Low-flow polytetrafluoroethylene accesses: ultrasound surveillance and preemptive interventions ensure long-term patency.

BACKGROUND: Vascular accesses (especially polytetrafluoroethylene grafts) with a permanently low flow (Qa <600 ml/min) are prone to thrombosis and thus have short patency. The reason for a permanently low flow is usually medial calcinosis of the inflow artery in diabetics. We retrospectively studied the long-term patency of low-flow grafts with careful ultrasound surveillance and preemptive interventions. METHODS: Twenty subjects with Qa permanently <600 ml/min were included. Ultrasound surveillance was performed every 3 months in addition to classical monitoring techniques. Significant stenosis was strictly defined as the combination of B-mode narrowing >50% + >2-fold peak systolic velocity increase + 1 additional criterion (residual diameter <2.0 mm or flow volume decrease by >20%). Such stenoses were treated by preemptive percutaneous intervention. Primary and secondary patencies were calculated. RESULTS: The primary patency was 357 ± 316 days and the secondary (cumulative) patency was 996 ± 702 days. The number of interventions was 2.09/patient year, but >10 in 6 (33%) subjects. 93 and 80% of grafts were patent 1 and 2 years after access creation, respectively. CONCLUSION: Low-flow accesses undergoing ultrasound surveillance with strict diagnostic criteria and preemptive interventions had patencies similar to accesses with normal Qa in our study. This was enabled by a relatively high rate of interventions.

Standard reference material 2036 near-infrared reflection wavelength standard.

Standard Reference Material 2036 (SRM 2036) is a certified transfer standard intended for the verification and calibration of the wavelength/wavenumber scale of near-infrared (NIR) spectrometers operating in diffuse or trans-reflectance mode. SRM 2036 Near-Infrared Wavelength/Wavenumber Reflection Standard is a combination of a rare earth oxide glass of a composition similar to that of SRM 2035 Near-Infrared Transmission Wavelength/Wavenumber Standard and SRM 2065 Ultraviolet-Visible-Near-Infrared Transmission Wavelength/Wavenumber Standard, but is in physical contact with a piece of sintered poly(tetrafluoroethylene) (PTFE). The combination of glass contacted with a nearly ideal diffusely reflecting backing provides reflection-absorption bands that range from 15% R to 40% R. SRM 2036 is certified for the 10% band fraction air wavelength centroid location, (10%)B, of seven bands spanning the spectral region from 975 nm to 1946 nm. It is also certified for the vacuum wavenumber (10%)B of the same seven bands in the spectral region from 10 300 cm(-1) to 5130 cm(-1) at 8 cm(-1) resolution. Informational values are provided for the locations of thirteen additional bands from 334 nm to 804 nm.

Physical characteristics of implanted polytetrafluoroethylene grafts: a preliminary report.

Despite the widespread clinical use of polytetrafluoroethylene (PTFE) grafts, few reports dealing with their physical properties have appeared in the literature. In the past 20 months, 17 such grafts have been implanted into 15 patients threatened with limb loss, with an 88% immediate graft patency. Postoperatively, all patients underwent periodic evaluations; arteriograms were obtained in four. The effect of knee flexion on graft function was also studied. All grafts were found capable of withstanding cuff pressures in excess of 300 mm Hg without occlusion. With 90 degrees flexion, the grafts kinked crossing the knee joint but a pressure gradient or decrease in pulsatile blood flow did not develop. This remarkable resistance to external compression should render these grafts especially valuable for extra-anatomic bypass.

Changes in the manufacture of expanded microporous polytetrafluoroethylene: effects on patency and histological behavior when used to replace the superior vena cava.

Polytetrafluoroethylene (PTFE) has been used clinically and experimentally as a vein substitute. Since its introduction, changes have been made in the manufacture of the material. This study was designed to evaluate the effects of pore size (fibril length), PTFE cover, and spiral tube support on long-term patency and histological behavior when this material is used as a replacement for the precava in the dog. A graft of 30-mu pore size has adequate fibroblastic ingrowth, a neointima of 200 mu or less, and the best long-term patency. The PTFE cover results in less fibroblastic involvement of the prosthetic graft and prevents late occlusion caused by transmural fibrosis in the 90-mu graft. The spiral support does not affect patency and may be indicated when external pressure on the tube must be avoided.

An eccentrically coated asymmetric antenna applicator for intracavitary hyperthermia treatment of cancer.

In this paper a model based on transmission line theory is used to predict the behavior of an eccentrically coated asymmetric antenna applicator for use in intracavitary hyperthermia. Theoretical results for the heating rate (HR) of the applicators are compared to experimental results. The experimental results were obtained at City of Hope National Medical Center using four different 915-MHz applicators, each with a different antenna size and eccentricity of the coating. A parameter delta is defined where delta << 1.0 is a thin wire approximation; delta is primarily a function of the eccentricity of the coating, the antenna diameter, and the coating diameter. It is found that when delta approximately less than 0.5, the theoretical model works well. In particular, it predicts the directivity due to the eccentricity of the coating. However, as this eccentricity is increased or as the antenna diameter is increased (delta approximately greater than 0.6), the model no longer accurately predicts directivity. Thus, the model that can be used to predict the HR profiles for an eccentrically coated asymmetric antenna only when delta approximately less than 0.5.

The reverse upper arm curved graft with ringed PTFE graft as an alternative vascular access procedure for hemodialysis.

AIM: Prosthetic arteriovenous accesses are the last resort after efforts to place autogenous accesses are exhausted. During reimplantation of the graft, it is sometimes not convenient to dissect out the vessels to be grafted, especially around the venous anastomotic site and under local anesthesia. METHODS: We describe a technique using the ringed PTFE graft for the construction of a reverse upper arm curved graft in 14 patients who had received upper arm grafts previously. RESULTS: The mean operative time was 61+/-13 minutes, and the follow-up interval extended to 20 months. No infections, pseudoaneurysm formations, or steal syndrome occurred during the follow-up period. The primary patency rate was calculated by Kaplan-Meier analysis, and the primary patency from graft insertion to clotting in the reverse graft was 91% at 3 months, 83% at 6 months, 66% at 9 months, and 57% at 12 months. CONCLUSION: These results suggest that using the reverse upper arm curved graft during the reimplantation procedure was an alternative prosthetic arteriovenous access with the advantage of less tissue dissection, shorter operation time, and favorable patency rate.

An animal model for the evaluation of graft thrombosis in the acute phase on carbon-lined PTFE prosthesis.

Forty-five carbon-lined (CL) and 45 standard (ST) 4 mm internal diameter polytetra-fluoroethylene (PTFE) grafts were implanted as aortic interposition in 90 rabbits. A pilot study of 20 animals: 10 CL and 10 ST grafts were used to develop microsurgical techniques, then 60 grafts were placed in 60 New Zealand rabbits with lower morbidity. The two hours graft patency (Doppler and angiographic studies) showed better patency rate in CL group (93% versus 80%). In 10 animals, platelet accumulation was investigated in vivo using gammacamera imaging after injection of autologous platelets labeled with Indium111. In vitro, radioactivity counting of the explanted midgraft sections at 2 hours revealed 6 times greater activity in ST grafts (6.60 +/- 1.98 x 10(3) platelets/mm2 versus 0.82 +/- 0.25 x 10(3) platelets/mm2; p < 0.05). Light microscopy found platelet and fibrin deposition (PFD) in nearly all ST grafts whereas PFD were found in only 13% of the CL grafts corresponding to those thrombosed (chi 2: 61.117, p < 0.001). Carbon-lining decreases platelet accumulation on PTFE grafts in the acute phase of a new experimental model.

Assessment of an epoxy-fixed pericardial patch with or without ionically bound heparin in a canine model.

In this study, an epoxy-fixed porcine pericardial patch with or without ionically bound heparin was evaluated in a canine model as an alternative to the glutaraldehyde-fixed biological patch for clinical applications. To evaluate the effectiveness of this epoxy-fixed patch, a composite membrane composed of: an epoxy-fixed porcine patch with ionically bound heparin; a glutaraldehyde-fixed porcine patch with ionically bound heparin; an ePTFE polymeric patch; a polyester polymeric patch; an epoxy-fixed porcine patch without ionically bound heparin; and a glutaraldehyde-fixed porcine patch without ionically bound heparin was made. This membrane was assessed orthopically in a canine model. The early results (1 approximately 4 weeks post implant) revealed that the biological patches with ionically bound heparin had the mildest tissue reactions (inflammatory reaction, fibrosis, and adhesion) among all the test samples. However, by 12 weeks postoperatively, all the test samples had mild to severe tissue reactions. The order of tissue reactions with increasing severity was: the biological patches with ionically bound heparin, the biological patches without ionically bound heparin, and the polymeric patches. The results suggest that heparin may be used to reduce adhesion. Additionally, the epoxy-fixed tissue caused a relatively lower degree of inflammatory reaction than the glutaraldehyde-fixed tissue.

A study on elongation and knot slacking of various sutures.

The tension holding capacity of suture materials was measured by in vitro and in vivo experiments. Silk and expanded polytetrafluoroethylene sutures showed large elongation and significant knot slacking after tight tying. Although ultrahigh molecular-weight polyethylene suture had excellent creep resistance, it showed a relatively low tension holding capacity because of substantial knot slacking. On the other hand, polyester and high-strength poly(vinyl alcohol) sutures showed an excellent in vivo tension holding capacity, along with low elongation and insignificant knot slacking. Clinical performance of these sutures was briefly discussed from the mechanical point of view.

Temperature and humidity within the clothing microenvironment.

The present study investigates clothing microenvironment conditions that may develop during prolonged exposure of workers to a hot environment. Five subjects were exposed to a linear increase in ambient temperature from 20-40 degrees C over a 90-min period, and then remained at 40 degrees C for an additional 90 min. During the exposures, subjects were clad in four types of helicopter personnel suits (Gore-Tex, Cotton Ventile, Nomex/Insulite, and Nomex/Neoprene), incorporating both dry-suit and wet-suit designs. Continuous assessment was made of skin temperature, rectal temperature, and of microenvironment temperature, relative humidity, and vapor pressure (T mu, RH mu, and VP mu) 8 mm from the surface of the skin. Results indicate that although microenvironment temperatures were similar among suits and slightly lower than that of the environment, the RH mu and VP mu were much greater than those of the ambient air. The Nomex/Insulite and Nomex/Neoprene suits showed the highest VP mu, of which only the Nomex/Insulite resulted in significantly greater increases in rectal temperature, likely due to complete covering of the body with the impermeable insulite component. The present study demonstrates the need to discern between the ambient conditions and the conditions encountered next to the skin when protective clothing is worn.

[Production and clinical application of fibrin sealant with high concentrated fibrin (fibrin patch)].

OBJECT: The sealing properties of fibrin sealant with high concentrated fibrin (fibrin patch) were examined. MATERIAL AND METHODS: A commercial fibrin sealant (Bolheal) produced from pooled human plasma was utilized for this study. The fibrin sealant made of fibrinogen and thrombin solutions mixed in a volume ratio 5:1 was applied as the fibrin sealant with high concentrated fibrin (fibrin patch). The burst pressure of the fibrin clots of either 1:1 or 5:1 mixing ratio, which sealed the small holes, was measured by a water-leak preventing model. The tensile strength of the fibrin patch was measured by the breaking pressure of the fibrin clot. The burst pressure of the fibrin patch, which sealed the dural defect with a diameter of 15 mm, was compared with that of expanded polytetrafluoroethylene (ePTFE). RESULTS: The burst pressure was elevated from 287 +/- 23.1 to 445 +/- 30.5 mmHg by changing the mixing ratio from 1:1 to 5:1. The breaking pressure of the fibrin patch showed 131 +/- 25.4 mmHg and that of the patch mixed at the ratio of 1:1 showed 46.6 +/- 9.9 mmHg. The result of dural repair with the fibrin patch revealed higher sealing effectiveness than that of ePTFE. The burst pressure averaged 70.5 +/- 21.4 mmHg in the fibrin patch samples and 51.4 +/- 13 mmHg in the ePTFE samples. CONCLUSION: The fibrin patch revealed higher performance as a sealant and has the potential to be a candidate for acceptance as the new dural repair material.

[Biocompatibility of ePTFE modified by ion beam irradiation].

Expanded polytetrafluoroethylene (ePTFE) is a stable polymer and widely used as a prosthesis because of its chemical inertness. However, ePTFE as an artificial dura mater is often associated with postoperative leakage of the cerebrospinal fluid (CSF) due to its very low adhesiveness to fibrin glue and surrounding tissue. To overcome this shortcoming the authors examined the effects of ion beam irradiation to ePTFE surface. The surfaces of ePTFE were irradiated with 150keV--He+, Ne-, Ar+ and Kr+ ions with fluences of 1 x 10(14), 5 x 10(14) and 1 x 10(15) ions/cm2. L929 fibroblasts were cultured for 24 hours on ePTFE sheets that had both ion beam irradiated and un-irradiated regions. It was confirmed that fibroblasts still adhered to the ion beam irradiated area. This phenomenon was observed under different condition of ion beam irradiation. Adhesive strength of fibrin glue to ion beam irradiated ePTFE was evaluated by tensile strength and burst pressure test using ePTFE patch. Both tensile strength and burst pressure were remarkably enhanced by ion beam irradiation. SEM study indicated that fibrin glue infiltrated and anchored into the gaps induced by the ion beam irradiation. Thus ion beam irradiation improved biocompatibility of the surface of ePTFE.

[Replacement of portal vein with E-PTFE vascular graft; experimental study on process of the endothelialization].

Expanded polytetrafluoroethylene (E-PTFE) vascular graft was been exposed to intestinal content and evaluated the process of endothelialization and as to whether or not the material was feasible for its use under condition similar to clinical pancreatic surgery. In group A, E-PTFE tubular graft was inserted into the portal vein defect. In group B, choledochojejunostomy was also performed combined with the E-PTFE graft interposition. In other groups, bile (group C) or suspension of Escherichia Coli (group D) was put on graft implanted in the portal vein. The grafts were removed from the dogs for histological and scanning electronmicroscopic evaluation at intervals varying from 12 hours to 4 years and 8 months after surgery. Thirty one of 38 grafts were patent (patency rate; 82%). Complete formation of the inner capsule of the graft was essential to endothelialization. Direct extension of the endothelium was seen from the anastomotic site. Sporadic endothelialization was observed, however, communications among islet formed endothelialized portions. It were remarkable and endothelium derived from the host vein. These results demonstrated the feasibleness of clinical application of the E-PTFE graft to portal vein reconstruction with combination of the digestive surgery.

Biocompatibility of membranes with unrestricted somatic stem cells.

AIM: The biocompatibility of human osteoblasts (HOB) and human unrestricted somatic stem cells (USSCs) with membranes (BioGide®, GORE-TEX®, GENTA-FOIL resorb®, RESODONT®, BioMend®, BioMend® Extend™) was evaluated. MATERIALS AND METHODS: After osteogenic differentiation (dexamethasone, ascorbic acid and ß-glycerolphosphate) cells were seeded on membranes. On days 1, 3 and 7, attachment, proliferation, cell vitality, cytotoxicty and cell morphology were analyzed. RESULTS: Cells on BioGide® and RESODONT® exhibited significantly higher attachment (p<0.005) and proliferation (p<0.005). On BioMend® cells showed a significantly higher attachment compared to BioMend® Extend™ (p<0.005), whereas on BioMend® Extend™ cells had significantly higher proliferation (p<0.005). The vitality of cells was significantly better on BioGide® and RESODONT® (p<0.005). There were no significant differences between USSCs and HOBs. Scanning electron microscopy confirmed these results. CONCLUSION: BioGide® and RESODONT® had the best biocompatibility and are appropriate membranes for use in stem cell-derived regeneration of bone.

Withstand pressure of a simple fibrin glue sealant: experimental study of mimicked sellar reconstruction in extended transsphenoidal surgery.

BACKGROUND: To examine the strength and tolerance of the fibrin glue sealant in a situation of extended transsphenoidal surgery. The withstand pressure of fibrin glue sealant was measured using a simple sellar reconstruction model. METHODS: A 15-mm diameter hole at the bottom of a 51-cm high cylinder was covered with a Gore-Tex (Gore-Tex, Tokyo, Japan) sheet. A small plate was placed on the center for a brief fixation, and 3 mL of fibrin glue was applied over the entire bottom. Then water was gradually filled in five cylinders, and the water level at leakage was measured as withstand pressures at 10 minutes and 24 hours after sealant application. The stability of the sealant under pressures of 20 and 30 cm H(2)O for 12 hours was also examined. RESULTS: The median initial withstand pressure at 10 minutes was 32 cm H(2)O (n = 5), and was significantly increased to 47.5 cm H(2)O after 24 hours (n = 4). In four of five cylinders, fibrin glue sealants were stable against a pressure of 20 cm H(2)O for 12 hours and 30 cm H(2)O for the next 12 hours. CONCLUSIONS: The withstand pressure of simple fibrin glue sealant without other biological reactions could be estimated to be more than 20 cm H(2)O after application, and increased to more than 40 cm H(2)O after 24 hours. These data are practical for neurosurgeons to comprehend the strength and limit of fibrin glue sealant and suggests the importance to control the intracranial pressure to less than 20 cm H(2)O, especially for the first 12 to 24 hours.

Filling the nasal dorsum with Gore-tex in rhinoplasties / Uso do Gore-tex para preenchimento do dorso nasal em rinoplastias

BACKGROUND: Many autogenous and exogenous materials have been frequently used for the production of grafts and implants in rhinoplasties. The ideal graft or implant should be biocompatible, biointegrated, non-absorbable, and easily moldable and should not cause an inflammatory response. Gore-tex, an expandable form of polytetrafluoroethylene (PTFE) has been used since the 1970s for vascular graft production. Although Gore-tex is extremely versatile and has extensive uses and low complication rates, the demonstration of Gore-tex use in aesthetic surgery is very limited in medical literature. METHODS: We performed a retrospective study of 7 patients who received Gore-tex implants in order to fill the nasal dorsum from January 2005 to December 2007. All patients were assessed for aesthetic and functional factors and for the presence or absence of complications. RESULTS: All patients had good postoperative evolution, with great satisfaction in terms of aesthetic and functional aspects and no complications. CONCLUSIONS: Gore-tex is a satisfactory synthetic material as it is inexpensive, easily moldable, has good biocompatibility, and has shown no incidence of extrusion or infection in implants used for nasal dorsum filling in previously reported cases.

INTRODUÇÃO: Muitos materiais autógenos e exógenos vêm sendo utilizados com frequência para confecção de enxertos e implantes nas rinoplastias. O enxerto ou implante ideal deve ser biocompatível, biointegrável, não-absorvível, facilmente moldável e não deve causar resposta inflamatória. O Gore-tex, uma forma expansível do politetrafluoretileno (PTFE), é usado desde a década de 1970 na confecção de próteses vasculares. Apesar de seu uso ser extremamente versátil e extenso, oferecendo baixas taxas de complicação, a demonstração na literatura médica de seus resultados, quando usado na cirurgia estética, é muito restrita. MÉTODO: Realizado estudo retrospectivo sobre a evolução de 7 pacientes submetidos a implantes de Gore-tex visando ao preenchimento do dorso nasal, no período de janeiro de 2005 a dezembro de 2007. Todos os pacientes foram avaliados quanto a fatores estéticos e funcionais, e quanto à presença ou não de complicações. RESULTADOS: Todos os pacientes tiveram boa evolução pós-operatória, com grande satisfação do ponto de vista estético e funcional, e sem complicações. CONCLUSÕES: O Gore-tex mostrou-se um material sintético satisfatório, de baixo custo, facilmente moldável, com boa biocompatibilidade e com incidência nula de extrusão ou infecção para implantes de preenchimento de dorso nasal nos casos apresentados.

[Report after 3 years experience with the plastic material "proplast" in the maxillofacial region]. / Resumee nach dreijähriger Erfahrung mit dem Kunststoffmaterial "Proplast" im Kiefer-Gesichtsbereich

"Proplast" is the propriety name for a recently developed artificial substance developed from Teflon. This porous material is said to be firmly incorporated within 6-8 weeks through tissue ingrowth. It is still under clinical assessment. We report our experiences with 30 Proplast implants in the region of the jaws and face.

Human osteoblast response to PTFE surfaces.

Recently, expanded polytetrafluoroethylene (ePTFE, Gortex) vascular grafts have been rolled and used for interpositional arthroplasties of the carpus in the wrist. Little data, however, are available on the response of human osteoblasts to ePTFE. In-vitro cell culture is a useful method to determine initial cell-biomaterial interactions. The present study explores the morphological and mitogenic response of human bone cells cultured on vascular grade ePTFE grafts. The present findings suggest that neither the inner nor the outer surface of ePTFE, in its present form, support osteoblast growth. PTFE may be a suitable material to act as a space filler for carpal bone interpositional arthroplasties.

Proplast and Plastipore.

Sixteen Proplast and 52 Plastipore prostheses, removed at revision surgery, have been examined histologically and the findings illustrated. The macroscopic appearance of the prostheses was preserved. Fibrous tissue capsule formation was common. It has been expected that the prostheses will be invaded by fibrous tissue and thereby stabilized. Fibrous tissue ingrowth was consistently seen in Proplast but not Plastipore prostheses. Multinucleated foreign body giant cells were present in large numbers in both types. There was histological evidence of breakdown of the prostheses.