Biomedical subjects

M Mahesh

Publications and source records attributed to M Mahesh.

11 recordsLinked to original sources

PubMed2006

Imino Diels-Alder adducts. XII. Two pyrano[3,2-c]quinolines.

The crystal structures of pyranoquinolines 9-fluoro-5-phenyl-3,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c]quinoline, C18H18FNO, and 9-methyl-5-phenyl-3,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c]quinoline, C19H21NO, are isomorphous. In both structures, the pyran ring is exo to the six-membered N-heterocyclic ring formed in the cycloaddition step. The torsion angles across the phenyl linkage for the two structures are -91.2 (1) and -88.3 (2) degrees. The striking feature in both crystal packings is that they do not contain the expected conventional hydrogen bonds, in spite of the presence of good hydrogen-bonding functionalities. Possible C-H...pi interactions are, however, observed.

Crystallography, X-Ray↗

PubMed2006

Human protein reference database--2006 update.

Human Protein Reference Database (HPRD) (http://www.hprd.org) was developed to serve as a comprehensive collection of protein features, post-translational modifications (PTMs) and protein-protein interactions. Since the original report, this database has increased to >20 000 proteins entries and has become the largest database for literature-derived protein-protein interactions (>30 000) and PTMs (>8000) for human proteins. We have also introduced several new features in HPRD including: (i) protein isoforms, (ii) enhanced search options, (iii) linking of pathway annotations and (iv) integration of a novel browser, GenProt Viewer (http://www.genprot.org), developed by us that allows integration of genomic and proteomic information. With the continued support and active participation by the biomedical community, we expect HPRD to become a unique source of curated information for the human proteome and spur biomedical discoveries based on integration of genomic, transcriptomic and proteomic data.

Databases, Protein↗

PubMed2005

Imino Diels-Alder adducts. II. Two pyrano[3,2-c]quinolines.

8-Chloro-9-fluoro-5-phenyl-3,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c]quinoline and 10-chloro-9-fluoro-5-phenyl-3,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c]quinoline, both C18H17ClFNO, are diastereoisomers, formed as the result of the imino Diels-Alder reactions of N-benzylideneanilines with 3,4-dihydro-2H-pyran. The crystal structures reveal the stereochemistry of the pyran ring, which is endo/exo to the quinoline ring system formed in the cycloaddition step. In both structures, the pyran ring adopts a chair conformation, while the nitrogen-containing heterocyclic ring prefers a half-chair conformation. The structures differ essentially in the relative orientation of the ring junction H atoms.

Crystallography, X-Ray↗

PubMed2005

Plasma Proteome Database as a resource for proteomics research.

Plasma is one of the best studied compartments in the human body and serves as an ideal body fluid for the diagnosis of diseases. This report provides a detailed functional annotation of all the plasma proteins identified to date. In all, gene products encoded by 3778 distinct genes were annotated based on proteins previously published in the literature as plasma proteins and the identification of multiple peptides from proteins under HUPO's Plasma Proteome Project. Our analysis revealed that 51% of these genes encoded more than one protein isoform. All single nucleotide polymorphisms involving protein-coding regions were mapped onto the protein sequences. We found a number of examples of isoform-specific subcellular localization as well as tissue expression. This database is an attempt at comprehensive annotation of a complex subproteome and is available on the web at http://www.plasmaproteomedatabase.org.

Amino Acid Motifs↗

PubMed2004

Imino Diels-Alder adducts. I. Two furo[3,2-c]quinoline diastereoisomers.

The structures of two diastereoisomers of 9-chloro-8-fluoro-4-phenyl-2,3,3a,4,5,9b-hexahydrofuro[3,2-c]quinoline, C(17)H(15)ClFNO, are very similar. The orientation of the furan ring, as a result of its fusion to the quinoline nucleus, constitutes the significant difference between the two structures. The dihedral angles between the furan and phenyl rings are 73.4 (1) and 63.8 (1) degrees.

Journal Article↗

PubMed2001

Dose and pitch relationship for a particular multislice CT scanner.

OBJECTIVE: With single-slice helical CT, an increased pitch can decrease the radiation dose to the patient if all other parameters are constant. The purpose of this study was to determine whether the same relationship holds for a particular multislice helical CT system (Somatom Plus 4 VZ multislice helical CT scanner, version A11A) in our department. CONCLUSION: The measured radiation dose to the phantom was identical for all pitch selections on the multislice helical CT system we tested. This unexpected result was because of an automatic proportionate increase in the tube current when the pitch selection was increased. Radiologists and physicists should exercise caution when extrapolating dose reduction strategies from single-slice to multislice helical CT systems, and they must acquire a detailed understanding of the multislice helical CT scanner of their chosen manufacturer.

Equipment Design↗

PubMed1998

Predictors of fluoroscopy time and estimated radiation exposure during radiofrequency catheter ablation procedures.

The objective of this study was to identify factors that predict fluoroscopy duration and radiation exposure during catheter ablation procedures. The patient population included 859 patients who participated in the Atakr Ablation System clinical trial at 1 of 9 centers (398 male and 461 female patients, aged 36 +/- 21 years). Each patient underwent catheter ablation of an accessory pathway, the atrioventricular junction, or atrioventricular nodal reentrant tachycardia using standard techniques. The duration of fluoroscopy was 53 +/- 50 minutes. Factors identified as independent predictors of fluoroscopy duration included patient age and sex, the success or failure of the ablation procedure, and the institution at which the ablation was performed. Catheter ablation in adults required longer fluoroscopy exposure than it did in children. Men required longer durations of fluoroscopy exposure than did women. The mean estimated "entrance" radiation dose was 1.3 +/- 1.3 Sv. The dose needed to cause radiation skin injury was exceeded during 22% of procedures. The overall mean effective absorbed dose from catheter ablation procedures was 0.025 Sv for female patients and 0.017 Sv for male patients. This degree of radiation exposure would result in an estimated 1,400 excess fatal malignancies in female patients and 2,600 excess fatal malignancies in male patients per 1 million patients.

Adolescent↗

PubMed1997

Acute radiation dermatitis following radiofrequency catheter ablation of atrioventricular nodal reentrant tachycardia.

Radiation exposure during fluoroscopic imaging poses potential risks to patients and physicians, especially during protracted cardiovascular or radiological interventional procedures. We describe a woman with refractory paroxysmal supraventricular tachycardia who underwent radiofrequency catheter ablation of the slow pathway involved in atrioventricular nodal reentrant tachycardia. The patient subsequently returned 4 weeks later with acute radiation dermatitis that was retrospectively attributed to a malfunction in the fluoroscopy unit that lacked a maximum current output cut-off switch. Using dose reconstruction studies and her estimated biological response, we determined that she received between 15 and 20 Gy (1 Gy = 100 rads) to the skin on her back during the procedure. The exposure will result in an increase in her lifelong risk of skin and lung cancer. This article underscores the potential for radiation-induced injury during lengthy therapeutic procedures using x-ray equipment.

Acute Disease↗

PubMed1994

Comparison of nuclear magnetic resonance spectroscopy with dual-photon absorptiometry and dual-energy X-ray absorptiometry in the measurement of thoracic vertebral bone mineral density: compressive force versus bone mineral.

31P nuclear magnetic resonance spectroscopy (NMRS) measurements were made on human T2 and T3 vertebral bodies. The bone mineral content (BMC) of isolated vertebral bodies minus the posterior elements and disks was measured using (1) NMRS on a 3.5 T, 85 mm bore GE Medical Systems NT-150 superconducting spectrometer, (2) a Lunar Corporation DPX-L dual-energy X-ray absorptiometry (DXA) scanner in an anterior-posterior (AP) orientation, (3) a Norland Corporation XR26 DXA scanner, also in an AP direction, and (4) a Norland Corporation model 2600 dual-photon absorptiometry (DPA) densitometer in both the AP and superior-inferior (SI) directions. Vertebral body volumes were measured using a water displacement technique to determine volume bone mineral densities (VBMD). They were then compressed to failure using an electrohydraulic testing device, followed by ashing in a muffle furnace at 700 degrees C for 18 h. Correlations of BMC between NMRS and DPA, DXA and ashing were excellent (0.96 < or = r < or = 0.99); in a one-way analysis of variance (ANOVA) test, means were not statistically different at a p level of 0.757. The correlations of VBMD between NMRS and the other methods were not as good (0.83 < or = r < or = 0.95); in a one-way ANOVA test, means were not statistically different at a p level of 0.089. BMC was a better predictor of ultimate compressive failure than VBMD for all six methods. For NMRS, the regression coefficient for BMC was r2 = 0.806, compared with r2 = 0.505 for VBMD. NMRS may prove an alternative to present methods of determining bone mineral.

Absorptiometry, Photon↗

PubMed1992

The biomechanics of lumbar facetectomy under compression-flexion.

Alterations of posterior spinal elements including the facet joints are commonly associated with a variety of lumbar operative procedures. Under continuous physiologic compression-flexion load application L2-L3 and L4-L5 functional units were tested as intact preparations and then sequentially altered with unilateral facetectomy, bilateral facetectomy, posterior ligament transection, and partial discectomy. Using a method of continuous motion analysis, the movement of the individual spinal components (disc, facet joint, interspinous process distance) were statistically compared between the various surgical alterations. Higher physiologic loads produced significant increases in overall deflection from BF to BFL alterations indicating a preference to preserve the posterior ligaments for this surgical approach. Although insignificant changes in the force-deflection response from one surgical alteration to the next sequential alteration were noted, statistically significant increases in localized facet joint motion may suggest the potential for acceleration of segmental degenerative changes.

Aged↗

PubMedDate not supplied

Fluoroscopy: patient radiation exposure issues.

Fluoroscopic procedures (particularly prolonged interventional procedures) may involve high patient radiation doses. The radiation dose depends on the type of examination, the patient size, the equipment, the technique, and many other factors. The performance of the fluoroscopy system with respect to radiation dose is best characterized by the receptor entrance exposure and skin entrance exposure rates, which should be assessed at regular intervals. Management of patient exposure involves not only measurement of these rates but also clinical monitoring of patient doses. Direct monitoring of patient skin doses during procedures is highly desirable, but current methods still have serious limitations. Skin doses may be reduced by using intermittent exposures, grid removal, last image hold, dose spreading, beam filtration, pulsed fluoroscopy, and other dose reduction techniques. Proper training of fluoroscopic operators, understanding the factors that influence radiation dose, and use of various dose reduction techniques may allow effective management of patient dose.

Fluoroscopy↗