Nonlinear dependence (on ionic strength, pH) of surface charge density and zeta potential in microchannel electrokinetic flow.

In this work, a numerical method is proposed to predict the electrokinetic phenomena and combined with an experimental study of the surface charge density (ρs) and zeta potential (ζ) behavior is investigated for borosilicate immersed in KCl and NaCl electrolytes, and for imogolite immersed in KCl, CaCl2, and MgCl2 electrolytes. Simulations and experiments of the electrokinetic flows with electrolyte solutions were performed to accurately determine the electric double layer (EDL), ζ, and ρs at various electrolyte concentrations and pH. The zeta potential was experimentally determined and numerically predicted by solving the coupled governing equations of mass, species, momentum, and electrical field iteratively. Our numerical prediction shows that ζ for borosilicate develops strong nonlinear behavior with the ion concentration following a power-law. Likewise, the ρs obeys a nonlinear behavior, decreasing as the concentration increases. Moreover, for imogolite, both ζ and the ρs behave nonlinearly with the pH. The EDL for borosilicate and imogolite becomes thinner as the electrolyte concentration and pH increase; this behavior is caused by increased ρs, resulting in the higher attraction of the free charges. The reported nonlinear behavior describes more accurately the interaction of the nanoparticle surface charge with the electrolytes and its effect on the electrolyte transport properties.

[Craniorachischisis: a case report]. / Craneorraquisquisis: reporte de un caso.

Background: Neural tube defects are a heterogeneous group of alterations of the central nervous system with multifactorial origin, mainly caused by a failure in the mechanisms of closure of the neural tube which involves skin, paravertebral muscles, connective tissue, bone and spinal cord. Clinical case: 36-year-old woman with a pregnancy of 25.3 weeks, corroborated by second trimester ultrasound. She had a previous pregnancy with anencephaly and a poor prenatal care in the actual pregnancy. An obstetric ultrasound was performed with the diagnosis of craniorachischisis, which is why the delivery was performed by vaginal birth with labor induction with prostaglandins. Conclusions: The craniorachischisis is a rare defect of the neural tube that must be diagnosed early because it is a pathology incompatible with life.

Introducción: los defectos del tubo neural son un grupo heterogéneo de alteraciones del sistema nervioso central, de origen multifactorial, principalmente ocasionados por una falla en los mecanismos de cierre del tubo neural, la cual involucra: piel, músculos paravertebrales, tejido conectivo, hueso y médula espinal. La craneorraquisquisis es la variante más grave y rara de los defectos del tubo neural. Caso clínico: Mujer de 36 años con un embarazo de 25.3 semanas, corroborado por ultrasonido del segundo trimestre, con el antecedente de un embarazo previo con anencefalia y mal control prenatal en el embarazo actual. Se le realizó un ultrasonido que diagnosticó craneorraquisquisis, por lo que se procedió a finalizar el embarazo por inducción de trabajo de aborto con prostaglandinas. Conclusiones: la craneorraquisquisis es un defecto raro del tubo neural que debe diagnosticarse tempranamente por ser una patología incompatible con la vida.

Craneorraquisquisis: reporte de un caso / Craniorachischisis: a case report

Introducción: los defectos del tubo neural son un grupo heterogéneo de alteraciones del sistema nervioso central, de origen multifactorial, principalmente ocasionados por una falla en los mecanismos de cierre del tubo neural, la cual involucra: piel, músculos paravertebrales, tejido conectivo, hueso y médula espinal. La craneorraquisquisis es la variante más grave y rara de los defectos del tubo neural. Caso clínico: Mujer de 36 años con un embarazo de 25.3 semanas, corroborado por ultrasonido del segundo trimestre, con el antecedente de un embarazo previo con anencefalia y mal control prenatal en el embarazo actual. Se le realizó un ultrasonido que diagnosticó craneorraquisquisis, por lo que se procedió a finalizar el embarazo por inducción de trabajo de aborto con prostaglandinas. Conclusiones: la craneorraquisquisis es un defecto raro del tubo neural que debe diagnosticarse tempranamente por ser una patología incompatible con la vida.

Background: Neural tube defects are a heterogeneous group of alterations of the central nervous system with multifactorial origin, mainly caused by a failure in the mechanisms of closure of the neural tube which involves skin, paravertebral muscles, connective tissue, bone and spinal cord. Clinical case: 36-year-old woman with a pregnancy of 25.3 weeks, corroborated by second trimester ultrasound. She had a previous pregnancy with anencephaly and a poor prenatal care in the actual pregnancy. An obstetric ultrasound was performed with the diagnosis of craniorachischisis, which is why the delivery was performed by vaginal birth with labor induction with prostaglandins. Conclusions: The craniorachischisis is a rare defect of the neural tube that must be diagnosed early because it is a pathology incompatible with life.

Prensión del lápiz y escritura en universitarios / Prehension of the pencil and writing in university students

Introducción. El tipo adecuado de prensión del lápiz permite realizar movimientos coordinados al escribir. Los tipos inadecuados de prensión pueden causar dificultades en la legibilidad escrita. La escritura es un proceso de aprendizaje en el que intervienen factores conceptuales, sintácticos y motores que permiten la comunicación. Objetivo. Describir el tipo de prensión del lápiz y la legibilidad en la escritura de universitarios de 18 a 24 años de edad. Material y métodos. Estudio observacional, descriptivo, transversal y prospectivo. Participaron 60 estudiantes (30 mujeres y 30 hombres) de lateralidad diestra de la Licenciatura en Psicología. En forma individual, se realizaron tareas de escritura en donde se describió el tipo de prensión y la legibilidad en la escritura de los participantes. Resultados. El 93% de los casos presentaron tipos inadecuados de prensión del lápiz. El 68% de esos casos tuvieron escritura legible predominando en los casos que presentaban presión en los dedos. Los casos con prensión adecuada no presentaron ilegibilidad en escritura. Discusión y conclusiones. No se encontró un patrón específico entre el tipo de prensión y la legibilidad en la escritura. Se deben generar estrategias para proponer la corrección de los tipos inadecuados de prensión del lápiz desde la educación básica.

Introduction. Adequate pencil grip permits coordinated movements used in writing. Inadequate pencil grip can generate difficulties in writing legibility. Writing is a learning process in which conceptual, syntactic and motor factors are involved, who allows the communication. Objective. Describe the type of pencil grip and the legibility of 18 to 24 years old undergraduate’s writing. Material and methods. An observational, descriptive, transversal and prospective study. Sixty right-handed Psychology undergraduate students (30 women and 30 men) participated. In an individual manner, subjects realized writing tasks in which we described the type of grip and the legibility on the participant’s writing. Results. 93% of cases presented inadequate pencil grip. 68% of those cases showed legible writing prevailing on the cases that presented pressure on their fingers. The cases with adequate pencil grip did not present illegibility in writing. Discussion and conclusions. We did not find a specific pattern between the type of pencil grip and writing. It is necessary to suggest strategies for correcting inadequate pencil grip from basic education.

Beyond disease, how biomedical engineering can improve global health.

Biomedical engineering tools can be harnessed to address some of the world's most challenging nondisease-focused problems.

Epilepsia de ausencia juvenil. evaluación neuropsicológica de dos casos / Absence epilepsy in young people. Neuropsychological evaluation of two cases

Introducción: Las epilepsias constituyen trastornos de la función neuronal expresados en crisis de episodios limitados causadas por descargas anormales de grupos de neuronas. La epilepsia de ausencia juvenil inicia entre los 10 y 17 años, con ausencias típicas y en ocasiones crisis tónico-clónicas. Ambos sexos son igualmente afectados. El electroencefalograma (EEG) intercrítico presenta descargas de punta-onda de 3 Hz con buena respuesta al medicamento. Las evaluaciones neuropsicológicas permiten determinar la presencia de cambios cognoscitivos y comportamentales. Material y métodos: Estudio observacional, descriptivo, transversal, prospectivo. Se evaluaron dos estudiantes de la Licenciatura en Psicología (casos A y B), de 19 años de edad, de lateralidad diestra, sexo femenino. En ambos casos se reportaron crisis de ausencia con inicio en la adolescencia; el caso B presentaba además crisis tónico-clónicas. Ambas se encontraban tomando medicamento en el momento de la evaluación. En forma individual, en un cubículo bien iluminado, libre de distractores, se aplicaron en dos sesiones de 45 minutos en promedio la evaluación neuropsicológica breve en español (NEUROPSI), el test de clasificación de Wisconsin versión computarizada (WISCONPC) y la escala de somnolencia Epworth. Resultados: En NEUROPSI, el caso A, obtuvo puntaje total de 118 (normal alto) y el caso B, 106 (normal) con dificultades en atención, evocación de estímulos verbales y comprensión lectora. En WISCONPC, el caso A completó seis categorías, mientras que el B completó dos, presentando incapacidad para mantener la organización. En la escala Epworth, el caso B reportó no dormir suficiente. Discusión y conclusiones: Las evaluaciones neuropsicológicas nos permitieron conocer el estado actual de los procesos cognoscitivos de los casos evaluados e indicar estrategias de corrección en los procesos observados con dificultades

Introduction: Epilepsy constitutes disorders of neuronal function expressed as limited crisis episodes caused by abnormal discharges of groups of neurons. Juvenil absence epilepsy begins between 10 and 17 years old, with typical absences and sometimes tonic-clonic seizures. Intecritical electroencephalogram (EEG) presents 3 Hz spike-and-wave discharges with a good response to medication. Neuropsychological assessments allow determining the presence of cognitive and behavioral changes. Material and methods: Observational, descriptive, transversal and prospective research. We evaluated two righthanded female, 19 years old, Psychology undergraduate students (Subjects A and B). Both subjects reported absence seizures beginning in adolescence, subject B also reported tonic-clonic seizures. In a well illuminated room, free of distractors, in an individual manner, we applied the brief neuropsychological test in spanish (NEUROPSI), the Wisconsin card sorting test computerized version (WISCONPC) and the Epworth Sleepiness Scale in two 45-minutes sessions. Results: In the NEUROPSI, subject A, got a total score of 118 (high normal) and subject B a score of 106 (normal) with difficulties in attention, recall of verbal stimuli and reading comprehension. In the WISCONPC, subject A, completed six categories while B completed two categories, with an inability to keep the organization. In the Epworth Scale, subject B reported not sleeping enough. Discussion and conclusions: Neuropshychologycal assessments allowed us to know the current condition of cognitive processes of evaluated subjects and to suggest corrective strategies in the identified processes with difficulties

Flow-induced wall mechanics of patient-specific aneurysmal cerebral arteries: Nonlinear isotropic versus anisotropic wall stress.

Fluid-structure interaction simulations of three patient-specific models of cerebral aneurysms were carried out with the objective of quantifying the effects of non-Newtonian blood flow and the vessel mechanical behavior on the time-dependent fluid shear and normal stresses, and structural stress and stretch. The average wall shear stress at peak systole was found to be approximately one order of magnitude smaller than the shear stresses in the proximal communicating arteries, regardless of the shape or size of the aneurysms. Spatial distributions of oscillatory shear index were consistent with the reciprocal of wall shear stress distributions at peak systole for all aneurysm geometries, demonstrating that oscillatory shear index correlates inversely with wall shear at this time point in the cardiac cycle. An aneurysm wall modeled with an isotropic material resulted in an underestimation of both the maximum principal stress and stretch, compared to the anisotropic material model. For the three aneurysm geometries, anisotropic peak wall stresses were approximately 50% higher than for an isotropic material. Regardless of the constitutive material, the maximum stresses were consistently located at the aneurysm neck; stresses in the dome were 30% of those in the neck.

Retención de cápsula endoscópica como complicación de enteritis actínica: reporte de un caso / Retention of capsule endoscopy as a complication of radiation enteritis: a case report

La cápsula endoscópica es un método, que ha modificado el enfoque diagnóstico de numerosos procesos patológicos en el intestino delgado, sin embargo presenta complicaciones como la retención de la misma. Se estima en la literatura mundial que esta suele ocurrir en menos del 2% de los casos. Femenino de 40 años de edad, con antecedente de cáncer de cuello uterino (2011) en tratamiento con quimioterapia, radioterapia convencional y braquiterapia, que presenta cuadro clínico caracterizado por dolor urente en mesogastrio, y emesis de aspecto biliosos. Ruidos hidroaéreos presentes, dolor a la palpación de mesogastrio sin irritación peritoneal. Radiografía de abdomen y ecosonograma abdominal normales. TAC abdomino pélvica con contraste oral con adecuada progresión de contraste hasta el recto. Se practica gastroscopia y colonoscopia sin evidencia de alteraciones. En vista de persistencia de sintomatología se indica realización de cápsula endoscópica observando en íleon distal, a los 246 minutos del paso duodenal, área muy congestiva, con una úlcera circunferencial friable, que no permite el avance de la misma. Se indica tratamiento médico con laxantes por 72 horas, el cual es infructuoso, por lo cual es llevada a mesa operatoria por presentar signos francos de obstrucción intestinal. Los hallazgos fueron: adherencias en flanco y fosa ilíaca derecha, las cuales fueron liberadas, y segmento de íleon a 10 cm de la válvula ileocecal con inflamación franca, practicándose resección y anastomosis termino-lateral. El estudio histopatológico reportó enteritis crónica activa exulcerada, necrosis fibrinoide de pequeños vasos, y fibrosis en la submucosa. Paciente con post-operatorio exitoso decidiéndose el egreso de la institución. Excelente correlación entre los hallazgos de la cápsula endoscópica y la intervención quirúrgica. Los hallazgos de la cirugía se encuentran relacionados al uso de radioterapia convencional, por lo cual recomendamos la realización de pexia...

Capsule endoscopy is a method that has changed the diagnostic approach to many pathological processes in the small intestine, but it has complications such as retention of the same, is estimated in the literature that this usually occurs in less than 2% cases. Women 40 years of age, with a history of cervical cancer (2011) undergoing chemotherapy, conventional radiation therapy, and brachytherapy, presenting clinical picture characterized by burning pain in midgut, and bilious emesis aspect. Present bowel sounds, tenderness of mesogastrium without peritoneal irritation. Abdominal radiography and abdominal ultrasonography normal. Pelvic CT with oral contrast Abdomino with progression adequate contrast to the rectum. Gastroscopy and colonoscopy was performed without evidence of tampering. In view of the persistence of symptoms embodiment shown in watching endoscopic capsule distal ileum, to 246 minutes of step duodenal study, very congestive area with a circumferential friable ulcer which does not allow the advance thereof. Indicated medical treatment with laxatives for 72 hours being fruitless, operating table being carried by presenting overt signs of intestinal obstruction. The findings were: adhesions flank and right lower quadrant, which were released and ileal segment 10 cm from the ileocecal valve with frank inflammation resection and end-side anastomosis. Histopathological study reported chronic active enteritis exulcerada, fibrinoid necrosis of small vessels, and fibrosis in the submucosa. Postoperative patient deciding successful graduation from the institution. Excellent correlation between the findings of capsule endoscopy and surgery. The findings at surgery are related to the use of conventional radiotherapy, so we recommend an pexia of the organs that are in the radiation field, prior to it, and intestinal transit before indicating capsule endoscopy

Aspectos clínicos y epidemiológicos de pacientes con carcinoma hepatocelular en dos centros de referencia de Venezuela / Clinical and epidemiological aspects of patients with hepatocellular carcinoma in two reference centers Venezuela

El carcinoma hepatocelular (CHC) es la neoplasia primaria del hígado más frecuente, constituyendo un problema mundial de salud pública por su alta prevalencia y tasa de mortalidad. Evaluar las características clínicas y epidemiológicas de los pacientes con carcinoma hepatocelular. Estudio de casos consecutivos con revisión retrospectiva de los registros médicos de pacientes con diagnóstico de CHC que acudieron a la consulta de hepatología de dos centros caraqueños entre 1997 y 2011. Se evaluaron características clínicas, epidemiológicas y de estadiaje según Barcelona Clinic Liver Cancer, BCLC. Se incluyó 116 pacientes con diagnóstico de CHC. La edad media fue 61,34 ± 12,02 años, 75% eran hombres y 89,7% de los pacientes tenían cirrosis hepática subyacente, siendo confirmada histológicamente en 33,7%. El 70,7% de los pacientes tenían alguna complicación asociada a hipertensión portal. El virus de la hepatitis C (VHC) constituyó la principal etiología de enfermedad hepática (31%), alcohol (21,6%), virus de la hepatitis B, VHB (14,7%) y enfermedad hepática grasa no alcohólica (14,7%). El hepatocarcinoma fue diagnosticado más frecuentemente en pacientes con cirrosis por HBV 15,56%. El 56% de los casos tenían niveles de alfafetoproteína mayores de 300 ng/ml. El lóbulo derecho fue la localización más frecuente (64,7%) y 79,3% de las lesiones mostraron patrón vascular típico en los estudios radiológicos. El estadio tumoral según los criterios de Barcelona Clinic Liver Cancer (BCLC) fueron estadio C (37,9%) D (25,9%), B (24,1%), A (7,8%) y 0 (2,6%). La infección por HCV es la etiología más frecuente de cirrosis hepática en pacientes con CHC, pero la infección por VHB tiene mayor impacto en términos relativos. El diagnóstico se hace en forma tardía (estadios intermedios o avanzados), siendo necesario intensificar medidas de pesquisa en estos pacientes

The hepatocellular carcinoma (HCC) is the main primary liver neoplasia and is a public health problem in the world due to high prevalence and mortality. Evaluate clinical and epidemiological characteristics in patients with Hepatocellular carcinoma. A retrospective analysis of a prospectively maintained database of 116 patients with diagnosis of HCC in two centers of Caracas between 1997 and 2011 was conducted. We evaluated epidemiological, clinical, biochemical and tumor aspects according to Barcelona Clínic Liver Cancer in patients with HCC. Mean age was 61.34 ± 12.02 years, 75% were male and 89.7% of patients had liver cirrhosis. Portal hypertension complications (ascites, hepatic encephalopathy, esophageal varices) were present in 70.7% of patients. Hepatitis C virus (HCV) was the main etiology of hepatic disease (31%) followed by alcohol (21.6%), hepatitis B virus (14.7%) and non alcoholic steatohepatitis (14.7%). HCC was more frequent in patients with cirrhosis associated to HBV infection. The 56% of patients had alpha-fetoprotein levels higher than 300 ng/ml. The 64.7% of tumors were localized in the right lobe of liver and 79.3% of tumor lesions demonstrated typical pattern in radiologic studies. The most patients had advanced disease according to Barcelona Clinic Liver Cancer (BCLC) staging classification (Stage C, 37.9%; stage D, 25.9%; stage B, 24.1%; stage A, 7.8% and stage 0, 2.6%). HCV infection was main cause of cirrhosis in patients with HCC, but HBV infection had higher impact in these patients. Our study showed that the diagnosis of these patients undergo late and is very important intensify screening measures in patients with liver cirrhosis

Carcinoma neuroendocrino de papila de vater: Reporte de un caso y revisión de la literatura

Los tumores de la papila de Vater constituyen tumores de aparición inusual. Su incidencia es menor al 5% de los tumores del tracto gastrointestinal. La edad de aparición es variable siendo mayor entre los 50-70 años, predominando en el sexo masculino. Una incidencia menor lo constituyen los tumores neuroendocrinos de la ampolla, los cuales tienen aproximadamente 105 casos como reporte en la literatura mundial. Presentamos a un paciente masculino de 53 años de edad, quien consulta por pérdida de peso, dolor abdominal, ictericia obstructiva. Ultrasónido Abdominal y TAC abdomino pelvica: Hepatomegalia. LOEs hepáticos. Barro vesicular. Dilatación de vías biliares intra y extrahepáticas, LOE de cabeza de pancreas. Se le realiza duodeno pancreatectomia de Whipple con hemorragia digestiva a repetición. El estudio histológico mostró un carcinoma neuroendocrino de la papila duodenal, tipo I (epitelial) grado III.

Tumors of the papilla are unusual entities. The incidence is less than 5 % of all new digestive tract neoplasms. It may occur in all age groups, but they are more prevalent in people aged 50-70 years, a slight male predominance. Endocrine neoplasms have a less incidence and only 105 cases are reported in the literature. A case of a 53-year-old male with weight loss, abdominal pain, obstructive jaundice is reported. Abdominal ultrasonography showed hepatomegaly, hepatic lesions, biliary sludge, and pancreatic lesion with intra-extra hepatic biliary tract dilatation. He had a successive upper digestive bleeding, pancreaticoduodenectomy was performed. Histological evaluation showed neuroendocrine carcinoma of the ampulla of Vater, Type I (epithelial) Grade III.

Blood flow dynamics in saccular aneurysm models of the basilar artery.

Blood flow dynamics under physiologically realistic pulsatile conditions plays an important role in the growth, rupture, and surgical treatment of intracranial aneurysms. The temporal and spatial variations of wall pressure and wall shear stress in the aneurysm are hypothesized to be correlated with its continuous expansion and eventual rupture. In addition, the assessment of the velocity field in the aneurysm dome and neck is important for the correct placement of endovascular coils. This paper describes the flow dynamics in two representative models of a terminal aneurysm of the basilar artery under Newtonian and non-Newtonian fluid assumptions, and compares their hemodynamics with that of a healthy basilar artery. Virtual aneurysm models are investigated numerically, with geometric features defined by beta = 0 deg and beta = 23.2 deg, where beta is the tilt angle of the aneurysm dome with respect to the basilar artery. The intra-aneurysmal pulsatile flow shows complex ring vortex structures for beta = 0 deg and single recirculation regions for beta = 23.2 deg during both systole and diastole. The pressure and shear stress on the aneurysm wall exhibit large temporal and spatial variations for both models. When compared to a non-Newtonian fluid, the symmetric aneurysm model (beta = 0 deg) exhibits a more unstable Newtonian flow dynamics, although with a lower peak wall shear stress than the asymmetric model (beta = 23.2 deg). The non-Newtonian fluid assumption yields more stable flows than a Newtonian fluid, for the same inlet flow rate. Both fluid modeling assumptions, however, lead to asymmetric oscillatory flows inside the aneurysm dome.

Flow mixing enhancement from balloon pulsations in an intravenous oxygenator.

Computational investigations of flow mixing and oxygen transfer characteristics in an intravenous membrane oxygenator (IMO) are performed by direct numerical simulations of the conservation of mass, momentum, and species equations. Three-dimensional computational models are developed to investigate flow-mixing and oxygen-transfer characteristics for stationary and pulsating balloons, using the spectral element method. For a stationary balloon, the effect of the fiber placement within the fiber bundle and the number of fiber rings is investigated. In a pulsating balloon, the flow mixing characteristics are determined and the oxygen transfer rate is evaluated. For a stationary balloon, numerical simulations show two well-defined flow patterns that depend on the region of the IMO device. Successive increases of the Reynolds number raise the longitudinal velocity without creating secondary flow. This characteristic is not affected by staggered or non-staggered fiber placement within the fiber bundle. For a pulsating balloon, the flow mixing is enhanced by generating a three-dimensional time-dependent flow characterized by oscillatory radial, pulsatile longitudinal, and both oscillatory and random tangential velocities. This three-dimensional flow increases the flow mixing due to an active time-dependent secondary flow, particularly around the fibers. Analytical models show the fiber bundle placement effect on the pressure gradient and flow pattern. The oxygen transport from the fiber surface to the mean flow is due to a dominant radial diffusion mechanism, for the stationary balloon. The oxygen transfer rate reaches an asymptotic behavior at relatively low Reynolds numbers. For a pulsating balloon, the time-dependent oxygen-concentration field resembles the oscillatory and wavy nature of the time-dependent flow. Sherwood number evaluations demonstrate that balloon pulsations enhance the oxygen transfer rate, even for smaller flow rates.

Methodology for predicting oxygen transport on an intravenous membrane oxygenator combining computational and analytical models.

A computational methodology for accurately predicting flow and oxygen-transport characteristics and performance of an intravenous membrane oxygenator (IMO) device is developed, tested, and validated. This methodology uses extensive numerical simulations of three-dimensional computational models to determine flow-mixing characteristics and oxygen-transfer performance, and analytical models to indirectly validate numerical predictions with experimental data, using both blood and water as working fluids. Direct numerical simulations for IMO stationary and pulsating balloons predict flow field and oxygen transport performance in response to changes in the device length, number of and balloon pulsation frequency. Multifiber models are used to investigate interfiber interference and length effects for a stationary balloon whereas a single fiber model is used to analyze the effect of balloon pulsations on velocity and oxygen concentration fields and to evaluate oxygen transfer rates. An analytical lumped model is developed and validated by comparing its numerical predictions with experimental data. Numerical results demonstrate that oxygen transfer rates for a stationary balloon regime decrease with increasing number of fibers, independent of the fluid type. The oxygen transfer rate ratio obtained with blood and water is approximately two. Balloon pulsations show an effective and enhanced flow mixing, with time-dependent recirculating flows around the fibers regions which induce higher oxygen transfer rates. The mass transfer rates increase approximately 100% and 80%, with water and blood, respectively, compared with stationary balloon operation. Calculations with combinations of frequency, number of fibers, fiber length and diameter, and inlet volumetric flow rates, agree well with the reported experimental results, and provide a solid comparative base for analysis, predictions, and comparisons with numerical and experimental data.

Flow and Oxygen Transfer Characteristics of an Intravenous Membrane Oxygenator: A Computational Study.

Spectral element computational simulations of the conservation of mass, momentum and species equations are performed to investigate the flow and oxygen transfer characteristics of an Intravenous Membrane Oxygenator (IMO). The simulations consider a three-dimensional IMO computational model consisting of equally-spaced fibers, an elastic balloon with non-permeable walls positioned longitudinally within the vena cava, and a Newtonian and time-dependent incompressible flow. Flow characteristics and oxygen transfer parameters are determined for operating conditions of a stationary and a pulsating balloon. For the stationary balloon configuration the flow is two-dimensional, parallel, laminar and without secondary flows for the Reynolds number range of 5.7-455.2. Evaluations of the oxygen transfer characteristics for the stationary balloon indicate that the main transport mechanisms are diffusion and convection in the crosswise and streamwise directions, respectively. Additionally, evaluations of oxygen transfer rates and Sherwood numbers in this Reynolds number range indicate that the oxygen transfer rate reaches an asymptotic limit at relatively moderate Reynolds numbers. For the pulsating balloon, flow characteristic results demonstrate the existence of a strong secondary flow around the fiber, and between the balloon and the fiber. This secondary flow induces oscillatory crosswise and streamwise velocities and a seemingly random spanwise flow which enhances the flow mixing as well as the transport of oxygen from the fiber surface to the bulk flow.