Furanones as potential anti-bacterial coatings on biomaterials.

A major barrier to the long-term use of medical devices is development of infection. Staphylococcus epidermidis is one of the most common bacterial isolates from these infections with biofilm formation being their main virulence factor. Currently, antibiotics are used as the main form of therapy. However with the emergence of staphylococcal resistance, this form of therapy is fast becoming ineffective. In this study, the ability of a novel furanone antimicrobial compound to inhibit S. epidermidis adhesion and slime production on biomaterials was assessed. Furanones were physically adsorbed to various biomaterials and bacterial load determined using radioactivity. Slime production was assessed using a colorimetric method. Additionally, the effect of the furanone coating on material surface characteristics such as hydrophobicity and surface roughness was also investigated. The results of this study indicated that there was no significant change in the material characteristics after furanone coating. Bacterial load on all furanone-coated materials was significantly reduced (p<0.001) as was slime production (p<0.001). There is a potential for furanone-coated biomaterials to be used to reduce medical device-associated infections.

Thought Field Therapy-soothing the bad moments of Kosovo.

Trauma in Kosovo was treated with Thought Field Therapy (TFT) during five separate trips by members of the Global Institute of Thought Field Therapy, in the year 2000. Clinicians from Sweden, the United Kingdom, and the United States were joined in Kosovo by four physicians who transported them to remote war-torn villages where patients with severe trauma were treated. Treatment was given to 105 patients with 249 separate traumas. Total relief was reported by 103 of the patients, and for 247 of the separate traumas. Follow-up data averaging five months revealed no instance of relapse.

Acute cellular interaction with textured surfaces in blood contact.

Textured blood-contacting surfaces can promote the formation of a blood-compatible pseudo-neointima. We hypothesized that by controlling the surface texturing, the pseudo-neointima thickness could be controlled. The hypothesis was tested experimentally by fabricating the polyurethane textured surfaces with three different fiber lengths, and exposing them simultaneously to the flowing blood in an ovine ex vivo carotid-jugular series shunt for periods up to 4 h. The textured surface consisted of regularly spaced tapered micro-fibers of defined length on a smooth base-plane surface. Because of the simple surface topography, detailed computational fluid-dynamic modeling of the surface could be obtained as a parallel study. Experimental results showed that white cell was the predominant cell type deposited on the textured surfaces, whereas macroscopic thrombus formation occurred only in one of nine blood-contacting experiments. White cell density on the textured base-plane surface was subsequently quantified by image-analyzing the electron micrographs of blood-contacted textured surfaces. The statistical analysis of cell densities on individual textured surfaces showed effects of wall shear stress on the textured base plane (which was obtained from the fluid-dynamic modeling), the longitudinal position of the test section in the series shunt, and blood-contact time.

Efficacy of insulin pump therapy: mealtime delivery is the key factor.

OBJECTIVE: To investigate, in a clinical setting, the effect of implementation of continuous subcutaneous insulin infusion (CSII) on control of plasma glucose and to identify factors associated with improved glycemic control in patients with type 1 diabetes mellitus. METHODS: Nineteen patients (16 women and 3 men) with type 1 diabetes were studied retrospectively. Their mean age was 42.6 years (range, 30 to 58), and the mean duration of diabetes was 21 years. The subjects underwent follow-up for a mean of 14 months after conversion to CSII therapy. With use of paired t tests, pre-CSII and follow-up data were evaluated relative to changes in weight, insulin dosing, and glycosylated hemoglobin (HbA(1c)). RESULTS: At follow-up, the total daily dose of insulin had decreased by 18%, from a baseline mean value of 45.2 IU to 37.1 IU (P = 0.02). HbA(1c) was reduced from 8.4% to 7.7% (P<0.01). The total daily insulin-to-weight ratio also significantly decreased from 0.66 IU/kg to 0.53 IU/kg (P<0.05). Before insulin pump use, the regular/NPH insulin ratio was 0.5 IU; at follow-up, the pump bolus/basal insulin ratio was 1.0 IU (P = 0.02). No weight gain was observed; the mean weight of the study patients decreased 0.2 kg, from 69.4 kg at baseline to 69.2 kg at follow-up (not significantly different). CONCLUSION: In a clinical setting, CSII therapy in patients with type 1 diabetes improves glycemic control and lowers the total daily basal insulin dose without affecting weight. Improved glycemic control was associated with a shift in insulin therapy from a high percentage of intermediate-acting insulin to a greater percentage of insulin administered in a meal-associated bolus form. This study emphasizes the importance of mealtime insulin adjustment for tight glycemic control in patients using CSII therapy. Future studies evaluating the benefits of decreased total insulin and an increased bolus/basal insulin ratio may be important in helping to understand how to avoid long-term complications of diabetes.

Analysis of growth kinetics by division tracking.

Cell division tracking using fluorescent dyes, such as carboxyfluorescein diacetate succinimidyl ester, provides a unique opportunity for analysis of cell growth kinetics. The present review article presents new methods for enhancing resolution of division tracking data as well as derivation of quantities that characterize growth from time-series data. These include the average time between successive divisions, the proportion of cells that survive and the proliferation per division. The physical significance of these measured quantities is interpreted by formulation of a two-compartment model of cell cycle transit characterized by stochastic and deterministic cell residence times, respectively. The model confirmed that survival is directly related to the proportion of cells that enter the next cell generation. The proportion of time that cells reside in the stochastic compartment is directly related to the proliferation per generation. This form of analysis provides a starting point for more sophisticated physical and biochemical models of cell cycle regulation.

Comparison between the clonogenic, MTT, and SRB assays for determining radiosensitivity in a panel of human bladder cancer cell lines and a ureteral cell line.

Using a series of human bladder cancer cell lines and an immortalised normal ureteral cell line, radiosensitivities measured by three different methods after a single dose of X-radiation are compared. Clear differences between cell survival curves obtained using the clonogenic, microtetrazoline (MTT) and sulforhodamine B (SRB) assays are shown. The most sensitive of the assays investigated was the clonogenic assay. The MTT and SRB assays were found to be relatively insensitive especially at lower radiation levels, suggesting that these assays may not be suitable for predicting therapeutic dose schedules in vivo, but will be important for investigating radio-sensitivity in cell lines with very low plating efficiencies. Each assay discriminated between a range of sensitivities in the cell lines examined, and with some minor differences, the ordering of sensitivities using the three assays was similar. Possible explanations for the differences between results obtained with the three assays are discussed.

Survival, intracranial lesions, and neurodevelopmental outcome in infants with congenital diaphragmatic hernia treated with extracorporeal membrane oxygenation.

OBJECTIVE: Before the use of extracorporeal membrane oxygenation (ECMO), infants with a severe form of congenital diaphragmatic hernia (CDH) had a high mortality and morbidity. Recent studies have shown an improvement in the survival of these infants after ECMO treatment; however, the existing data do not provide sufficient informations regarding the quality of survival and developmental outcome of these infants. The objective of this study was to evaluate survival, intracranial lesions, and the neurodevelopmental outcome of infants with CDH treated with ECMO. METHODS: We retrieved data for 51 (n = 51) infants with CDH who were treated with ECMO at Huntington Memorial Hospital between 1985 and 1994. Their mean gestational age was 38.5 +/- 2.4 weeks (mean +/- SD); their mean birth weight was 3170 +/- 620 gm. Vital signs, arterial blood gases, chest radiographs, cranial and cardiac ultrasonography were routinely obtained before ECMO treatment. Cranial ultrasounds were performed daily on all infants while on ECMO; computerized tomography scans were obtained on all infants after completion of ECMO treatment. The surviving infants were followed at our neonatal follow-up clinic for neurodevelopmental assessment. RESULTS: A total of 39 infants were placed on venoarterial ECMO and 12 infants were placed on venovenous ECMO; a total of 35 infants had CDH repair before ECMO, whereas 16 infants had delayed surgery. A total of 31 infants (61%) survived. The infants who survived had a mean pH of 7.33 +/- 0.20, mean airway pressure of 19.6 +/- 5.8 cm H2O, and an oxygenation index (OI) of 87 +/- 55 before ECMO intervention. The infants who expired (n = 20) had a mean pH of 7.31 +/- 0.15, mean airway pressure of 23.1 +/- 5.5 cm H2O, and a mean oxygenation index of 127 +/- 56 before ECMO treatment. Before ECMO, survivors had a significantly lower oxygenation index and a higher Pao2 compared with nonsurvivors (p < 0.01). A total of 18 infants (35%) had abnormal central nervous system findings. Of the 51 infants, 10 had ventricular dilatation, 6 had intracranial hemorrhage, and 11 had focal or diffuse cerebral atrophy diagnosed by computerized tomography scan or at autopsy (1 patient had an infarct). Eight infants had more than one central nervous system abnormality. A total of 16 survivors had a neurodevelopmental evaluation at 12 months, and 11 of these survivors were evaluated at 24 months of age (Bayley Scales of Infant Development). The developmental progress of these infants falls within the low-average range of cognitive and motor abilities. Their mean Bayley Mental Developmental Index was 85 +/- 25 (50 to 145) at 24 months; their Psychomotor Developmental Index was 89 +/- 21 (50 to 113) at 24 months of age. Follow-up at 4 and 6 years of age is in progress. CONCLUSION: Our preliminary findings indicate that 35% of infants with severe CDH requiring ECMO had central nervous system abnormalities (intracranial lesions, including ventricular dilatation). The survival rate in our study population is consistent with recent reports. As a group, infants with severe CDH display mild neuromotor and cognitive delay in development at 24 months of age.

Five-year results of single-incision arthroscopic anterior cruciate ligament reconstruction with patellar tendon autograft.

We performed a retrospective study on 80 patients who underwent single-incision arthroscopic anterior cruciate ligament reconstruction with patellar tendon autograft and interference fit screw fixation in 1989. Twelve patients were lost to followup, allowing a clinical assessment of 68 patients to be conducted by independent examiners at 1 and 5 years after surgery, with radiographic assessment at 5 years. Thirty-three patients had chronic anterior cruciate ligament-deficient knees. Three patients reruptured their grafts during sports at 29, 48, and 56 months. At 5 years, 64 patients (98%) had grade 0 or 1 Lachman and pivot shift tests with manual stability testing. Fifty patients (77%) were participating in level I or II activities according to the International Knee Documentation Committee scale. Twenty-nine patients (45%) experienced low levels of pain when performing at their highest activity level. Five (8%) had thigh atrophy greater than 1 cm, and three (5%) had an extension loss of more than 3 degrees. Eleven patients (17%) had tenderness over the graft site when kneeling. Fifteen of 62 patients (24%) had degenerative changes on radiographs, and this was more common in patients with chronic anterior cruciate ligament-deficient knees. Fifty-two patients (80%) had normal or nearly normal knees according to the overall International Knee Documentation Committee score.

Nutritional requirements of the corneal epithelium and anterior stroma: clinical findings.

PURPOSE: To monitor the health of the epithelium and the anterior stroma when porous membranes are implanted into the feline cornea and to determine membrane diffusivity characteristics needed to maintain corneal integrity. METHODS: Filtration membranes in a range of effective pore sizes of less than 15 nm (groups 1 and 2, n = 11), 25 nm (group 3, n = 8), 50 nm (group 4, n = 16), and 100 nm (group 5, n = 15) were implanted into an interlamellar corneal pocket of the stroma. The implanted membranes ranged in thickness from 6 nm to 15 nm and were between 8 mm and 12 mm in diameter. Animals were monitored for clinical signs of intolerance to the implants. RESULTS: At 1 month, thinning and ulceration had occurred in the epithelium and the anterior stroma of all animals in groups 1 and 2; epithelial changes, anterior stromal thinning, and ulceration had developed in 75% of animals of group 3; 50% of animals showed vascularization and only 7% showed epithelial degeneration in group 4; and local anterior stromal thinning was observed in 7% of animals in group 5, indicating clinical acceptance of the implanted membrane. In the long term (greater than 50 days), 30% and 73% of the group 4 and 5 corneas, respectively, were clinically quiet. Analysis of the failure times indicated an inverse relation between failure rate and pore size: less than 15 nm > 25 nm > 50 nm > 100 nm. The difference between the 100-nm and 50-nm membranes was significant (P = 0.03). CONCLUSIONS: A corneal implant must have a porosity greater than that provided by 50-nm membranes. The 100-nm membranes used in this study establish the porosity needed to satisfy the nutritional requirements of the cornea.

Dialysis neutropenia: the role of the cytoskeleton.

Dialysis neutropenia is the result of pulmonary sequestration of neutrophils after complement activation by the dialyzer membrane. Increased expression of neutrophil adhesion receptors, such as CD11b/CD18, suggests that neutrophil adhesion to the capillary endothelium is a possible mechanism. An alternative hypothesis is that the complement fragment C5a modulates neutrophil mechanical properties via the cytoskeleton-largely filamentous actin (F-actin)-stiffening them and thereby slowing their passage through the pulmonary capillaries. To investigate this hypothesis, we developed an assay to measure the F-actin content of neutrophils in whole blood using flow cytometry and the stain NBD-phallacidin. We measured neutrophil F-actin content during hemodialysis of patients with polysulfone (N = 6), Hemophan (N = 6), and Cuprophan membranes sterilized with either ethylene oxide (N = 5) or steam (N = 6). Cell counts, neutrophil and monocyte CD11b expression and plasma C5a concentrations were also measured. The results confirm the strong relationship between the degree of neutropenia, increases in CD11b expression and plasma C5a levels reported by previous researchers. Modulation of the F-actin content of neutrophils was also strongly related to C5a levels, indicating that the neutrophil cytoskeleton is active during dialysis. Modeling of cell counts suggests that with Cuprophan a substantial fraction of neutrophils and monocytes are sequestered before they even pass through the dialyzer, suggesting some form of systemic activation of these cells. Evidence for systemic activation was also seen in measurements of F-actin content, but not CD11b expression, a finding that strengthens the case for the involvement of the cytoskeleton in dialysis neutropenia.

Electrosurgery: principles and safety issues.

The use of monopolar electrosurgical energy has been the "gold standard" for the past 50 years. It has diverse capabilities, such as fulguration, precise vaporization, and coaptation of large vessels. Technologic advances in performance and safety have positioned this device as a useful tool in a surgeon's armamentarium. The adaptation of active electrode monitoring for stray energy as a result of insulation failure or capacitive coupling and the use of completely metal trocar cannulas will increase the confidence of the surgeon and the safety of his/ her patient. It is the author's opinion that its use will prove itself in laparoscopy. As with any surgical tool or energy source, education and skill are required. This introduction on the principal of the biophysics of electrical energy on tissue and the safety consideration is a start to further one's understanding of this surgical tool.

Use of pulse oximetry to monitor venous saturation during extracorporeal life support.

OBJECTIVE: To assess the ability of two different pulse oximeters to display continuous venous oxygen saturation through an extracorporeal bypass circuit with a degree of accuracy comparable to direct in-line oximetry. DESIGN: Prospective, comparison study of pulse oximeters (test oximeter 1 or test oximeter 2) and an in-line oximeter (test oximeter 3). SETTING: A tertiary care neonatal intensive care unit. PATIENTS: Sixty-five consecutive neonates with severe cardiorespiratory failure undergoing extracorporeal life support. INTERVENTIONS: The accuracy of the oximeters was determined by simultaneously comparing the saturation displayed by the pulse oximeters (test oximeters 1 and 2) and/or the in-line oximeter (test oximeter 3) with the measured fractional venous oxygen saturation obtained at regular intervals from the extracorporeal circuit. MAIN OUTCOME MEASURES: Venous oxygen saturation was the criterion standard used to determine accuracy. Bias was defined as the mean difference between observed pulse oximeter or in-line oximeter values and the measured venous oxygen saturation. Mean biases were calculated for venous oxygen saturation measurements between 55% and 99% at intervals of 10%. Precision (the standard deviation of the bias) was calculated for low (55% to 75%), medium (76% to 81%), and high (82% to 99%) venous oxygen saturation values. A total of 983 venous oxygen saturation measurements were made and compared with simultaneous oximeter readings from test oximeter 1 (n = 600), test oximeter 2 (n = 478), and test oximeter 3 (n = 587). RESULTS: Test oximeter 1 was the most precise instrument at each level of venous oxygen saturation (SD, 4.0 to 4.8). Test oximeter 3 demonstrated the most consistent mean bias (range, 8), but was the most inaccurate oximeter across all levels of venous oxygen saturation. CONCLUSIONS: In addition to its known clinical usefulness, pulse oximetry may serve as an adequate substitute for in-line oximetry during extracorporeal life support.

Identification and certification of extracorporeal membrane oxygenation specialists in the United States.

Extracorporeal membrane oxygenation (ECMO) is a highly specialized technique widely practiced in many hospitals. Despite the proliferation of ECMO, little information has been generated relating to ECMO specialists, a new professional group responsible for managing the extracorporeal life support (ELS) system. A telephone survey of ECMO centers in the United States was conducted to determine the number of ECMO specialists, team composition by profession, and clinical components of ECMO specialist certification. Data were obtained in May 1991 from all 63 (100%) active ELS centers. The survey found that the average ECMO program performs 3,770 +/- 1,019 clinical hours of ELS per year with a team of 23 +/- 11 specialists. There are 1,431 practicing ECMO specialists in the United States: 73% registered nurses, 22% respiratory therapists, and 5% others. Most ECMO specialist teams (56%) are comprised of a single profession, with 44% of programs using a mixture of professions. The average ECMO specialist manages the ELS system 171 +/- 91 hr/yr. Thirty-six (57%) programs have a mean yearly clinical requirement of 77 +/- 23 ELS hours per specialist. These results represent the first complete report identifying the number of ECMO specialists in the United States. In addition, program demographics demonstrate variability in ECMO experience and certification requirements.

Congenital pulmonary alveolar proteinosis: failure of treatment with extracorporeal life support.

Pulmonary alveolar proteinosis, a rare disease in neonates, is characterized by the accumulation of insoluble amorphous material within the alveoli. We describe two pairs of siblings with pulmonary alveolar proteinosis in two otherwise unaffected families. All four patients were term neonates in whom severe pulmonary failure developed within hours after birth; three had mature lung profiles. Radiographic lung markings were characterized by an early granular pattern followed by lung opacification. All patients were treated with extracorporeal life support for periods of 212 to 381 hours, but none survived. Life spans ranged from 16 to 190 days. We speculate that pulmonary alveolar proteinosis in neonates results from a genetic defect in surfactant processing that may not be amenable to conventional or unconventional therapies, including extracorporeal life support.

Beta 2-microglobulin kinetics in end-stage renal failure.

The kinetics of beta 2-microglobulin (beta 2m) were studied in five anephric or anuric hemodialysis patients. Human beta 2m was isolated from peritoneal dialysate using ion-exchange and gel chromatography and radiolabeled with 125I. Patients were injected with 10 microCi labeled beta 2m. In one study (N = 4), plasma activity was measured over 72 hours. In a second study (N = 4), patients received low-flux dialysis 24 hours after injection and high-clearance dialysis (Bellco BL655) at 48 hours. Plasma activities were fitted to a three-compartment, variable volume model. Endogenous beta 2m levels (radioimmunoassay) were 56 +/- 6 mg/liter. The beta 2m distribution volume was 12.7 +/- 2.0 liter (0.20 +/- 0.03 liter/kg) and the non-renal clearance was 3.0 +/- 0.4 ml/min. The generation rate, 9.9 +/- 1.7 mg/hr (0.16 +/- 0.04 mg/kg/hr), was similar to that measured in subjects with normal renal function. The three compartment model derived from the turnover data gave an adequate fit of the arterial concentrations of endogenous and exogenous beta 2m during low-flux (nil beta 2m clearance) and high-clearance (beta 2m clearance of 19 ml/min) dialysis. Simulations based on this model indicate that extracorporeal treatment can at best remove about 50% of weekly production. These results suggest that beta 2m production is not increased in dialysis patients, that there is substantial non-renal beta 2m clearance, and that the amount of beta 2m that can be removed by extracorporeal therapy is therefore limited.

Beta 2-microglobulin kinetics in an ovine model.

The kinetics of 125I-beta 2 microglobulin (beta 2M) and 51Cr-EDTA were measured in normal and nephrectomized sheep. In normal sheep the beta 2M clearance was similar to that of EDTA (i.e., glomerular filtration rate), as were the distribution volumes. In anephric sheep the beta 2M clearance was 7.7 +/- 1.4 ml/min.

Transcatheter desiccation of the canine left ventricle using radiofrequency energy: a pilot study.

Catheter ablation of cardiac tissue by means of direct-current electrical energy is associated with several complications. We assessed the efficacy and safety of closed-chest catheter desiccation of the left ventricular myocardium with microbipolar radiofrequency (RF) energy (750 kHz) in five dogs. The unipolar configuration was used with RF energy delivered between the tip electrode of a standard No. 7F tripolar catheter in the left ventricle and an external patch electrode on the left lateral chest wall. A single application with different RF energy settings (100 J, 200 J, and 300 J) was delivered to three individual endocardial sites of the left ventricle. Ventricular tachycardia or fibrillation was not observed during energy application and 24 hours after ablation, as assessed by a Holter recording. There was no damage to the electrode catheter. Dogs were killed on the fifth day. Pathology showed well-delineated ovoid or round-shaped coagulation necrosis at the ablation sites. Microscopic findings consisted of circumscribed areas of necrosis surrounded by a zone of fibroblastic and mononuclear proliferation. In conclusion, catheter ablation of the ventricular myocardium with RF energy is an apparently safe procedure and can effectively produce discrete areas of injury without destruction of surrounding uninvolved myocardium. This method offers potential clinical utility for catheter ablation of refractory sustained ventricular tachycardia.

A model of ultrafiltration and glucose mass transfer kinetics in peritoneal dialysis.

We have investigated the variation with dwell time of dialysate volume and glucose concentration during continuous ambulatory peritoneal dialysis using a one-pool model. No assumption was made regarding the ultrafiltration rate that was calculated by the model. Results show that the volume ultrafiltered during dwell time is an increasing function of peritoneal membrane hydraulic permeability and a decreasing function of glucose mass transfer coefficient (MTC). For large MTC and low initial glucose concentration there is reabsorption of dialysate into the blood at large dwell times. For a 6 h dwell time, glycerol (92 daltons) is a more effective osmotic agent than glucose (198 daltons) at the same weight concentration. These results are in quantitative agreement with published clinical studies.