Theme 4: Lecture 3 - Gas exchange and gas transport

Question 1

What are the 2 functions of the lungs

Answer 1

• Ventilation

- Gas exchange

Question 2

What is ventilation

Answer 2

Movement of air in and out of the lungs

Question 3

What is gas exchange

Answer 3

The exchange of oxygen and carbon dioxide between the airspace of the alveoli and the blood

Question 4

Ventilation/Perfusion (V/Q) matching

Answer 4

• Uneven distribution of air is inspired into the lungs throughout the lung – lower zones more compliant so have more air
• Pulmonary circulation is a low pressure system (15 mmHg). The upright position has barely enough pressure to perfuse the apices and there’s overperfusion of the bases
• Therefore areas with more air inspired are also better perfused

Question 5

What does the amount of CO2 produced by the body and the amount of O2 absorbed depend on

Answer 5

The metabolic activity of the body

Question 6

Respiratory quotient equation

Answer 6

RQ = CO2 produced/ O2 absorbed

Question 7

What is the value of the respiratory quotient at rest

Answer 7

0.8

Question 8

What does a respiratory quotient greater than 1 mean

Answer 8

That someone is in the anaerobic process of exercise

Question 9

What is the respiratory quotient in fat metabolism

Answer 9

0.7

Question 10

What is the respiratory quotient in carbohydrate metabolism

Answer 10

1.0

Question 11

What does increased alveolar ventilation cause in terms of CO2

Answer 11

Decreased partial pressure of CO2 in the alveoli

Question 12

What does decreased alveolar ventilation cause in terms of CO2

Answer 12

Increased partial pressure of CO2 in the alveoli

Question 13

What does increased alveolar ventilation cause in terms of O2

Answer 13

• Increased partial pressure of O2 in the alveoli
• A large enough increase in alveolar ventilation will allow the partial pressure of O2 in the alveoli reach the partial pressure of O2 in the atmosphere

Question 14

What does decreased alveolar ventilation cause in terms of O2

Answer 14

Decreased partial pressure of O2 in the alveoli

Question 15

How does gas get into the blood

Answer 15

• Diffusion through tissues is described by Fick’s Law
• The rate of transfer of a gas through a tissue is proportional to the tissue area and the difference in gas partial pressure between the two sides, and inversely proportional to the tissue thickness

Question 16

What does a low V/Q result in

Answer 16

• Decreased ventilation relative to blood flow
• This leads to increased arterial PCO2 and a decrease in PO2 (Dissociation curve produces a rise in arterial CO2 content and a reduction in arterial O2 content)

Question 17

What does a high V/Q result in

Answer 17

• Increased ventilation relative to blood flow
• This leads to a decrease in arterial PCO2 and an increase in PO2 (Dissociation curve produces a fall in arterial CO2 content but no increase in arterial O2 content)

Question 18

Partial pressure

Answer 18

the pressure that would be exerted by one of the gases in a mixture if it occupied the same volume on its own.

Question 19

What summarises the relationship between the partial pressure of arterial CO2 and the partial pressure of arterial O2

Answer 19

The alveolar gas equation

Question 20

Type 2 respiratory failure

Answer 20

Pure underventilation leads to an increased partial pressure of arterial CO2 and a proportionate fall in partial pressure of arterial O2

Question 21

Type 1 respiratory failure

Answer 21

Disturbance in V/Q matching leads to a fall in the partial pressure of arterial O2 with no change in the partial pressure of arterial CO2

Question 22

Can type 1 and type 2 respiratory failure occur at the same time

Answer 22

Yes

Question 23

What does the alveolar gas equation allow

Answer 23

It allows determination if an observed reduction in the partial pressure of arterial O2 is related to underventilation alone or weather there is an intrinsic lung issue

Question 24

State the alveolar gas equation

Answer 24

Partial pressure of alveoli O2 = Partial pressure of inspired O2 - (partial pressure of arterial CO2/0.8)