Some Remarks on the Use of Physico-Chemical Methods in Lung Surfactant Research

Abstract

Since the introduction of a modified Wilhelmy balance by Clements [1] physico-chemical methods have been of major importance in the development of the concepts concerning lung surfactant (LS) function and the occurrence of RDS [2]. The Langmuir — Wilhelmy method (LWM) has proven a strong means in determining surface properties of single and multicomponent synthetic monolayers [3, 4], as well as of natural surfactants [5, 6]. The LWM showed its value in experiments revealing the influence of many factors — including, temperature, ions, pH, subphase composition, the surface tension (σ) — area (A) relation [7, 8]. However, objections were also raised, both against the LWM and against what might be called the “classical” model of LS function. The former objections mainly concerned leakage of monolayer material and contact-angle problems at the Wilhelmy plate (WP). The objections to the model concerned the existence of a continuous liquid lining layer, the geometry of the alveoli and the relevance of surface tension [9, 10]. In the mid-sixties the oscillating bubble method (OBM) was introduced [11]. This method has certain advantages over the LWM: its small dimensions allow for a better control of temperature, and the required (surfactant) volume is far less than for trough measurements. In addition, no measurement device disturbs the interface. Finally, an often emphasized advantage is the shape similarity between alveolus and bubble [12–14].

Parts of this paper are described in more detail in Gieles [17].