Alveolar ventilation-perfusion relations: regional lung ventilation differences, can use radioactive xenon to detect how much ventilation is received by various parts of lung. Bottom of lung gets more ventilation than top: weight of lung causes greater pressures at lower lung. So intrapleural pressure is more positive at bottom of lung: alveolar pressure equal in all parts of lung. Causes transpulmonary pressure to be less at bottom of lung. Lower transpulmonary pressure alveoli less expanded (inflated) in lower lung regions at rest: not sure of these reasons for increased intrapleural pressure going down lung. Absolute values constant across mammalian species varying 10^4 in body size: lower resting volume and lower transpulmonary pressure puts bottom portions of lung lower and to the left. If varate/qrate is normal, then logarithmic plot of end tidal fn2 versus breath number is linear: this is b/c at tidal volume ventilation, percentage decr of.