Some thoughts on the effect of non-linearity on innovation in urological surgery.

Abstract

Nature works in an interconnected, holistic and non–linear way: every part of a system affects another part and also, the system itself. Yet very little is written about non–linearity in medicine or research medicine in mainstream journals. One famous description as to how Nature works was written by Marcus Aurelius, the Roman Emperor and Stoic philosopher [1]. Always think of the Universe as one living organism, with a single substance, and a single soul; and observe how all things are submitted to the single perceptivity of this one whole; all are moved by its single impulse, and all play their part in the causation of every event that happens. Remark the intricacy of the skein, and the complexity of the web. This description emphasizes one fundamental scientific fact: Medicine, like Nature, consists of complex nonlinear systems operating in every part of the body. These systems are balanced and interact with each other. A pure reductionist approach, therefore, has little place in the study of such a system, as it is literally impossible to isolate just one single factor unrelated to anything else. One has to look at the whole picture. One example of this is the practice of using single urodynamic flow rate values in articles on “obstructed” micturition. The flow of urine through the urethra is non–linear in that it is inversely related to the 5th power of the radius [2] for non–laminar flow (doubling the radius increases the resistance to urine flow by a factor of 32); the urethral tube is opened (and closed) by an external striated muscle mechanism reliant on intact suspensory ligaments, so even the slightest difference in tissue tension or timing is exponentially magnified to the 5th power, ensuring that flow rate can never be adequately reproducible [3] he same criticism applies against drawing conclusions from single pressure values of “detrusor overactivity” (“DO”) obtained during urodynamic testing; the instantaneous “DO” pressure recorded ultimately reflects the instantaneous urethral radius and therefore resistance, a resultant of the interplay of the natural urethral closure mechanisms which close the urethral tube [3] and the micturition reflex which opens it out [2]. The characteristic sinuous curve characteristic of “DO” is consistent with the slight time delay taken to switch from domination of the closure reflex (raised urethral pressure) to domination of the micturition reflex (fall in urethral pressure). “DO” as applied today is reductionist, in that it takes a single reading from an exponentially determined dynamic process and draws important conclusions, for instance, in a patient with mixed incontinence, whether to operate or not. First steps in innovation – towards a hypothesis The first step is for an “innovative” scientist is to “discover” how it works, then to apply that knowledge in solving a difficult clinical problem. Popper [4] describes two mechanisms, induction and deduction. Induction, simplistically, takes an idea or observation towards a hypothesis. The hypothesis then has to be tested in a valid way, by deductive experimentation: “if “a” is so, then “b” follows. In 1986, the 1st author, PP, noted a dense collagenous tissue reaction to implanted Teflon tape. PP had previously noted that pressing a hemostat directly upwards immediately behind the pubic bone controlled urine loss on coughing (USI). Two hypotheses were formed, The cause of USI is a loose pubourethral ligament (PUL). Implantation of a tape will reinforce the damaged PUL by creating an artificial collagenous neoligament. How non–linearity (randomness) may inadvertently affect research directions PP obtained permission from the hospital IRB to perform two prototype midurethral sling operations in 1986. Both worked immediately, the patients passed urine immediately, went home the same day and were continent 10 years later. However, when a systematic study was commenced a year later, results in the 1st case series showed only a 50% cure rate. On this basis, the probability of achieving 2/2 success in the initial 1986 operations was only 25%. Conversely, there was an equivalent 25% probability of 2/2 failures. If this had occurred, there would be no midurethral sling today. What this means is that the Innovative Scientist cannot assume the concept is wrong (or correct) on the basis of 2 cases. One needs some luck and a lot of persistence. Marion Sims, the fistula pioneer, had many attempts at fistula repair before he finally succeeded with silver wire. Variation Nonlinearity describes variation and Chaos Theory describes the feedback control mechanisms which drive non–linear systems. The challenge is to create a management system which makes allowance for variation and to avoid the rare “Black Swan” events inherent in Chaotically controlled systems. The Integral Theory System (ITS) is to our knowledge, the only management system to date which recognizes variation and nonlinear dynamics in its diagnostic and surgical systems.