Figure 4. The relation between mean (±SEM) lung volume (as a percentage of the maximum lung volume) and mean (±SEM) airway diameter cubed.

Both variables were measured at the five airway pressures (0, 12, 25, 32, and 45 cm H₂O) under the four conditions: baseline (before aerosol, open squares), atropine (before catheter, open triangles), aerosol histamine challenge (black squares), and individual airway catheter challenge (black triangles). Airway diameter cubed is substantially and significantly less dependent on lung volume with the local catheter challenge significantly with airway pressure (p<0.001) at all lung volumes above FRC (0 cm H₂0 Paw).