Cilia are microscopic, about 10Ám long and 300nm thick hair-like extensions of the cell membrane that cover the surface of many protozoan cells or the inner surface in various parts of the human body. Their most prominent location in the body is the bronchial tract, where they participate in the "mucociliary escalator", a sophisticated mechanism for cleaning the lung from inhaled particles. The particles are trapped in a visco-elastic mucous layer covering the epithelium and the mucus carpet is propelled by ciliary motion. The motor of the mucus propelling "escalator" are beating cilia, fuelled by ATP. It is obvious that in order to achieve efficient directed transport, the ciliary motions must be, at least locally coordinated. Indeed, ciliated epithelial layers in the upper airways as well as in the oviduct show a coordinated beat pattern. This pattern, resulting from a constant shift in the beat phase between individual cilia, is referred to as "metachronal wave". Immotile cilia or lack of coordination are made responsible for different severe diseases, such as primary ciliary dyskinesia, therefore there is a demand for reliable diagnostic techniques.
The starting point of every diagnosis is a sound knowledge of the healthy system. Hence, one part of our work is the characterization of the metachronal wavefield from a physicists point of view. We use high speed video imaging and advanced image processing to extract a characteristic set of parameters like cilia beat frequency, wavelength, wave velocity and speed of the mucociliary transport from every image sequence. We are using this technique for an inter-species comparative study involving cow, sheep, pig, rabbit and turkey.
In the search of a new diagnosis techniques, an apparatus for minimally-invasive in vivo measurements of the ciliary beat frequency (CBF) has been developed. The instrument is based on speckle interferometry technique, because the contrast and the resolution of conventional endoscopy are entirely insufficient for direct observation of the ciliary activity. Since the everyday diagnostic standard is still based on ex vivo motility analysis of cilia, a less invasive analytical technique for in vivo measurement of the CBF is eagerly awaited for a long time.
Andy Burn, Manuel Ryser