The following two forces oppose lung collapse:
1. Surfactant – which breaks the hydrogen bonds which maintain surface tension of the alvioli. Some babies who are born immaturely or prematurely will have undevelloped lungs, or may not yet developed surfactant; consequently, the surface tension (due to hydrogen bonding at the alvioli) causes the alvioli to collapse.
2. Intrapleaural Pressure (the pressure in the lungs) which causes the alvioli to remain open. This is why Bipap, C-pap and PEEP (possitive end expiratory pressure) works, because it forces the alvioli to remain open allowing a greater exchange of gas (O2 for Co2).