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Biomedical subjects

H Singh

Publications and source records attributed to H Singh.

At least 73 records · Page 4Linked to original sources
PubMed2001

Projectile cylinder accidents resulting from the presence of ferromagnetic nitrous oxide or oxygen tanks in the MR suite.

OBJECTIVE: The purpose of this study is to alert MR users to the potentially lethal consequences of projectile cylinder accidents in the MR environment. CONCLUSION: Projectile cylinder tank accidents still occur and may be increasing, despite adherence to screening policies before MR imaging and safety education of hospital personnel. Four of the last five accidents at our institutions occurred within the past 3 years.

Accidents↗
PubMed2000

Regulation of B lymphocyte and macrophage development by graded expression of PU.1.

The ets family transcription factor PU.1 is required for the development of multiple lineages of the immune system. Using retroviral transduction of PU.1 complementary DNA into mutant hematopoietic progenitors, we demonstrate that differing concentrations of the protein regulate the development of B lymphocytes as compared with macrophages. A low concentration of PU. 1 protein induces the B cell fate, whereas a high concentration promotes macrophage differentiation and blocks B cell development. Conversely, a transcriptionally weakened mutant protein preferentially induces B cell generation. Our results suggest that graded expression of a transcription factor can be used to specify distinct cell fates in the hematopoietic system.

Animals↗
PubMed2000

A school and community outbreak of tuberculosis in Auckland.

AIM: To describe a school and community outbreak of tuberculosis in South Auckland in 1997/8. METHODS: Cases were diagnosed according to national guidelines at Middlemore, Green Lane and Starship Hospitals. Public health follow-up was conducted by Auckland Healthcare. RESULTS: Twelve cases were diagnosed during the outbreak. Nine cases were from the same South Auckland secondary school; six reported no association outside school. Three cases were in younger children who had close household contact with two of the school cases. Nine cases (including eight from the school) had identical Mycobacterium tuberculosis isolates on restriction fragment length polymorphism testing. No microbiological culture was obtained from the three remaining cases. Contact investigation detected five of the cases. Chemoprophylaxis was prescribed for twenty-six school students, two adult staff, and nine household contacts. CONCLUSION: This is the first published account of a tuberculosis outbreak in a New Zealand school setting for decades. Recognition of the outbreak was delayed. DNA fingerprinting played a valuable role in the investigation. The source case may have been a school student. The social impact of the outbreak and preventability with routine adolescent BCG vaccination are discussed.

Adolescent↗
PubMed2000

Creation of radiopaque thrombi for in vivo experiments.

PURPOSE: A number of percutaneous thrombectomy devices are undergoing investigation for treatment of patients with venous thromboembolism. Use of radiopaque thrombus to monitor thrombus delivery and assess thrombectomy has been previously reported. The purpose of this project was to quantitatively test the effect of mixing different ratios of blood and contrast material to facilitate maximum thrombus formation and radiopacity. MATERIALS AND METHODS: The following ratios of blood and contrast material were mixed: 2 mL blood to 8 mL contrast material (ratio = 0.25), 4 mL blood to 6 mL contrast material (ratio = 0.67), 6 mL blood to 4 mL contrast material (ratio = 1.5), and 8 mL blood to 2 mL contrast material (ratio = 4). Contrast material was added at day 0, 3, or 6. Each sample received one of two ionic contrast agents to opacify the clots. At day 14, thrombus mass and opacity were determined. RESULTS: Three combinations of blood and contrast material produced maximum thrombus and radiopacity. These were sodium iothalamate 30% with a ratio of 4 with contrast material added on day 0 and sodium iothalamate 60% with a ratio of 1.5 with contrast material added on day 3 or 6. CONCLUSIONS: When forming radiopaque thrombi, significant differences can result from the ratio of blood to contrast material used. Contrast material type can also affect radiopacity and mass formed. The use of optimal ratios of blood to contrast material should maximize device evaluation with minimal wasting of valuable resources such as test subjects, physician time, and equipment.

Contrast Media↗
PubMed2000

Rheological properties of milk gels formed by a combination of rennet and glucono-delta-lactone.

The effects of heat treatment of milk, and a range of rennet and glucono-delta-lactone (GDL) concentrations on the rheological properties, at small and large deformation, of milk gels were investigated. Gels were made from reconstituted skim milk at 30 degrees C, with two levels each of rennet and GDL. Together with controls this gave a total of sixteen gelation conditions, eight for unheated and eight for heated milk. Acid gels made from unheated milks had low storage moduli (G') of < 20 Pa. Heating milks at 80 degrees C for 30 min resulted in a large increase in the G' value of acid gels. Rennet-induced gels made from unheated milk had G' values in the range approximately 80-190 Pa. However, heat treatment severely impaired rennet coagulation: no gel was formed at low rennet levels and only a very weak gel was formed at high levels. In gels made with a combination of rennet and GDL unusual rheological behaviour was observed. After gelation, G' initially increased rapidly but then remained steady or even decreased, and at long ageing times G' values increased moderately or remained low. The loss tangent (tan delta) of acid gels made from heated milk increased after gelation to attain a maximum at pH approximately 5.1 but no maximum was observed in gels made from unheated milk. Gels made by a combination of rennet and GDL also exhibited a maximum in tan delta, indicating increased relaxation behaviour of the protein-protein bonds. We suggest that this maximum in tan delta was caused by a loosening of the intermolecular forces in casein particles caused by solubilization of colloidal calcium phosphate. We also suggest that in combination gels made from unheated milk a low value for the fracture stress and a high tan delta during gelation indicated an increased susceptibility of the network to excessive large scale rearrangements. In contrast. combination gels made from heated milk formed firmer gels crosslinked by denatured whey proteins and underwent fewer large scale rearrangements.

Animals↗
PubMed2000

Formation of new protein structures in heated mixtures of BSA and alpha-lactalbumin.

The heat-induced protein-protein interactions of alpha-lactalbumin (alpha-La) and bovine serum albumin (BSA), dispersed in a pH 6.8, 10% whey protein concentrates (WPC) permeate, were followed using alkaline and sodium dodecyl sulfate (SDS) 1D and 2D polyacrylamide gel electrophoresis (PAGE) and size-exclusion high-performance liquid chromatography (SE-HPLC). Heated (75 degrees C) 5% BSA solution contained large disulfide-bonded BSA aggregates, although some monomer BSA (SDS-monomeric BSA) could be dissociated from the aggregates by SDS. In contrast, similarly heated alpha-La solutions contained small quantities of several monomeric forms of alpha-La and dimeric alpha-La but no large aggregates. When 10% solutions of 1:1 (w/w) mixtures of alpha-La and BSA were heated, large disulfide-bonded aggregates and SDS-monomeric BSA and alpha-La were present. However, heated 2% mixtures contained more modified alpha-La monomers, alpha-La-dimers, and alpha-La-trimers, fewer large disulfide-bonded aggregates, and less SDS-monomeric alpha-La or BSA. These results suggest that BSA forms disulfide-bonded aggregates that contain available thiol groups that can catalyze the formation of differently structured alpha-La monomers, dimers, higher polymers, and adducts of alpha-La with BSA.

Animals↗
PubMed2000

Characterization of commercial and experimental sodium caseinates by multiangle laser light scattering and size-exclusion chromatography.

A range of sodium caseinate samples were characterized by a multiangle laser light scattering (MALLS) system or by the use of MALLS as an on-line detector with size-exclusion chromatography (SEC). Sodium caseinate solutions, analyzed using a MALLS system alone, gave weight-average molar mass (M(w)) values in the range 1200-4700 kDa and z-average root-mean-square radius (R(g)) values ranged from approximately 50 to 120 nm. When these solutions were ultracentrifuged at 90000g for 1 h, a cloudy top layer was formed; the subnatant was carefully removed and analyzed by SEC-MALLS. The M(w) values were found to be in the range approximately 30-575 kDa, and R(g) values ranged from approximately 22 to 49 nm. During SEC, the MALLS system detected some very large-sized material that eluted close to the void volume; this material was hardly detected by the concentration detectors, i.e., ultra-violet (UV) and differential refractive index (DRI). The intensity of the light scattering (LS) signal from this very large sized material was greatly reduced in the subnatant. SEC of sodium caseinate samples revealed two main peaks with M(w) of approximately 420-750 kDa and 39-69 kDa, respectively. The R(g) values were very large for a protein molecule, and initial calculations suggested that the shape of caseinate molecules was likely to be highly elongated.

Caseins↗
PubMed2000

Influence of calcium, magnesium, or potassium ions on the formation and stability of emulsions prepared using highly hydrolyzed whey proteins.

Oil-in-water emulsions (4 wt % soy oil) containing 4 wt % whey protein hydrolysate (WPH) (27% degree of hydrolysis) and different levels of calcium, magnesium, or potassium chloride were prepared in a two-stage homogenizer. Other emulsions containing 4 wt % WPH but including 0.35 wt % hydroxylated lecithin and different levels of the above minerals were similarly prepared. The formation and stability of these emulsions were determined by measuring oil droplet size distributions using laser light scattering and by confocal scanning laser microscopy and a gravity creaming test. Both lecithin-free and lecithin-containing emulsions showed no change in droplet size distributions with increasing concentration of potassium in the range 0-37.5 mM. In contrast, the diameter of emulsion droplets increased with increasing calcium or magnesium concentration >12.5 mM. Emulsions containing hydroxylated lecithin were more sensitive to the addition of calcium or magnesium than the lecithin-free emulsions. Storage of emulsions at 20 degrees C for 24 h further increased the diameter of droplets and resulted in extensive creaming in emulsions containing >25 mM calcium or magnesium. It appears that both flocculation and coalescence processes were involved in the destabilization of emulsions induced by the addition of divalent cations.

Calcium↗
PubMed2000

Carcinoma of the gallbladder--is it a sequel of typhoid?

Gallbladder diseases, including carcinoma, are common in the northern part of India and so are Salmonella typhi infection and typhoid carrier state. This study was aimed to find out the association of typhoid carrier state in patients with cholelithiasis, carcinoma of the gallbladder, and controls. The three groups are comparable in age and sex composition. This is the first study of its kind from an area of high endemicity for both typhoid infection and carcinoma of the gallbladder. A case-control study was carried out to detect typhoid carrier state among the patients with biliary diseases and healthy controls, using indirect haemagglutination assay measuring antibodies against highly purified S. typhi Vi polysaccharide antigen. A significantly high Vi positivity was observed in patients with gallbladder carcinoma (29.4%) compared to controls (5%) (chi2 = 6.325, P < 0.004, OR = 7.19) and patients with cholelithiasis (10.7%) (chi2 = 5.066, P < 0.01, OR = 3.86). There is 8.47 times more risk of developing carcinoma of the gallbladder in culture-positive typhoid carriers than the noncarriers. The present study suggests the typhoid carrier state to be one of the possible mechanisms of gallbladder carcinogenesis.

Adult↗
PubMed2000

A replication-deficient rSV40 mediates liver-directed gene transfer and a long-term amelioration of jaundice in gunn rats.

BACKGROUND & AIMS: In the quest for a recombinant viral vector for liver-directed gene therapy that would permit both prolonged and efficient transgene expression in quiescent hepatocytes in vivo and repeated administration, we evaluated a recombinant simian virus 40 (rSV40). METHODS: The rSV40 was generated through replacement of the DNA encoding for the T antigens (Tag) by the coding region of human bilirubin-uridine 5'-diphosphate-glucuronosyl-transferase (BUGT) complementary DNA (SV-hBUGT). Helper-free rSV40 units were generated at infectious titers of 5 x 10(9) to 1 x 10(10) infectious units (IU)/mL in a Tag-producing packaging cell line (COS-7 cells). RESULTS: After 1, 3, or 7 daily infusions of 3 x 10(9) IU of SV-hBUGT through an indwelling portal vein catheter in bilirubin-UGT-deficient jaundiced Gunn rats, mean serum bilirubin concentrations decreased by 40%, 60% and 70%, respectively, in 3 weeks and remained at those levels throughout the duration of the study (40 days). Results of liver biopsies from SV-hBUGT-treated Gunn rats, but not from controls, were positive for human BUGT DNA, messenger RNA, and protein. Bilirubin-UGT activity in liver homogenates was 8%-12% of normal, and bilirubin glucuronides were excreted in bile. Immunostaining showed that >50%-60% of hepatocytes stably expressed the transgene. Portal vein infusion of an rSV40 expressing hepatitis B surface antigen (HBsAg) in a naive Gunn rat and a Gunn rat that had received 7 injections of SV-BUGT resulted in approximately equal levels of hepatic expression of HBsAg, indicating that multiple inoculations of SV-BUGT did not elicit neutralizing antibodies. Plasma alanine aminotransferase levels and liver histology remained normal despite repeated injections of rSV40. CONCLUSIONS: rSV40 vectors may represent a significant advance toward gene therapy for metabolic diseases.

Animals↗
PubMed2000

Hysteresis studies in a noisy autoassociative neural network

We define magnetization for a noisy autoassociative neural network driven by an external periodic field. Numerical simulations are carried out to investigate the effect of drive amplitude and frequency and noise strength on the area of the hysteresis loop. We observe that in the presence of weak periodic signal, the network exhibits a maximum in the hysteresis loop area at a nonzero noise intensity indicating maximum synchronization between the periodic signal and the response. It also goes through a maximum as a function of signal frequency.

Journal Article↗
PubMed2000

Stochastic resonance without an external periodic drive in a simple prey-predator model

We have investigated the effect of noise on a simple prey-predator model where the oscillations are triggered by the internal dynamics of the system without the aid of any external periodic drive. We report the occurrence of stochastic resonancelike behavior in this system, which does not have a threshold or a potential barrier, in the absence of an external drive.

Journal Article↗