Juan Mejia | Carnegie Mellon University (original) (raw)

Papers by Juan Mejia

Mechanical stresses and flow dynamics alteration in a stented artery region are known to stimulat... more Mechanical stresses and flow dynamics alteration in a stented artery region are known to stimulate intimal thickening and increase the risk of restenosis, the closure of a revascularized artery. Particle imaging velocimetry flow visualization technique (PIV) can be useful in characterizing the local flow dynamics around stents. However, usual cylindrical stent models present some visualization and optical difficulties when studying fluid dynamics using PIV. A flat stent model has two main advantages over the usual cylindrical models. First, planar stent models are cheaper to manufacture than cylindrical ones. Secondly, it is easier with a flat model to get data acquisition planes cutting through the model without inducing diffraction errors due to the cylindrical model’s curvature. The wall shear stress distribution, which is believed to be of primary importance in stented artery restenosis, should be comparable in both the flat and cylindrical stent models for the regions of intere...

Arquivos brasileiros de cardiologia, 2007

There are two techniques to surgically repair a coronary fistula: ligation or external obliterati... more There are two techniques to surgically repair a coronary fistula: ligation or external obliteration of the fistula, with or without distal revascularization of the coronary and closure from within the heart chamber². The second intervention was used in this case and is associated with a lower recurrence rate³.

HPB, 2018

4,484 AE 2,678UI/L, respectively). Serum ionized calcium (iCa) and potassium (K) levels were sign... more 4,484 AE 2,678UI/L, respectively). Serum ionized calcium (iCa) and potassium (K) levels were significantly increased in HFIP group (5.256 AE 0.7 mg/dL and 6.813 AE 0.645 mEq/ L, respectively) compared to Control (4.773 AE 0.256 mg/dL and 6.086 AE 0.422 mEq/L, respectively). Base excess, bicarbonate, lactate, chloride and glucose levels in HFIP group were not significantly different from Control. Conclusion: In experimental normothremic liver IR injury, HFIP protects the liver demonstrated by marked decrease in liver transaminases. The ionic imbalance of serum K and iCa maybe related to increased intracellular release of both electrolytes involved in the main mechanism of preconditioning liver protection effect. Intravenous HFIP can emerge as a new strategy to liver protection mainly in situations where volatile anaesthetics cannot be applied.

PloS one, 2017

Hispanic/Latino populations are a genetically admixed and heterogeneous group, with variable frac... more Hispanic/Latino populations are a genetically admixed and heterogeneous group, with variable fractions of European, Indigenous American and African ancestries. The molecular profile of breast cancer has been widely described in non-Hispanic Whites but equivalent knowledge is lacking in Hispanic/Latinas. We have previously reported that the most prevalent breast cancer intrinsic subtype in Colombian women was Luminal B as defined by St. Gallen 2013 criteria. In this study we explored ancestry-associated differences in molecular profiles of Luminal B tumors among these highly admixed women. We performed whole-transcriptome RNA-seq analysis in 42 Luminal tumors (21 Luminal A and 21 Luminal B) from Colombian women. Genetic ancestry was estimated from a panel of 80 ancestry-informative markers (AIM). We categorized patients according to Luminal subtype and to the proportion of European and Indigenous American ancestry and performed differential expression analysis comparing Luminal B aga...

Journal of surgical case reports, 2017

To the best of our knowledge this is the first case of this nature described in the literature. S... more To the best of our knowledge this is the first case of this nature described in the literature. Sharing the authors experience with this case, particularly the technical challenges and post-operative management may aid other physicians facing similar scenarios. In this report, we describe a pancreaticoduodenectomy for pancreatic adenocarcinoma in a patient with a previous left ventricular assist device (LVAD). A multidisciplinary approach, particularly close involvement of the advanced heart failure, mechanical heart and pancreas surgery teams was key to the success of this case. Major abdominal surgery in the setting of previous LVAD should be considered carefully, however, the LVAD should not be generalized as an absolute contraindication.

Cancer Genomics & Proteomics, 2016

Background: There exists limited information on the role of hTERT methylation, and its associatio... more Background: There exists limited information on the role of hTERT methylation, and its association with type-specific HPV infections in cervical cancer. Materials and Methods: Eighty-seven frozen samples were analyzed for type-specific HPV infection using a GP5 + /GP6 + PCR-RLB assay (RLB). hTERT DNA methylation analysis was performed using a newly developed PCR-RLB-hTERT. Results: Ninety-three percent of samples were HPV-positive and fifteen different types were detected. hTERT methylation analysis of region 1 revealed no methylation in 78.8% of the samples and partial methylation in 21.2%. In region two, 68.2% showed no methylation and 31.8% showed a pattern of partial methylation. An association between the alpha 9 and alpha 7 species with a pattern of no methylation of hTERT in the region 1 was established (p=0.02 and p=0.03, respectively). Conclusion: Differences in patterns of methylation of the hTERT core promoter [region 1 (nt-208 to-1) and region 2 (nt +1 to +104) relative to first ATG] are related to the HPV species present.

Surgical Neurology International, 2016

Background: Isolated giant cerebral varix (IGV) is an uncommon vascular lesion that represents a ... more Background: Isolated giant cerebral varix (IGV) is an uncommon vascular lesion that represents a diagnostic challenge and requires dynamic vascular studies for its characterization. The IGV is considered a benign, low-flow venous lesion with very low risk of bleeding that might cause secondary symptoms mainly due to compression of the adjacent parenchyma. Case Description: A 12-year-old female patient with non-contributory medical history presented with headache for the last 2 months. Upon admission, her neurological examination was unremarkable. Magnetic resonance imaging (MRI) and computed tomography angiography (CTA) images demonstrated a large varicose dilation of the superficial Sylvian vein, located anterior to the left temporal pole, with no evidence of abnormal arteriovenous connections or tumoral lesions. This finding was considered incidental and unrelated to her symptoms. In this case, we considered that the combination of CTA and MRIs was enough to establish an accurate diagnosis, excluding the need to perform invasive imaging studies. Taking into account these considerations, the patient was managed with conservative treatment and has been followed up for 1 year, remaining asymptomatic. Conclusion: Cerebral IGVs are rare vascular lesions that are treated conservatively when asymptomatic and surgically in the case of rupture or compression of adjacent structures. Given our observation of a high unlikelihood of vascular connections to arteries, and the information obtained with non-invasive imaging techniques such as CTA and MRI was enough to make a clinical decision and avoid the evaluation with invasive procedures.

Bud rot is considered the most limiting disease of oil palm in South America because it causes di... more Bud rot is considered the most limiting disease of oil palm in South America because it causes direct production losses on thousands of hectares dedicated to the crop. A Phytophthora sp. was isolated from commercial plantations cultivated in Ecuador, Brazil, and Colombia showing typical symptoms of bud rot. Pathogenicity was evaluated in 6- and 24-month-old palms under controlled conditions in the greenhouse and in leaf fragments placed in humidity chambers. Isolates of this Phytophthora sp. were found to be pathogenic on both 6 and 24-month-old palms, and Phytophthora sp. was re-isolated from infected tissue, therefore fulfilling Koch’s postulates. Through PCR, the causal agent was identified using A2/I2 primers specific to the genus Phytophthora, which amplified a 788-bp fragment located in the internal transcribed spacer (ITS) region. The PCR product was digested with the restriction enzymes MspI, RsaI, and TaqI, generating fragments that corresponded to P. palmivora. With the se...

Plant Disease, 2015

Five Andean blackberry Rubus genotypes, three resistant and two susceptible to anthracnose, were ... more Five Andean blackberry Rubus genotypes, three resistant and two susceptible to anthracnose, were used to identify regions in the Rubus genome with homology to disease-resistance genes found in other plant species. Polymerase chain reaction amplification with 12 pairs of primers and fragment cloning yielded 520 clones, of which 151 showed inserts between 500 and 700 bp long. When sequenced, 47 clones showed homology with two types of resistance genes, non-Toll/interleukin-1 receptor (TIR) nucleotide binding site (NBS) leucine-rich repeat (LRR) and TIR-NBS-LRR, thereby confirming their designation as resistance gene analogs (RGAs). The number of RGAs detected per Rubus genotype ranged from 7 to 11, with the highest in a wild resistant and a cultivated susceptible genotype. Rubus RGAs were also homologous with several non-TIR- and TIR-type RGAs found in other members of the Rosaceae family (Rosa hybrid cultivar, Rosa roxburghii, Malus × domestica, M. prunifolia, M. baccata, M. floribun...

Biomédica, 2010

Introducción. El cáncer de cuello uterino constituye la primera causa de muerte entre la població... more Introducción. El cáncer de cuello uterino constituye la primera causa de muerte entre la población femenino por cáncer en Colombia. El bajo impacto que ha tenido el uso de la citología en algunos países, se ha atribuido a la baja reproducibilidad de los resultados y las altas tasas de falsos negativos. Objetivo. Evaluar la calidad de la lectura de citologías de cuello uterino en cuatro departamentos de Colombia, mediante un análisis de concordancia entre el reporte original y el reporte de un grupo de referencia conformado por patólogos expertos. Materiales y métodos. Se diseñó una muestra probabilística de citologías por medio de un muestreo aleatorio estratificado simple. Se definieron tres estratos según el reporte citológico del departamento (insatisfactorio, negativo y positivo). Todas las láminas fueron leídas de manera ciega e independiente por dos patólogos expertos y calificadas según el sistema Bethesda 2001. Se empleó el coeficiente kappa no ponderado para describir la concordancia. Resultados. La concordancia con respecto a la evaluación de la calidad de la citología fue muy baja en todos los departamentos (kappa=0,03; IC95% 0 a 0,06). La concordancia con respecto a la evaluación de anormalidades de células escamosas fue moderada (kappa=0,47; IC95% 0,41 a 0,53). Se insinuó una concordancia más alta en Tolima y Magdalena, comparada con la de Boyacá y Caldas. Conclusión. Existen problemas en la calidad de lectura de las citologías que pueden explicar el bajo impacto de la citología en la mortalidad por cáncer de cuello uterino en Colombia. Palabras clave: citología, frotis vaginal, tamización masiva, neoplasias del cuello uterino, variaciones dependientes del observador, Colombia. Quality of vaginal smear for cervical cancer screening: a concordance study Introduction. Cervical cancer is the leading cause of cancer deaths in the female population in Colombia. The low impact of Papanicolaou smears in reducing cervical cancer mortality in some countries has been attributed to their low reproducibility and high rates of false negatives. Objective. To evaluate the quality of the Papanicolaou smears in four regions of Colombia comparing the original report given by provincial cytologists or pathologists with a second report made by a team of expert pathologists from the Instituto Nacional de Cancerología of Colombia. Materials and methods. A sample of 4,863 Papanicolau smears was selected by a simple stratified randomized sampling method. Three strata were defined according to the original cytological report as negative, positive and unsatisfactory. All slides were newly interpreted with Bethesda 2001 by two independent experienced pathologists blinded to the first results. Non-weighted kappa values were calculated for degree of agreement. Results. Overall, the concordance between the two evaluations was very low with a kappa value of 0.03 (95% CI: 0-0.06). With regard to abnormalities in squamous cells, evaluation concordance was moderate with a value of 0.47 (95% CI: 0.41-0.53); a trend was noted suggesting higher levels of concordance in the evaluations from the Tolima and Magdalena Provinces. Conclusion. Problems related with the quality of Papanicolau smears or the accurate reading thereof may be factors that explain the low impact of massive screening in cervical cancer mortality in Colombia.

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Biomédica : revista del Instituto Nacional de Salud

Cervical cancer is the leading cause of cancer deaths in the female population in Colombia. The l... more Cervical cancer is the leading cause of cancer deaths in the female population in Colombia. The low impact of Papanicolaou smears in reducing cervical cancer mortality in some countries has been attributed to their low reproducibility and high rates of false negatives. To evaluate the quality of the Papanicolaou smears in four regions of Colombia comparing the original report given by provincial cytologists or pathologists with a second report made by a team of expert pathologists from the Instituto Nacional de Cancerología of Colombia. A sample of 4,863 Papanicolau smears was selected by a simple stratified randomized sampling method. Three strata were defined according to the original cytological report as negative, positive and unsatisfactory. All slides were newly interpreted with Bethesda 2001 by two independent experienced pathologists blinded to the first results. Non-weighted kappa values were calculated for degree of agreement. Overall, the concordance between the two evalu...

Revista Brasileira de Cirurgia Cardiovascular, 2012

Objective: To evaluate patient with cardiomyopathy's progress after cardiac transplant, by analyz... more Objective: To evaluate patient with cardiomyopathy's progress after cardiac transplant, by analyzing his survival, complications and cardiovascular responses after nearly four years of surgery. Methods: The survey was conducted from February to May 2011, with patients undergoing cardiac transplantation at Dr. Carlos Alberto Studart Gomes Hospital-Messejana Hospital (HDM). The sample consisted of all transplanted patients in 2007 in this hospital. Initially an evaluation form developed by the researchers, which was based on collected data from patients' medical records, was applied, about trans and postoperative period. After collecting these informations, patients underwent the six-minute walk test (6WT). The marks found in walking distance were compared with reference marks expected for this population by using Enright and Sherrill's equation. Results: From all the 24 patients who underwent cardiac transplantation in HDM in 2007, 14 were evaluated and 10 were excluded. Regarding the complications, in the transoperatory period, the most evident was the right ventricular dysfunction (64.3%) and tachycardia (64.3%) was more evident on the postoperative period. Analyzing the 6WT it was observed a decrease of 11.6% in walking distance when compared with the estimated distance (486 ± 55 m, 550 ± 59 m, respectively). Conclusion: Survival of heart transplant patients was equivalent to about 70%. The results of this study before the 6WT showed that patients' cardiovascular responses are below the estimated, nevertheless within the normal range established.

Seminars in Plastic Surgery, 2009

The contour of the neck is a very important determinant of facial aesthetics. Precise knowledge o... more The contour of the neck is a very important determinant of facial aesthetics. Precise knowledge of neck anatomy is essential for adequate planning and execution of this procedure. There are three anatomic and surgical planes involved in the management of the aging neck; the superficial plane (subcutaneous fat), the intermediate plane (platysma muscles and the fat between the two muscles), and the deep plane (subplatysmal fat, the anterior belly of the digastric muscles, and the submandibular glands). These planes need to be thoroughly evaluated in the preoperative assessment and dealt with according to each patient's needs. Even though this article focuses on isolated management of the aging neck, careful evaluation of the neck and its relationship to the lower third of the face is fundamental. If there is significant jowling and descent of the neck-face interface, an isolated neck-lift procedure will not address that problem and will lead to a suboptimal result. In these patients, a face and neck lift is a more appropriate operation.

Revista Brasileira de Cirurgia Cardiovascular, 2009

Bandagem da artéria pulmonar: uma cirurgia simples? Uma análise crítica em um centro terciário

Revista Brasileira de Cirurgia Cardiovascular, 2003

Object: This paper aims to define the prescribility (therapeutic efficacy and bio-safety) of gene... more Object: This paper aims to define the prescribility (therapeutic efficacy and bio-safety) of generic microemulsion Cyclosporin (Sigmasporin Microral®). Method: Casuistic: Twenty heart transplantation patients, 13 males and 7 females, with a mean age of 49.6 years, began immunosuppression treatment with generic microemulsion cyclosporin (Sigmasporin Microral®). They underwent clinical and laboratory evaluation during a minimum of three months. Procedures included clinic evaluation with electro and echocardiogram, endomyocardial biopsy, routine biochemical and hematological tests. Results: The mean follow-up was 10 months with a maximum of 16 months. A total of 151 endomyocardial biopsies were evaluated: 31.7% were degree 0, 43.7% 1a and 23.1% 1b. We had only one case of acute clinical rejection confirmed by biopsy as IIIa, and one patient with mediastinitis, both of whom had a good evolution. The mean cyclosporin blood level was 303 Ng/mL. All other parameters also showed a good evolution. Conclusion: Generic microemulsion cyclosporin (Sigmasporin Microral®) shows therapeutic efficacy and an excellent bio-safety profile. Its Prescribility is confirmed.

SSRN Electronic Journal, 2008

The current paper analyzes the importance and potentials of the tourism sector for economic devel... more The current paper analyzes the importance and potentials of the tourism sector for economic development. It is divided into four major parts. After a short introduction, section two presents some theoretical insights into the topic of economic development. Commenting on the most relevant components of the catching-up theory by Abramovitz (1986) and the structural change theory by Baumol (1967) and others, it could be realized that growth and the accompanying structural changes in the distribution of employment and GDP have their sources in the sector industry. But at the moment of incorporating the demand side explanation of structural change, the service sectors offer growth potentials as well. Furthermore, the basic characteristics and importance of the tourism sector for economic development and employment are emphasized, examining the so-called "social capabilities" and the innovation potential within the process of economic growth of any nation. A short survey of literature concerning the contribution of this sector to economic growth makes clear that tourism should be considered not just from the perspective of the benefits, but also from the costs associated with it. Section three provides an analysis of the economic impact of tourism in a developing country, namely Colombia, based on time-series analysis and data gathered supported on the "Tourism Satellite Account" Methodology. Some relevant indicators produced by the World Economic Forum through its "Travel and Tourism Competitiveness Report", are also evaluated. Finally, some conclusions are drawn with respect to the potentialities, as well as the challenges identified for the Colombian case.

Rev Colomb Cir, 2012

Given the increasing use of imaging in the diagnosis process and the technological advances in re... more Given the increasing use of imaging in the diagnosis process and the technological advances in resolution and quality of the images, many pathologic entities not yet clearly defined, even those asymptomatic, are now incidentally detected. Such is the case with the pancreatic cystic lesions, which could not de diagnosed some 30 years ago because most of them are asymptomatic. The majority of symptomatic cystic lesions that affect the pancreatic parenchyma are due to the presence of non-neoplastic pseudocysts whose management may be just drainage or clinical follow-up, while those asymptomatic cystic lesions are generally neoplastic.

Rev. colomb. …, 2003

clinical manifestation simulating Ewing´s Sarcoma is presented. Supplementary studies with light ... more clinical manifestation simulating Ewing´s Sarcoma is presented. Supplementary studies with light microscopy, immunophenotypic, and cytogenetic evaluation confirm pre-B lymphoblastic lymphoma, with t(1;19)(q23:p13) translocation. The characteristics of this neoplasia, and the importance of complementary inmunophenotypic, and cytogenetic studies, to perform an accurate diagnosis are discussed.

Plant Disease, 2007

Coffee crispiness (“crespera”), a disease of uncertain etiology, has been endemic in coffee (Coff... more Coffee crispiness (“crespera”), a disease of uncertain etiology, has been endemic in coffee (Coffea arabica L.) plantations in Colombia for at least 60 years. Symptoms typically consist of bud proliferation, abundant short and narrow leaves, phyllody, floral abortion, monospermic fruit, and dwarfing of plants. In severe cases, coffee crispiness disease (CCD) can affect production significantly. In this study, association of a phytoplasma with CCD was indicated by the accumulation of Diene's stain, or 4′, 6-diamidino-2-phenylindole fluorescence, only in phloem of affected plant tissues. The presence of polymorphic phytoplasma cells in phloem sieve tube elements was confirmed by transmission electron microscopy. The disease was transmitted successfully by grafting symptomatic shoots from CCD-affected C. arabica plants onto young, healthy rootstocks; however, symptoms failed to develop after mechanical inoculation of young plants with extracts derived from diseased plant tissues. A...

Journal of Phytopathology, 2008

Since 1992, anthracnose of Andean blackberry (Rubus glaucus) has generated losses as high as 40% ... more Since 1992, anthracnose of Andean blackberry (Rubus glaucus) has generated losses as high as 40% for farmers in Colombia. In this study, our goal was to characterize 240 Colletotrichum isolates from Andean blackberry in eight areas of Colombia. These isolates were evaluated according to morphological characteristics, sensitivity to benomyl, pathogenicity, and genetic variability. Identification of the genus Colletotrichum was achieved by using species complex-specific polymerase chain reaction primers. A multilocus phylogeny approach was used to identify isolates to the species level with sequences from the ribosomal internal transcribed spacer region and partial sequences of the actin, βtubulin 2, calmodulin, chitin synthase 1, glutamine synthetase, and glyceraldehyde-3-phosphate dehydrogenase genes. Most of the isolates were identified as Colletotrichum gloeosporioides sensu lato, were associated with the Castilla ecotype, showed high sensitivity to benomyl, and were highly aggressive. Isolates identified as C. acutatum sensu lato were found mainly on the Thornless ecotype, were highly resistant to benomyl, and showed intermediate aggressiveness. Only three isolates were identified as C. boninense sensu lato. The species identified included C. fructicola, C. kahawae subsp. ciggaro, C. godetiae, C. karstii, C. brassicicola, and undetermined Colletotrichum spp. This study is the first report of these species associated with anthracnose in Andean blackberry.