Comment on “finite element models—a template for future urodynamics: Comparison of different computer models of the neural control system of the lower urinary tract,” Neurourol Urodynam (2000) 19:289–310
✍ Scribed by Peter Petros
- Publisher
- John Wiley and Sons
- Year
- 2001
- Tongue
- English
- Weight
- 42 KB
- Volume
- 20
- Category
- Article
- ISSN
- 0733-2467
No coin nor oath required. For personal study only.
✦ Synopsis
The authors introduced a major new approach, a future template for urodynamics. Such a system approach potentially addresses the major defect of conventional urodynamics, that it captures only a singular ``snapshot'' of what is really a complex ongoing non-linear process. A series of ®nite element models is presented. These attempt to ®nd a combination of variables that ®t measured ¯ow, urethral, and detrusor pressure measurements. Major problems in weighting of inputs and thresholds and more minor problems involving hypothetical assumptions are identi®ed. I believe that to re¯ect more accurately the workings of a particular system, the equations will need to incorporate dynamic anatomical measurements (urethral diameter, rate of bladder volume reduction, length and volume of pelvic striated muscles), biomechanical measurements (biomechanical characteristics of urogenital tissues) calculations of striated pelvic muscle power, detrusor muscle power, and most importantly, formulae for non-linear feedback control mechanisms. These parameters are natural derivatives from a musculoelastic external micturition control mechanism activated by the posterior striated muscles of the pelvic ¯oor . Direct measurement of the aforementioned parameters will no doubt require dynamic three-dimensional imaging and other technologies not yet available.
Video radiographic and EMG studies [Petros and ] demonstrated that the out¯ow tract is actively stretched open between midurethra and bladder base, a result of relaxation of the anterior pelvic ¯oor muscles (``rhabdosphincter''), and contraction of the posterior pelvic ¯oor muscles. The latter stretch the vaginal hammock backward to open out the urethra and bladder neck. One effect of this external opening mechanism is to reduce the resistance to ¯ow from the detrusor inversely to the fourth power of the radius, i.e., doubling the out¯ow diameter reduces the motive detrusor pressure required for urine expulsion by a factor of 16 (e.g., from 160 to 10 cm H 2 O) for a comparable ¯ow rate. This system is non-linear. A slight variation in any part of this system will make a profound difference to the maximal ¯ow rate achievable for that cycle of micturition, and therefore, the expulsion pressure recorded. We attributed