Design and analysis of a burst strength device for testing vascular grafts.

The design and analysis of a device to measure the burst strength (strength under a state of pure radial internal pressure) and compliance of vascular grafts and flexible pressurized tubes is presented. The device comprises three main sections, viz., a clean air-dry pressure controller, a test specimen holder, and automated software for control and data collection. Air pressure is controlled by means of a valve and a dedicated mechanism allowing reaching up to 120 psi in increments of 1 psi, and recording pressure changes with 0.04 psi resolution. The circumferential strain is determined by measuring the radial displacement of the vascular graft using an optical arrangement capable of determining a maximum radial displacement of 10 mm with 0.02 mm resolution. The instrument provides a low uncertainty in compliance (±0.32%/100 mm Hg-1) and burst strength measurements. Due to its simplicity, the device can easily be reproduced in other laboratories contributing to a dedicated instrument with high resolution at low cost. The reliability of the apparatus is further confirmed by conducting finite element analysis, elasticity solutions for pressurized cylinders, and testing of small diameter vascular grafts made of a commercial aliphatic polyurethane tested under radial internal pressure.

Prediction of circumferential compliance and burst strength of polymeric vascular grafts.

The circumferential compliance and burst strength of vascular grafts are predicted through the conically modified von Mises and elasticity theories, providing an analytical closed form solution for both parameters. Besides the graft's radii, the model for circumferential compliance depends solely on the elastic modulus and Poisson's ratio of the polymer material, and its accuracy was verified by finite element analysis and measurements. The analytical expression of the burst strength requires accurate determination of the material's tensile and compressive yield stress, which were carefully obtained by using digital image correlation measurements in uniaxial tensile and compressive tests of the constitutive material. The average measured circumferential compliance and burst strength of an 8mm graft made of a commonly used biomaterial, Tecoflex® SG-80A, are 1.05%/100mmHg-1 and 34.1psi (1763mmHg) and the proposed analytical predictions fall within the experimental scattering. Thus, it is shown that the circumferential compliance and burst strength of vascular grafts can be analytically predicted by knowing the elastic and yield material properties accurately, without needing to actually test the graft under radial pressure. This is a major advantage which can aid in the design and tailoring of vascular grafts.

Dynamics of carbon nanotube alignment by electric fields.

The dynamics of multiwall carbon nanotube (MWCNT) alignment inside viscous media using electric fields is investigated. Electrical current measurements were performed in situ during the application of an electric field to liquid solutions of deionized water or dissolved polymer containing MWCNTs. The variation of electrical current over time was associated to the dynamics of the MWCNT network formation. The influence of the electric field magnitude and frequency on the MWCNT network formation was studied. MWCNT migration towards the negative electrode was observed when a direct current electric field was applied, whereas formation of an aligned MWCNT network was achieved for an alternating current electric field. The increase of the electric field frequency promotes a faster formation of an aligned MWCNT network and thinner MWCNT bundles. A higher viscosity of the liquid medium yields slower MWCNT alignment evidenced by a slower change of electrical current through the viscous system. An analytical model based on the dielectrophoresis-induced torque, which considers the viscosity of the medium, is also proposed to explain the dynamics of MWCNT alignment. Furthermore, aligned MWCNT/polysulfone solid composites were fabricated and electrically characterized. The solid composites presented anisotropic electrical conductivity, which was more evident for low MWCNT concentrations (0.1-0.2 wt%).

Incontinencia urinaria neurógena: tratamiento quirúrgico / Neurogena incontinence urinary: surgical treatment

Entre 1984 y 1996, hemos atendido 263 niños con edades compredidas entre 3 meses y 18 años, portadores de vejiga neurogénica en su mayoría (91,81 por ciento) de origen congénito. De ellos, 213 (80,98 por ciento) presentaban incontinencia urinaria y en 22 (10,33 por ciento) fue necesario recurrir a la cirugía por fracasar el tratamiento conservador. En 14 casos realizamos una cistoplastia de aumento combinada con implante de esfínter artificial en 7 y con reimplante ureteral en 4. El esfínter artificial aislado se colocó en 2 pacientes y un tercero se trató con una cincha aponeurótica. En 2 pacientes se realizó una plastia de cuello vesical y finalmente en 3 procedimos a una derivación continente tipo mitrofanoff. Uno de los esfínteres no ha funcionado adecuadamente. Todos los demás pacientes están secos al menos por 3 horas aunque una de las derivaciones tiene pérdidas ocasionales

Incontinencia urinaria neurógena: tratamiento médico / Neurogena incontinence urinary: medical treatment

Entre 1984 y 1996 hemos estudiado 263 niños con edades entre 3 meses y 18 años, portadores de vejiga neurogénica, la mayoría (91,81 por ciento) de orígen congénito. De este grupo, 213 (80,98 por ciento) sufrían incontinencia urinaria acompañada en 123 (57,75 por ciento) de infección. En 169 (79,34 por ciento) existía hiperreflexia del detrusor y en 107 (50,32 por ciento) hipertonía del esfínter coexistiendo ambos problemas en 50 (23,47 por ciento). En 18 casos (8,92 por ciento) no se instaló tratamiento médico en razón de la edad o mínima lesión. El resto 194 (91,08 por ciento) fue tratado en forma conservadora: 54 (27,45 por ciento) con fármacos, 47 (23,76 por ciento) con cateterismo intermitente y 96 (48,77 por ciento) con ambos métodos. Tan solo 164 pacientes (62,26 por ciento) tienen control al menos de 1 año y alrededor de la mitad cumple irregularmente. En 105 (64,23 por ciento) el estado actual es satisfactorio, en 38 (23,36 por ciento) regular y en 21 (12,40 por ciento) malo

[Negative effect of the components of the lysis-centrifugation system in the growth of mycobacteria in MGIT and Septi-Chek AFB liquid media]. / Efecto negativo de los componentes del sistema lisis-centrifugación en el crecimiento de micobacterias en los medios líquidos MGIT y Septi-Chek AFB.

BACKGROUND: The lysis-centrifugation system (Isolator system) is a technique with excellent results in the recovery of mycobacteria from blood specimens. This system consists mainly of saponin (SAP), polypropylenglycol (PPG), and sodium polianthol sulfonate (SPS). The objective of this work was to determine the effect of SAP, PPG, and SPS on the growth of Mycobacterium avium, M. kansasii, M. tuberculosis, and M. xenopi in fluid culture media MGIT and Septi-Chek AFB. METHODS: Two concentrations each of SAP, PPG, and SPS were prepared, and were added in 0.1 ml amounts (alone, in pairs and in combination) to fluid media MGIT and Septi-Chek AFB. Fluid culture media were then in individually inoculated with two different concentrations (10(3) and 10(5) CFU/ml) of each of the four mycobacterial strains used in this study. Culture media were incubated at 37 degrees C and were checked for growth daily. RESULTS: SAP, PPG, and SPS did not inhibit growth of mycobacteria but growth of these strains was indeed retarded (a lengthier time was required for detection of bacterial growth compared with the positive control). Final concentrations of SAP, PPG, and SPS which retarded mycobacterial growth varied, depending upon species, mycobacterial inoculum size, and fluid culture media used. CONCLUSIONS: Components included in the lysy-centrifugation system (SAP, PPG, and SPS), either alone or in combination retarded growth of M. avium, M. kansasii, M. tuberculosis, and M. xenopi in 10(3) and 10(5) CFU/ml concentrations in fluid culture media MGIT and Septi-Chek AFB. These results suggest that strategies should be adopted to decrease the concentrations of these three components, present in the sediment of the processed blood by the Isolator System, which eventually are going to be added to fluid media MGIT and Septi-Check AFB.

[Evaluation of screening methods (catalase, sediment, reactive strip and Gram stain) in urinary tract infection in a Colombian university hospital]. / Evaluación de los métodos de cribado (catalasa, sedimento, tira reactiva y Gram) en la infección del tracto urinario en un hospital universitario de Colombia.

BACKGROUND: To evaluate the catalase test as a screening method in urinary tract infection (UTI) versus sediment, reactive strip and Gram. METHODS: Two hundred forty-five's stain urine samples were prospectively analyzed in the Hospital Universitario San Ignacio de Bogotá (Colombia). The culture was used as a reference test for the evaluation of the screening parameters in UTI patients. RESULTS: Of the 245 urine samples 45 were discarded. The remaining 200 urine samples were cultured being 100 positive and 100 negative. The former were analyzed by screening methods. The sensitivity and specificity of the catalase test was 97% and 94%, respectively with a positive predictive value of 94% and negative of 97%. The most frequently isolated microorganism was E. coli (84%), followed by Proteus sp. (6%). CONCLUSIONS: The use of the catalase test in urinary tract infection is a safe, economic and rapid method providing advantages due to its high sensitivity and specificity values, its good correlation with the different parameters evaluated in this study (sediment, strip, Gram's stain), and offers optimum diagnosis in urinary tract infection in developing countries such as Colombia.

[Pulmonary thromboendarterectomy as a treatment of chronic pulmonary arterial hypertension secondary to unresolved pulmonary thromboembolism. A preliminary report]. / Tromboendarterectomía pulmonar como tratamiento de la hipertensión arterial pulmonar crónica secundaria a tromboembolia pulmonar no resuelta. Comunicación preliminar.

This is a preliminary report of our initial experience with thromboendarterectomy in the treatment of four patients with chronic major-vessel thromboembolic pulmonary hypertension. Before surgery, these patients all had severe pulmonary hypertension and cor pulmonale as well as significant abnormalities in lung function (mechanics and gas exchange). They were in class III-IV (NYHA). One of our patients died immediately after the procedure as a result of major bleeding. The remaining three surviving patients have shown a remarkable improvement in both, pulmonary hemodynamics and lung function which has been translated in an also significant improvement in their clinical condition. Although there is still a significant risk involved with this procedure, the thromboendarterectomy represents a reasonable and useful therapeutic approach for selected patients with this deadly form of chronic pulmonary hypertension in which other forms of treatment have proved to be unsuccessful.

[Infectious agents in diarrhea of hospitalized children in Costa Rica]. / Agentes infecciosos en la diarrea del niño hospitalizado en Costa Rica.

Shigella, toxigenic Escherichia coli (stable toxin) and rotaviruses were frequently found among 50 children hospitalized with diarrhea studied during one year. These agents were less common among 45 controls without diarrhea, of comparable age and from the same wards as the cases reported. There was a greater frequency of respiratory symptoms in the diarrhea associated with rotaviruses. These were characterized by frequent bowel movements and vomiting and often fever. The bacterial diarrheas showed, in general, a more severe clinical picture than the viral ones. The rotaviruses had a low endemic level during April-October, but their prevalence increased in December and January; in such months these viruses were found in more than 50 per cent of the diarrheal cases.