Designing for Maximum Catheter Elongation


The following write up illustrates the practical use of the CathCAD® Modelling software to develop the proximal end of a catheter design. In this example, the proximal end of a catheter (being developed) was determined to have the following required performance attributes:

  • ID:  0.070″ – 0.080″
  • OD:  0.089″ Maximum
  • Kink radius <= 2 inches
  • The proximal end cannot elongate more than 0.1 percent when subjected to an axial force of 5 N (note that 5 N = 1.124 lb).

Stress strain equation (Hooke’s Law)

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Substituting (F/A) for stress

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We rearrange equation (2) so that we get the quantity EA which is computed by CathCAD®

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In this design case, the quantity EA is a minimum and anything larger works for the customer. We also have to convert from Newtons to pounds as the software works in English units.

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The CathCAD® software may now be used to model/design a tube to meet the following complete set of constraints

  • ID:  0.070″ – 0.080″ (the input range)
  • OD:  0.089″ maximum
  • Design:  As determined by the user. You might get away with a uniform material and/or you might have to design a braid reinforced tube. There are potentially an infinite number of solutions to the problem.
  • EA >= 1,124 lb. If the computed EA of the design is greater than 1,124 lbs then the design will meet the maximum elongation requirement of 0.1 percent
  • Kink radius <= 2 inches

If  you have any particular design example you wish to formulated in order to be solved by the software, please email us at