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Juan Carlos Jimenez

Publications and source records attributed to Juan Carlos Jimenez.

9 recordsLinked to original sources
PubMed2006

Nonlinear local electrovascular coupling. I: A theoretical model.

Here we present a detailed biophysical model of how brain electrical and vascular dynamics are generated within a basic cortical unit. The model was obtained from coupling a canonical neuronal mass and an expandable vasculature. In this proposal, we address several aspects related to electroencephalographic and functional magnetic resonance imaging data fusion: (1) the impact of the cerebral architecture (at different physical levels) on the observations; (2) the physiology involved in electrovascular coupling; and (3) energetic considerations to gain a better understanding of how the glucose budget is used during neuronal activity. The model has three components. The first is the canonical neural mass model of three subpopulations of neurons that respond to incoming excitatory synaptic inputs. The generation of the membrane potentials in the somas of these neurons and the electric currents flowing in the neuropil are modeled by this component. The second and third components model the electrovascular coupling and the dynamics of vascular states in an extended balloon approach, respectively. In the first part we describe, in some detail, the biophysical model and establish its face validity using simulations of visually evoked responses under different flickering frequencies and luminous contrasts. In a second part, a recursive optimization algorithm is developed and used to make statistical inferences about this forward/generative model from actual data.

Brain↗
PubMed2005

Recurrent gastrointestinal tract bleeding secondary to jejunal gastric heterotopia.

A 4-year-old Latino boy with a history of malrotation, nonobstructing annular pancreas, and a Ladd procedure during infancy presented with recurrent severe gastrointestinal tract bleeding. Investigations revealed a large mass in the proximal small bowel. At laparotomy, the proximal jejunal segment containing the mass was resected. Pathological examinations revealed a large intraluminal polyp composed of ectopic gastric mucosa. The patient presented 10 months later with recurrent bleeding, and subsequent laparotomy demonstrated a newly acquired segment of jejunal polyposis not present at the first operation. The case is presented, along with a plan of patient surveillance and a review of the pertinent literature.

Child, Preschool↗
PubMed2004

Annular pancreas in children: a recent decade's experience.

PURPOSE: Annular pancreas is a recognized cause of duodenal obstruction in children. The authors sought to characterize the clinical, radiologic, and prognostic findings in this disorder through a 10-year review of all patients with annular pancreas. METHODS: A retrospective review of all annular pancreas cases identified between 1993 and 2002 at 2 tertiary pediatric surgical centers was completed. Factors analyzed included patient demographics, presenting symptoms, associated anomalies, radiologic findings, operation performed, postoperative outcomes, and complications. RESULTS: Sixteen patients were identified. Four patients (25%) were premature. Twelve patients (75%) presented during the first week of life and the remainder within the first year. All patients presented with vomiting, which was nonbilious in 15 (94%). Five patients (31 %) had chromosomal anomalies, and 6 (38%) had other major congenital malformations. Eleven patients (69%) presented with partial duodenal obstruction. Operations performed were duodenoduodenostomy in 14 (88%), duodenojejunostomy in 1 (6%), and Ladd's procedure in 1 (6%). Enteral feedings were started, and full enteral feeding was achieved at an average of 8.4 days and 15.9 days after operation, respectively. All patients survived and were discharged after an average hospitalization of 24.0 days. CONCLUSIONS: Patients with annular pancreas have preampullary duodenal obstruction, which is more commonly partial. Duodenoduodenostomy is the appropriate treatment. Prognosis is excellent, despite the frequent association with chromosomal anomalies and major congenital malformations.

Duodenal Obstruction↗
PubMed2004

Human embryonic kidney cells (HEK-293 cells): characterization and dose-response relationship for modulated release of nerve growth factor for nerve regeneration.

The development of engineered constructs to bridge nerve gaps may hold the key to improved functional outcomes in the repair of injured peripheral nerves. These constructs must be rendered bioactive by providing the growth factors required for successful peripheral nerve regeneration. Previous studies demonstrated that harvested human and rat dermal fibroblasts could be genetically engineered to release nerve growth factor (NGF) both in vitro and in vivo. The use of fibroblasts, however, has the potential to cause scarring, and the expression of NGF from those cells was transient. To overcome these potential difficulties, human embryonic kidney cells were modified for use with the ecdysone-inducible mammalian expression system. These cells (hNGF-EcR-293) have been engineered and regulated to secrete human NGF in response to the ecdysone analogue ponasterone A. HEK-293 cells were transfected with human NGF cDNA with the ecdysone-inducible mammalian expression system (Invitrogen, Carlsbad, Calif.). Stable clones were then selected. Ponasterone A, an analogue of ecdysone, was used as the inducing agent. The secretion of NGF into the medium was analyzed with two different methods. After 24 hours of exposure to the inducing agent, cell medium was transferred to PC-12 cells seeded in 12-well plates, for determination of whether the secreted NGF was bioactive. Medium from untreated or ponasterone A-treated hNGF-EcR-293 cells was deemed bioactive on the basis of its ability to induce PC-12 cell differentiation. The concentrations of secreted NGF were also quantified with an enzyme-linked immunosorbent assay, in triplicate. NGF production was measured in successive samples of the same medium during a 9-day period, with maximal release of 9.05 +/- 2.6 ng/ml at day 9. Maximal NGF production was 8.46 +/- 2.1 pg/10(3) cells at day 9. These levels were statistically significantly different from levels in noninduced samples (p <or= 0.05). Differences in NGF secretion with the three different concentrations of ponasterone A (1, 2, and 3 microM) were not statistically significant. PC-12 cells exposed to medium from induced transfected HEK-293 cells demonstrated markedly higher levels of differentiation, compared with control levels, indicating bioactive protein secretion. It was demonstrated that this regulated delivery system could secrete bioactive NGF for up to 9 days and might be useful for in vivo applications. This regulated delivery system should be useful for tissue-engineered nerve constructs.

Cell Differentiation↗
PubMed2003

Carcinoid tumors of the common bile duct: report of two cases.

We report two cases of carcinoid tumors of the common bile duct. The first patient was a 65-year-old woman in whom a carcinoid tumor of the distal bile duct was incidentally found during an open cholecystectomy for cholecystitis. The second patient was a 27-year-old man in whom a distal common bile duct carcinoid was incidentally found during orthotopic liver transplantation for sclerosing cholangitis and multiple biliary strictures. There are few reports of carcinoid tumors of the extrahepatic ducts, and a brief review of the relevant literature is discussed following these case reports.

Adult↗
PubMed2003

Prophylaxis of infection for elective colorectal surgery.

BACKGROUND: Influenced by the key results of the clinical trials conducted in the early 1970s by Condon, Nichols, and Gorbach, surgeons have adopted the routine use of mechanical bowel prep and antimicrobial prophylaxis prior to elective colorectal procedures as a widely established practice. Recent clinical trial data, however, led us to reexamine the benefits of mechanical bowel preparation, methods of antimicrobial prophylaxis and to assess the role of new, specific risk factors for surgical site infection after colorectal operations. METHODS: Pertinent studies on antimicrobial prophylaxis for elective colorectal surgery were identified from a Medline search of English language publications since 1966. RESULTS: We found credible clinical trial data that mechanical bowel preparation prior to elective colorectal surgery may not be essential. Timing of the administration of prophylactic antimicrobials is often inaccurate in current practice and suggests the need for a long-acting, broad-spectrum agent that would deemphasize precision in time of preoperative infusion. New risk factors have been identified that increase infection after colorectal surgery, including patient core temperature and tissue oxygenation. Independent observers identify postoperative surgical site infection at a higher rate than physician self-reporting and should be incorporated into future clinical trials. CONCLUSION: The once settled area of antimicrobial prophylaxis for colorectal surgery is again controversial. Cooperative clinical trials will be needed to resolve key questions such as the efficacy for bowel preparation and how to obtain effective timing of antimicrobial prophylaxis.

Antibiotic Prophylaxis↗
PubMed2002

Intra-abdominal Sepsis in Elderly Persons.

Elderly patients represent a greater percentage of the population now than ever before, with 12.4% of North Americans being >65 years of age. Intra-abdominal illnesses in this population often have different etiologies than those seen in younger populations. Because of a variety of physiologic changes that occur as people age, elderly persons have different sites of infection, may present with vague symptoms and longer histories, are more gravely ill, and, overall, have worse prognoses. The major causes of intra-abdominal sepsis in elderly persons are reviewed, explanations for the differences in presentation and prognosis are offered, and the treatments of each cause are reviewed.

Abdominal Abscess↗
PubMedDate not supplied

Sexual dysfunction in men after open or endovascular repair of abdominal aortic aneurysms.

Few studies have thoroughly investigated the incidence and detailed the degree of sexual disability after aortic aneurysm surgery. Reports prior to 1990 vary greatly in the incidence of postoperative dysfunction mostly because of nonstandardized methods of assessment. In this article, we compare the incidence of reported sexual dysfunction after aortic reconstruction, open and endovascular abdominal aortic aneurysm repair. Pertinent studies on sexual dysfunction following open and endovascular aortic aneurysm repair were identified from a MEDLINE search of English-language publications since 1966. Newer standardized methods of assessment have identified relatively high rates of sexual dysfunction prior to and after intervention. Aortic aneurysm patients have a baseline incidence of sexual dysfunction of approximately 30%, which doubles over the next 7 years. Patients who had open aortic operations reported significantly increased sexual dysfunction during the first postoperative year. Endovascular repair with unilateral internal iliac occlusion results in new sexual dysfunction in approximately 10% of patients, but this increases significantly with bilateral internal iliac occlusion. When compared with open operation, the incidence of sexual dysfunction is lower overall in patients with endovascular aortic aneurysm repairs, which includes those who have internal iliac artery occlusion, but it is increased with bilateral iliac occlusion. Surgeons should be aware of the preoperative prevalence of sexual dysfunction in patients undergoing aortic procedures.

Aortic Aneurysm, Abdominal↗