In vitro assessment of back pressure on ventriculoperitoneal shunt valves

Background: Whereas there are case reports of laparoscopy in patients with ventriculoperitoneal shunts, there are no studies assessing the potential failure of shunt valves with the increased intra-abdominal pressure of laparoscopy. This study aims to assess this factor. Methods: An in vitro model was used to assess the potential for retrograde failure of ventriculoperitoneal shunt valves in a commonly used shunt. Nine shunts were subjected to graded increases in back pressure and observed for retrograde valve leak. Results: None of the shunts tested showed any signs of leak associated with the increased back pressure. However, disruption of shunt seals was noted in seven of the nine shunts, occurring at the minimal pressure of 80 mmHg. Conclusions: There appears to be minimal risk of retrograde failure of the valve system in the ventriculoperitoneal shunt tested. However, tests on different types of ventriculoperitoneal shunts would be needed to confirm these results if laparoscopy is to be considered safe in patients with ventriculoperitoneal shunts in situ. Received: 2 February 1998/Accepted: 6 July 1998     

In vitro testing of explanted shunt valves in hydrocephalic patients with suspected valve malfunction

Neurosurgical Review - Diagnosis of symptomatic valve malfunction in hydrocephalic patients treated with VP-Shunt (VPS) might be difficult. Clinical symptoms such as headache or nausea are...     

Comparison of programmable shunt valves vs standard valves for communicating hydrocephalus of adults: a retrospective analysis of 407 patients

BACKGROUND: The aim of the present study was to clarify whether programmable shunt valves are advantageous in the treatment of adults with communicating hydrocephalus with respect to valve-related shunt complications and surgical shunt revisions, in comparison with standard valves. METHODS: Adult patients with communicating hydrocephalus treated with Codman Hakim programmable (CHP) valves or Hakim (H) standard valves during 12 years were retrospectively studied. Patients were analyzed for demographic data, implantation diagnosis, valve type, opening pressure at implantation, opening pressure adjustments, and incidence of shunt complications, especially valve-related complications. The end point of the study was a surgical shunt revision. RESULTS: In 407 patients, 247 CHP valves and 160 H valves were implanted. Median opening pressure of CHP at implantation was 110 mm H(2)O, while 3 low-pressure, 153 medium-pressure, and 4 high-pressure H valves were implanted. Opening pressure adjustments were performed in 39% of CHP patients--1.44 adjustments per adjusted valve. Overall complication rate as well as the rate of surgical revisions for infections and catheter- and valve-related problems did not show any significant difference between CHP and H valves. The incidence of nontraumatic subdural hematomas and hygromas was significantly higher in the CHP group; however, the rate of surgical decompressions did not differ. CONCLUSIONS: The advantage of reprogramming of CHP did not translate into a reduction in surgical shunt revisions. Therefore, in conjunction with the present data, we believe it is still justified to implant H standard valves in adult patients with communicating hydrocephalus.     

The portable Glostavent: a new anaesthetic machine for use in difficult situations

A portable version of the Glostavent anaesthetic machine is described in which recent developments in draw-over technology are incorporated into a traditional draw-over anaesthetic system. The additional features include a more efficient reservoir and an improved vaporiser which have enhanced the performance and versatility. The portable Glostavent weighs less than 10 kg and is transported in a container the size of a small suitcase. It can be used to provide inhalational anaesthesia safely and economically in situations where there are no support facilities. It is ideal for use in battlefield or disaster situations and in isolated hospitals in disadvantaged regions of the world.     

Tissue engineering of heart valves: in vitro experiences

BACKGROUND: Tissue engineering is a new approach, whereby techniques are being developed to transplant autologous cells onto biodegradable scaffolds to ultimately form new functional tissue in vitro and in vivo. Our laboratory has focused on the tissue engineering of heart valves, and we have fabricated a trileaflet heart valve scaffold from a biodegradable polymer, a polyhydroxyalkanoate. In this experiment we evaluated the suitability of this scaffold material as well as in vitro conditioning to create viable tissue for tissue engineering of a trileaflet heart valve. METHODS: We constructed a biodegradable and biocompatible trileaflet heart valve scaffold from a porous polyhydroxyalkanoate (Meatabolix Inc, Cambridge, MA). The scaffold consisted of a cylindrical stent (1 x 15 x 20 mm inner diameter) and leaflets (0.3 mm thick), which were attached to the stent by thermal processing techniques. The porous heart valve scaffold (pore size 100 to 240 microm) was seeded with vascular cells grown and expanded from an ovine carotid artery and placed into a pulsatile flow bioreactor for 1, 4, and 8 days. Analysis of the engineered tissue included biochemical examination, enviromental scanning electron microscopy, and histology. RESULTS: It was possible to create a trileaflet heart valve scaffold from polyhydroxyalkanoate, which opened and closed synchronously in a pulsatile flow bioreactor. The cells grew into the pores and formed a confluent layer after incubation and pulsatile flow exposure. The cells were mostly viable and formed connective tissue between the inside and the outside of the porous heart valve scaffold. Additionally, we demonstrated cell proliferation (DNA assay) and the capacity to generate collagen as measured by hydroxyproline assay and movat-stained glycosaminoglycans under in vitro pulsatile flow conditions. CONCLUSIONS: Polyhydroxyalkanoates can be used to fabricate a porous, biodegradable heart valve scaffold. The cells appear to be viable and extracellular matrix formation was induced after pulsatile flow exposure.     

The bladder in boys with posterior urethral valves: a urodynamic assessment.

Urodynamic evaluation was performed on 8 of 62 boys (13 per cent) with persistent voiding difficulties after fulguration of posterior urethral valves. All had varying degrees of incontinence when evaluated. The striated muscle component of the external urethral sphincter was intact in each child. Five different types of bladder function were noted in the 8 children. Three boys had had a prior Y-V plasty of the bladder neck to improve upper and lower urinary tract emptying, which may have contributed to the subsequent incontinence. One additional boy had significant bladder neck obstruction requiring a unilateral bladder neck incision to improve voiding. Appropriate treatment plans were instituted based on the urodynamic findings of the bladder, bladder neck and external sphincter areas, and 6 of the 8 children are now completely continent.     

In vitro endothelialization of a mesosystemic shunt: A clinical case report

The existence of a confluently covering endothelium that is free of any thrombotic appositions can be proved 30 days after clinical implantation of an in vitro endothelialized expanded polytetrafluoroethylene graft. The recipient of the mesosystemic H-graft was a 69-year-old man who had a thrombosed portal vein following pancreatitis. Autologous endothelial cells were obtained from the external jugular vein under local anesthesia, applying the in situ cannulation technique. After low-density plating, first-passage mass cultures of 1.22 × 10⁶ endothelial cells were obtained 14 days after vein excision. After precoating was accomplished with fibrinolytically inhibited fibrin glue, a 10 mm expanded polytetrafluoroethylene graft was confluently lined with the autologous endothelial cells at a seeding density of 1.2 × 10⁵ cells/cm². After a maturation period of an additional 9 days and the microbiologic exclusion of a possible infection, an 11 cm graft segment was implanted between the superior mesenteric vein and the inferior vena cava. In spite of a patent shunt the patient had a repeat bleeding episode, needed parenteral nutrition, and died of sepsis on day 30. Immediately after the graft had been taken out, specimens were processed by scanning electron microscopy and light microscopy for the immunohistochemical proof of the endothelial nature of the surface-covering cell layer. The entire graft surface displayed a confluent cell lining that was free of any thrombotic appositions. A strongly positive stain result for both factor VIII – related antigen and the fixation-resistant CD34 molecule identified these cells as endothelial. No α-actin – positive cells could be detected. The underlying protein matrix was well preserved and unaltered in thickness and appearance, compared with preimplantation samples. None of the specimens showed any evidence of infection. This human demonstration of an intact endothelium on a patent venous prosthesis further establishes in vitro lining as a method that actually creates a persistent and functioning endothelium on a synthetic graft surface. (J VASC SURG 1994;19:549-54.)     

Prevention of allograft rejection by in vitro generated tolerogenic dendritic cells

Achieving immunological tolerance in transplantation has been a long sought-after goal since the 1960s. It is, therefore, interesting that the dendritic cells (DC), which are classically known as the most potent stimulators of T cell activation, are now also considered putative tools for tolerance induction. In line with this, much work has been performed using DC for vaccination and immune stimulation. Recently, great interest has been generated regarding the ability of DC to act as immune regulatory cells. Specific subsets of DC or immature DC (iDC) appear to be responsible for maintaining self-tolerance. In this review we will highlight our efforts at elucidating the contribution of DC in transplant tolerant in mice. Specifically, four strategies will be outlined that are currently being used for the generation of DC that have tolerogenic properties in the prevention of allograft rejection. The present study demonstrates that modulated iDC with blunted T cell stimulatory or antigen presentation abilities can afford transplant tolerance by minimizing T cell activation and proinflammatory cytokine production. Moreover, in an alternate strategy, normally matured DC have also been modulated such that alloreactive T cells are specifically targeted for deletion.     

Experimental results of the tracheoesophageal tissue connector for improved fixation of shunt valves in laryngectomized patients

BACKGROUND: After total laryngectomy and voice rehabilitation using a tracheoesophageal shunt valve, patients often have valve-related complications such as leakage. To solve these problems, a tracheoesophageal tissue connector (TE-TC) was devised to serve as an interface between the patient's tissue (trachea and esophagus) and the shunt valve. METHODS: The TE-TC is a permucosal connection constructed from a titanium ring (filled with a silicon rubber plug) combined with polypropylene or titanium mesh. After implantation in adult goats for 12 weeks the implants were submitted to histologic investigation. RESULTS: Firm implant fixation was achieved. In nearly all (18/19), no signs of infection of the implant were seen; 11 of 19 animals died before the end of the experiment owing to complications not related to the implant. CONCLUSIONS: The TE-TC is a new device with potential in the solution for fixation-related problems in tracheoesophageal voice rehabilitation.     

Working in the magnetic field of ultrahigh field MRI

Development of magnetic resonance imaging (MRI) device technology continues to increase the static magnetic flux densities applied and consequently leads to considerably increased occupational exposure. This has already made it necessary to review limits of occupational exposure and to postpone European legal regulations for occupational exposure to electromagnetic fields. This raises the question whether and if so which adverse health effects and health risks might be associated with occupational exposure to MRI ultra-high static magnetic fields. Based on a survey on interaction mechanisms recommendations and safety rules are presented to help minimize adverse health effects of emerging ultra-high field MRI.     

Strong static magnetic field stimulates bone formation to a definite orientation in vitro and in vivo.

The induction of bone formation to an intentional orientation is a potentially viable clinical treatment for bone disorders. Among the many chemical and physical factors, a static magnetic field (SMF) of tesla order can regulate the shapes of blood cells and matrix fibers. This study investigated the effects of a strong SMF (8 T) on bone formation in both in vivo and in vitro systems. After 60 h of exposure to the SMF, cultured mouse osteoblastic MC3T3-E1 cells were transformed to rodlike shapes and were orientated in the direction parallel to the magnetic field. Although this strong SMF exposure did not affect cell proliferation, it up-regulated cell differentiation and matrix synthesis as determined by ALP and alizarin red stainings, respectively. The SMF also stimulated ectopic bone formation in and around subcutaneously implanted bone morphogenetic protein (BMP) 2-containing pellets in mice, in which the orientation of bone formation was parallel to the magnetic field. It is concluded that a strong SMF has the potency not only to stimulate bone formation, but also to regulate its orientation in both in vitro and in vivo models. This is the first study to show the regulation of the orientation of adherent cells by a magnetic field. We propose that the combination of a strong SMF and a potent osteogenic agent such as BMP possibly may lead to an effective treatment of bone fractures and defects.     

Dynamic in vitro calcification of bioprosthetic porcine valves: evidence of apatite crystallization

OBJECTIVE: Calcification is the most important cause of structural deterioration of glutaraldehyde-fixed bioprosthetic valves. Devitalization of tissue favors calcium deposits in the shape of apatite crystals. Host factors influence the extent and progression of calcification, but the phenomenon can also occur in vitro in the absence of a viable milieu. Whether calcific deposits obtained in vitro are similar to those found in vivo is unknown. METHODS: Four porcine frame-mounted bioprostheses (St Jude Medical Bioimplant; St Jude Medical, Inc, St Paul, Minn) were tested in vitro by using a pulsatile accelerated calcification testing device at a frequency of 300 cycles per minute at 37 degrees C for 19 x 10(6) cycles with a rapid synthetic calcification solution (final product [calcium x phosphate], 130 mg/dL(2)). Three of the same type of xenografts explanted from human subjects because of calcific failure (time in place, 108 +/- 25.63 mo) served as control grafts. Each sample underwent gross and x-ray examination, histology, transmission and scanning electron microscopy, atomic absorption spectroscopy, electron microprobe analysis, and x-ray powder diffraction methods. RESULTS: All in vitro bioprostheses were heavily calcific, with intrinsic Von Kossa stain-positive deposits and a mean calcium content of 205.285 +/- 64.87 mg/g dry weight. At transmission electron microscopy, nuclei of calcification involved mostly collagen fibers and interfibrillar spaces and, more rarely, cell debris and nuclei. Electron microprobe analysis showed a Ca/P atoms ratio of 4.5:3, a value intermediate between hydroxyapatite and its precursor, octacalciumphosphate. X-ray powder diffraction showed a well-separated and sharp peak, which is typical of hydroxyapatite. Aggregates of plate-like crystals up to 8 microm in size were observed at scanning electron microscopy, with a typical tabular hexagonal shape consistent with apatite. The morphologic and chemical findings in human explants were similar. CONCLUSIONS: Intrinsic calcification of glutaraldehyde-fixed porcine valves was induced in vitro. Electron microprobe analysis and x-ray powder diffraction findings were in keeping with apatite crystallization, such as that occurring in valve xenografts implanted in vivo. The model may be of value to accelerate the screening of anticalcific agents and may reduce the need for animal experiments.     

Treatment of symptomatic syringomyelia with a ventriculoperitoneal shunt: a case report with magnetic resonance scan correlation

This report describes a patient with communicating syringomyelia associated with enlarged cerebral ventricles who was managed by placing a ventriculoperitoneal shunt. His clinical improvement was rapid and dramatic. A comparison of preoperative and postoperative magnetic resonance scans documents shrinkage of the cervical syrinx.     

Lymphaticovenous shunt for the treatment of chylous reflux by subcutaneous vein grafts with valves between megalymphatics and the great saphenous vein: A case report

Chylous reflux is a rare disorder in which chyle flows antidromically from its normal route to the extremities, thorax, abdominal cavity, or other parts of the body. We present a case of chylous reflux with megalymphatics in a 28‐year‐old boy who presented chylorrhea in the foot, leg, and external genitalia, lymphedema, and hemangioma in the affected limb. Lymphaticovenous shunts using subcutaneous vein grafts with valves were applied to the patient for treatment of repeated chylorrhea. After surgery, the patient has not complained of chylorrhea and been freed from conservative physiotherapy such as bandaging or application of compression stockings for lymphedema for two years. A subcutaneous vein graft with valves may be considered a useful method as a shunt between incompetent and dilated lymphatics and veins instead of a saphenous vein graft in the treatment of chylous reflux in lower extremities. We discuss these treatments based on the literature about chylous disorders. © 2010 Wiley‐Liss, Inc. Microsurgery 30:553–556, 2010.     

Evaluation of the safety of a new portable pump for continuous epidural infusion of local anesthetics

The safety of a new portable pump (Baxter Infusor), was evaluated for continuous epidural infusion of local anesthetics. The experimental flows at different temperatures were 1.87 ml.hr-1 at 28 degrees C and 2.14-2.15 ml.hr-1 at 33 degrees C. The average temperature of local anesthetics in this pump attached to patients was 29 degrees C. Concentration of mepivacaine reached the maximal value (1.129 +/- 0.439 micrograms.ml-1) at 12 hours after the application of the infusor. The concentration of mepivacaine was maintained at a constant level from 6th hour to 24th hour. The result indicates that Infusor is a safe device for continuous infusion of local anesthetics because of constant flow and low level of local anesthetics.