Effect of zonal conditions and posture on pulmonary blood flow distribution to subpleural and interior lung

Observations made on vessels seen directly beneath the pleura may not accur ately reflect what occurs in vessels located deeper in the interior of the lung. We quantified flow to subpleural and deeper, interior regions under z one 1 or 2 conditions in excised (n = 5) and in vivo (n = 6) rabbit lungs, in the head-up or inverted position. After infusion of radiolabeled microsp heres, lungs were dried at alveolar pressure of 25 cmH(2)O and sliced in 1- cm sections along the gravitational plane and in three planes in the dorsal -ventral axis. Regions located <1 mm from the pleural surface were dissecte d away from the remaining tissue. in both zonal conditions, 1) weight-norma lized flow to the interior exceeded that found in subpleural regions; and 2 ) flow followed the gravitational gradient, with the correlation varying wi th the scale of measurement. We conclude that flow through subpleural vesse ls is less than that which occurs deeper in the interior, but the regional distributions of flow and the effects of zonal conditions are similar in th e two regions.