Surfactant acts to maintain the lung compliance by decreasing the following factor:

Surfactant is a mixture of dipalmitoylphosphatidylcholine (DPPC), other lipids, and proteins. The low surface tension when the alveoli are small is due to the presence of surfactant in the fluid lining the alveoli. If the surface tension is not kept low when the alveoli become smaller during expiration, they collapse in accordance with the law of Laplace. Surfactant also helps to prevent pulmonary edema. Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 34. Introduction to Pulmonary Structure and Mechanics. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong's Review of Medical Physiology, 24e.