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Biomedical subjects

S Chakravarty

Publications and source records attributed to S Chakravarty.

102 records · Page 6Linked to original sources
PubMed1982

Dynamic response of arterial walls in vivo.

By the use of non-linear constitutive equations suitable for the characterization of anisotropic viscoelastic incompressible materials under finite deformations, the paper is devoted to analytical study on the dynamic stress field in arterial walls under the combined action of the pressure of blood on the inner surface and the pressure from the neighbouring components of the body on the outer surface. By using short time range approximations, the magnitudes of the radial and circumferential stresses are examined at various locations of the vascular wall and for different time intervals. It is observed that consideration of the mechanical influence of the external tissues and the inertial forces makes the derived stress field quite close to the experimental results reported recently by Fung et al. (1979), in comparison to the results of Cheung et al. (1972), who did not consider the aforementioned factors. It can thus be concluded that these factors need be considered for the studies of the stress field in arteries in vivo.

Animals↗
PubMed1981

Congenital absence of superior vena cava: unusual anomaly of superior systemic veins complicating pacemaker placement.

Congenital anomalies of the superior systemic veins can complicate placement of transvenous pacemaker electrode leads. Persistent left superior vena cava is the most common congenital anomaly; in this paper, we describe the case of a patient who had congenital absence of both superior venae cavae, which has not been reported previously. The superior systemic veins drained into persistent double azygos veins subdiaphragmatically. The anomaly was verified by venography. Temporary cardiac pacing was established by passing the electrode lead through the femoral vein, and a permanent epicardial pacemaker lead was placed thereafter. This appears to be the first recorded case of such an anomaly.

Adult↗
PubMed1977

Late evaluation of patients undergoing valve replacement with the Björk-Shiley prosthesis.

This study analyzes 484 patients who survived mitral, aortic, or mitral and aortic valve replacement using the Björk-Shiley prosthesis from January, 1970, through December 31, 1974. Long-term follow-up of 1 1/2 to 6 1/2 years (mean, 3.67 yr) was done on 435 patients (98.2%). Eighty to 85% of the patients have improved noticeably. Thromboembolic problems occurred in 6.9%, representing 1.5 emboli per 1,000 patient-months. Anticoagulant bleeding problems occurred in 6.4% of the patients; late mortality was 15%. Actuarial survival curves showed patients at risk to 6 years having a 79% chance of survival. The same analysis according to preoperative New York Heart Association Functional Classification showed a striking reduction in survival in class IV patients. The Björk-Shiley prosthesis is a good choice for valve replacement today. Earlier diagnosis and treatment are needed to obtain better long-term survival.

Adolescent↗
PubMed1977

A novel spray reagent for phospholipid detection.

Ammonium pentachlorooxomolybdate in a solution of 7-9 N H2SO4 was found to be an excellent spray reagent for the specific detection of phospholipids on thin-layer chromatograms. It is better than the usual molybdenum blue reagent due to its greater sensitivity and its ability to eliminate the problem of the development of background blue color on prolonged exposure.

Animals↗
PubMed1977

Gait study in evaluation of results in intramedullary nailing for femoral shaft fractures.

The present preliminary investigation conducted on six adult males whose femur shaft fractures had been fixed internally by means of Hansen-Street intermedullary nails indicated that our gait study technic helps confirm the clinical findings in such cases. Five patients, although their fractures had united and they had resumed their usual activities, were not deemed quite normal as yet and the causes for their gait abnormality were identified in the clinical examination. The gait study technic thus provided fairly accurate quantitative support of the clinical findings.

Evaluation Studies as Topic↗
PubMedDate not supplied

Solid phase synthesis of combinatorial libraries using anhydrides as templates.

A simple and general approach to the synthesis of chemical libraries based on a universal anhydride template allows the preparation of large number of compounds. Various cyclic/acyclic amines, primary/secondary amines, differentially protected bifunctional amines were used as nucleophiles to react with anhydrides. The free carboxylic acid generated was then coupled with solid-bound amines. The facile and rapid generation of compounds through this multi-component assembly can be accomplished in a combinatorial parallel synthesis.

Acylation↗
PubMedDate not supplied

Novel pseudopeptides with high affinities for the human bradykinin B2 receptor.

We recently proposed a model of bradykinin bound to the rat bradykinin B2 receptor that is constructed on the basis of structural homology modeling to the criomicroscopic structure of the seven transmembrane domains of bacteriorhodopsin, extensive conformational searches and experimental mutagenesis results. On the basis of that model, a novel third-generation pseudopeptide antagonist, NPC 18325 (D-Arg1-Arg2-[aminotridecanoyl]3-Ser4-D-Tic5-Oic6++ +-Arg7) (Ki = 440 nM, guinea pig ileum), was designed and also reported. NPC 18325 has been proposed to adopt a C-terminal beta turn separated from N-terminal positive charges by a linear 12 carbon chain spacer. Experimentally, the four amino acids making up the C-terminus have been shown by NMR to preferentially adopt a beta turn at neutral pH in aqueous solution. We now present a series of peptides, related to and including NPC 18325, that explore the relationship between the length of the carbon chain and the affinity to the human bradykinin B2 receptor. The results show that there is a structure-activity relationship (SAR) associated with the chain length and that these pseudopeptides have better affinity to the human bradykinin receptor than they have to the guinea pig ileal-derived B2 receptor. Specifically, peptide I (a 12-methylene linker) had a measured Ki of 31 nM and peptide V (a 4-methylene linker) had a Ki of 471 nM. Implications regarding conformation and hydrophobicity are also described.

Amino Acid Sequence↗
PubMedDate not supplied

Hydroxyamidines as new extracting reagents for spectrophotometric determination of cadmium with 4-(2-pyridylazo)naphthol in industrial effluents, coal, and fly ash.

A simple, sensitive, and selective extractive spectrophotometric method for the determination of cadmium in trace quantities with N1-hydroxy-N1,N2-diphenylbenzamidine (HDPBA) and 4-(2-pyridylazo)naphthol (PAN) is described. The method is based on the extraction of cadmium with HDPBA into chloroform at pH 9.0 +/- 0.2 and simultaneous spectrophotometric determination with PAN. The binary Cd(II)-HDPBA complex extracted into chloroform has a molar absorptivity of 1.96 x 10(4) L/mol/cm at lambda max 400 nm. The sensitivity of the yellow Cd(II)-HDPBA complex was increased remarkably by the addition of PAN to the binary complex. With 6 different hydroxyamidines tested, the red-orange complex in chloroform exhibited maximum absorbance at 530-550 nm, with molar absorptivity values of 3.2-5.6 x 10(4) L/mol/cm. The method adheres to Beer's law up to 1.5 micrograms cadmium/mL organic phase. The detection limit of the method is 0.02 micrograms Cd/mL. Investigations of the effect of foreign ions revealed that the present method is free from matrix interference of most of the common ions (e.g., Fe(III), Ni(II), Cu(II), Mn(II), V(V), Co(II), Al(III), Cu(II), Mg(II), and Mo(VI)). The relative standard deviation for 10 repetitive analyses of the metal was 1.4%. The validity of the method was tested successfully with various environmental samples.

Amidines↗