Bubble clicking: Oscillations induced by the lung surfactant

The bubble clicking test is a promising technique for rapid lung surfactant assessment. It is based on observing bubble oscillations when a sufficiently high concentration of the lung surfactant is present in the studied sample. This paper presents the theoretical conditions for bubble clicking to occur: (a) the possible coexistence of two states of the bubble having the same volume but different surface tensions and shapes and (b) sufficiently small Gibbs energy difference between these two states. It is shown that these conditions may indeed be fulfilled when the surface tension is sufficiently low (sufficiently high surfactant concentration), within a specified bubble volume range. The present theoretical conclusions qualitatively agree with known experimental observations.