title: Design of a factorial experiment with randomization restrictions to assess medical device performance on vascular tissue.
abstract: BACKGROUND
  Energy-based surgical scalpels are designed to efficiently transect and seal blood vessels using thermal energy to promote protein denaturation and coagulation. Assessment and design improvement of ultrasonic scalpel performance relies on both in vivo and ex vivo testing. The objective of this work was to design and implement a robust, experimental test matrix with randomization restrictions and predictive statistical power, which allowed for identification of those experimental variables that may affect the quality of the seal obtained ex vivo.
  
  
  METHODS
  The design of the experiment included three factors: temperature (two levels); the type of solution used to perfuse the artery during transection (three types); and artery type (two types) resulting in a total of twelve possible treatment combinations. Burst pressures of porcine carotid and renal arteries sealed ex vivo were assigned as the response variable.
  
  
  RESULTS
  The experimental test matrix was designed and carried out as a split-plot experiment in order to assess the contributions of several variables and their interactions while accounting for randomization restrictions present in the experimental setup. The statistical software package SAS was utilized and PROC MIXED was used to account for the randomization restrictions in the split-plot design. The combination of temperature, solution, and vessel type had a statistically significant impact on seal quality.
  
  
  CONCLUSIONS
  The design and implementation of a split-plot experimental test-matrix provided a mechanism for addressing the existing technical randomization restrictions of ex vivo ultrasonic scalpel performance testing, while preserving the ability to examine the potential effects of independent factors or variables. This method for generating the experimental design and the statistical analyses of the resulting data are adaptable to a wide variety of experimental problems involving large-scale tissue-based studies of medical or experimental device efficacy and performance.
authors: Department of Mathematics, University of Dayton, 300 College Park Ave., Dayton, OH 45469, USA. Wiebke.Diestelkamp@notes.udayton.edu
authors: Wiebke S
authors: WS
authors: Diestelkamp
authors: Carissa M
authors: CM
authors: Krane
authors: Margaret F
authors: MF
authors: Pinnell
references: Surg Endosc. 2002 May;16(5):814-9
references: 11997829
references: Vet Surg. 2005 May-Jun;34(3):289-93
references: 16115087
references: Ultrasound Med Biol. 2003 Feb;29(2):301-9
references: 12659918
references: J Minim Invasive Gynecol. 2010 Jan-Feb;17(1):70-7
references: 19944653
references: Surg Innov. 2005 Jun;12(2):155-60
references: 16034506
references: Surg Endosc. 2010 Oct;24(10):2465-74
references: 20354868
references: J Urol. 2003 Feb;169(2):697-700
references: 12544345
references: Surg Endosc. 2003 Aug;17(8):1228-30
references: 12799888
references: J Minim Invasive Gynecol. 2009 Sep-Oct;16(5):599-603
references: 19577964