ventilation

Question 1

significance of ventilation and perfusion at lung apex

Answer 1

alveoli stretched by gravity, so need greater pressure to inflate (less compliant and perform less ventilation); simultaneously, blood is pulled downwards, achieving a lower intravascular pressure, causing reduced perfusion

Question 2

significance of ventilation and perfusion at lung base

Answer 2

intrapleural fluid pulled down by gravity, causing a greater transmural pressure (less -ve); smaller transmural gradient; smaller alveoli so can inflate more (more compliant), performing more ventilation; simultaneously blood is pulled downwards to produce a higher intravascular pressure, increasing perfusion of the parenchyma

Question 3

pattern of ventilation perfusion matching from apex to base

Answer 3

perfusion and ventilation both increase from apex to base, but perfusion does so at a greater rate

Question 4

where does wasted ventilation occur and why

Answer 4

apex because perfusion cannot meet the demands of the ventilation supplied

Question 5

where does wasted perfusion occur and why

Answer 5

base because ventilation cannot meet the demands of the blood perfused

Question 6

ventilation-perfusion ratio if matched

Answer 6

1

Question 7

why is ventilation-perfusion ratio not 1, and what is it in fact

Answer 7

gravity means changes regionally (calculated as alveolar ventilation/cardiac output) - averages approx. 0.84 in a healthy lung