Ventilation - Perfusion relationship

Question 1

What should the normal V/Q ratio be?

Answer 1

1

Question 2

What happens when pulmonary capillary pO2 is low?

Answer 2

Hypoxic vasoconstriction of pulmonary arterioles occurs to divert blood

Question 3

What happens when alveolar pCO2 is low?

Answer 3

Bronchoconstriction occurs to divert air to a better perfused lung

Question 4

What happens to the ratio and partial pressures when there is a lack of perfusion?

Answer 4

Ratio > 1 and pCO2 rises, pO2 falls

Question 5

What can cause a ratio of less than 1?

Answer 5

Asthma, COPD, RDS in newborns, Pulmonary odema

Question 6

Why is the pO2 of oxygen less than expected in mixed blood ? (poorly ventilated & well ventilated)

Answer 6

Hb is binding to the oxygen available so less is dissolved in the blood, giving a low partial pressure

Question 7

Why is the pCO2 directly proportional to the CO2 content in the blood?

Answer 7

Because CO2 doesnt have a carrier molecule, it is dissolved in the blood

Question 8

What is the effect of hyperventilation due to poor ventilation?

Answer 8

small increase in pO2 but pCO2 is significantly lowered, hypoxia keeps stimulating hyperventilation