Regional lung expansion and vertical pleural pressure gradients in normal human subjects

Using 133Xe and a single slow inspiration from near residual volume (RV) to total lung capacity (TLC), we measured regional lung volume continuously in six regions as a fraction of volume at maximal inflation in 57 normal non-smoking subjects (age: 20 to 82 years). We found that regional initial (i.e., near RV) volume/TLC increased significantly with aging in all regions for females whereas the increase in males was significant only in the upper regions. These results suggest that the aging process in the lung is accelerated in females. Some variability in regional volume measurements occurred when inspiration started from FRC rather than near RV. Although the patterns of regional expansion generally confirm those previously reported, it was found that the volume of vertically adjacent regions do frequently become equal and cross-over one another. Using the measurements of static compliance, regional V/TLC at FRC, and a passive model based upon an isotropic distribtion of intrinsic elasticity throughout the lung, the mean vertical pleural pressure gradient between upper and middle regions and middle and lower regions were estimated as 0.246 cmH2O/cm and 0.267 cmH2O/cm respectively. We believe that the regional expansion patterns which we observed can be explained by the interaction between a variable thoraco-diaphragm/abdominal motion and a passive elastic lung.