Chapter 5

Question 1

What is the alveolar PO2 largely determined by?

Answer 1

Alveolar ventilation

Question 2

What are causes of hypoventilation?

Answer 2

Barbiturates and morphine
damage to chest wall
paralysis of respiratory muscles
high resistance to breathing (ex very dense gas at great depth underwater)

Question 3

Which takes longer to reach steady state, CO2 or O2?

Answer 3

CO2 takes longer to reach steady state because the stores are greater than the O2 stores (more CO2 in blood and interstitial fluid)
CO2 takes longer to equilibrate during the nonsteady state

R value of expired gas is high as CO2 stores are washed out

Question 4

Which causes of hypoxemia also cause increased CO2?

Answer 4

Hypoventilation
V/Q mismatch

Note: for V/Q mismatch you will increased your ventilation so CO2 may be normal

Shunt - you increase your ventilation

Question 5

How does each compare at apex vs base of lung:
Vol
VA
Q
VA/Q
PO2
PCO2 
N2 
pH

Answer 5

Vol - higher base
VA - higher base
Q - higher base 
VA/Q - higher apex 
PO2 - higher apex 
PCO2  - higher base 
N2 - higher base 
pH - higher apex (more alkalotic)

Question 6

What is wasted ventilation?

Answer 6

Ventilation in excess of what is normally required
Patients with V/Q mismatch have ventilation in excess of what they would normally require because lung units with high V/Q ratios are inefficient at eliminating CO2

This is alveolar dead space