Intrapulmonary small-sized bubble formation is governed by solute-liquid density and airspace geometry

Small bubbles are formed normally at birth from secreted surfactants and from surfactants within fetal pulmonary liquid. Theoretically, the process can be effectuated both during inspiration and expiration, but the mechanism should predictably vary with respiratory phase: during inspiration the bubbles may form by gas dispersion in liquid where the terminal bronchioles serve as regulators or ´spargers´; during expiration the formation may proceed by film scission as length:diameter ratio increases. Direct stereomicroscopic observation and high-speed cinemicrography provide direct supporting evidence. Because immature lungs cannot form small-sized bubbles and because bubble formation persists in normal lungs in direct relation to the density of surfactants and liquid, the question is of fundamental importance to normal pulmonary function, alveolar stability, and therapeutic measures in which exogenous surfactants are administered intratracheally to the infant.<>