Three Dimensional Registration of Mechanical Bladder Activity using Polystyrene Fluorescent Spheres: A Technical Note

Abstract

Optical marker tracing methods have been applied successfully in recent years to quantify local material deformation of heart tissue, skin and striated muscles. In this study, polystyrene fluorescent spheres (d = 0.6 mm) are glued to the ventral serosal bladder wall in the rabbit. Three dimensional video registration of the polystyrene spheres is used to calculate two directions of principal strain (∈₁, ∈₂) on the bladder surface in vivo. The aim is to investigate the feasibility of the technique for this new application in two experimental circumstances: during spontaneous bladder wall activity and after electrical stimulation of bladder innervating nerve fibers. During spontaneous activity, random contraction and relaxation occured sim ultaneously and separately across the bladder wall for the two principal strains ∈₁ and ∈₂. After extradural electrical stimulation of sacral nerve root S2, the principal strains ∈₁ and ∈₂ synchronized in time in such a way that ∈₁ and ∈₂ both represented contraction or both represented relaxation. One and the same bladder wall area passed through phases of contraction followed by relaxation and vice versa. After multiple stimulation periods, the coordination between the two principal strains during stimulation was reduced. This technique allows to identify local areas of contraction and relaxation in the intact bladder wall in vivo. Three dimensional video registration of polystyrene fluorescent spheres to study bladder wall contraction and its relaxation proved to be a feasible technique, with which electrical stimulation effects and spontaneous activity could be measu red.