Oxygen partial pressure (pO₂) CF airways in vivo and in thick films of ASL on human airway epithelial cultures. (a) pO₂ in CF airways. First 30 minutes represents measurement in a nonobstructed region of the airway lumen. The arrow indicates insertion of oxygen probe into a mucopurulent mass. The pO₂ returned to basal values after probe retraction from the adherent mass into the nonobstructed airway region. (b) pO₂ in nonobstructed CF airway lumens (L) and CF mucopurulent masses (M) in vivo. n = 3 CF subjects; *P = 0.001. (c) Plots of pO₂ gradients under thick film conditions at 37°C in NL (squares; eight cultures/five subjects) and CF cultures (circles; six cultures/four subjects). (d) pO₂ gradients under thick film conditions measured at 4°C in NL (squares; five cultures/three subjects) and CF cultures (circles; five cultures/three subjects). (e) pO₂ gradients in CF mucus that had accumulated for 48 hours on CF culture surfaces and had become stationary due to volume hyperabsorption (inverted triangles). Mucus transport was restored in these cultures by addition of 30 μl PBS, and pO₂ gradients remeasured 1–2 hours later (triangles; six cultures; three subjects each). (f) Comparison of pO₂ gradients in NL (squares; nine cultures/six subjects) and PCD (diamonds; five cultures/two subjects) cultures under thick film conditions. Data are shown as mean ± SEM. *Significantly different (P < 0.05) from pO₂ at the air-liquid interface (0 μm). ^†Significant difference (P < 0.05) between NL and CF.