Biomedical subjects

N T Nguyen

Publications and source records attributed to N T Nguyen.

At least 19 recordsLinked to original sources

PubMed2006

Characterization of salt tolerance in ectoine-transformed tobacco plants (Nicotiana tabaccum): photosynthesis, osmotic adjustment, and nitrogen partitioning.

Ectoine (1,4,5,6-tetrahydro-2-methyl-4-pyrimidinecarboxylic acid) biosynthetic genes (ect. ABC) from Halomonas elongata were introduced to tobacco plants using an Agrobacterium-mediated gene delivery system. The genes for ectoine biosynthesis were integrated in a stable manner into the tobacco genome and the corresponding transcripts were expressed. The concentration of ectoine under salt-stress conditions was higher in the roots than in leaves. A close relationship was found between stomatal conductance and the amount of transported nitrogen, suggesting that water transport through the xylem in the stem and transpiration may be involved in nitrogen transport to leaves. The data indicate that the turgor values of the ectoine transgenic lines increased with increasing salt concentration. The data revealed two ways in which ectoine enhanced salinity tolerance of tobacco plants. First, ectoine improved the maintenance of root function so that water is taken up consistently and supplied to shoots under saline conditions. Second, ectoine enhanced the nitrogen supply to leaves by increasing transpiration and by protecting Rubisco proteins from deleterious effects of salt, thereby improving the rate of photosynthesis.

Adaptation, Physiological↗

PubMed2005

The SAGES Bariatric Surgery Outcome Initiative.

BACKGROUND: The recent initiative for identifying centers of excellence in bariatric surgery calls for documentation of surgical outcomes. The SAGES Outcomes Initiative is a national database introduced in 1999 as a method for surgeons to accumulate and compare their data with summary national data. A bariatric-specific dataset was established later in 2001. The aim of this study was to compare the outcomes of bariatric surgery from the Society of American Gastrointestinal Endoscopic Surgeons' (SAGES) bariatric database with data derived from a national administrative database of academic centers. METHODS: Between 2001 and 2004, 24 surgeons with 1,954 patients participated in the SAGES Bariatric Outcome Initiative, and 97 institutions with 42,847 patients participated in the University HealthSystem Consortium (UHC) database. Only 7 of the 24 surgeons participating in the SAGES Bariatric Outcome Initiative submitted more than 50 cases. The main outcome measures included demographics, comorbidities, type of bariatric procedure, operative time, length of hospital stay, short- and long-term complications, mortality, and weight loss. RESULTS: Both datasets were comparable for gender. Roux-en-Y gastric bypass had been performed for 88% of the patients in the SAGES database and 96% of the patients in the UHC database. Associated comorbidities were similar between the two groups except for a higher rate of hyperlipidemia for the patients in the SAGES database. The SAGES database contains more bariatric-specific information such as body mass index, operative time, blood loss, bariatric-specific complications, long-term complications, and weight loss data than the UHC database. According to the available data, no statistically significant differences exist between the two datasets in terms of perioperative complications and mortality. CONCLUSIONS: The SAGES Bariatric Outcome Initiative provides valuable bariatric-specific data not currently available in an administrative database that may be useful for benchmarking purposes. However, this database is currently underutilized.

Adult↗

PubMed2005

Hypoglycemic effects of the wood of Taxus yunnanensis on streptozotocin-induced diabetic rats and its active components.

Hypoglycemic effects of the H(2)O and MeOH extracts of the wood of Taxus yunnanensis were examined in streptozotocin (STZ)-induced diabetic rats. The H(2)O extract significantly lowered the fasting blood glucose level by 33.7% at a 100mg/kg dose on intraperitoneal administration. From the active H(2)O extract of the wood, three lignans, i.e., isotaxiresinol (1), secoisolariciresinol (2) and taxiresinol (3), were isolated as major components. These lignans were further tested for their hypoglycemic effects on the same experimental model. At a dose of 100mg/kg (i.p.), isotaxiresinol (1) reduced the fasting blood glucose level of diabetic rats by 34.5%, while secoisolariciresinol (2) and taxiresinol (3) reduced by 33.4% and 20.9%, respectively. The blood glucose lowering effects of 1 and 2 were stronger than the mixture of tolbutamide (200mg/kg) and buformin (1mg/kg) used as a positive control, which lowered fasting blood glucose level by 24.0%.

Animals↗

PubMed2005

The impact of laparoscopy on bariatric surgery.

The rising popularity of bariatric surgery over the past several years is attributable in part to the development of laparoscopic bariatric surgery. Morbidly obese patients have associated comorbid conditions that may predispose them to postoperative morbidity. The laparoscopic approach to bariatric surgery offers a minimally invasive option that reduces the physiologic stress and provides clinical benefits, as compared with the open approach. This review summarizes the impact of laparoscopic surgery on bariatric surgery, the various risk factors that could potentially predispose morbidly obese patients to postoperative morbidity, the fundamental differences between laparoscopic and open bariatric surgery, and the physiology of reduced tissue injury associated with laparoscopic bariatric surgery.

Bariatric Surgery↗

PubMed2005

Effect of resonator dimensions on nonlinear standing waves.

An investigation of the effect of resonator dimensions on nonlinear standing waves in shaped resonators is conducted. Simple forms of the shear viscosity term in the momentum equations are developed for an axisymmetric (2D) resonator and a low aspect ratio rectangular (3D) resonator. The cross sections of the resonators are exponentially expanded and the one-dimensional wave equations are solved by using the Galerkin's method. The quality factors, pressure waveforms, compression ratios, and resonance frequencies are calculated for different dimensionless cross sections and lengths of the resonators. The results show that, apart from the resonator length, the ratio of the cross-section dimension to the length of the resonator is an important parameter. If the ratio is greater than 0.04, the characteristics of the shaped resonator are not affected significantly. However, when the ratio is less than 0.01, the resonance becomes weak, the compression ratio drops substantially, and the frequency response changes as well.

Acoustic Stimulation↗

PubMed2005

Laparoscopic esophagectomy.

Minimally invasive esophagectomy is emerging as an alternative option to open esophagectomy for benign and malignant esophageal diseases. This article provides a detailed review of the history of minimally invasive esophagectomy and an update on the currently accepted techniques for minimally invasive esophagectomy and its outcomes.

Esophagectomy↗

PubMed2004

Current status of minimally invasive esophagectomy.

Minimally invasive esophagectomy is emerging as an option in the management of benign and malignant esophageal diseases. With minimally invasive esophagectomy, the conventional laparotomy is substituted with laparoscopy and the open thoracotomy with thoracoscopy. This article discusses the surgical techniques and outcomes for a variety of minimally invasive esophagectomy options.

Esophageal Neoplasms↗

PubMed2003

Effects of pneumoperitoneum on intraoperative pulmonary mechanics and gas exchange during laparoscopic gastric bypass.

BACKGROUND: Hypercarbia and elevated intraabdominal pressure resulting from carbon dioxide (CO2) pneumoperitoneum can adversely affect respiratory mechanics. This study examined the changes in mechanical ventilation, CO2 homeostasis, and pulmonary gas exchange in morbidly obese patients undergoing a laparoscopic or open gastric bypass (GBP) procedure. METHODS: In this study, 58 patients with a body mass index (BMI) of 40 to 60 kg/m2 were randomly allocated to laparoscopic ( n = 31) or open ( n = 27) GBP. Minute ventilation was adjusted to maintain a low normal arterial partial pressure of CO2 (PaCO2), low normal end-tidal partial pressure of CO2 (ETCO2), and low airway pressure. Respiratory compliance, ETCO2, peak inspiratory pressure (PIP), total exhaled CO2 per minute (VCO2), and pulse oximetry (SO2) were measured at 30-min intervals. The acid-base balance was determined by arterial blood gas analysis at 1-h intervals. The pulmonary gas exchange was evaluated by calculation of the alveolar dead space-to-tidal volume ratio (V(Dalv)/V(T)) and alveolar-arterial oxygen gradient (PAO2-PaO2). RESULTS: The two groups were similar in age, gender, and BMI. As compared with open GBP, laparoscopic GBP resulted in higher ETCO2, PIP, and VCO2, and a lower respiratory compliance. Arterial blood gas analysis demonstrated higher PaCO2 and lower pH during laparoscopic GBP than during open GBP ( p < 0.05). The V(Dalv)/V(T) ratio and PAO2-PaO2 gradient did not change significantly during laparoscopic GBP. Intraoperative oxygen desaturation (SO2 < 90%) did not develop in any of the patients in either group. CONCLUSIONS: Laparoscopic GBP alters intraoperative pulmonary mechanics and acid-base balance but does not significantly affect pulmonary oxygen exchange. Changes in pulmonary mechanics are well tolerated in morbidly obese patients when proper ventilator adjustments are maintained.

Acid-Base Equilibrium↗

PubMed2003

Optical breakdown versus filamentation in fused silica by use of femtosecond infrared laser pulses.

The competition between optical breakdown (OB) and laser-pulse filamentation (FL) in bulk fused silica is investigated by using a 1-kHz femtosecond infrared laser. We measure input powers corresponding to the threshold of OB and FL in terms of external focusing conditions. The results demonstrate that OB precedes FL for tight focusing, whereas for sufficiently long focal lengths FL takes places at a lower power than OB does.

Journal Article↗

PubMed2002

Duplex ultrasound assessment of femoral venous flow during laparoscopic and open gastric bypass.

BACKGROUND: Pneumoperitoneum (PP) and the reverse Trendelenburg (RT) position have been shown to decrease femoral blood flow, resulting in venous stasis. However the effects of PP and RT on femoral venous flow have not been evaluated in morbidly obese patients undergoing laparoscopic gastric bypass (GBP). We analyzed the effects of PP and RT on peak systolic velocity and the cross-sectional area of the femoral vein during laparoscopic and open GBP. We further examined the efficacy of intermittent sequential compression devices in reversing the reduction of femoral peak systolic velocity. METHODS: Thirty patients with a body mass index (BMI) of 40-60 were randomly allocated to under go either laparoscopic (n = 14) or open (n = 16) GBP. A duplex ultrasound examination of the femoral vein was performed at baseline, during PP and combined PP and RT in the laparoscopic group, and at baseline and during RT in the open group. The ultrasound exam was performed first without the use of sequential compression devices and then with the sequential compression devices inflated to 45 mmHg. RESULTS: The two groups were similar in age, sex, BMI, and calf and thigh circumferences. During laparoscopic GBP, PP resulted in a 43% decrease in peak systolic velocity and a 52% increase in the cross-sectional area of the femoral vein; the combination of PP and RT decreased peak systolic velocity to 57% of baseline and increased the femoral cross-sectional area to 121% of baseline. During laparoscopic GBP, the use of sequential compression devices during PP and RT partially reversed the reduction of femoral peak systolic velocity, but femoral peak systolic velocity was still lower than baseline by 38%. During open GBP, RT resulted in a 38% reduction in peak systolic velocity and a 69% increase in the cross-sectional area of the femoral vein; the use of sequential compression devices during RT partially reversed these changes by increasing femoral peak systolic velocity by 26%; however, it was still lower than baseline by 22%. CONCLUSIONS: Pneumoperitoneum and reverse Trendelenburg position during laparoscopic and open GBP are independent factors for the development of venous stasis. Combining the reverse Trendelenburg position with pneumoperitoneum during laparoscopic GBP further reduces femoral peak systolic velocity and hence increases venous stasis. The use of sequential compression devices was partially effective in reversing the reduction of femoral peak systolic velocity, but it did not return femoral peak systolic velocity to baseline levels.

Adult↗

PubMed2002

Effect of heated and humidified carbon dioxide gas on core temperature and postoperative pain: a randomized trial.

BACKGROUND: Intraoperative hypothermia is a common event during laparoscopic operations. An external warming blanket has been shown to be effective in preventing hypothermia. It has now been proposed that using heated and humidified insufflation gas can prevent hypothermia and decrease postoperative pain. Therefore, we examined the extent of intraoperative hypothermia in patients undergoing laparoscopic Nissen fundoplication using an upper body warming blanket. We also attempted to determine whether using heated and humidified insufflation gas in addition to an external warming blanket would help to maintain intraoperative core temperature or decrease postoperative pain. METHODS: Twenty patients were randomized to receive either standard carbon dioxide (CO2) gas (control, n = 10) or heated and humidified gas (heated and humidified, n = 10). After the induction of anesthesia, an external warming blanket was placed on all patients in both groups. Intraoperative core temperature and intraabdominal temperature were measured at 15-min intervals. Postoperative pain intensity was assessed using a visual analogue pain scale, and the amount of analgesic consumption was recorded. Volume of gas delivered, number of lens-fogging episodes, intraoperative urine output, and hemodynamic data were also recorded. RESULTS: There was no significant difference between the two groups in age, length of operation, or volume of CO2 gas delivered. Compared with baseline value, mean core temperature increased by 0.4 degrees C in the heated and humidified group and by 0.3 degrees C in the control group at 1.5 h after surgical incision. Intraabdominal temperature increased by 0.2 degrees C in the heated and humidified group but decreased by 0.5 degrees C in the control group at 1.5 h after abdominal insufflation. There was no significant difference between the two groups in visual analog pain scale (5.4 +/- 1.6 control vs 4.5 +/- 2.8 heated and humidified), morphine consumed (27 +/- 26 mg control vs 32 +/- 19 mg heated and humidified), urine output, lens-fogging episodes, or hemodynamic parameters. CONCLUSION: Heated and humidified gas, when used in addition to an external warming blanket, minimized the reduction of intraabdominal temperature but did not alter core temperature or reduce postoperative pain.

Adult↗

PubMed2002

Current status of laparoscopic gastric bypass.

Laparoscopic gastric bypass is emerging as a commonly performed procedure for the treatment of morbid obesity. This article discusses the indications for surgery, patient selection, surgical technique, management of complications, and outcomes of laparoscopic gastric bypass.

Gastric Bypass↗

PubMed2001

[Heavy white coats are not the cause of physicians' headaches and shoulder pain].

The weight of doctors' white coats was examined and correlated to the degree of headache and muscle pain in the shoulders. The coat weight of doctors was 1.5 kg (1.1 kg-1.9 kg) (median with 25%-75% in parenthesis). The highest weight was found in the coats of young physicians 2.0 kg (1.7 kg-2.2 kg), which was higher than those of young surgeons. No correlation was seen in the degree of headache and muscle pain in the shoulders. With the long walking distances in hospitals, it would seem that internal medicine is not only an intellectually, but also a physically, demanding job.

Female↗

PubMed2001

Comparative analysis of folding and substrate binding sites between regulated hexameric type II citrate synthases and unregulated dimeric type I enzymes.

We describe the first structure determination of a type II citrate synthase, an enzyme uniquely found in Gram-negative bacteria. Such enzymes are hexameric and are strongly and specifically inhibited by NADH through an allosteric mechanism. This is in contrast to the widespread dimeric type I citrate synthases found in other organisms, which do not show allosteric properties. Our structure of the hexameric type II citrate synthase from Escherichia coli is composed of three identical dimer units arranged about a central 3-fold axis. The interactions that lead to hexamer formation are concentrated in a relatively small region composed of helix F, FG and IJ helical turns, and a seven-residue loop between helices J and K. This latter loop is present only in type II citrate synthase sequences. Running through the middle of the hexamer complex, and along the 3-fold axis relating dimer units, is a remarkable pore lined with 18 cationic residues and an associated hydrogen-bonded network. Also unexpected was the observation of a novel N-terminal domain, formed by the collective interactions of the first 52 residues from the two subunits of each dimer. The domain formed is rich in beta-sheet structure and has no counterpart in previous structural studies of type I citrate synthases. This domain is located well away from the dimer-dimer contacts that form the hexamer, and it is not involved in hexamer formation. Another surprising observation from the structure of type II E. coli citrate synthase is the unusual polypeptide chain folding found at the putative acetylcoenzyme A binding site. Key parts of this region, including His264 and a portion of polypeptide chain known from type I structures to form an adenine binding loop (residues 299-303), are shifted by as much as 10 A from where they must be for substrate binding and catalysis to occur. Furthermore, the adjacent polypeptide chain composed of residues 267-297 is extremely mobile in our structure. Thus, acetylcoenzyme A binding to type II E. coli citrate synthase would require substantial structural shifts and a concerted refolding of the polypeptide chain to form an appropriate binding subsite. We propose that this essential rearrangement of the acetylcoenzyme A binding part of the active site is also a major feature of allostery in type II citrate synthases. Overall, this study suggests that the evolutionary development of hexameric association, the elaboration of a novel N-terminal domain, introduction of a NADH binding site, and the need to refold a key substrate binding site are all elements that have been developed to allow for the allosteric control of catalysis in the type II citrate synthases.

Amino Acid Sequence↗

PubMed2001

Cardiac function during laparoscopic vs open gastric bypass.

BACKGROUND: Hypercarbia and increased intraabdominal pressure during prolonged pneumoperitoneum can adversely affect cardiac function. This study compared the intraoperative hemodynamics of morbidly obese patients during laparoscopic and open gastric bypass (GBP). METHODS: Fifty-one patients with a body mass index (BMI) of 40-60 kg/m2 were randomly allocated to undergo laparoscopic (n = 25) or open (n = 26) GBP. Cardiac output (CO), mean pulmonary artery pressure (MPAP), pulmonary artery wedge pressure (PAWP), central venous pressure (CVP), heart rate (HR), and mean arterial pressure (MAP) were recorded at baseline, intraoperatively at 30-min intervals, and in the recovery room. Systemic vascular resistance (SVR) and stroke volume (SV) were also calculated. RESULTS: The two groups were similar in terms of age, weight, and BMI. Operative time was longer in the laparoscopic than in the open group (p < 0.05). The HR and MAP increased significantly from baseline intraoperatively, but there was no significant difference between the two groups. In the laparoscopic group, CO was unchanged after insufflation, but it increased by 5.3% at 2.5 h compared to baseline and by 43% compared to baseline in the recovery room. In contrast, during open GBP, CO increased significantly by 25% after surgical incision and remained elevated throughout the operation. CO was higher during open GBP than during laparoscopic GBP at 0.5 h and at 1 h after surgical incision (p < 0.05). During laparoscopic GBP, CVP, MPAP, and SVR increased transiently and PAWP remained unchanged. During open GBP, CVP, MPAP, and PAWP decreased transiently and SVR remained unchanged. There was no significant difference in the amount of intraoperative fluid administered during laparoscopic (5.5 +/- 1.6 L) and open (5.6 +/- 1.7 L) GBP. CONCLUSION: Prolonged pneumoperitoneum during laparoscopic gastric bypass does not impair cardiac function and is well tolerated by morbidly obese patients.

Adult↗

PubMed2001

BBG2Na an RSV subunit vaccine candidate intramuscularly injected to human confers protection against viral challenge after nasal immunization in mice.

Respiratory syncytial virus (RSV) is a major respiratory pathogen responsible for severe pulmonary disease. We have developed a parenterally administered vaccine, BBG2Na, which is currently in a phase III clinical trial. BBG2Na comprises residues 130--230 of RSV-A G protein (G2Na) fused to the BB carrier protein. In this study, we show that BBG2Na can be delivered by the nasal route and generates both mucosal and systemic antibody responses when co-administered with cholera toxin B or a newly described delivery system, zwittergent 3--14. We found that nasal BBG2Na administration protects against RSV challenge and does not induce lung immunopathology upon subsequent RSV challenge.

Administration, Intranasal↗

PubMed2001

Up-regulation of vascular endothelial growth factor in breast cancer cells by the heregulin-beta1-activated p38 signaling pathway enhances endothelial cell migration.

Heregulin (HRG) belongs to a family of polypeptide growth factors that bind to receptor tyrosine kinases ErbB3 and ErbB4. HRG binding induces ErbB3 and ErbB4 heterodimerization with ErbB2, activating downstream signal transduction. Vascular endothelial growth factor (VEGF) is a primary regulator of physiological angiogenesis and is a major mediator of pathological angiogenesis, such as tumor-associated neovascularization. In this study, we demonstrate that HRG-beta1 increased secretion of VEGF from breast cancer cells in a time- and dosage-dependent manner and that this increase resulted from up-regulation of VEGF mRNA expression via transcriptional activation of the VEGF promoter. Deletion and mutational analysis revealed that a CA-rich upstream HRG response element located between nucleotide-2249 and -2242 in the VEGF promoter mediated HRG-induced transcriptional up-regulation of VEGF. While investigating the downstream signaling pathways involved in HRG-mediated up-regulation of VEGF, we found that HRG activated extracellular signal-regulated protein kinases, Akt kinase, and p38 mitogen-activated protein kinase (MAPK). However, only the specific inhibitor of p38 MAPK (SB203580), not extracellular signal-regulated kinase inhibitor PD98059 nor the inhibitor of phosphatidylinositol 3-kinase-Akt pathway (Wortmannin), blocked the up-regulation of VEGF by HRG. The HRG-stimulated secretion of VEGF from breast cancer cells resulted in increased migration of murine lung endothelial cells, an activity that was inhibited by either VEGF-neutralizing antibody or SB203580. These results show that HRG can activate p38 MAPK to enhance VEGF transcription via an upstream HRG response element, leading to increased VEGF secretion and angiogenic response in breast cancer cells.

Breast Neoplasms↗

PubMed2001

Systemic coagulation and fibrinolysis after laparoscopic and open gastric bypass.

HYPOTHESIS: Laparoscopic gastric bypass (GBP) induces a postoperative hypercoagulable state that is similar or reduced compared with open GBP. SETTING: University hospital. PATIENTS: Between May 1999 and June 2000, 70 patients were randomly assigned to laparoscopic (n = 36) or open (n = 34) GBP. Deep venous thrombosis (DVT) prophylaxis consisted of antiembolism stockings and sequential pneumatic compression devices. MAIN OUTCOME MEASURES: Plasminogen, thrombin-antithrombin complex (TAT), prothrombin fragment 1.2 (F1.2), fibrinogen, D-dimer, antithrombin III (AT), and protein C levels were measured at baseline and at 1, 24, 48, and 72 hours postoperatively. A venous duplex examination of both lower extremities was performed preoperatively and between the third and fifth day postoperatively. RESULTS: The 2 groups were similar in age, weight, and body mass index. Plasminogen levels decreased, and TAT, F1.2, and fibrinogen levels increased after laparoscopic and open GBP. There was no significant difference in these levels between groups. D-dimer levels increased in both groups, but the levels were significantly higher after open GBP than after laparoscopic GBP (P<.01). Antithrombin III and protein C levels decreased in both groups. The reduction of AT (at 1 hour) and protein C (at 72 hours) was significantly less after laparoscopic GBP than after open GBP (P<.05). Postoperative venous duplex examination revealed DVT in 1 (2.9%) of 34 patients after open GBP but in none of 36 patients after laparoscopic GBP. One patient developed pulmonary embolism after open GBP. CONCLUSIONS: Laparoscopic GBP induces a hypercoagulable state similar to that of open GBP. Our findings suggest that DVT prophylaxis should be used during laparoscopic GBP as in open GBP.

Adult↗