gas exchange & gas transport

Question 1

what are the 2 functions of the lungs?

Answer 1

1) ventilation

2) gas exchange

Question 2

how does gas exchange work?

Answer 2

• the lung is ventilated by air and perfused by blood
• air is inspired into the lungs
• pulmonary circulation is a low-pressure system (15 mmHg)
• otherwise known as ventilation/perfusion (V/Q) matching

Question 3

what is the respiratory quotient (RQ)?

Answer 3

the amount of carbon dioxide produced by the body and the amount of oxygen absorbed depends upon the metabolic activity of the body

Question 4

what is the respiratory quotient equation?

Answer 4

carbon dioxide produced/oxygen absorbed

Question 5

what is the respiratory quotient for fat metabolism?

Answer 5

0.7

Question 6

what is the respiratory quotient for carbohydrate metabolism?

Answer 6

1.0

Question 7

what happens to carbon dioxide if there is an increase in alveolar ventilation?

Answer 7

decrease in partial pressure of carbon dioxide in the alveoli

Question 8

what happens to carbon dioxide if there is a decrease in alveolar ventilation?

Answer 8

increase in partial pressure of carbon dioxide in the alveoli

Question 9

what happens to oxygen if there is an increase in alveolar ventilation?

Answer 9

increase in partial pressure of oxygen in alveoli

Question 10

what happens to oxygen if there is a decrease in alveolar ventilation?

Answer 10

decrease in partial pressure of oxygen in alveoli

Question 11

what is Fick’s law?

Answer 11

the diffusion through tissue

Question 12

how does Fick’s law work graphically?

Answer 12

• 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 2 sides
• inversely proportional to the tissue thickness

Question 13

what happens when there is a low V/Q?

Answer 13

there is lower ventilation relative to blood flow leading to an increase arterial partial pressure of carbon dioxide and decrease in partial pressure of oxygen

Question 14

what happens when there is a high V/Q?

Answer 14

there is increased ventilation relative to blood flow leading to a decrease in arterial partial pressure of carbon dioxide and an increase in the partial pressure of oxygen

Question 15

what does the alveolar gas equation summarise?

Answer 15

the relationship between PaCO2 and PaO2

Question 16

what happens with pure underventilation?

Answer 16

leads to an increased PaCO2 and a proportional fall in PaO2

Question 17

what condition is associated with pure underventilation?

Answer 17

type 2 respiratory failure

Question 18

what causes type 1 respiratory failure?

Answer 18

the disturbance in V/Q matching leading to a fall in PaO2 with no change in PaCO2

Question 19

what is the alveolar-arterial (A-a) gradient?

Answer 19

a difference between alveolar and arterial PO2

Question 20

what size is a healthy young adults A-a gradient?

Answer 20

small (<2kPa)

Question 21

what does an abnormality in the blood gas suggest?

Answer 21

there is an abnormality intrinsic to the lungs or its vasculature causing a V/Q mismatch