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Biomedical subjects

P Ravindran

Publications and source records attributed to P Ravindran.

At least 19 recordsLinked to original sources
PubMed2006

Genotypic changes in human immunodeficiency virus type 1 envelope glycoproteins on treatment with the fusion inhibitor enfuvirtide and their influence on changes in drug susceptibility in vitro.

BACKGROUND: Previous studies have established the importance of substitutions at amino acids 36-45 of HIV-1 gp41 in the development of viral resistance to the peptide fusion inhibitor enfuvirtide. However, the influence of other loci in the HIV-1 envelope is not well established. OBJECTIVE: To identify positions showing genotypic changes that are associated with particularly high levels of changes in enfuvirtide susceptibility. STUDY DESIGN: We examined full-length baseline and on treatment sequences of gp120 and gp41 for isolates from 369 patients in Phase III studies of enfuvirtide, including 281 patients receiving ENF+OB and 88 patients receiving OB alone. Individual changes in gp41 and gp120 were evaluated for correlations with on treatment phenotype changes by analysis of variance (ANOVA). This modeling was done with (two-way) and without (one-way) ANOVA adjusting for the effects of any changes in gp41 amino acids 36-45 modeled as a single variable (ANY(36-45)). Positions displaying significance levels of p<0.05 by either one- or two-way ANOVA were then studied by multi-way ANOVA (stepwise regression). RESULTS: In addition to changes at gp41 amino acids 36-45, changes at three positions in the HR2 domain (126, 129 and 133) occurred significantly more often in patients undergoing virologic failure on enfuvirtide. However, ANY(36-45) alone accounted for slightly more than 90% of the variation in phenotype explained by the ANOVA models. Relative to ANY(36-45) alone, significant increases in the geometric mean of the fold-change in inhibitory concentration (19.6-236.3-fold higher) were observed for amino acid changes at positions gp41: 18, 42,126, 247, 256 and 312; gp120: 330, 389 and 424 and significant reductions (18.8-29.7-fold lower) for gp41: 3, 46, 165, 232 and 324. CONCLUSIONS: This study represents a statistical approach to highlight positions in HIV envelope that undergo mutations in the presence of enfuvirtide. Several of the identified positions have been implicated in the viral fusion process by other studies. The specific impact of positions 330. Three hundred and eighty-nine and 424 on viral fusion kinetics remains to be studied further by site-directed mutagenesis experiments.

Amino Acid Sequence↗
PubMed2005

Topography of the potential energy hypersurface and criteria for fast-ion conduction in perovskite-related A2B2O5 oxides.

We discuss the importance of the topography of the potential energy hypersurface for the ionic conductivity of perovskite-related A(2)B(2)O(5) oxides. A correlation between the energetic preference of the cations for different coordination geometries and the ionic conductivity is proposed based on a first principles periodic density functional theory study of selected possible structures for Ba(2)In(2)O(5), Sr(2)Fe(2)O(5), Sr(2)Mn(2)O(5), and La(2)Ni(2)O(5). There are a large number of low-energy local minima on the potential energy hypersurfaces of the two first compounds due to an energetic preference for BO(4) tetrahedra. Tetrahedral environments are energetically unfavorable for Mn(III) in Sr(2)Mn(2)O(5) and for Ni(II) in La(2)Ni(2)O(5), and the number of low-energy configurations is relatively low in these two cases. Consistent with our findings, in contrast to Sr(2)Fe(2)O(5) and Ba(2)In(2)O(5), Sr(2)Mn(2)O(5) and La(2)Ni(2)O(5) do not exhibit transitions to disordered phases on heating, and there appear to be no reports of enhanced ionic conductivity for these compounds. Thus we suggest that the possibility of many different oxygen orderings associated with a variety of low-energy connectivity schemes within tetrahedral layers such as in the brownmillerite-based structures of Sr(2)Fe(2)O(5) and Ba(2)In(2)O(5) is a prerequisite for high ionic conductivity in perovskite-related A(2)B(2)O(5) oxides.

Journal Article↗
PubMed2004

Assessment of allergenicity to Mallotus phillipensis pollen in atopic patients in India: a new allergen.

OBJECTIVE: Pollen grains of the Euphorbiaceae family are well known causative agents of respiratory allergies in India, European countries and USA. Mallotus phillipensis belongs to the same family and may have some common allergenic properties. It has thus been evaluated for the first time in Indian population for its pollinosis causing properties. METHODS: Pollen antigen of Mallotus phillipensis (MP) was extracted and characterized for its protein components by biochemical methods. Pollinosis potency of crude extract of MP pollen was evaluated by skin prick test on population residing in different parts of India. Specific IgE binding characteristics of the extract were determined by ELISA and Immunoblot. RESULTS: Marked skin reactivity in 5.7% atopic population was recorded and subjects constituting 23.8% of the total patients tested showed skin sensitivity to the MP pollen antigen. Significantly raised specific IgE against MP pollen were recorded in 50% of the skin test positive patients. A number of protein bands were detected in a wide Molecular weight range as well as in acidic pI range, by SDS-PAGE and IEF, respectively. A total 11 protein fractions were detected by the specific IgE antibodies on immunoblotting with patient's sera and were considered allergenic. CONCLUSION: Patients from different geographical regions have shown sensitization to MP pollen antigen. Many proteins have similar molecular weights and pI as other allergenic members of the family (Ricinus communis and Putranjiva roxburghii) found in India, which constitutes a good reason for studying cross reactivity among the members of family Euphorbiaceae, in the future.

Allergens↗
PubMed2003

Tailor-made electronic and magnetic properties in one-dimensional pure and Y-substituted Ca3Co2O6.

Full-potential density-functional calculations show that the electronic structure of one-dimensional ferrimagnetic Ca3Co2O6 varies from metal to half metal to insulator as its magnetic ordering changes from the ferrimagnetic through the ferromagnetic to the paramagnetic state. The present Letter is the first to establish the occurrence of half metallicity in one-dimensional oxides. Moreover, the electronic and magnetic properties of this material can be tuned by substitution of Y for Ca, as shown by our detailed study on Ca(3-x)YxCo2O6 (x = 0, 0.3, 0.75, and 1). The Co ions are in two different valence states [Co4+ (low-spin) and Co2+ (high-spin)], and hence the occurrence of charge ordering in addition to spin ordering is established. For specific Y concentrations we predict a rarely seen combination of ferromagnetic and insulating behavior.

Journal Article↗
PubMed2002

Pressure-induced structural transitions in MgH2.

The stability of MgH2 has been studied up to 20 GPa using density-functional total-energy calculations. At ambient pressure alpha-MgH2 takes a TiO2-rutile-type structure. alpha-MgH2 is predicted to transform into gamma-MgH2 at 0.39 GPa. The calculated structural data for alpha- and gamma-MgH2 are in very good agreement with experimental values. At equilibrium the energy difference between these modifications is very small, and as a result both phases coexist in a certain volume and pressure field. Above 3.84 GPa gamma-MgH2 transforms into beta-MgH2, consistent with experimental findings. Two further transformations have been identified at still higher pressure: (i) beta- to delta-MgH2 at 6.73 GPa and (ii) delta- to epsilon-MgH2 at 10.26 GPa.

Journal Article↗
PubMed2002

Violation of the minimum h-h separation "Rule" for metal hydrides.

Using gradient-corrected, full-potential, density-functional calculations, including structural relaxations, it is found that the metal hydrides RTInH1.333 (R=La, Ce, Pr, or Nd; T= Ni, Pd, or Pt) possess unusually short H-H separations. The most extreme value (1.454 A) ever obtained for metal hydrides occurs for LaPtInH1.333. This finding violates the empirical rule for metal hydrides, which states that the minimum H-H separation is 2 A. The paired, localized, and bosonic nature of the electron distribution at the H site are polarized towards La and In which reduces the repulsive interaction between negatively charged H atoms. Also, R-R interactions contribute to shielding of the repulsive interactions between the H atoms.

Journal Article↗
PubMed2000

Dosimetric study of the narrow beams of 60Co teletherapy unit for stereotactic radiosurgery.

This study explores the possibility of using a telecobalt unit for radiosurgery. A dosimetric study was performed for the narrow beam of Cobalt 60 (60Co) unit with circular radiation fields in diameters of 11, 17, 20, 27, 32, 35, 40, and 44 mm. Percentage depth dose and off-axis ratio were measured with ion chamber and radiographic film. The tissue air ratio values derived from measurements agreed well with the calculated values for all cone sizes and depths, ranging from the depth of maximum ionization of 24 cm in water. A quantitative evaluation of treatment plans with 60Co and 6-MV photon beams was carried out. The penumbra of the narrow beam of 60Co was larger than that of the 6-MV beam by 1.3 mm on average. This difference in penumbra can be attributed to the large source size of 60Co units. The feasibility of using narrow-beam 60Co for stereotactic radiosurgery/radiotherapy is discussed.

Cobalt Radioisotopes↗
PubMed1999

Unusual radiological presentation and rapid fatal progression of invasive pulmonary aspergillosis in an immunocompetent young patient.

Invasive aspergillosis occurs very rarely in immunocompetent hosts. We describe a 21-year-old female with no obvious immunosuppression or underlying lung disease, who presented with minimal symptoms and bilateral hilar prominence on chest X-ray. Invasive aspergillosis was diagnosed on an open lung biopsy. She deteriorated in the ensuing 2 weeks and died of a sudden massive haemoptysis. This initial radiological abnormality and the rapid clinical course of the disease in young immunocompetent patients have not been previously reported.

Adult↗
PubMed1998

Reductions in hospital use from self management training for chronic asthmatics.

The purpose of this study was to assess the impact of asthma Self Management Training on the health status and resource use of patients with chronic asthma. The study consisted of a randomized control design of chronic asthmatic patients in a tertiary care center in India. The intervention group (153 patients) received four training sessions in addition to the regular care provided to the control group (150 patients). Health status and resource use were measured at baseline and over a one year follow-up period. The intervention group had significantly better health status (measured by breathing ability), fewer productive days lost, and lower resource use (hospitalizations and emergency room visits) than the control group. Total annual costs (direct and indirect) were also lower, though physician costs were not included in the assessment. Therefore, incorporation of asthma Self Management Training as part of clinical management of asthma can result in improvements in health status and reductions in hospital use.

Adolescent↗
PubMed1993

Concurrent catamenial hemothorax and hemopneumothorax.

We describe a case of catamenial hemothorax and hemopneumothorax occurring on both sides simultaneously; the patient responded remarkably with danazol therapy. To our knowledge, this is previously unreported in the literature.

Adult↗
PubMed1985

Anatomical factors influencing fixation of endocardial pacing leads in the right ventricle.

The anatomical factors influencing fixation of endocardial pacing leads were studied in 50 hearts. Many variations were found in the anterior, posterior and septal papillary muscles, interpapillary connections, and the moderator band. Those variations conducive to lead fixation are illustrated. Vertical bands of muscle that could influence lead fixation were seen inside the right ventricle. Variations in the conus papillary muscle and right ventricular outflow tract that facilitate lead fixation are also illustrated. In a few hearts, attention is drawn to slender support of the anterior cusp of the tricuspid valve.

Journal Article↗