Colonoscope flexural rigidity measurement.

Abstract

A testing device is developed that determines the stiffness, or flexural 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. The endoscope is made to deform in a similar fashion to a slender buckled column and the force causing this deformation is related to the flexural rigidity using column buckling theory. A direct relationship between the critical load needed to cause buckling and the square of column length L is demonstrated experimentally and is expected theoretically, 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 obtained by subjecting the endoscope to a transverse load, determining deflection, and modelling the endoscope as a bent elastic beam. Several makes and models of endoscopes were tested, with flexural rigidity values typically ranging between 160 to 240 Ncm2. The effect of a metal stiffener inserted in an endoscope's accessory channel is quantified, as is the change in flexural rigidity down the insertion shaft of a graded-stiffness endoscope. Significant differences in flexural rigidity were obtained between identical endoscopes, each sharing similar usage histories, indicating the need for flexural rigidity measurements for each individual endoscope of a particular model line, though a more extensive study is required to reliably determine scope-to-scope stiffness variations for a particular model line.