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John D Denstedt

Publications and source records attributed to John D Denstedt.

At least 19 recordsLinked to original sources
PubMed2006

A randomized, controlled, prospective study validating the acquisition of percutaneous renal collecting system access skills using a computer based hybrid virtual reality surgical simulator: phase I.

PURPOSE: The need to develop new methods of surgical training combined with advances in computing has led to the development of sophisticated virtual reality surgical simulators. The PERC Mentortrade mark is designed to train the user in percutaneous renal collecting system access puncture. We evaluated and established face, content and construct validation of the simulator in this task. MATERIALS AND METHODS: A total of 63 trainees underwent baseline testing on the simulator, consisting of percutaneous renal puncture followed by the introduction of a guidewire into the collecting system. Subjects were then randomized to an intervention arm, in which they underwent 2, 30-minute training sessions on the simulator, and a control arm, in which no further training was given, followed by repeat testing. Performance was assessed using a global rating scale and by virtual reality derived parameters. RESULTS: There were no significant differences between the 2 groups with respect to baseline measures. Subjects who underwent training with the simulator demonstrated significant improvement in objective and subjective parameters compared to their baseline performance and compared to the untrained control group. Spearman rank correlations demonstrated a significant relationship between multiple parameters of the objective and subjective data. CONCLUSIONS: Training on the simulator improves virtual reality skills. It may allow trainees to develop the basic skills necessary to perform percutaneous renal collecting system access. Face and content validity were demonstrated and construct validity was supported by establishing convergent validity.

Computer Simulation↗
PubMed2006

Triclosan loaded ureteral stents decrease proteus mirabilis 296 infection in a rabbit urinary tract infection model.

PURPOSE: Infection and encrustation remain major limitations of ureteral stent use and to our knowledge no device has completely overcome these obstacles to date. Triclosan is a biocide currently used in a plethora of consumer and medical products that has recently been loaded into a ureteral stent. Using a rabbit model of UTI we examined the effects of triclosan impregnated stent segments on the growth and survival of Proteus mirabilis, a uropathogen commonly associated with device related UTI and encrustation. MATERIALS AND METHODS: A total of 48 male New Zealand White rabbits were instilled transurethrally with 1 x 10(6) P. mirabilis 296. A stent curl from a triclosan eluting, Percuflex Plus or Optima ureteral stent was placed intravesically. Urine was cultured on days 1, 3 and 7. On day 7 the stents were assessed for encrustation and viable organisms, while the bladders were scored for the degree of inflammation. RESULTS: Throughout the study urine isolated from the triclosan group contained significantly fewer viable organisms than controls with 7 of 13 animals completely clearing the infection by day 7. Similarly 9 of 13 triclosan eluting stents showed no viable organisms upon recovery and the remaining 4 showed significantly fewer organisms than controls. Urine and stents in all controls were positive for P. mirabilis at all time points. Although there was no significant difference in encrustation among the groups, bladders harvested from the triclosan group demonstrated significantly less inflammation. CONCLUSIONS: Triclosan eluting stents greatly decreased P. mirabilis growth and survival in a rabbit UTI model compared to controls. These stents may prove useful for decreasing device related P. mirabilis UTIs.

Animals↗
PubMed2006

Establishing composition and structure of intact urinary calculi by x-ray coherent scatter for clinical laboratory investigations.

PURPOSE: Current urinary stone analysis techniques are limited in their abilities to simultaneously characterize composition and structure. Laboratory techniques such as IRS and x-ray diffractometry require small powdered samples for analysis, rendering composition results dependent on the choice of sample and its preparation. We investigated the application of x-ray CS analysis to identify topographic urinary stone composition ex vivo. CS is essentially a transmission based x-ray diffractometry method that depends on molecular structure and, therefore, can distinguish different compounds. Diagnostic x-ray equipment facilitates the examination of structural arrangements of minerals in intact calculi. MATERIALS AND METHODS: Tomographic images of intact calculi CS properties were acquired with a purposely built scanner. Composition is extracted from CS by fitting a library of common pure stone component CS signatures to those of the unknown sample in each image pixel. Two zones per stone were isolated (powdered) for IRS composition analysis for comparison with CS maps at these locations. Each stone was also independently analyzed for bulk composition by IRS analysis. RESULTS: CS composition maps revealed the spatial arrangement of minerals in intact calculi. IRS results showed good agreement with CS in the selected regions of interest. Bulk composition by IRS was noted to miss some important stone components, indicating that the choice of sample may skew composition results. CONCLUSIONS: CS from diagnostic x-rays can be used to identify structure and composition in mixed urinary calculi nondestructively. The tissue specific CS images presented support the development of CS analysis as a means of identifying stone composition characteristics in the laboratory.

Crystallography, X-Ray↗
PubMed2006

In-vitro activity of triclosan-eluting ureteral stents against common bacterial uropathogens.

BACKGROUND AND PURPOSE: Ureteral stents are commonly used in urology today, but the biofilms that form on them within hours of placement may harbor bacteria that can result in infection or encrustation. Triclosan is an antimicrobial commonly used in consumer and medical products that inhibits bacterial fatty-acid synthesis. The bactericidal and bacteriostatic effect of a triclosan-eluting ureteral stent was tested against clinical isolates of common bacterial uropathogens in an in-vitro setting. MATERIALS AND METHODS: Triclosan eluted from a drug-loaded ureteral stent was suspended in artificial urine with bacterial pathogens (Escherichia coli C1214, Proteus mirabilis 296, Enterococcus faecalis 1131, Klebsiella pneumoniae 280, Staphylococcus aureus Newman, Pseudomonas aeruginosa AK1) to assess growth, virulence-promoter activity, and bacterial adherence to the stent. Generic stents were utilized as controls. RESULTS: Triclosan inhibited the growth of E. faecalis, K. pneumoniae, S. aureus, and P. mirabilis in a dose-dependent manner. Pseudomonas aeruginosa demonstrated significant resistance. Lower concentrations of triclosan downregulated E. coli virulence-factor promoters of outer membrane protein X and p-fimbriae. Triclosan stents had significantly fewer adherent viable bacteria than control stents. CONCLUSIONS: Triclosan-eluting ureteral stents inhibit the growth of common bacterial uropathogens and thus may reduce the incidence of urinary-tract infections and, potentially, encrustation. This drug-eluting stent provides both mechanical drainage of the upper urinary tract and local antibiosis.

Anti-Infective Agents, Local↗
PubMed2006

Minimizing symptoms in patients with ureteric stents.

PURPOSE OF REVIEW: The current approaches for minimizing symptoms in patients with ureteric stents were reviewed utilizing a literature search on Pubmed using the keywords stent, symptom, and ureter. RECENT FINDINGS: Ureteral stents are widely used in urological procedures for maintaining upper urinary tract drainage to relieve obstruction, pain, or infection. Indwelling stents, however, are associated with significant morbidity such as infection, encrustation, hematuria, and bothersome symptoms. Minimizing these issues has become paramount in the design of new ureteral stents. This article will review current and novel ways to minimize stent-related morbidity. SUMMARY: Currently, there is no ideal stent that relieves obstruction, is resistant to infection and encrustation, and is comfortable for patients. Advances in biomaterials and design will result in a more biocompatible stent that also has patient comfort in mind.

Humans↗
PubMed2006

New developments in ureteral stent design, materials and coatings.

Ureteral stents are used in a variety of urological diseases and procedures. The majority of patients with indwelling ureteral stents experience bothersome symptoms and are at increased risk for urinary tract infection. Stent encrustation and the associated complications can also result in significant patient morbidity. The development of new stent designs using novel biomaterials, stent coatings and drug-eluting technologies are being applied to reduce the disadvantageous features of ureteral stents.

Coated Materials, Biocompatible↗
PubMed2005

Laboratory coherent-scatter analysis of intact urinary stones with crystalline composition: a tomographic approach.

Knowledge of urinary stone composition and structure provides important insights in guiding treatment and preventing recurrence. No current method can successfully provide information relating structure and composition of intact stones. We are developing a tomographic technique that uses measures of coherently scattered diagnostic x-rays to yield stone composition. Coherent-scatter (CS) properties depend on molecular structure and are, therefore, sensitive to material composition. Powdered, amorphous or polycrystalline materials with no significant orientation produce circularly symmetric CS patterns. However, in materials with preferred crystallite orientation, like urinary stones, bright spots in CS patterns are observed. This compromises a composition analysis based on comparing CS measurements from calculi to a library of CS signatures from powdered chemicals. We show that a computed tomographic reconstruction of CS measurements using filtered backprojection (CSCT) effectively eliminates bright spots and yields CS patterns equivalent to powdered materials. This allows for direct comparison with a powdered chemical reference library to establish composition. Validation is achieved through a tomographic CS analysis of an aluminium (Al) rod phantom. Much like calculi, CS patterns from a solid polycrystalline Al rod exhibit diffraction spots, absent in the ring-like Al powder CS pattern. We show that the reconstructed Al CS cross-section is equivalent to its powdered counterpart and results in clearly defined composition images. The potential of CSCT to identify stone composition is demonstrated through images of intact stones deemed chemically pure by infrared spectroscopy. Computed tomographic reconstruction of CS signals allowed the generation of composition maps, showing the distribution of stone components. These images provide strong evidence that current laboratory techniques risk missing critical stone components due to inadequate sampling. This is of particular importance since follow-up treatments are based on these composition analyses. CS analysis can distinguish common stone components and can provide topographic composition maps of intact stones. Such details offer invaluable clinical information regarding stone formation, treatment and follow-up, and thus support the development of CS analysis as a laboratory stone analysis technique.

Calcium↗
PubMed2005

Analysis of urinary stone components by x-ray coherent scatter: characterizing composition beyond laboratory x-ray diffractometry.

Monoenergetic x-ray diffraction (XRD) analysis is an established standard for the assessment of urinary stone composition. The inherent low energy of x-rays used (8 keV), however, restricts penetration depth and imposes a requirement for small powdered samples. A technique capable of producing detailed information regarding component structural arrangements in calculi non-destructively would provide clearer insights into causes of formation and subsequent growth and allow the selection of more appropriate courses of therapy. We describe a new method based on the detection of coherent scatter (CS) in stone components using polyenergetic x-rays (70 kVp) from diagnostic equipment. While the higher energy allows the analysis of intact calculi, the polyenergetic source causes an angular broadening of measured CS patterns. We show that it is possible to relate the polyenergetic (CS) and monoenergetic (XRD) measurements through a superposition integral of the monoenergetic XRD cross-section with a function representative of the polyenergetic spectrum used in CS. Experimentally acquired diffractometry cross-sections of the seven major urinary stone components were subjected to this operation, revealing good agreement of diffraction features with CS. Therefore, our CS analysis is sensitive to stone component structure, similar to conventional XRD analysis. This indicates that CS analysis can be used as a basis to classify urinary calculi by composition. The potential of identifying stone components non-destructively was demonstrated from a tomographic CS analysis of a stone-mimicking phantom. Tomographic composition maps were generated from CS patterns, showing the structural arrangement of multiple stone components within the phantom. CS analysis has the ability to detect components in the presence of many others. The ability to perform CS measurements in intact calculi would allow for the identification of stone structures critical to patient metaprophylaxis.

Algorithms↗
PubMed2005

Design of functional simulation of renal cancer in virtual reality environments.

OBJECTIVES: The preoperative planning of partial nephrectomy can be facilitated by the ability to view the tumor and surrounding tissue in three-dimensional (3D) virtual reality (VR). A technique to convert Digital Imaging and Communications in Medicine computed tomography scan data into a fully 3D VR environment was developed. The model can be transferred to a personal computer, allowing the surgeon to view the 3D model in the operating room. METHODS: Computed tomography data from a patient with multifocal renal masses was converted into a 3D polygonal mesh using Amira running on a desktop personal computer with Windows XP Professional. A Silicon Graphics Monster Onyx2 running the Linux operating system was used to view the 3D stereo model in the VR environments: either the CAVE or a specialized desk called the Immersadesk. An application to view and interact with the model on a desktop personal computer was written in C++. RESULTS: A 3D model of the kidney, the multiple tumors, and the associated systems was created. The model could be viewed and manipulated in a true VR environment and on a desktop personal computer. CONCLUSIONS: This project completed two major goals. First, a 3D model of a kidney containing multiple masses was created and viewed in a VR environment. Second, an interface to display the model on a desktop personal computer in the operating room was created. This is the first step in bringing VR technology to the operating room to assist the surgeon directly.

Aged↗
PubMed2005

Performance and safety of holmium: YAG laser optical fibers.

BACKGROUND AND PURPOSE: Lower-pole ureteronephroscopy requires transmission of holmium:YAG energy along a deflected fiber. Current ureteroscopes are capable of high degrees of deflection, which may stress laser fibers beyond safe limits during lower-pole use. We hypothesized that optical fiber and safety measures differ among manufacturers. MATERIALS AND METHODS: Small (200-273-microm) and medium-diameter (300-400-microm) Ho:YAG fibers were tested in a straight and 180 degrees bent configuration. Energy transmission was measured by an energy detector. Fiber durability was assessed by firing the laser in sequentially tighter bending diameters. The fibers were bent to 180 degrees with a diameter of 6 cm and run at 200- to 4000-mJ pulse energy to determine the minimum energy required to fracture the fiber. The bending diameter was decreased by 1-cm increments and testing repeated until a bending diameter of 1 cm was reached. The maximum deflection of the ACMI DUR-8E ureteroscope with each fiber in the working channel was recorded. The flow rate through the working channel of the DUR-8E was measured for each fiber. RESULTS: The mean energy transmission differed among fibers (P < 0.001). The Lumenis SL 200 and the InnovaQuartz 400 were the best small and medium-diameter fibers, respectively, in resisting thermal breakdown (P < 0.01). The Dornier Lightguide Super 200 fractured repeatedly at a bend diameter of 2 cm and with the lowest energy (200 mJ). The other small fibers fractured only at a bend diameter of 1 cm. The Sharplan 200 and InnovaQuartz Sureflex 273T were the most flexible fibers, the Lumenis SL 365 the least. The flow rate was inversely proportional to four times the power of the diameter of the fiber. CONCLUSIONS: Optical performance and safety differ among fibers. Fibers transmit various amounts of energy to their cladding when bent. During lower-pole nephroscopy with the fiber deflected, there is a risk of fiber fracture from thermal breakdown and laser-energy transmission to the endoscope. Some available laser fibers carry a risk of ureteroscope damage.

Aluminum↗
PubMed2005

Long-term results of microwave thermotherapy for symptomatic benign prostatic hyperplasia.

PURPOSE: To study the long-term outcomes of men with moderately severe symptomatic benign prostatic hyperplasia (BPH) who were treated with transurethral microwave thermotherapy (TUMT) with the Dornier Urowave machine. PATIENTS AND METHODS: A total of 220 patients (mean age 66.2 years) with clinical BPH, an American Urological Association (AUA) Symptom Score of >or=13, and a peak urinary flow rate (Qmax) of <or=12 mL/sec were enrolled in a multicenter randomized, double-blind, sham-controlled trial. Sham and active treatments were conducted under local anesthesia as an outpatient procedure. Patients were followed up at 1 week and at 1, 3, and 6 months. Patients in the sham-treatment arm who still met the initial enrollment criteria were then offered active treatment. The 6-month interim analysis of the safety and efficacy of this treatment has been previously reported (Urology 1998;51:19). Patients were then followed at 6-month intervals out to 60 months after treatment. At our center, 34 men (mean age 64+/-6 years) continued on the recommended long-term follow-up protocol. RESULTS: Among the 34 men from our center initially entered in the study, 15 completed the entire 5-year follow-up. Four of the men available for follow-up at the 5-year mark were on alpha-blocker medication, and six men had required transurethral surgery for symptom relief. At 5 years, this cohort of patients maintained improvement in AUA Score (from 20.5+/-6.2 to 11.5+/-5.0; P<0.001) and Quality of Life score (from 3.7+/-1.3 to 1.9+/-1.0; P<0.001) but showed no significant improvement in Qmax (8.2+/-1.9 mL/sec to 8.4+/-4.3 mL/sec). At 5 years, 11 of the 15 patients available for review had not required additional therapy. CONCLUSIONS: While improvement in voiding symptoms and Quality of Life scores were maintained without the need for adjuvant treatment in approximately one third of men 5 years after TUMT, a significant number had required salvage therapies for symptom relief.

Aged↗
PubMed2004

Surface-enhanced laser desorption/ionization-time of flight-mass spectrometry (SELDI-TOF-MS): a new proteomic urinary test for patients with urolithiasis.

SELDI-TOF-MS is a highly sensitive protein-analysis tool capable of detecting minute protein profile differences between biological samples. As proteins have been associated with urinary tract calculi, protein-based urinalysis may offer insights into their diagnosis. The purpose of this study was to evaluate SELDI-TOF-MS as a potential method for identifying urinary biomarkers of urolithiasis. Midstream sterile urine samples were obtained from 25 male patients with a confirmed diagnosis of urolithiasis (test group) and 25 male subjects with no known history of the disease (controls). Urinary levels of oxalate, total protein, albumin, and osteopontin were determined. Protein profiles were generated using SELDI-TOF-MS.SELDI-TOF-MS profiling revealed a relationship between protein peak intensities at 67 and 24 kDa that differed between the two groups. The ratio of p67:p24 was found to be less than 1.0 in all of the control samples (mean 0.26), while 18 out of 25 (72%) of the test group samples displayed a ratio greater than 1.0 (total group mean 4.75, P<0.001). Albumin, total protein, and oxalate levels were higher in the test group than the controls. Although SELDI-TOF-MS is not yet in widespread use in hospital and diagnostic laboratories, this system represents a promising new method for rapidly identifying patients with urolithiasis.

Albumins↗
PubMed2004

Percutaneous antegrade endopyelotomy: long-term results from one institution.

OBJECTIVES: To assess the long-term efficacy of percutaneous antegrade endopyelotomy for the treatment of ureteropelvic junction (UPJ) obstruction performed at a single institution during a 10-year period. We provide alterations in investigation and management strategies on the basis of the results. METHODS: From July 1990 to June 2001, 80 patients with clinical and radiographic evidence of UPJ obstruction underwent percutaneous endopyelotomy for the treatment of primary (n = 61) or secondary (n = 19) UPJ obstruction. The mean patient age was 35 years (range 4 to 76). Percutaneous endopyelotomy was performed in a standard fashion using either a hooked-knife (n = 77) or holmium laser (n = 3). RESULTS: With a mean patient follow-up of 55 months (range 16 to 138), the overall success rate was 67% (53 of 79). The success rate for primary and secondary UPJ obstruction was 65% (39 of 60) and 74% (14 of 19), respectively. The mean time to failure was 15 months (range 1 to 79). Operative intervention for 24 of 26 patients with failure included open pyeloplasty (n = 18, 75%), indwelling ureteral stenting (n = 2, 8%), retrograde balloon dilation (n = 1, 4%), and nephrectomy (n = 3, 13%). Two asymptomatic patients with recurrent radiographic evidence of obstruction elected conservative follow-up. Significant crossing vessels were encountered at open pyeloplasty in 15 (83%) of 18 patients. CONCLUSIONS: Our long-term results of percutaneous endopyelotomy demonstrated somewhat lower success rates than that reported in published studies. Long-term follow-up is critical in identifying late failures. The high prevalence of crossing vessels encountered at open pyeloplasty provided further evidence to support its role in endopyelotomy failure. Routine preoperative helical computed tomography to detect significant crossing vessels is recommended. Patients with crossing vessels are likely better served with operative techniques that specifically address this issue, namely open or laparoscopic pyeloplasty.

Adolescent↗
PubMed2004

Stenting after ureteroscopy: pros and cons.

The results of the numerous trials evaluating stenting after uncomplicated ureteroscopy suggest that the routine placement of a stent is no longer necessary. Patients with stents seem to have significantly more pain and irritative voiding symptoms. In addition, the routine placement of a stent significantly adds to the overall cost of the procedure. There is a subgroup of patients who would likely benefit from a stent as evidenced by the higher readmission to hospital rate than in nonstented patients. Ideally, future trials will help unmask a method to identify these patients.

Equipment Failure↗
PubMed2004

Technology insight: Novel ureteral stent materials and designs.

Ureteral stents are an important tool for aiding upper urinary tract drainage, but can cause significant patient morbidity. Common problems include stent-induced pain, hematuria, dysuria, infection, and encrustation. From a urologist's perspective, stents must be easy to maneuver in the urinary tract, radiopaque, and affordable. Since the development of the modern day stent in 1978, stents have evolved to include softer biomaterials that are more resistant to encrustation and infection. An ideal biomaterial is one that is not affected by its environment and does not elicit reactive changes in surrounding tissues. To date, the ideal biomaterial or stent does not exist. This review discusses developments that address the issues of infection, biofilm formation, encrustation, and patient comfort. Stent materials including polyurethane, silicone, biodegradable substances and new combination polymers are reviewed, in addition to novel stent coatings such as heparin, hydrogel, and silver nitrate. Ureteral stent technologies currently lag behind vascular stents, particularly drug-eluting stents, but new developments will continue to improve these essential urological tools.

Biocompatible Materials↗
PubMed2004

Double-blind randomized controlled trial assessing the safety and efficacy of intravesical agents for ureteral stent symptoms after extracorporeal shockwave lithotripsy.

BACKGROUND AND PURPOSE: Ureteral stents are a significant source of pain and discomfort for many urologic patients. A novel approach to addressing this problem is the intravesical instillation of a selected pharmacologic agent after stent insertion. The purpose of this study was to assess the safety and efficacy of intravesical instillation of various agents in reducing ureteral stent-associated discomfort in patients requiring a stent after extracorporeal shockwave lithotripsy (SWL). PATIENTS AND METHODS: In this double-blind prospective trial, 42 patients were randomized to receive intravesical instillation of one of three agents (oxybutynin, alkalinized lidocaine, or ketorolac) or a control solution (0.9% sodium chloride) immediately after stent insertion at time of SWL. The four groups of patients were demographically similar. Preoperative, intraoperative, and postoperative data were collected prospectively and analyzed statistically. The primary outcome measure was reduction in ureteral stent symptoms, and the secondary outcome measure was the safety of intravesical instillation of each agent through assessment of drug-related adverse events. RESULTS: There were no intraoperative or postoperative complications, nor were there any serious side effects attributable to any of the intravesically instilled agents. There was a statistically significant decrease in stent-related discomfort at the 1-hour time point in the group of patients who received intravesical ketorolac compared with the control group. CONCLUSIONS: Intravesical instillation represents a novel approach to the problem of ureteral stent-related discomfort. From our results, ketorolac appears to be the most effective intravesical agent in reducing stent-related patient discomfort, and we have established that intravesical instillation of ketorolac is safe in humans.

Administration, Intravesical↗
PubMed2004

The use of stents in contemporary urology.

PURPOSE OF REVIEW: Ureteral stents are a mainstay of today's urological armamentarium. This review critically evaluates the recent literature and provides a concise summary of the use of stents in urology today. While stents are used in many reconstructive urologic procedures, this review focuses on the use of stents in urolithiasis as it pertains to ureteroscopy, shockwave lithotripsy, and ureteropelvic junction obstruction. RECENT FINDINGS: Ureteral stents are associated with irritative symptoms, hematuria, infection, and encrustation. A new validated quality of life and impact questionnaire has been developed and has shown that 76% of patients suffer at least some type of morbidity related to the stent. Many studies in the recent literature have re-examined our use of stents today. For example, concepts regarding stenting following ureteroscopy, before shockwave lithotripsy, and following endopyelotomy have undergone an evolution based on the results of randomized, prospective studies. SUMMARY: The ureteral stent is an invaluable urological tool and its indications are evolving as are new stent technologies to improve patient care and comfort.

Biocompatible Materials↗