|Ph.D Student||Yitzhak Dror|
|Subject||Surfactant Transport and Particles Clearance from the|
Alveolar Liquid Lining
|Department||Department of Mechanical Engineering||Supervisor||Professor Emeritus Shimon Haber|
|Full Thesis text - in Hebrew|
The alveoli of human lungs are coated with a thin fluid layer that is covered with a surfactant monolayer 50nm in thickness. Several researches have been carried out in the past examining the changes in surfactant concentration during breathing. A basic assumption was that the solution is axisymmetic disregarding the effect of air flowing over the alveoli surface invalidating the axisymmetric assumption. In the first part of this research we address the impact of air flow inside the alveoli on the fluid layer lining the alveolus and in the second part we explore its effect on the mechanisms of hydrodynamic cleansing of alveoli.
The solution of the governing differential equation can be shown to depend on a known analytical form in one of the spatial dimensions. It made it possible to distinguish between the different mechanisms affecting the motion of a particle embedded in the fluid lining the alveolar surface: the effect of surfactants concentration heterogeneity and the shear stress exerted by the air flow over the fluid lining interface.
We showed that in most cases a particle does not float above the fluid layer. The bigger the particle the greater the likelihood it would not drift. The research focused on particles which can float and thus can be removed from inside the alveoli. We found that three mechanisms can cause particle motion: Brownian motion, variation in surfactant concentration and gravity.
We found that the brownian motion plays a major role especially on particles of 0.1µm in diameter and smaller. Gravitation, on the other hand, influences particles with bigger diameter (1µm and higher). The influence of surfactant concentration change which in turn causes variation in surface tension does not strongly depend on particle diameter.
Finally, particles of about 0.2µm in diameter, such as cigarette smoke particles, have the greatest potential to remain the longest time in the fluid lining the alveolar surface.