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Biomedical subjects

P F Keane

Publications and source records attributed to P F Keane.

At least 19 recordsLinked to original sources
PubMed1998

Characterization and assessment of a novel poly(ethylene oxide)/polyurethane composite hydrogel (Aquavene) as a ureteral stent biomaterial.

The effective long-term use of indwelling ureteral stents is often hindered by the formation of encrusting deposits which may cause obstruction and blockage of the stent. Development of improved ureteral stent biomaterials capable of preventing or reducing encrustation is therefore particularly desirable. In this study, the suitability as a ureteral stent biomaterial of Aquavene, a novel poly(ethylene oxide)/polyurethane composite hydrogel was compared with that of silicone and polyurethane, two materials widely employed in ureteral stent manufacture. Examination of Aquavene in dry and hydrated states by confocal laser scanning microscopy, scanning electron microscopy, and atomic force microscopy showed the presence of numerous channels within a cellular matrix structure. The channel size increased considerably to as much as 10 microm in diameter in the hydrated state. Aquavene provided superior resistance to encrustation and intraluminal blockage over a 24-week period in a simulated urine flow model. Unobstructed urine flow continued with Aquavene at 24 weeks, whereas silicone and polyurethane stents became blocked with encrustation at 8 and 10 weeks, respectively. Weight loss within Aquavene on the order of 9% (w/w) over the 24-week flow period indicates that extraction of the noncrosslinked poly(ethylene oxide) hydrogel may be responsible for the prevention of encrustation blockage of this biomaterial. In the dry state, Aquavene was significantly harder than either silicone or polyurethane, as shown by Young's modulus, and rapidly became soft on hydration. These additional properties of Aquavene would facilitate ease of stent insertion in the dry state past obstructions in the ureter and provide improved patient comfort on subsequent biomaterial hydration in situ. Aquavene is a promising candidate for use in the urinary tract, as it is probable that effective long-term urine drainage would be maintained in vivo. Further evaluation of this novel biomaterial is therefore warranted.

Biocompatible Materials↗
PubMed1998

Clinical response to an oral prostaglandin analogue in patients with interstitial cystitis.

OBJECTIVE: To assess the efficacy of the oral prostaglandin analogue misoprostol in controlling the symptoms of interstitial cystitis in patients with refractory disease. METHODS: Twenty-five patients were commenced on misoprostol 600 micrograms daily for 3 months. Patients who responded to therapy were offered treatment for a further 6 months. Assessment of the response was by a voiding log and an interstitial cystitis symptom score. RESULTS: At 3 months, 14 patients (56%) had significantly improved, and after a further 6 months, 12 patients (48%) had a sustained response. The incidence of adverse drug effects was 64%. Most side effects were minimal, and the response rate in patients who were able to tolerate the drug was 87% at 3 months and 75% at 9 months. CONCLUSIONS: The oral prostaglandin analogue misoprostol is effective in treating the symptoms of interstitial cystitis. It is possible that prostaglandins have a cytoprotective action in the urinary bladder.

Administration, Oral↗
PubMed1998

The haematuria clinic--referral patterns in Northern Ireland.

One hundred consecutive patients with haematuria were seen over a three month period at the haematuria clinic, Belfast City Hospital. 14% of patients were found to have transitional cell carcinoma of the urinary bladder; all of these presented with frank haematuria and were over 50 years of age. No malignancy was detected in the microscopic haematuria group. 14% of patients with macroscopic haematuria held back for longer than one month before seeking advice from their general practitioner. 23% with macroscopic and 30% with microscopic haematuria had their symptoms noted by the general practitioner for more than a month before they were referred for investigation. The waiting time for initial investigation at the haematuria clinic took longer than six weeks in 52% with macroscopic and 39% with microscopic haematuria. Our study has identified a high-risk group who need immediate referral and investigation. The importance of patient education, rapid referral by general practitioners and also the need to increase the capacity of the haematuria clinic are emphasized.

Adult↗
PubMed1997

Assessment of urinary tract biomaterial encrustation using a modified Robbins device continuous flow model.

Encrustation of biomaterials employed in the urinary tract remains a major problem resulting in obstruction or blockage of catheters and stents. Therefore, resistance to encrustation is a desirable feature of biomaterials employed in such devices. The novel assessment of biomaterial encrustation employing a continuous flow model based on a modified Robbins device is described. Artificial urine was used in conjunction with 5% CO2 to simulate the physiological environment within the upper urinary tract. The widely used urinary device biomaterials, silicone and polyurethane, were investigated in the model for hydroxyapatite and struvite encrustation. Scanning electron microscopy, energy dispersive X-ray analysis, and atomic absorption spectroscopy all showed that silicone was less prone to encrustation than polyurethane and that hydroxyapatite deposition was predominant on both surfaces. The model has the advantage that a large number of biomaterials may be investigated simultaneously because several Robbins devices may be placed in parallel. The model is recommended for comparative evaluation of biomaterial candidates for use in urinary tract devices.

Biocompatible Materials↗
PubMed1997

Mechanical performance of polyurethane ureteral stents in vitro and ex vivo.

A serious problem associated with the use of ureteral stents is fracture in situ. Following clinical observations of fracture of polyurethane stents in vivo, this study examined the mechanical properties of 17 polyurethane stents (double-J containing drainage holes) retrieved from patients over a 24-week period of insertion. In addition, stents were immersed in human and artificial urine in an in vitro model at 37 degrees C to determine their general propensity to fracture. Mechanical properties of ureteral stents were examined using the standard ASTM D-412 tensile test and by the novel application of dynamic mechanical analysis (DMA). The ultimate tensile strength and elongation at break (but not the Young's modulus) of unused polyurethane stent sections containing side-drainage holes were greater than stent sections devoid of side-drainage holes. No correlations were observed between increased or decreased Young's modulus, ultimate tensile strength or elongation at break of polyurethane stents and their time of immersion in either human urine or artificial urine in simulated upper urinary tract conditions of 37 degrees C and 5% CO2. Similarly, no correlations were observed between Young's modulus, ultimate tensile strength or elongation of polyurethane stents and stent dwell time in situ. DMA of retrieved stents revealed that their tan delta value and storage modulus did not differ significantly from unused stents following dwell times in situ of up to 24 weeks. No changes in the glass transition temperatures were observed in retrieved stents. Although patient variation was observed, the results indicate that the polyurethane stents examined in vitro and following removal from patients did not exhibit any greater propensity to fracture than their unused counterparts. Fracture of retrieved polyurethane stents, arising in vivo and also during subsequent tensile testing, was observed to occur along the drainage holes, suggesting that elimination of these holes will reduce the incidence of polyurethane ureteral stent fracture in use.

Biocompatible Materials↗
PubMed1997

Validation of a rapid method to quantify apoptosis in superficial bladder cancer.

OBJECTIVES: To derive and validate a rapid method for calculating apoptotic indices in superficial transitional cell carcinoma (TCC) as a measure of chemosensitivity to mitomycin. MATERIALS AND METHODS: Apoptotic cells, identified by light microscopy in 20 superficial TCC specimens, were expressed as an index of the total tumour cell population within defined fields. For a given field, the total cell population was estimated by: (i) an exhaustive count of the total number of cells in the field and (ii) an abbreviated method in which the number of cells in a subfield was multiplied to provide an estimate of the total field number. Field and specimen estimates were compared using agreement statistics and the intra- and inter-observer reproducibility of apoptotic indices calculated. RESULTS: Cellularity and apoptotic indices obtained using method (ii) were correlated significantly with the true cell counts (P < 0.001). Agreement statistics showed that only 9.4% of counts fell outside two standard deviations (SD) from the mean in field analysis, and only 10% of counts fell outside 2 SD from the mean in specimen analysis. There was a fivefold variation in tumour cell counts among individual fields. CONCLUSIONS: The reported variation in cellularity among fields shows that the calculation of apoptosis must use the total cell population as the reference. The limits of agreement for the estimated and true cell counts are small enough to be confident that the shorter method to estimate cellularity can be used in place of counting all cells.

Antibiotics, Antineoplastic↗
PubMed1997

Symptomatic outcome following clam ileocystoplasty.

OBJECTIVE: This study was designed to assess the outcome of clam ileocystoplasty (CI) based on patients' subjective perception and objectively validated scoring systems. Quality-of-life parameters were also examined as aspects of outcome. MATERIAL AND METHODS: Between 1989 and 1994, 27 patients (15 male and 12 female) underwent CI. The median age was 41 years (13-75 years). CI was performed after failed pharmacological treatment. The mean length of follow-up for this patient cohort was 18 months (range: 1-4 years). RESULTS: Overall cure rate was objectively assessed at 61%. Seventy-two percent of patients described a subjective improvement of symptoms, and a small number of patients (12.5%) were subjectively worse following the operation. Quality of life was improved in 75% of patients, with 12.5% showing no improvement and 12.5% being worse. Fifty-six percent of patients noted a minor degree of voiding dysfunction, whereas 25% noted moderate and 19% noted severe voiding dysfunction. CONCLUSIONS: CI offered improvement with satisfaction in the group of patients studied, however not all patients achieved a satisfactory outcome. The patients who were worse following the procedure were all young females with detrusor instability. Careful patient selection and pre-operative counselling may reduce the failure rate. Outcome analysis based on standardised questionnaires allows patients and surgeons to make informed decisions with realistic expectations.

Adolescent↗
PubMed1996

Development of a model for assessment of biomaterial encrustation in the upper urinary tract.

A need exists for ureteral stent materials capable of preventing or reducing encrustation. The aim of this study, therefore, was to develop an in vitro model producing biomaterial encrustation similar to that on stents in vivo. Three models were designed and evaluated. Polyurethane stent sections were immersed in human urine (37 degrees C, 5% CO2): (1) with and (2) without crushed human kidney stone and (3) in an artificial urine (37 degrees C, 5% CO2). Encrustation of similar composition, as determined by infrared spectroscopy, X-ray diffraction and energy dispersive X-ray analysis, formed on stent materials in vivo, in artificial urine and in human urine with crushed kidney stone. Magnesium ammonium phosphate (struvite) and calcium phosphate (hydroxyapatite) predominated in all encrustations. The reproducibility and ease of use of the artificial urine model provided optimum encrustation assessment of materials presently used in ureteral stents and evaluation of novel biomaterials.

Calcium Phosphates↗
PubMed1996

Comparative assessment of ureteral stent biomaterial encrustation.

Long-term use of ureteral stents is hindered by the inherent problem of biomaterial encrustation which may lead to stone formation and attendant problems. The wide variety of polymeric biomaterials currently used for stent fabrication suggests that no single material is significantly superior to the others at resisting encrustation. A model representing upper urinary tract conditions was employed to compare the long-term struvite and hydroxyapatite encrustation of five materials currently used in the fabrication of ureteral stents. Silicone was least prone to struvite encrustation, followed by polyurethane, silitek, percuflex and hydrogel-coated polyurethane, in rank order. Similarly, silicone was least prone to hydroxyapatite encrustation, followed by silitek, polyurethane, percuflex and hydrogel-coated polyurethane. This study has shown that the problem of encrustation may limit the long-term use of ureteral stent biomaterials and suggests directions for improvement of biomaterials in this regard.

Analysis of Variance↗
PubMed1995

Laser lithotripsy for ureteric calculi: results in 250 patients.

Two hundred and fifty patients with 290 stones presenting to the Department of Urology were treated with the Candela MDL 2000 Laser Lithotripter. Overall stone clearance rate was 95%. The more proximal the calculus the lower the success rate. Ninety eight percent of stones in the lower ureter, 95% of mid ureteric and 91% of upper ureteric stones were cleared. The major complication was perforation which occurred in 6% of cases. This procedure is a safe and effective treatment for ureteric calculi and is associated with a low complication rate and a high clearance rate. Laser lithotripsy is the optimum ureteroscopic method of treating ureteric calculi and is complimentary to extra corporeal shock wave lithotripsy.

Adolescent↗
PubMed1994

Characterization of biofilm and encrustation on ureteric stents in vivo.

OBJECTIVE: To examine the relationship between encrustation and microbial biofilm formation on indwelling ureteric stents. PATIENTS AND METHODS: Ureteric stents from 40 patients were examined for the presence of a microbial biofilm and encrustations. Bacteria in stent biofilms were isolated and identified. RESULTS: A profuse biofilm (> 10(4) c.f.u. cm-3) was identified on 11 (28%) stents. Enterococcus faecalis was the most common biofilm organism identified and Proteus spp. were not present. Encrustation was seen in 23 (58%) of stents and was not associated with the level of urinary calcium. The major risk factor for stent encrustation was the presence of urolithiasis. Importantly, there was no causative link between stent biofilm formation and encrustation. Both biofilm formation and encrustation increased with the duration of stenting. CONCLUSION: The results indicate that polyurethane is readily encrusted and colonized by bacteria in vivo despite antibiotic prophylaxis. Newer materials must be sought if effective long-term stenting is to be achieved.

Adult↗