COLONOSCOPE FLEXURAL RIGIDITY MEASUREMENT

A testing device is developed that determines the stiffness, or flexur al rigidity, of an endoscope at specific locations down its length by subjecting it to a compressive axial force, a situation similar to the actual forces applied to the endoscope during a clinical procedure. T he endoscope is made to deform in a similar fashion to a slender buckl ed column and the force causing this deformation is related to the fle xural rigidity using column buckling theory. A direct relationship bet ween the critical load needed to cause buckling and the square of colu mn length L is demonstrated experimentally and is expected theoretical ly, giving confidence in the application of column buckling theory to endoscope testing. Additional confidence in the validity of the column buckling test results is obtained by their similarity to data obtaine d by subjecting the endoscope to a transverse load, determining deflec tion, and modelling the endoscope as a bent elastic beam. Several make s and models of endoscopes were tested, with flexural rigidity values typically ranging between 160 to 240 Ncm(2). The effect of a metal sti ffener inserted in an endoscope's accessory channel is quantified, as is the change in flexural rigidity down the insertion shaft of a grade d-stiffness endoscope. Significant differences in flexural rigidity we re obtained between identical endoscopes, each sharing similar usage h istories, indicating the need for flexural rigidity measurements for e ach individual endoscope of a particular model line, though a more ext ensive study is required to reliably determine scope-to-scope stiffnes s variations for a particular model line.