Pressure-Volume Relationship of a Model Alveolus

Abstract

The pressure-volume relationship of a model alveolus was determined and the effects of cycling rate, bubble size and surfactant concentration on the pressure-volume relationship were studied. When the bubble was coated with the white layer isolated from lung wash of 22 dogs and pulsated between 650μ and 400μ in diameter at a rate of 12 cycles/minute, the maximal pressure was -32.0±4.2 mm H₂O and minimal pressure was -2.2±1.4mm H₂O. The pressure-volume curve showed a large hysteresis loop. The calculated surface tensions at 650μ and 400μ were 36.7±6.2 dynes/cm and 3.7±1.5 dynes/cm respectively. The pressure-volume relationship remained unchanged when the pulsation rate was varied from 6 to 180 cycles/minute. The results on the lung wash from three newborn lambs were similar to those obtained from the dogs, even though the white layer was diluted 50 times. With further dilution of the white layer, the pressure-volume relationship changed by bubble size and concentration of the white layer. As the bubble size decreased and/or the surfactant concentration increased, negative pressure at minimal bubble size decreased and the hysteresis loop increased. These findings indicated that a certain surface concentration of surfactant was necessary to achieve the surface activity and pulmonary hysteresis.