no- sometimes it could be normal, but there are other clincial symptoms

•In lobar pneumonia,

–ventilation to the affected lobe is decreased.

–This produces hypoxic vasoconstriction in the pulmonary capillary bed supplying the lobe

–resulting in decreased perfusion.

–

•Therefore, the V/Q ratio is normal but both ventilation and perfusion are reduced.

Question 22

how does the V/Q ratio differ between regions of the lung itself?

Answer 22

apex = very good ventilation here, but poor diffusion b/c of gravity

at base= perfusion is great, but ventilation is poor b/c we often do not breath deep enough

Question 23

what is arterial hypoxemia?

Answer 23

–Arterial PO2 less than 80 mm Hg in an adult breathing room air at sea level.

Question 25

what is hypoxia?

Answer 25

–Insufficient O2 to carry out normal metabolic functions – usually when arterial PO2 is less than 60 mm Hg

–

–Low V/Q (well perfused, under ventilated)

Question 26

what is hypercapnia?

Answer 26

–Increase in arterial PCO2 above the normal range (40 mm Hg)

–Hypoventilation (low V/Q))

Question 27

what is hypocapnia?

Answer 27

•Hypocapnia

–Abnormally low arterial PCO2 (usually less than 35 mm Hg)

–Hyperventilation (high V/Q)

*give them a paper bag b/c they are bringing their own CO2 back into their blood*

Question 28

at a high altitude, would you hyperventilate or hypoventilate?

Answer 28

hyperventilate b/c at a high altitude you’re always a little hypoxic

Question 29

hypercapnia is associated with what illnesses?

Answer 29

associated with COPD

Question 30

what causes hypocapnia?

Answer 30

hyperventilation

• arterial PCO2 falls
• leads to vasoconstriction and less flow to the brain

Question 31

how would you get a V/Q = 0?

Answer 31

only if there is no ventilation

Question 32

how do you get a V/Q approaching infinity?

Answer 32

When profusion is equal to 0 = wasted ventilation = you’re breathing but not exchanging

Question 33

How does V/Q change in respiratory disease?

Answer 33

• Increased (overventilation/underperfusion)
• decreased (underventilation/overperfusion)

•

• An increased V/Q ratio means an increase in alveolar dead space and “wasted ventilation”
• Good Ventilation; bad/no perfusion

•

• A decreased V/Q ratio means “shunting”
• deoxygenated venous blood bypasses the exchange area and enters the left heart causing arterial hypoxaemia
• Bad/No Ventilation ; Good Perfusion

Question 34

what is the result of good ventilation but no perfusion?

Answer 34

V/q= infinity

wasted ventilation

Question 36

what is the result of an obstructive respiratory disease of v/Q ?

Answer 36

obstructive = low ventilation

normal profusion

therefore V/Q = very small

*this is called shunting b/c the deoxygenated blood is brought to better regions of the lung where it’s possibly less obstructed*

Question 37

what happens to the airway smooth muscle and pulmonary arterioles in hypoxic pulmonary vasoconstriction?

Answer 37

• Relative underventilation/overperfusion
• decreases alveolar PO2 and increases PCO2

•

• A decrease in PAO2 and an increase in PACO2 causes relaxation of airway smooth muscle but contraction of pulmonary arterioles\
• Hypoxic pulmonary vasoconstriction causes diversion of blood away from poorly ventilated/overperfused alveoli and therefore limits “shunting”
• However, long-term alveolar hypoxia (altitude, some respiratory diseases) will cause pulmonary hypertension

Question 38

what occurs to V/Q in pulmonary vasodilation?

Answer 38

Question 39

What is hyperpnea?

Answer 39

• Increased ventilation that matches increased metabolic demand
• During exercise

Question 40

•Explain how airway obstruction would cause hypoxaemia.

•

•What is shunting ?

•

Describe the pulmonary circulation network.