Determination of Alveolar PCO2 (PK4)

Question 1

Partial pressure of oxygen and CO2 in the mouth

Answer 1

• O2 = 20kPa
• CO2 = 0kPa

Question 2

Partial pressure of oxygen and CO2 in the conducting zone (inspiration)

Answer 2

• O2 = 20kPa
• CO2 = 0kPa

Question 3

Partial pressure of oxygen and CO2 in the conducting zone (expiration)

Answer 3

• O2 = 13kPa
• CO2 = 5kPa

Question 4

Partial pressure of oxygen and CO2 in the alveolar space

Answer 4

• O2 = 13kPa
• CO2 = 5kPa

Question 5

Partial pressure of oxygen and CO2 in venous blood

Answer 5

• O2 = 5kPa
• CO2 = 6kPa

Question 6

Partial pressure of oxygen and CO2 in arterial blood

Answer 6

• O2 = 13kPa
• CO2 = 5kPa

Question 7

What determines the PCO2 and PO2 in blood leaving the lungs?

Answer 7

Alveolar PCO2 + PO2

Question 8

Effect of increased V̇CO2 on alveolar PCO2

Answer 8

Increases it (more CO2 in blood to diffuse into alveoli)

Question 9

Effect of increased V̇A on alveolar PCO2

Answer 9

Decreases it (more air breathed out, so CO2 removed more quickly)

Question 10

Equation linking alveolar PCO2, V̇CO2 and alveolar ventilation

Answer 10

PACO2 α V̇CO2 / V̇A

Question 11

What constant is added to the equation for alveolar PCO2 for calculations?

Answer 11

• 115kPa
• PACO2 = 115 x (V̇CO2 / V̇A)