Surface tension properties of surfactant.

Surface tension area relations from pulmonary surfactants (natural, lipid extract, synthetic) are obtained with a leak-free captive bubble of controllable size. One of the most sensitive parameters to consider is the area change required to achieve minimum surface tension. For synthetic surfactant, this change can be minimized by increasing the cycling speed of the films. Film area reduction at minimum surface tension causes collapse and decreased surface activity for all surfactants investigated. To avoid film collapse, positive end-expiratory pressure becomes important during surfactant replacement therapy.