title: The hydrodynamic basis of the vacuum cleaner effect in continuous-flow PCNL instruments: an empiric approach and mathematical model.
abstract: OBJECTIVE
  Passive removal of stone fragments in the irrigation stream is one of the characteristics in continuous-flow PCNL instruments. So far the physical principle of this so-called vacuum cleaner effect has not been fully understood yet. The aim of the study was to empirically prove the existence of the vacuum cleaner effect and to develop a physical hypothesis and generate a mathematical model for this phenomenon.
  
  
  METHODS
  In an empiric approach, common low-pressure PCNL instruments and conventional PCNL sheaths were tested using an in vitro model. Flow characteristics were visualized by coloring of irrigation fluid. Influence of irrigation pressure, sheath diameter, sheath design, nephroscope design and position of the nephroscope was assessed. Experiments were digitally recorded for further slow-motion analysis to deduce a physical model.
  
  
  RESULTS
  In each tested nephroscope design, we could observe the vacuum cleaner effect. Increase in irrigation pressure and reduction in cross section of sheath sustained the effect. Slow-motion analysis of colored flow revealed a synergism of two effects causing suction and transportation of the stone. For the first time, our model showed a flow reversal in the sheath as an integral part of the origin of the stone transportation during vacuum cleaner effect. The application of Bernoulli's equation provided the explanation of these effects and confirmed our experimental results.
  
  
  CONCLUSIONS
  We widen the understanding of PCNL with a conclusive physical model, which explains fluid mechanics of the vacuum cleaner effect.
authors.affiliation: Department of Urology and Paediatric Urology, University Hospital Frankfurt, Theodor-Stern-Kai 7, 60590, Frankfurt, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Mager
authors.affiliation: ExperTeach GmbH, Waldstraße 94, 63128, Dietzenbach, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Balzereit
authors.affiliation: Department of Urology and Paediatric Urology, University Hospital Frankfurt, Theodor-Stern-Kai 7, 60590, Frankfurt, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Gust
authors.affiliation: Department of Urology and Paediatric Urology, University Hospital Frankfurt, Theodor-Stern-Kai 7, 60590, Frankfurt, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Hüsch
authors.affiliation: Department of Urology and Urologic Oncology, Hannover Medical School, Carl-Neuberg-Straße 1, 30625, Hannover, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Herrmann
authors.affiliation: Department of Urology and Andrology, General Hospital Hall, Milser Straße 10, 6060, Hall in Tirol, Austria.
authors.forename: U
authors.initials: U
authors.lastname: Nagele
authors.affiliation: Department of Urology and Paediatric Urology, University Hospital Frankfurt, Theodor-Stern-Kai 7, 60590, Frankfurt, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Haferkamp
authors.affiliation: Department of Urology and Paediatric Urology, University Hospital Frankfurt, Theodor-Stern-Kai 7, 60590, Frankfurt, Germany. schilling_david@hotmail.com.
authors.forename: D
authors.initials: D
authors.lastname: Schilling
mesh_terms: D004867:Equipment Design; D057446:Hydrodynamics; D008962:Models, Theoretical; D009403:Nephrostomy, Percutaneous / Q000295:instrumentation* / Q000379:methods*; D014618:Vacuum
keywords: Fluid dynamics; MIP; Percutaneous nephrolithotomy; Stone retrieval; Vacuum cleaner effect; miniPCNL