CAUSES OF HIGH AaDO₂ (continued)

D. Alternative terminology

1. Alveolar-capillary block: more or less equivalent to diffusion limitation

2. Venous admixture: more or less equivalent to shunt

3. Alveolar dead space: refers to alveolar volume ventilated but not adding appreciable O2 to pulmonary blood because of relatively low blood flow to the region; follows from ventilation/perfusion non-uniformity

PHYSIOLOGICAL = ANATOMICAL + ALVEOLAR
DEAD SPACE      DEAD SPACE   DEAD SPACE
                (airways)    (over ventilated/under perfused)