Three dimensional registration of mechanical bladder activity using polystyrene fluorescent spheres: A technical note

Optical marker tracing methods have been applied succesfully in recent year s to quantify local material deformation of heart tissue, skin and striated muscles. In this study, polystyrene fluorescent spheres (d = 0.6 mm) are g lued to the ventral serosal bladder wall in the rabbit. Three dimensional v ideo registration of the polystyrene spheres is used to calculate two direc tions of principal strain (epsilon(1), epsilon(2)) on the bladder surface i n vivo. The aim is to investigate the feasibility of the technique for this new application in two experimental circumstances: during spontaneous blad der wall activity and after electrical stimulation of bladder innervating n erve fibers. During spontaneous activity, random contraction and relaxation occured simultaneously and separately across the bladder wall for the two principal strains epsilon(1) and epsilon(2). After extradural electrical st imulation of sacral nerve root S2, the principal strains epsilon(1) and eps ilon(2) synchronized in time in such a way that epsilon(1) and epsilon(2) b oth represented contraction or both represented relaxation. One and the sam e bladder wall area passed through phases of contraction followed by relaxa tion and vice versa. After multiple stimulation periods, the coordination b etween the two principal strains during stimulation was reduced. This techn ique allows to identify local areas of contraction and relaxation in the in tact bladder wall in vivo. Three dimensional video registration of polystyr ene fluorescent spheres to study bladder wall contraction and its relaxatio n proved to be a feasible technique, with which electrical stimulation effe cts and spontaneous activity could be measured.