Search PubMed⌕ Search

Biomedical subjects

S Radhakrishnan

Publications and source records attributed to S Radhakrishnan.

At least 19 recordsLinked to original sources
PubMed2006

Molecular orbital calculations on polythiophenes containing heterocyclic substituents: effect of structure on electronic transitions.

Molecular orbital calculations have been performed on thiophene oligomers bearing heterocyclic substituents at the third position in order to understand the interplay of effects such as the nature of substituent, skeletal substitution pattern, heteroatom identity, etc. on electronic transitions. The geometry optimization was carried out using the semiempirical AM1 method, and the electronic transitions predicted for the oligomers were extrapolated for polymers using an oligomeric approach. The experimentally determined optical transitions were found to follow the predicted trend of electronic transitions of monomers and polymers.

Electrochemistry↗
PubMed2006

p27(SJ), a novel protein in St John's Wort, that suppresses expression of HIV-1 genome.

Transcription of the HIV-1 genome is controlled by the cooperation of viral regulatory proteins and several host factors which bind to specific DNA sequences within the viral promoter spanning the long terminal repeat, (LTR). Here, we describe the identification of a novel protein, p27(SJ), present in a laboratory callus culture of Hypericum perforatum (St John's Wort) that suppresses transcription of the HIV-1 genome in several human cell types including primary culture of microglia and astrocytes. p27(SJ) associates with C/EBPbeta, a transcription factor that regulates expression of the HIV-1 genome in macrophages and monocytic cells, and the viral transactivator, Tat. The association of p27(SJ) with C/EBPbeta and Tat alters their subcellular localization, causing their accumulation in the perinuclear cytoplasmic compartment of the cells. Fusion of a nuclear localization signal to p27(SJ) forces its entry into the nucleus and diminishes the capacity of p27(SJ) to suppress Tat activity, but does not alter its ability to suppress C/EBPbeta activation of the LTR. Results from binding assays showed the inhibitory effect of p27(SJ) on C/EBPbeta interaction with DNA. Finally, our results demonstrate that expression of p27(SJ) decreases the level of viral replication in HIV-1-infected cells. These observations suggest the potential for the development of a therapeutic advance based on p27(SJ) protein to control HIV-1 transcription and replication in cells associated with HIV-1 infection in the brain.

Astrocytes↗
PubMed2006

Immunomodulation using the recombinant monoclonal human B7-DC cross-linking antibody rHIgM12.

A patient with Waldenstrom's macroglobulinaemia expresses a high titre IgM antibody in serum that binds both mouse and human dendritic cells (DC) in a B7-DC (PD-L2)-dependent manner. We have reported previously that purified antibody from patient serum activates immature and mature DC in vitro, enhancing the ability of these professional antigen-presenting cells to activate naive T cells, take up antigen, resist a cytokine-depleted environment and secrete immunomodulatory cytokines, such as interleukin (IL)-6 and tumour necrosis factor (TNF)-alpha. Systemic treatment of experimental animals with this antibody induces potent anti-melanoma immunity and modulates protectively the recall response against antigen challenge through the airway in an experimental model of inflammatory airway disease. Here we describe a monoclonal IgM antibody derived from this serum immunoglobulin that recapitulates each of these earlier observations, providing direct evidence that M protein from the Waldenstrom's patient mediates these potent immunomodulatory effects. Furthermore, cell lines expressing this recombinant form of the human antibody provide the basis for developing this reagent for clinical application.

Amino Acid Sequence↗
PubMed2005

Brain tissue phantoms for optical near infrared imaging.

In this study, solid, stable, and cost-effective optical phantoms of scalp-skull, white matter and grey matter are developed by inverse method. To begin with, to obtain a range of optical parameters, absorption and reduced scattering coefficients (mu(a) and mu(s)', respectively), 20 homogeneous phantoms were made of paraffin wax by using optically contrast black and highly scattering white colouring materials in different combination. By comparing the measured reflectance values for each phantom got from the four channel reflectometer with that obtained from steady-state diffusion equation, the values of mu(a) and mu(s)' were determined. Next, phantoms which exhibit specific optical properties of scalp-skull, white and grey matter are developed iteratively by comparing actual reflectance measurements got by adjusting the colour concentration with the predicted reflectance values from the diffusion equation. This is done as follows: to obtain mu(a) of 0.04 mm(-1) for scalp-skull, 9.5 mg of black dye per 100 ml of wax added since more attenuation of light occurs in bone tissue. To obtain a mu(s)' 6.0 mm(-1) for white matter in brain tissue, 190 mg of white dye per 100 ml of wax was used to facilitate more scatter of light. The colour concentrations of phantoms were then adjusted to obtain the predetermined values of optical parameters for scalp-skull, grey and white matter.

Animals↗
PubMed2005

Quantum chemical studies on polythiophenes containing heterocyclic substituents: effect of structure on the band gap.

Color tuning by the tailoring of substituents at the 3-position of thiophene is very encouraging, and comparative experimental and theoretical studies proved to be powerful in the search for a suitable design for the above. Since the novel polythiophene-based materials substituted with five-membered/six-membered ring containing sulphur and nitrogen at different positions are proven to be potential candidates for electron-transporting hole blocking functions, the structure-property relationship of these systems have been focused in the present study. Molecular-orbital calculations are applied to obtain the optimized geometries and band gaps of the thiophene oligomers. An oligomeric approach has been implemented for calculating the band gaps, and the theoretically obtained band gaps for the different model compounds are compared. Density-functional theory B3LYP6-31G* predicted band-gap values are compared with the experimental band gaps obtained from optical-absorption edge. The predicted values show little deviations from experimental band gaps, but the trend in band gap is found to be the same in experimental and theoretical results in most of the cases. Hence, this study illustrates the usefulness of quantum-mechanical calculations in understanding the effects of various structural parameters on optical band gap.

Journal Article↗
PubMed2005

Repeat survey of current practice regarding corticosteroid prophylaxis for patients at increased risk of adverse reaction to intravascular contrast agents.

AIM: To compare the findings of a survey undertaken by us in 2002 regarding steroid premedication given in radiology departments to reduce the risk of adverse reactions in patients at increased risk of intravascular contrast media reactions with a similar survey published in 1994 by R. Seymour et al. The high risk patients considered in our survey were patients with history of asthma, drug allergies, hay fever and eczema. MATERIALS AND METHODS: A total of 225 questionnaires were sent to the consultant in charge for audit for radiology departments from the list given by the Royal College of Radiologists. 175 of the 225 questionnaires were returned (response rate 77.8%) and of these 172 were analysed with respect to the type, dose and duration of steroids. RESULTS: Compared to the survey in 1994, it was found that the number of departments who use steroid cover for all category of risk factors had increased compared to previous survey (73.8% in 2002 versus 55.3% in 1994 (p=0.001). There is now almost universal use of non-ionic contrast 98.8% versus 82.4% in 1994 (p=0.001). There is no agreed policy among radiology departments for the need or the dose or duration of steroid cover. CONCLUSION: Despite the more widespread use of non-ionic contrast media, the use of steroid premedication has increased which is contrary to what is expected as the incidence of adverse reaction to non ionic media is less than ionic contrast media.

Consultants↗
PubMed2004

Three-dimensional stress analysis for the mechanics of plantar ulcers in diabetic neuropathy.

In diabetic neuropathic subjects, the hardness of foot sole soft tissue increases, and its thickness reduces, in different foot sole areas. Finite element analysis (FEA) of a three-dimensional two-arch model of the foot was performed to evaluate the effect of foot sole stresses on plantar ulcer development. Three sets of foot sole soft-tissue properties, i.e. isotropic (with control hardness value), diabetic isotropic (with higher hardness value) and anisotropic diabetic conditions, were simulated in the push-off phase, with decreasing foot sole soft-tissue thicknesses in the forefoot region, and the corresponding stresses were calculated. The results of the stress analyses for diabetic subject (anisotropic) foot models showed that, with non-uniformly increased hardness and decreased foot sole soft-tissue thickness, the normal and shear stresses at the foot sole increased (compared with control values) by 52.6% and 53.4%, respectively. Stress analyses also showed high ratios of gradients of normal and shear stresses of the order of 6.6 and 3.3 times the control values on the surface of the foot sole, and high relative values of stress gradients for normal and shear stresses of 6.25 and 4.35 times control values, respectively, between the foot sole surface and the adjacent inner layer of the foot sole, around a particular region of the foot sole with anisotropic properties. These ratios of high gradients and relative gradients of stresses due to changes in soft-tissue properties may be responsible for the development of plantar ulcers in diabetic neuropathic feet.

Diabetic Foot↗
PubMed2004

Role of transition zone sampling by TURP in patients with raised PSA and multiple negative transrectal ultrasound-guided prostatic biopsies.

The purpose of the study was to determine the role of transurethral resection of the prostate (TURP) to detect prostate cancer in patients with consistently negative transrectal ultrasound-guided biopsies of the prostate. We retrospectively identified and analysed the patients who also had at least two sets of transrectal ultrasound guided sextant prostate biopsies before their TURP during the period between 1998 and 2002. A total of 14 such patients were identified and the outcome of TURP was analysed. Three patients were found to have cancer in the resected specimen (3/14 = 21%). All three cancers were significant (Gleason scores between 6 and 8) and required further treatment. In patients who have rising levels of prostate-specific antigen and who have had multiple negative peripheral zone biopsies, the presence of biologically important transition zone cancers needs to be considered. This can be detected by transurethral resection of the prostate that samples the transition zone of the prostate.

Adult↗
PubMed2003

Natural history and predictors of moderate mitral regurgitation following balloon mitral valvuloplasty using Inoue balloon.

BACKGROUND: We studied the predictors and natural history of moderate mitral regurgitation following valvuloplasty using Inoue balloon since it has not been well documented in a large series. METHODS: Balloon mitral valvuloplasty was performed in 590 consecutive patients with severe mitral stenosis with mitral regurgitation of mild or lesser grade. Echocardiography and haemodynamics of patients who developed moderate mitral regurgitation were compared with those who did not. They were followed-up. Factors that predicted the development of moderate regurgitation were studied. RESULTS: 21 patients (3.5%) developed moderate regurgitation (identified by auscultation, haemodynamics, angiography and colour flow mapping). They were managed conservatively. At 3 months, regurgitation decreased in severity to mild grade in 12 patients. At 1 year, it was trivial in 5, mild in 11 and remained moderate in 5. There was progressive symptomatic improvement. No clinical, echocardiographic, hemodynamic or procedural variables could predict the development of moderate mitral regurgitation. CONCLUSIONS: Patients with moderate regurgitation after mitral valvuloplasty show gradual improvement in regurgitation and symptoms. There were no factors-clinical, echocardiographic, hemodynamic or procedural-that predicted the occurrence of moderate MR after BMV.

Adolescent↗
PubMed2003

Dextrocardia: an analysis of cardiac structures in 125 patients.

BACKGROUND: Dextrocardia is associated with multiple and complex congenital cardiac anomalies. Precise anatomical diagnosis is essential for successful surgery. Spectrum of congenital malformations in cases of dextrocardia is based primarily on two-dimensional echocardiographic studies. The purpose of the current study was to use colour Doppler echocardiography in large number of patients. METHODS: Patients of dextrocardia were studied retrospectively, by reviewing database of our echocardiographic laboratory over last 10 years. Standard criteria for diagnosis of situs were used. Detailed segmental analysis for cardiac anatomy and associated malformations was done using previously suggested and well accepted terms and definitions. Cardiac anatomy was confirmed on catheterization and during surgery in few cases. RESULTS: Of total 125 patients, dextrocardia was most common with situs inversus (39.2%) followed by situs solitus (34.4%) and situs ambiguous [26.4% (right isomerism in 18.4% and left isomerism in 8.0%)]. Mean age was 9.2+/-11.2 years (range; 3 days to 60 years), 82 males and 43 females. In situs inversus dextrocardia, majority (73.4%) had concordant atrioventricular (AV) connections while discordant AV connections and univentricular atrioventricular connections (UVAVC) were present in 12.2 and 14.3% patients, respectively. Majority of patients with concordant AV connections (72.2%) also had concordant VA (ventriculo-arterial) connections (conotruncal anomalies were commonest). Similarly, majority of patients with discordant AV connections (66.7%) also had discordant VA connections. Commonly (44.9%), these patients presented with decreased pulmonary blood flow (Qp). Total 28.6% patients had normal intracardiac anatomy (10.2% presented with rheumatic heart disease). In situs solitus dextrocardia, majority (51.2%) had AV concordance while discordant AV connections and UVAVC were present in 41.9 and 7.0% patients, respectively. In patients with concordant AV connections, majority (77.2%) had VA concordance (majority presented with increased Qp due to pre or post-tricuspid shunts). Similarly, majority of patients with discordant AV connections (88.9%) also had discordant VA connections (88.9% presented with decreased Qp). Only 7.0% patients with situs solitus dextrocardia had normal intracardiac anatomy. The striking features of right isomerism were male predominance (male:female ratio 2.2:1), cyanosis with decreased Qp in 86.9%, and high incidence of UVAVC and venous system anomalies (39.1% each). Striking features of left isomerism were biventricular ambiguous AV connections in all except one, presentation with increased Qp in 60.0% and presence of inferior vena caval interruption in 60.0% patients. CONCLUSIONS: Present study, largest study of dextrocardia till date reconfirms that these patients have variable intracardiac anatomy depending upon their situs and types of segmental connections. These patients can present with different haemodynamic subsets, which can be correctly identified by colour Doppler echocardiography. Diagnostic accuracy and a better understanding of the various types of dextrocardia are essential, since improved surgical techniques have made it possible to correct many of these complex abnormalities.

Adolescent↗
PubMed2003

The role of skin hardness, thickness, and sensory loss on standing foot power in the development of plantar ulcers in patients with diabetes mellitus--a preliminary study.

This article presents the results of a study on patients with diabetic neuropathy to find the relationships between the foot pressures characterized by power ratio (PR), foot sole hardness (Shore values), and foot sole soft tissue thickness. The results showed that the increase in PR values for diabetic patients in the upper sensation loss levels (S = 7.5 to 10 g) compared to the corresponding increase in lower sensation loss (S=3 to 4.5 g)were of the order of 5 times in the lateral heel and big toe, respectively, and 4 times in the first metatarsal head regions. The increase in PR values for diabetic patients in the upper Shore value regions (30 to 40) compared to the corresponding increase in lower Shore value regions (20 to 30) were of the order of 3.4 times in lateral heel and 2.4, 2.0, and 2.3 times in the first, second, and lateral metatarsal head regions, respectively. At sites contiguous to frank ulcers for foot sole hardness (Shore values of 50) at sensation level > 10 g PR was as high as 59, and foot sole thickness values were also greater than the corresponding normal values. The study shows all measured parameters may play a part in the development of plantar ulcers.

Journal Article↗
PubMed2001

Real-time optical coherence tomography of the anterior segment at 1310 nm.

BACKGROUND: Recent advances in high-speed scanning technology have enabled a new generation of optical coherence tomographic (OCT) systems to perform imaging at video rate. Here, a handheld OCT probe capable of imaging the anterior segment of the eye at high frame rates is demonstrated for the first time. OBJECTIVE: To demonstrate real-time OCT imaging of anterior segment structures. DESIGN: Survey of anterior segment structures in normal human subjects. SETTING: Laboratory. MAIN OUTCOME MEASURES: Achieving real-time imaging of the anterior segment, satisfactory image quality, and convenience of a handheld probe. RESULTS: Optical coherence tomographic imaging of the anterior segment of the eyes of human subjects was performed using 1310-nm wavelength light with an image rate of 8 frames per second. Imaging trials demonstrated clear resolution of corneal epithelium and stroma, sclerocorneal junction, sclera, iris pigment epithelium and stroma, and anterior lens capsule. The anterior chamber angle was clearly visualized. Limited imaging of the ciliary body was performed. Real-time imaging of pupillary constriction in response to light stimulus was also performed. CONCLUSION: High-speed OCT at 1310-nm wavelength is a potentially useful technique for noninvasive assessment of anterior segment structures. CLINICAL RELEVANCE: Our results suggest that real-time OCT has potential applications in glaucoma evaluation and refractive surgery.

Anterior Chamber↗
PubMed2001

Severe thrombocytopenia possibly related to readministration of eptifibatide.

Thrombocytopenia following eptifibatide therapy is a rare event, and acute severe thrombocytopenia following readministration has not been reported. We describe a case of acute severe thrombocytopenia following reexposure to eptifibatide during percutaneous coronary intervention. We continue to monitor platelet counts at 2-4 hr and 16-24 hr following administration of any glycoprotein IIb/IIIa inhibitor. Cathet Cardiovasc Intervent 2001;54:63-67.

Adult↗
PubMed2001

Non-surgical closure of large ductus arteriosus using Amplatzer Duct Occluder feasibility and early follow-up results.

The aim of the study was the assess feasibility of closing large patent arterial ducts (PDA) in infants and children using the new Amplatzer Duct Occluder. All patients diagnosed to be having PDA were considered as potential candidates to undergo the device closure. 19 patients were diagnosed to be having PDA larger than 4 mm. There were 10 males and 9 females, their age ranged from 6 months to 120 months with a mean of 45 months. Mean body weight was 14.5 kg with a range from 7 kg to 23 kg. The procedure was carried out under Ketamine sedation and local anesthesia. The device was implanted by the transvenous route in all. Mean PDA diameter was 5 mm (range 4 mm-6.7 mm). Complete closure was achieved in 16/18 (88%) within 24 hours of the procedure. All patient have been followed for 3 months, and have documented complete closure, there is no evidence of aortic or left pulmonary stenosis in any of our patients. The unsuccessful attempt was in a malnourished patient (weighing 4.7 kg) with an arterial duct measuring 6.7 mm on angiography. This duct was considered too big for device closure and the procedure was abandoned. This patient subsequently has undergone successful surgical ligation. Catheter closure of large PDA in small children is feasible, safe and efficacious. However, it may still not be possible to close large PDA in very small or underweight children, for the fear of causing obstruction to the descending aorta. Further long-term is follow-up required to show sustained benefits without any side effects.

Balloon Occlusion↗