Shunt versus Dead space

Variations in the distribution of ventilation in conjunction with distribution of perfusion, can run the gamut of perfusion without ventilation (known as physiologic dead space) to anatomic shunt (blood bypasses the lungs and directly enters the systemic circulation)

Anatomic shunt cause deoxygenated blood to transfer into the systemic circulation without passing through the pulmonary circulation:

Bronchial and Thebesian Veins

Accounts for 75% of the difference between alveolar O₂ and arterial O₂.

 

 

V/Q infinite:

ventilation with 0 perfusion – alveolar dead space

High V/Q:

P_AO₂ high, P_ACO₂ low

ventilation > normal, or perfusion < normal

Low V/Q: P_AO₂ low, P_ACO₂ high

Ventilation < normal, or Perfusion > normal

V/Q = 0

0 ventilation with perfusion – alveolar shunt

 

 

return to top | previous page