Papers by David klayton Herrera Vega
Background-Exposure to disturbed flow, including oscillatory shear stress, stimulates endothelial... more Background-Exposure to disturbed flow, including oscillatory shear stress, stimulates endothelial cells (ECs) to produce bone morphogenic protein (BMP) 4, which in turn activates inflammation, a critical atherogenic step. BMP activity is regulated by the level of BMP antagonists. Until now it was not known whether shear also regulates the expression of BMP antagonists and whether they play a role in EC pathophysiology. Methods and Results-BMP antagonists follistatin, noggin, and matrix Gla protein were expressed in cultured bovine and human arterial ECs. Surprisingly, oscillatory shear stress increased expression of the BMP antagonists in ECs, whereas unidirectional laminar shear decreased such expression. Immunohistochemical studies with mouse aortas showed data consistent with in vitro findings: Only ECs in the lesser curvature exposed to disturbed flow, but not those in the greater curvature and straight arterial regions exposed to undisturbed flow, showed coexpression of BMP4 and the BMP antagonists. Similarly, in human coronary arteries, expression of BMP4 and BMP antagonists in ECs positively correlated with the severity of atherosclerosis. Monocyte adhesion induced by oscillatory shear stress was inhibited by knockdown of BMP4 or treatment with recombinant follistatin or noggin, whereas it was increased by knockdown of follistatin and/or noggin. Conclusions-The present results suggest that ECs coexpress BMP antagonists along with BMP4 in an attempt to minimize the inflammatory response by oscillatory shear stress as part of a negative feedback mechanism. The balance between the agonist, BMP4, and its antagonists may play an important role in the overall control of inflammation and atherosclerosis.
Detection and Remediation Technologies for Mines and Minelike Targets IX, 2004
The presence of magnetic iron oxides in the soil can seriously hamper the performance of electrom... more The presence of magnetic iron oxides in the soil can seriously hamper the performance of electromagnetic sensors for the detection of buried land mines and unexploded ordnance (UXO). Previous work has shown that spatial variability in soil water content and texture affects the performance of ground penetrating radar and thermal sensors for land mine detection. In this paper we aim to study the spatial variability of iron oxides in tropical soils and the possible effect on electromagnetic induction sensors for buried low-metal land mine and UXO detection. We selected field sites in Panama, Hawaii, and Ghana. Along several horizontal transects in Panama and Hawaii we took closely spaced magnetic susceptibility readings using Bartington MS2D and MS2F sensors. In addition to the field measurements, we took soil samples from the selected sites for laboratory measurements of dual frequency magnetic susceptibility and textural characteristics of the material. The magnetic susceptibility values show a significant spatial variation in susceptibility and are comparable to values reported to hamper the operation of metal detectors in parts of Africa and Asia. The absolute values of susceptibility do not correlate with both frequency dependence and total iron content, which is an indication of the presence of different types of iron oxides in the studied material.
Medical Management of the Surgical Patient, 2013
Water Science and Technology Library
ABSTRACT Understanding the relationship between rainfall, and stream flow in mountain terrain req... more ABSTRACT Understanding the relationship between rainfall, and stream flow in mountain terrain requires the quantifying of rates of water movement into and through regolith covered hillslopes. General theory holds that infiltration rates in humid tropical are higher than rainfall intensities so surface runoff is minimal. However, soil profile characteristics can vary significantly on a hilslope, with concomitant changes in soil hydrologic characteristics. The pattern of soils within two small first order drainages was evaluated within the upper Río Chagres basin. Two main influences on soil distribution were identified. Mass movements primarily translational sliding and treefall result in stripping of the upper soil horizons and exposure of weathered saprolite. Soils forming in the deposits are characterized by higher infiltration rates and a more uneven surface topography than the stable soils. A catenary relationship was also observed with stable, oxidizing soil profiles in upper slope positions and reduced (gleyed) soils at the outlet of the drainage basin.
Innovations: Technology and Techniques in Cardiothoracic and Vascular Surgery, 2008
Objective The use of bilateral internal thoracic arteries (BITAs) during coronary artery bypass g... more Objective The use of bilateral internal thoracic arteries (BITAs) during coronary artery bypass grafting (CABG) improves long-term and event-free survival compared with single internal thoracic artery (SITA) grafting. It is controversial whether BITA grafting alters in-hospital adverse events after CABG. Methods Isolated CABG cases using BITA or SITA at a single US academic center between January 1, 1997 and June 30, 2006 were retrospectively reviewed. A propensity score was used as a covariate to balance the treatment groups (BITA and SITA) with respect to 44 preoperative risk factors. A multivariable logistic regression model tested whether treatment type was significantly associated with in-hospital death, deep sternal wound infection (DSWI), or hospital length of stay (LOS). Results There were 599 BITA and 10,212 SITA cases performed. Overall for all BITA versus SITA cases, adjusted mortality (0.8% vs. 1.7%, P = 0.85) was not different between the groups. However, adjusted incid...
SPIE Proceedings, 2007
Accurate estimation of sensible and latent heat fluxes as well as soil moisture from remotely sen... more Accurate estimation of sensible and latent heat fluxes as well as soil moisture from remotely sensed satellite images poses a great challenge. Yet, it is critical to face this challenge since the estimation of spatial and temporal distributions of these parameters over large areas is impossible ...
Water Science and Technology Library
Soil hydrologcal processes determine how precipitation is partitioned into infiltration, runoff, ... more Soil hydrologcal processes determine how precipitation is partitioned into infiltration, runoff, evapotranspiration, and ground water recharge in the upper Río Chagres basin. The focus of this study is to investigate the soil hydrological processes by which precipitation excess on first order drainage basins enters the streams feeding the upper Río Chagres and its major tributary rivers. Infiltration rates, water retention curves, and water repellency of surface soils have been measured. These measurements together with the soil morphological observations by Harrison et al. (2005, Chapter 7) and hydrological observations by Calvo et al. (2005, Chapter 9) and Niedzialek and Ogden (2005, Chapter 10) are used to formulate a comprehensive conceptual model of runoff production in the upper Río Chagres watershed.
Air, Soil and Water Research, 2013
The present investigation was focused on the variations in rainwater infiltration experienced by ... more The present investigation was focused on the variations in rainwater infiltration experienced by soils of Gamboa zone (Panama Canal Watershed) during various seasons of the year, employing a time-lapse analysis of electrical resistivity tomography (ERT). In 2009, a total of 3 geoelectrical tests were undertaken during the dry, transition and rainy seasons across a profile 47 m in length, strategically distributed on site. The results obtained in this study showed strong variations in calculated resistivity between these seasons, taking the dry season as a reference with decreases and increases of percent difference of resistivity between -20% and -100%, and between 50% and 100%, respectively. These decreases, when displayed through a sequence of time-lapse images, reveal a superficial extension of the water content variations along the entire profile, as well as strong inversion artifacts showing false increases of calculated electrical resistivity. Decreases are the product of the ...
Air, Soil and Water Research, 2012
This paper presents an estimation of the quantity of carbon fixed in trees in a one hectare (ha) ... more This paper presents an estimation of the quantity of carbon fixed in trees in a one hectare (ha) plot at the Cerro Pelado-Gamboa Hydrology Tropical Observatory, which is located in the province of Colon, Panama. The estimation of carbon fixed in trees may provide significant information on carbon flux due to water circulation, which may ultimately enable evaluation of the carbon cycle. All trees larger than 10 cm diameter at breast height (DBH) in the plot were investigated. Carbon fixed within these trees was estimated using a parameterized formula. Tree biomass estimations for the plot were 97.21 Mg ha-1. We identified a rare arboreal pear species ( Euphorbiaceous) with higher carbon density than other trees in the plot. The presence of this apparently unique species may be due to specific soil characteristics. The method was evaluated by comparing the results with a second study performed in 2011, which resulted in an estimate of net new carbon (biomass) increment (NNCI), which g...
Thrombosis Research, 2004
Background: DX-88 is a potent kallikrein inhibitor that is being studied for the treatment of her... more Background: DX-88 is a potent kallikrein inhibitor that is being studied for the treatment of hereditary angioedema (HAE) and represents a potential alternative to aprotinin in cardiac surgical patients. The current study was designed to evaluate in vitro effects of DX-88 on coagulation in comparison with aprotinin. Methods: Blood samples were obtained from consented 12 healthy volunteers. DX-88 or aprotinin was added to blood at 200 and 800 kallikrein inhibitory units (KIU) per milliliter for aprotinin, and at 1.1, 2.2, or 8.8 Ag/ml for DX-88. Thromboelastography (TEGR) was performed using celite, kaolin, or tissue factor (TF) activation. Kaolin-based activated clotting times (ACTs) were measured at different heparin levels. The whole blood prothrombin time (PT)/PTT values were also measured. The endogenous thrombin generation was assessed with a fluorogenic assay using platelet-poor plasma (PPP). Results: With celite and kaolin activation of TEG, the reaction time was prolonged with DX-88 and aprotinin. With tissue factor activation, TEG parameters were not affected. DX-88 caused dose-dependent kaolin-ACT prolongation that was augmented by increasing doses of heparin. DX-88 or aprotinin had no significant effects on the PT values, but PTT values were dose-dependently prolonged. Both agents delayed the onset of thrombin generation when PTT reagent was used as a trigger, whereas no change was observed when tissue factor was used. Conclusion: We found that DX-88 delayed contact activator induced coagulation without affecting tissue factor mediated coagulation.
Platelets, 2004
The use of clopidogrel (Plavix), an inhibitor of adenosine diphosphate (ADP)-induced platelet agg... more The use of clopidogrel (Plavix), an inhibitor of adenosine diphosphate (ADP)-induced platelet aggregation, has been proven to reduce ischemic events in cardiovascular patients, but little information is available for optimal monitoring of platelet function in patients receiving the drug preoperatively. In the first part of the study we compared different testing modalities (thrombelastography (TEG), platelet aggregometry, and whole blood aggregation) to assess platelet ADP receptor inhibition. Because clopidogrel is a pro-drug, we used an in vitro model of ADP inhibition with 5'-p-fluorosulfonylbenzoyladenosine (FSBA). FSBA at final concentration of 80 microM completely inhibited platelet aggregation but had no effect on TEG maximum amplitude (MA). In the second part of the study, antiplatelet effects of clopidogrel were clinically assessed and correlated to postoperative bleeding in 18 coronary bypass surgery patients. Preoperative TEG results were normal or hypercoagulable in clopidogrel-treated patients, although platelet aggregation responses to ADP were inhibited. Clopidogrel-treated patients who underwent cardiopulmonary bypass had a high incidence (84.6%) of platelet transfusion therapy due to increased chest tube drainage. In conclusion, we have demonstrated that normal preoperative TEG-MA does not preclude clopidogrel-induced ADP receptor blockade; however, TEG can be a reliable monitor for CPB-induced platelet dysfunction related to GPIIb/IIIa. For monitoring clopidogrel, it is necessary to perform more specific platelet function tests (aggregometry or platelet count ratio) using ADP as an activator.
Journal of Vascular Surgery, 2004
A 54-year-old man who underwent uneventful orthotopic heart transplantion 1 year previously had l... more A 54-year-old man who underwent uneventful orthotopic heart transplantion 1 year previously had low-grade fever and dyspnea. Imaging studies revealed an ascending aortic pseudoaneurysm (AAP), which was repaired with a 5-mm polyester patch, with circulatory arrest and cardiopulmonary bypass. Intraoperative cultures of the AAP grew methicillin-resistant Staphylococcus aureus, and the pseudoaneurysm recurred after 6 weeks despite intravenously administered antibiotic therapy. A 28.5-mm ؋ 3.3-cm Gore Excluder aortic cuff was deployed in the ascending aorta through a left axillary artery cutdown with use of combined transesophageal echocardiography and fluoroscopy. In addition, controlled hypotension and asystole were established with administration of adenosine to facilitate precise device deployment. Postoperative imaging with transesophageal echocardiography and magnetic resonance angiography revealed complete resolution of the AAP, and the patient had done well at 7-month follow-up. Treatment of a mycotic aortic pseudoaneurysm with an endoprosthesis in a patient without other treatment alternatives can be performed safely, with acceptable short-term results.
Journal of the American College of Surgeons, 2011
No abstract is available. To read the body of this article, please view the Full Text online. ...... more No abstract is available. To read the body of this article, please view the Full Text online. ... © 2011 American College of Surgeons. Published by Elsevier Inc. All rights reserved. ... Visit SciVerse ScienceDirect to see if you have access via your institution. ... Advertisements on this site ...
Endoscopy, 2003
ABSTRACT Endoscopic biliary stenting is an established treatment for malignant obstructive jaundi... more ABSTRACT Endoscopic biliary stenting is an established treatment for malignant obstructive jaundice. Stent clogging continues to be a major problem with plastic stents. The aim of this study was to carry out a prospective comparison of two stents with different materials and shapes: the Olympus DoubleLayer stent (DLS; perfluoro alkoxy, without sideholes) and the standard polyethylene (PE) stent (with sideholes). A total of 120 patients (70 women; mean age 71, range 36 - 91) with jaundice due to malignant strictures of the middle to distal third of the common bile duct were randomly assigned to receive either DLS (n = 60) or PE (n = 60) biliary stents. Patients with cholangitis, hemobilia, previous biliary drainage, hilar stricture, or ampullary cancer were excluded. In all, 28 DLS patients (47 %) and 17 PE stent patients (29 %) died without clinical evidence of stent occlusion after a mean of 114 and 105 days, respectively ( P < 0.05). Twenty-six DLS patients (43 %) and 38 PE stent patients (63 %) had symptoms of stent clogging after a mean of 144 and 99 days, respectively ( P < 0.05). Stent dysfunction (stent orifice impacted on the bile duct or duodenal wall, stent migration) was recorded in six DLS patients (10 %) and five PE patients (8 %) (n. s.). Kaplan-Meier analysis of DLS and PE stent clogging-free survival showed a significantly longer patency period with the DLS stents (P = 0.0005). These results show that DoubleLayer stents have a longer patency period than PE stents. Patients who received PE stents had a higher risk of stent occlusion (relative risk 3.05; 95 % CI, 1.57 - 5.89) before death than DLS patients.
Computer Physics Communications, 2002
The "atoms in molecules" theory (AIM) is very useful to extract significant information from the ... more The "atoms in molecules" theory (AIM) is very useful to extract significant information from the electronic density, ρ(r). In the present paper, we show the implementation in WIEN 97 of some algorithms to determine the main elements of this novel theory (critical points of ρ(r), bond paths, crystal graphs, interatomic surfaces, atomic basins and atomic properties). WIEN 97 program is one successful implementation of the full-potential linearized augmented-plane wave method (FPLAPW), which allows most accurate calculations of the electronic density of crystals and surfaces using density functional theory. In order to illustrate those algorithms, they were applied to Pt and PtS bulk as two selected examples. 2002 Published by Elsevier Science B.V.
Circulation Research, 2004
Atherosclerosis is an inflammatory disease occurring preferentially in arterial regions exposed t... more Atherosclerosis is an inflammatory disease occurring preferentially in arterial regions exposed to disturbed flow conditions including oscillatory shear stress (OS). OS exposure induces endothelial expression of bone morphogenic protein 4 (BMP4), which in turn may activate intercellular adhesion molecule-1 (ICAM-1) expression and monocyte adhesion. OS is also known to induce monocyte adhesion by producing reactive oxygen species (ROS) from reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidases, raising the possibility that BMP4 may stimulate the inflammatory response by ROS-dependent mechanisms. Here we show that ROS scavengers blocked ICAM-1 expression and monocyte adhesion induced by BMP4 or OS in endothelial cells (ECs). Similar to OS, BMP4 stimulated H 2 O 2 and O 2 − production in ECs. Next, we used ECs obtained from p47phox −/− mice (MAE-p47 −/− ), which do not produce ROS in response to OS, to determine the role of NADPH oxidases. Similar to OS, BMP4 failed to i...
Circulation, 2009
Background— Race has been shown to be an independent risk factor for operative mortality after co... more Background— Race has been shown to be an independent risk factor for operative mortality after coronary artery bypass grafting (CABG). This study sought to determine the extent to which race is a risk factor for adverse events, long-term mortality, and whether off-pump surgery (OPCAB) modifies that risk. Methods and Results— The Society of Thoracic Surgeons Adult Cardiac Database at Emory Healthcare affiliated hospitals was queried for all primary isolated CABG records from 1997 to 2007. A propensity score was formulated to balance the patient groups with respect to treatment assignment (OPCAB or CABG on cardiopulmonary bypass). Multivariable logistic regression was used to assess the impact of black race and OPCAB on in-hospital outcomes (death, stroke, myocardial infarction, and their composite, major adverse cardiac events). Cox proportional hazards regression model and Kaplan–Meier curves determined whether black race affected long-term all-cause mortality. Interaction terms wer...
Circulation, 2002
Background — NAD(P)H oxidases are important sources of superoxide in the vasculature, the activit... more Background — NAD(P)H oxidases are important sources of superoxide in the vasculature, the activity of which is associated with risk factors for human atherosclerosis. This study was designed to investigate the localization of superoxide production and the expression of the Nox family of NAD(P)H oxidase proteins (gp91phox, Nox1, and Nox4) in nonatherosclerotic and atherosclerotic human coronary arteries. Methods and Results — In coronary artery segments from explanted human hearts, we examined intracellular superoxide production with dihydroethidium. In nonatherosclerotic coronary arteries, superoxide was present homogenously throughout the intima, media, and adventitia. In atherosclerotic arteries, there was an additional intense area of superoxide in the plaque shoulder, which is rich in macrophages and α-actin–positive cells. p22phox colocalized with gp91phox mainly in macrophages, whereas Nox4 was found only in nonphagocytic vascular cells. Expression of gp91phox and p22phox mRNA...
Chest, 2002
Study objective: To demonstrate an association between saprophytic fungal infections occurring at... more Study objective: To demonstrate an association between saprophytic fungal infections occurring at the bronchial anastomosis (BA) and the development of additional complications arising at this site. Design: Retrospective review. Setting: University lung transplant center. Materials and methods: Review of all single-lung and double-lung transplant (LTX) recipients who underwent transplantation between June 1993 and December 2000. All recipients were subjected to surveillance bronchoscopy with biopsy at predetermined intervals and when clinically indicated. Bronchial wash fluid and biopsy material were examined using appropriate fungal stains and culture techniques. An infection was defined when fungal organisms were identified in tissue specimens. Results: Fifteen saprophytic fungal infections involving the BA were identified in 61 LTX recipients (24.6%) who survived a minimum of 75 days post-transplantation. Infections were attributed to Aspergillus sp (n ؍ 9), Candida sp (n ؍ 2), Torulopsis sp (n ؍ 1), and mixed flora (ie, Penicillium ؉ Candida, two patients; and Aspergillus ؉ Candida, one patient). Saprophytic fungal infections occurred by a median of postoperative day 35 (range, 13 to 159 days). Airway complications involving the BA ultimately developed in 11 of 61 recipients (18%). These complications included symptomatic bronchial stenosis (nine patients), bronchomalacia (one patient), and fatal hemorrhage (one patient). Bronchial complications arose in 7 of 15 recipients (46.7%) with saprophytic fungal infections of the BA in contrast to 4 of 46 (8.7%) without infections (p ؍ 0.003, Fisher exact test). Also demonstrated was a positive correlation between anastomotic infections and bronchial complications (⌽ coefficient ؍ 0.43; p ؍ 0.001), while logistic regression analysis revealed that the absence of anastomotic infections predicted the absence of such complications (p ؍ 0.002). The risk of developing an additional complication following an anastomotic infection in patients with infections was five times that of those recipients without an infection (relative risk, 5.36; 95% confidence interval [CI], 1.82 to 15.79). The odds in favor of a bronchial complication following an infection were eight times greater than in those recipients without infection (odds ratio, 8.31; 95% CI, 1.96 to 35.16). Conclusions: Following LTX, saprophytic fungal infections of the BA are associated with serious airway complications.
Cardiovascular Research, 2009
Time for primary review: 26 days Aims CYP1A1 and CYP1B1, members of the cytochrome P450 protein f... more Time for primary review: 26 days Aims CYP1A1 and CYP1B1, members of the cytochrome P450 protein family, are regulated by fluid shear stress. This study describes the effects of duration, magnitude and pattern of shear stress on CYP1A1 and CYP1B1 expressions in human endothelial cells, towards the goal of understanding the role(s) of these genes in pro-atherogenic or anti-atherogenic endothelial cell functions. Methods and results We investigated CYP1A1 and CYP1B1 expressions under different durations, levels, and patterns of shear stress. CYP1A1 and CYP1B1 mRNA, protein, and enzymatic activity were maximally up-regulated at 24 h of arterial levels of shear stress (15-25 dynes/cm 2). Expression of both genes was significantly attenuated by reversing shear stress when compared with 15 dynes/cm 2 steady shear stress. Small interfering RNA knockdown of CYP1A1 resulted in significantly reduced CYP1B1 and thrombospondin-1 expression, genes regulated by the aryl hydrocarbon receptor (AhR). Immunostaining of human coronary arteries showed constitutive CYP1A1 and CYP1B1 protein expressions in endothelial cells. Immunostaining of mouse aorta showed nuclear localization of AhR and increased expression of CYP1A1 in the descending thoracic aorta, whereas reduced nuclear localization of AhR and attenuated CYP1A1 expression were observed in the lesser curvature of the aortic arch. Conclusion CYP1A1 and CYP1B1 gene and protein expressions vary with time, magnitude, and pattern of shear stress. Increased CYP1A1 gene expression modulates AhR-regulated genes. Based on our in vitro reversing flow data and in vivo immunostained mouse aorta, we suggest that increased expression of both genes reflects an anti-atherogenic endothelial cell phenotype.
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Papers by David klayton Herrera Vega