Lecture 16 - Ventilation and O2 and CO2 exchange

Question 1

How do gases move across the alveolar capillary membrane?

Answer 1

Diffusion

Question 2

Why is the alveocapillary membrane thin?

Answer 2

Thinness is due to basement membrane of alveoli and capillary being fused together - single membrane

Question 3

What does Fickʼs Law of Diffusion describe?

Answer 3

Explains gas exchange through the membranes

Question 4

What is emphysema characterised by?

Answer 4

Emphysema is a disease characterized by dilation of the alveolar spaces and destruction of the alveolar walls.

Question 5

Why do patients with emphysema have
decreased PO2 in blood?

Answer 5

There is a decrease in the surface area of the lung (A) in emphysema. According to Fick’s law, when we have a decrease in A, we will have a decrease in F (Flux =Amount flowing)

Question 6

What does pulmonary fibrosis involve?

Answer 6

thickening and scarring of the alveolar membranes

Question 7

Why do patients with pulmonary fibrosis have
decreased PO2 in blood?

Answer 7

There is an increase in the thickness of the alveoli (T) in pulmonary fibrosis. According to Fick’s law, when there is an increase in diffusion distance, there will be a decrease in diffusion capacity/F

Question 8

What does pulmonary oedema refer to?

Answer 8

water accumulation in alveoli

Question 9

Why do patients with pulmonary oedema have
decreased PO2 in blood?

Answer 9

When water accumulates in alveoli, there will be an increase in diffusion distance. According to Fick’s law, when there is an increase in diffusion distance, there will be a decrease in diffusion capacity/F

Question 10

What is the main factor in flux (F)?

Answer 10

P1-P2 (alveolar – arterial)
Pressure difference drives diffusion

Question 11

What does PAO2 depend on?

Answer 11

1. PIO2 of inspired air
2. Alveolar ventilation
3. Oxygen consumption
   The atmospheric PO2 is usually constant,
   so it is the balance between oxygen
   consumption and alveolar ventilation that is
   most important.

Question 12

What does PACO2 depend on?

Answer 12

1. Alveolar ventilation
2. Carbon dioxide production
3. PICO2 of inspired air
   Alveolar PACO2 is usually determined
   only by the balance between carbon
   dioxide production and alveolar
   ventilation, because atmospheric PCO2
   is negligible.

Question 13

How can we measure partial pressures in arterial blood

Answer 13

Measure these from arterial blood sample
(“Arterial Blood Gas analysis ” – ABG)

Question 14

What is the respiratory quotient (RG)?

Answer 14

The amount of CO2 produced in relation to the amount of O2 consumed by metabolism and is dependent on caloric intake.
Considered as a measure of cell metabolism
RQ = VCO2/VO2

Question 15

MCQ: The movement of oxygen by diffusion between the alveoli and the pulmonary capillary blood is:

Answer 15

proportional to the partial pressure gradient between air-blood barrier

Question 16

How can we apply Fick’s law to understand diffusion during exercise?

Answer 16

During exercise more O2 consumed by the muscle. This increased VT and increased VA creates an increase alveolar surface (A)
More capillaries perfused due to ↑ capillary surface area and reduced diffusion distance for capillaries