Abnormal Gas Exchange

Question 1

What is ventilation/perfusion (V/Q) mismatch?

Answer 1

Poorly ventilated alveoli
V= reduced
Responds to O2

Question 2

What conditions does V/Q mismatch occur in?

Answer 2

Bronchitis
Bronchopneumonia
Airway obstruction +/- bronchopneumonia in COPD

Question 3

What is pathophysiology of shunt

Answer 3

V=0

Does not respond to O2

Question 4

What conditions does shunt occur in?

Answer 4

Severe bronchopneumonia +/- exacerbation of COPD

Question 5

What is Hypoventilation?

Answer 5

Problem with moving air in/out of lungs
Mechanical/functional aspect of ventilation rather than gas exchange
Responds to O2

Question 6

What conditions does Hypoventilation occur in?

Answer 6

Upper airway or tracheal obstruction

Mechanical problem-> Chest wall damage
Functional problem-> muscle paralysis, diaphragm damage
Neurological problem with breathing process:
- peripheral nerve damage/loss of function
- CNS problem- opiates, COPD (central chemoreceptors desensitised to ↑PaCO2)

Question 7

What is diffusion impairment?

Answer 7

Harder for O2 to diffuse across capillaries
Increased equilibration time- from 0.25 sec to 0.75 sec

Normal transit time 0.75 sec but in exercise transit time ↓= not enough time for O2 to diffuse = ↓↓PaO2
CO2 more soluble= no problem

Question 8

What conditions does diffusion impairment occur in?

Answer 8

Loss of surface area in emphysema

Fibrosis in interstitial lung disease