The Role of Bacteria in Urology by Dirk Lange & Ben Chew

Author:Dirk Lange & Ben Chew
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

Figure 5.2 illustrates how fluid flow and chemistry vary spatially. A fluid velocity field can be calculated based on the geometry of the system. Ureolysis depletes urea locally, producing ammonium and affecting the local saturation index of struvite as illustrated in Fig. 5.2. Ammonium concentrates within the biofilm and diffuses into the bulk fluid due to the concentration gradient, which can affect the saturation state downstream of the ureolytic biofilm. Although Fig. 5.2 shows a qualitative demonstration, commercial finite element software is available for accurate quantitative analyses. Finite element models split larger problems (i.e., large geometrical domains) into a system of smaller problems (elements) that can be solved and reconstructed. COMSOL Multiphysics (COMSOL Inc., USA) is one example of a user-friendly and flexible finite element modeling program that is capable of modeling all of the processes mentioned in this chapter. Studies by Bucs et al. [24] and Radu et al. [25] provide good examples of COMSOL being used to model biofilm growth and mineral precipitation.

Predicting an accurate saturation index is not straightforward in a complex liquid like urine, but geochemical equilibrium modeling software can make this easier. The influence of solid phases can be predicted, as well as the speciation of magnesium, phosphate and nitrogen, which are affected by fluid conditions and equilibria with other ions. For example, the dissolved species affecting struvite precipitation include at least H2PO4 −, H3PO4, OH−, NH3, MgOH+, MgPO4 −, MgH2PO4 +, MgHPO4, HPO4 2−, Mg2+, PO4 3−, and NH4 +.

A popular open source geochemical modeling software is PHREEQC [26], however other programs exist. Even though these geochemical models were developed for nonmedical purposes, such as groundwater chemistry modeling, they are useful for modeling stone formation. Effective geochemical modeling can also be coupled with or incorporated into finite element models for a more thorough description that accounts for location and fluid flow in organs of the urinary tract [27].

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