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Biomedical subjects

J Ramakrishna

Publications and source records attributed to J Ramakrishna.

At least 19 recordsLinked to original sources
PubMed2000

Powder MAS NMR lineshapes of quadrupolar nuclei in the presence of second-order quadrupole interaction.

We derive a complete analytical solution for the powder magic angle spinning (MAS) nuclear magnetic resonance (NMR) lineshape in the presence of second-order quadrupole interaction, considering a radiofrequency (rf) pulse of finite width, a finite MAS frequency, and a non-zero asymmetry parameter. (Ix) is calculated using two approaches. The first applies time-dependent perturbation theory in the presence of the rf pulse and stationary perturbation theory (SPT) in its absence. The second is based on the Magnus expansion of the density matrix in the interaction representation during the pulse and SPT in its absence. We solve the problem in the laboratory frame using the properties of the Fourier transform and spin operators. Diagonalisation is not required. Both approaches agree well with each other under all conditions and also with the transition probability approach for the central transition. The Magnus expansion exists at all times and the effect of the non-secular terms is negligible. We describe an analytical method of averaging (Ix) over the Euler angles and simulate the 11B MAS NMR lineshapes for crystalline and vitreous B2O3. A critical analysis is given of all earlier calculations of the MAS NMR lineshape.

Boron Compounds↗
PubMed1997

Evaluation of post-exposure vaccination against rabies in cattle.

Post-exposure vaccination of bovines against rabies with three anti-rabies vaccines viz. BHK21 cell culture inactivated vaccine. "Raksharab", Vero cell culture vaccine and Semple's vaccine was studied with different schedules of vaccination. The mean RFFIT and ELISA titres of animals vaccinated with Raksharab and Vero cell culture vaccine reached a peak 95 days post-exposure (dpe). The animals vaccinated with Semple's vaccine showed maximum RFFIT and ELISA titres on 40 dpe and the titres were lower than those induced by tissue culture rabies vaccines. All the calves vaccinated with Raksharab and Vero cell culture vaccine were protected. One out of six calves vaccinated with Semple's vaccine died of rabies on 16 dpe. All the control animals died of rabies between 14 and 22 dpe. Raksharab schedule of vaccination on days 0, 4, 7, 14, 28 and 90 dpe was effective when compared with other vaccines with similar and different schedules. Tissue culture rabies vaccine is superior to nervous tissue vaccine in eliciting satisfactory immune response required to protect animals exposed to virulent rabies virus.

Animals↗
PubMed1996

Combined use of cyclosporine and azathioprine or 6-mercaptopurine in pediatric inflammatory bowel disease.

The aim of this study was to assess whether in steroid-resistant patients with pediatric inflammatory bowel disease (IBD) a combination of cyclosporine and azathioprine (or 6-mercaptopurine) could induce remission and subsequently permit maintenance on azathioprine/6-mercaptopurine as the sole immunosuppressive agent. Two boys and six girls (six with ulcerative colitis and two with Crohn's disease; ages 3-17 years) received 100-200 micrograms/kg/day cyclosporine intravenously and then 4-10 mg/kg/day orally. Doses were adjusted to achieve trough serum cyclosporine levels of 100-200 mu/L (Abbott's TDX assay). Seven of the eight patients received azathioprine/6-mercaptopurine, and all were given a 5-aminosalicylate preparation and corticosteroids. The latter drugs were continued and then tapered off as clinical status allowed. Cyclosporine was continued for 3-10 months in those who responded. In seven of eight patients, there was a rapid clinical response; one patient showed a transient response, but recurrent bleeding led to total colectomy 9 days after starting cyclosporine. Of the seven responders, three were able to discontinue prednisone and cyclosporine and are doing well on azathioprine at long-term follow-up (2-5 years). One who did not receive azathioprine/6-mercaptopurine maintained remission for 2 years after cyclosporine was stopped, one experienced a disease flare-up 5 months after start of cyclosporine treatment and required colectomy, one who did not tolerate 6-mercaptopurine had a flare-up during cyclosporine tapering and underwent surgery at 6 months, and one started to flare up with cyclosporine tapering at 6 months and was scheduled for surgery. No significant complications of treatment were observed. Seven patients had an initial response and four of them have so far not required surgery. These preliminary findings suggest that azathioprine/6-mercaptopurine can be used safely to maintain cyclosporine-induced remission in children with IBD.

Adolescent↗
PubMed1996

Therapeutic strategies for pediatric Crohn disease.

The main aims of therapy for inflammatory bowel disease (Crohn disease) in children and adolescents are (1) the induction and maintenance of remission, (2) the correction of nutrient deficits and (3) the restoration of growth and maturation. These goals are reached with the use of a combination of therapeutic methods, including pharmacologic agents, nutritional and psychological support, and surgical intervention. The commonly used drugs sulfasalazine, corticosteroids and metronidazole have all been shown to be safe and efficacious when given to children. Newer steroid preparations that are rapidly degraded either in the target tissue or elsewhere are being studied. Of these, budesonide currently shows promise as an efficacious drug with few side effects, but its use in children needs further study. Newer 5-amino-salicylate preparations such as Asacol have been shown to be effective in children, but the number of patients studied is small. Immunomodulatory drugs such as azathioprine and 6-mercaptopurine appear to be safe and efficacious for children; cyclosporine has been used infrequently to treat refractory Crohn disease in children. The use of other agents such as methotrexate, tacrolimus, monoclonal antibodies to cytokines, antibiotics and specific dietary products such as fish oils have not been intensively studied in children with Crohn disease. Nutritional therapy remains a mainstay of treatment because it corrects nutritional deficits, replaces losses and stimulates growth.

Adolescent↗
PubMed1995

Analytical treatment of the variable-angle sample spinning nuclear magnetic resonance spectra in the presence of the second-order quadrupole interaction. Determination of the quadrupole parameters and the chemical shift tensor.

The analytical expressions for the transition probability of the central transition of the variable-angle sample spinning nuclear magnetic resonance (VAS NMR) spectrum for non-integral spins in the presence of second-order quadrupole interactions are derived on the basis of the stationary perturbation theory. The modulating parameters of the VAS NMR spectrum due to the time-dependent part of the quadrupole energy are found to be different (asymmetry parameter eta > 0.1) from those obtained from the average Hamiltonian theory. Using the conditions for saddle points and local maxima, it has been observed that there is a range of values for sample spinning angle beta around 32, 44 and 72 degrees to obtain the single peak; the range width can indicate the value of eta. Analytical expressions for the single-peak positions corresponding to beta around 32, 44 and 72 degrees are derived in terms of quadrupole parameters and chemical shift tensor. Further, we have described an analytical method to find the principal values of the chemical shift tensor in addition to the quadrupole parameters, using VAS NMR. As an illustration, the quadrupole parameters are computed for Na2MoO4 and Na2SO4 and compared with the values available in the literature (computed from wide-line NMR and magic-angle sample spinning (MAS) NMR data using the position of peaks and shoulders). For Na2MoO4 the principal values of the chemical shift tensor are found to be +17.5, -12 and -6.5 ppm. The present method is accurate and easy to apply as it involves only the positions of peaks and not of shoulders.(ABSTRACT TRUNCATED AT 250 WORDS)

Magnetic Resonance Spectroscopy↗
PubMed1995

Analytical expression for the magic-angle spinning nuclear magnetic resonance line shape in the presence of the second-order quadrupole interaction for the non-zero asymmetry parameter and large sample rotation frequency.

An analytical expression for the magic-angle spinning nuclear magnetic resonance (MAS NMR) line shape function for the non-zero asymmetry parameter and large sample rotation frequency has been derived using the time-independent part of the quadrupole transition energy based on the stationary perturbation theory. The averaging over Euler angles in the case of a powdered sample is also done analytically, which is so far implemented in the literature by a numerical simulation procedure. While the peak positions obtained from analytical and numerical averaging procedures agree well, the peak heights are significantly different, showing the need for an analytical solution for the averaging over Euler angles, as this would otherwise lead to erroneous values for the quadrupole parameters. The MAS NMR line shape function derived in this paper can be compared directly with the experimental MAS NMR spectrum for the large sample rotation frequency, and the values of the quadrupole parameters can be obtained. We have also described a method of evaluating the quadrupole parameters for the small sample rotation frequency, using the peak heights and peak separation of the central band of the experimental MAS NMR spectrum and the MAS NMR line shape function derived in the present paper. As an example, the quadrupole parameters for vitreous B2O3 are computed.

Magnetic Resonance Spectroscopy↗
PubMed1995

Protein Hpn: cloning and characterization of a histidine-rich metal-binding polypeptide in Helicobacter pylori and Helicobacter mustelae.

Helicobacter pylori is a human gastrointestinal pathogen involved in gastritis, duodenal ulcers, and gastric neoplasia. This microorganism produces large amounts of a urease which, like all known ureases, has nickel in the active site. We have identified a protein in clinical isolates of H. pylori and an identical protein in the ferret pathogen Helicobacter mustelae that strongly binds Ni2+ and Zn2+. This protein has been named Hpn to emphasize its origins in H. pylori and its affinity for nickel. The encoding hpn gene, cloned and expressed in Escherichia coli ER1793, has an open reading frame (180 bp) that specifies a protein with a calculated molecular mass of 7,077 Da and with the same amino-terminal sequence as that of wild-type Hpn. The deduced sequence of Hpn consists of 60 amino acids, of which 28 (47%) are histidines. The hpn gene does not map with the urease gene cluster on the H. pylori chromosome. An Hpn-negative, isogenic H. pylori strain, generated by hpn gene deletion and grown on blood agar, had the same urease activity that wild-type cells did. Thus, the role of Hpn in helicobacters is unknown.

Amino Acid Sequence↗
PubMed1995

Inflammatory bowel disease in the pediatric patient.

Inflammatory bowel disease is now recognized as a common diagnosis in the pediatric age group. Inflammatory bowel disease has been diagnosed as early as the first few months of life. In addition to the usual gastrointestinal symptoms, diarrhea, abdominal pain, and rectal bleeding, children may exhibit prominent extraintestinal manifestations, such as growth failure, weight loss, anemia, and joint symptoms.

Abdominal Pain↗
PubMed1993

Duck hepatitis B virus (DHBV) infection in Indian domestic ducks: a pilot study.

One hundred and two apparently healthy Indian domestic ducks from the Poultry Research Station, Madras were screened for duck hepatitis B virus (DHBV) infection by; 1. screening for the duck hepatitis B virus surface antigen (DHBsAg) in their sera using hepatitis B virus (HBV) reagents, 2. screening for DHBsAg using specific duck hepatitis B virus (DHBV) reagents and 3. demonstration of DHBV DNA using DHBV DNA probe by dot blot hybridisation. While 5 ducks (4.9%) were consistently positive with HBV reagents, use of DHBV reagents showed a total of 4 ducks (including 3 of the above 5) to be positive for DHBsAg. DNA hybridisation showed 6 ducks to be positive for DHBV DNA. On clinical examination, 5 out of these 6 ducks did not reveal abnormalities, the other one showed hepatomegaly and ascites. Post-mortem studies showed the presence of nodules on the surface of the liver in all 5 which were positive with HBV reagents including the one with hepatomegaly. On histopathological evaluation, they were found to be hepatocellular carcinoma with or without bile duct carcinoma. The present study is a pilot report on the occurrence of DHBV infection in Indian domestic ducks and the possibility of antigenic cross reactivity between human HBV and duck hepatitis B virus antigens.

Animals↗
PubMed1992

Health, illness, and immigration. East Indians in the United States.

East Indian immigrants to the United States represent the diversity in religion, language, and culture that exists in India, so it is difficult to make unequivocal statements about their health beliefs and behaviors. Despite the diversity, an understanding of Ayurvedic humoral concepts of health and illness provides a key to some pervasive and persistent ideas and practices. India has a pluralistic medical system in which Western medicine, which is increasingly popular for some ailments, is one option among many. Even those who are familiar with the "Western" medical system in India may find American medicine alien.

Attitude to Health↗
PubMed1991

Guineaworm control case study: planning a multi-strategy approach.

The planned global eradication of guineaworm (dracunculiasis) offers opportunities to learn about relatively complicated disease control situations. Unlike smallpox, which was eradicated over 10 years ago through immunization, the guineaworm problem has no one solution, but must rely on a variety of technologies to protect, treat or replace existing unsafe community water supplies which harbour the disease. Experiences in rural Nigeria have shown that a multi-strategy approach is necessary to account for differences in geographical settlement patterns, local culture and beliefs, geology of the area, economy of the villages and political clout of town leaders among the five major segments of the community. Through a self-help primary health care programme, residents of the Idere community were able to dig wells, produce and distribute cloth water filters bringing a reduction in disease incidence in some areas. It was also seen that generally low standards of living exacerbated by scattered outlying settlements made self-help difficult. Unfortunately occasional government and private efforts did not succeed because of a lack of community participation. Programme planners must involve the consumers in diagnosing these community characteristics and in planning, supervising and maintaining the resulting projects. The multi-strategy approach will help avoid wasted resources and false expectations that arise when project staff attempt to apply a "magic bullet" solution to a complex problem.

Case-Control Studies↗