ventilation and perfusion

Question 1

ventilation (V)

Answer 1

air that enters the alveoli

- air contributes to gas exchange and air that is breathed out

Question 2

perfusion (Q)

Answer 2

the amount of blood flow through the pulmonary capillaries

process by which deoxygenated blood become oxygenated by blood passing through the lungs

influenced by cardiac output
CO= HR x SV
= 5l/min (5000ml/min)

Question 3

alveolar ventilation rate equation

Answer 3

AVR = (Tidal Volume - Dead Space) x Respiration Rate

AVR = (500ml/breath - 150ml/breathe) x 12-18 breaths/min

Question 4

what is the relationship of ventilation and perfusion?

Answer 4

V/Q

Question 5

what is V/Q normally?

Answer 5

0.8 approx

Question 6

what is the conditions of good ventilation?

Answer 6

increased PO2
decreased PCO2

increased V; same Q
so V/Q is less than 0.8
- need more perfusion to increase value to normal

vasodialtion of capillary to increase blood flow

Question 7

good ventilation conditions effect on V/Q relationship

Answer 7

increased V; same Q
so V/Q is less than 0.8

so need more perfusion to increase value to normal

Question 8

how does O2 increase perfusion?

Answer 8

oxygen produces nitric oxide in smooth muscle cells

• causes relaxation as release potassium ions
• vasodilation

more perfusion

Question 9

what are the conditions for poor ventilation?

Answer 9

decreased PO2
increased PCO2

decreased V, same Q
so V/Q is more than 0.8
- need to decrease perfusion to decrease value to normal

vasoconstriction of capillary to decrease blood flow

Question 10

poor ventilation conditions on V/Q relationship

Answer 10

decreased V, same Q
so V/Q is more than 0.8
- need to decrease perfusion to decrease value to normal

Question 11

how does poor ventilation condition cause an increase in perfusion to correct the V/Q relationship?

Answer 11

decreased PO2 means there is decreased nitric oxide production in smooth muscle cells

potassium ions cannot leave the cell 
- so RMP increases
- reach threshold
- AP generated 
vasoconstriction 

lowering perfusion

Question 12

what is the difference in autoregulation in systemic blood vessels compared to pulmonary blood vessels?

Answer 12

autoregulation is OPPOSITE in systemic blood vessels compared to pulmonary blood vessels

Question 13

what is the effect of exercise on ventilation and perfusion?

Answer 13

exercise causes increased CO
- increased perfusion as more blood flow
need to increase ventilation to match as V/Q increases above 0.8

increased gas exchange
PCO2 in alveoli increases
- acts on bronchial smooth muscle, cause them to dilate
- decreasing resistance
- allowing greater flow of O2 into blood and CO2 out in exhale

Question 14

what is the effect of low perfusion on gas exchange?

Answer 14

low perfusion causes minimal gas exchange

decreased perfusion causes V/Q to be less that 0.8
- decrease ventilation to match low perfusion

CO2 acts on bronchial smooth muscle

• causes constriction
• increasing resistance, lowering gas flow

want lower volume of air entering alveoli so not to waste ventilation due to poor perfusion

air can be redirected to other better functioning alveoli

Question 15

what can cause a low perfusion?

Answer 15

pulmonary embolism
- occludes blood flow in capillary around alveoli

heart failure on right side