SURFACE BIOPHYSICS OF THE SURFACE MONOLAYER THEORY IS INCOMPATIBLE WITH REGIONAL LUNG-FUNCTION

The surface monolayer theory of Clements was tested on open surface fi lms of calf lung surfactant extract in a leak-free vertical film surfa ce balance in which alveolar area (A) changes in each lung zone were s imulated in accordance with the theory. We found that: 1) physiologica lly necessary low surface tension (gamma), <4 dyn/cm, was sustained on ly by continuous film compression (''expiration''); 2) compression fro m A equivalent to total lung capacity to functional residual capacity produced fleeting gamma reduction in all zones and quick reversal to h igh gamma with A changes that simulated tidal volume (V-T) breathing a t both 14 (adult) and 40 (neonatal) cpm; 3) phase differences between gamma and A axes of V-T loops that indicate mixed surface film composi tion may be attributable to film inertia and viscoelasticity; 4) estim ated alveolar retraction pressure due to gamma(P gamma) exceeds ''net' transpulmonary pressure, i.e., favors alveolar collapse, under virtua lly all conditions of the theory in all zones; 5) return to transient, fleeting low gamma in successive V-T cycles was determined by the inh erent difference in compression and decompression rates, which results in exhaustion of available A in very few cycles; 6) the ''sigh'', whi ch restores stable low gamma according to the theory, actually produce d unstable high gamma during virtually all phases of the maneuver. In contrast, closed bubble films of the surfactant were structurally stab le and produce stable near 0 gamma and P gamma.