Ventilation-Perfusion Relationships

Question 1

What are the issues with the alveolar lung?

Answer 1

Gas and Blood don’t flow past each other
Convective gas flow to a blind ended sack
Inspired air mixes with existing gas in lung
Arterial PO2 equilibrates to the PO2 of the alveolus
Much less efficient and thus consequences for V/Q Matching

Question 2

Why is insect tracheal gas exchange better?

Answer 2

highly efficient and supports highest aerobic metabolic rates
O2 delivery is carrier free

Question 3

Why is the fish gill exchange better?

Answer 3

Efficient gas/blood barrier

Involves counter-current gas exchange to efficiently oxygenate blood to environmental PO2

Question 4

Why is the bird parabronchial system better?

Answer 4

Constant uni-directional convective gas flow
perpendicular arrangement of air tubes and vasculature enables cross-current gas exchange
Venous blood oxygenates to within 90% of inspired PO2
Greater efficiency of oxygen uptake - allows flight at high altitude

Question 5

How does the ECMO machine take advantage of the design?

Answer 5

counter current gas exchange
all flow
no convection
inspired PO2 can be above atmospheric and above 21%

Question 6

What is ventilation?

Answer 6

the amount of O2 consumed

Question 7

What is perfusion?

Answer 7

the rate of O2 transfer from alveolus to blood

Question 8

What is the effect on V/Q as body size decreases?

Answer 8

there becomes a larger mismatch

Question 9

How does the shrew compensate for the mis-match?

Answer 9

higher HR and breathing rate - limit of heart and lung performance

Question 10

What causes a pulmonary embolism?

Answer 10

a high demand for oxygen placing high transmural pressure over blood gas barrier

Question 11

What does increased minute ventilation do?

Answer 11

increase pulmonary artery pressure and decreases alveolar pressure causing rupture as transmural pressure increases

Question 12

What does grunting do?

Answer 12

increases the air flow out of the lung during exhalation

Question 13

What is the equation used to measure pAO2?

Answer 13

pAO2 = FlO2(pATM-SVP)-paCO2(flO2 + 1-FlO2/RQ)

Question 14

What is FlO2(pATM-SVP)?

Answer 14

the proportion of oxygen in inhaled gas

Question 15

What is FlO2 +1-FlO2/RQ?

Answer 15

rate of O2 consumption by metabolism

Question 16

What is the standard vapour pressure of water?

Answer 16

SVP = 47mmHg

Question 17

What is the typical respiratory quotient?

Answer 17

0.8

Question 18

What is alveolar PO2 significantly affected by?

Answer 18

atmospheric PO2 and arterial carbon dioxide

Question 19

What happens if PCO2 increases?

Answer 19

alveolar PO2 decreases

Question 20

What happens if RQ increases?

Answer 20

alveolar PO2 increases

Question 21

How might you increase RQ?

Answer 21

eating high carbohydrate diet

Question 22

At high altitude how might you adapt to conserve pAO2?

Answer 22

increasing breathing frequency to decrease paCO2
high carbohydrate diet - RQ=1
climb when barometric pressure is high

Question 23

What are the adaptive breathing responses to hypoxia?

Answer 23

increase breathing depth and frequency

increasing blood flow rate through the lung by vasoconstriction

Question 24

What is the maximum O2 delivery set by/

Answer 24

tidal volume
breathing frequency
airway smooth muscle constriction

Question 25

What is the maximum O2 loadning into blood set by?

Answer 25

``` O2 in alveolus pulmonary artery blood pressure vascular smooth muscle tone blood flow (All alveolar-arterial pressure gradient) ```

Question 26

What are the effects of raising pulmonary artery blood pressure through constriction?

Answer 26

redirects blood flow to alveoli | speeds up transit time of blood through lung

Question 27

What are the problems of raising pulmonary artery blood pressure through constriction?

Answer 27

greater resistance for blood to enter lung vascular tree | rapid transit time through alveolus reduces time for gas exchange

Question 28

What does increase breathing depth and frequency do?

Answer 28

raises alveolar PO2 which increases drive to blood

Question 29

What does the right shift in the oxy-hemoglobin curve do?

Answer 29

favour off-loading to tissues

Question 30

What else can be done to increase oxygen availability?

Answer 30

increase no of RBCs increase no. of peripheral vessels increase capacity for tissue anaerobic metabolism

Question 31

What does hypoxia do to the alveolar-arterial oxygen partial pressure gradient?

Answer 31

increases the gradient due to low venous return to the lung

Question 32

What would happen without the HPV response?

Answer 32

arterial pO2 would wall and p[A-a] collapses resulting in death

Question 33

What does HPV response do?

Answer 33

increases RBCs to increase O2 carrying capacity | increased breathing brings pAO2 closer to atmospheric

Question 34

What happens with poor ventilation and large blood flow?

Answer 34

need to reduce perfusion - so hypoxia constricts pulmonary arterioles - redirects blood to well ventilated areas

Question 35

What happens with good ventilation and poor blood flow?

Answer 35

need to reduce ventilation - low CO2 constricts bronchioles - redirects air to better vascularised areas