O 2 diffusion may be limiting in pulmonary disease if there is thickening of alveloi, or reduced alveolar surface area CO 2 diffusion is more rapid, rarely limiting. Disruption of alveolar walls and capillaries causes abnormal perfusion.
Obstruction causes abnormal ventilation.
O 2 bound to Hb does not contribute directly to the pO 2 . However, it acts as a reservoir, sops up O 2 molecules Fig. Venous pO 2 is only 40 mm Hg. Reflex mediated by peripheral Chemoreceptors Fig. 15-29 Effects of increased ventilation Fig.