Distribution of pores within alveoli in the human lung

Usually the wall opposite the orifice of alveoli has been used to study interalveolar pores by scanning electron microscopy. To ascertain whether biased results may be obtained from this, the distribution of pores within alveoli was studied in human lungs. By the use of scanning electron photomicrographs, the number, major axes of pores, and proportional area of pores to the alveolar wall were estimated. The alveolar wall seen opposite the orifice was defined as the bottom wall. Average number of pores per alveolus was 13-21, and one-half of them was located in the bottom walls. The average length of major axes was 7-19 micron, and average area fractions were 0.8-5%. The distribution of the numerical density, area fraction, and size of pores was uniform regardless of their location within the alveolus and the size of alveoli. Thus pores can be compared using the bottom walls of alveoli. This will facilitate the study of the effects of age, smoking, and topography on pore size and frequency in humans.