Breathing is a nonequilibrium process which exhibits pressure volume hysteresis apparently due to surface tension. The cause of this hysteresis must arise from dynamical physicochemical interactions of various parts of the alveolus. The authors sought to explore theoretically several possible basic mechanisms, including: a liquid soluble surfactant with its sorption rate at the gas liquid interface determined by diffusion in the liquid; a liquid soluble surfactant with its sorption rate determined by interfacial kinetics; an insoluble viscoelastic surface layer; and a viscoelastic alveolar lining liquid. The model alveolus is a spherical gas bubble, with thick liquid wall, of harmonically oscillating radius. Dimensionless parameters are derived which fully characterize each mechanism. Results show: a viscoelastic liquid can contribute to hysteresis only if it has at least the viscosity of pitch; dipalmitoyl lecithin is too insoluble to enable a solubility mechanism to operate in vivo; a viscoelastic surface layer could be the source of hysteresis but it must have a spectrum of relaxation times.
|Original language||English (US)|
|Pages (from-to)||No. 1165|
|State||Published - Jan 1 1975|
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