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Biomedical subjects

B R Mehta

Publications and source records attributed to B R Mehta.

16 recordsLinked to original sources
PubMed2007

Modification of the crystal habit of celecoxib for improved processability.

Crystallization is often used in the pharmaceutical industry for purification and isolation of drugs, and also as a means of generating polymorphs or isomorphs. The aim of this study was to investigate the role of extrinsic crystallization parameters on the crystallized product, with special emphasis on improving the mechanical properties of acicular celecoxib. Celecoxib isomorphs were prepared using different techniques (solvent crystallization and vapour diffusion) and crystallization conditions (solvents, stirring, degree of supersaturation, crystallization temperature and seeding). Powder X-ray diffractometry, spectroscopic and thermal methods were used to investigate physical characteristics of crystals. Growth kinetics and aggregation dynamics of crystallization in polar and non-polar solvents were simulated using a dynamic light scattering method. The quick appearance of broad peaks over the range of 10-8000 nm in chloroform during crystallization simulation studies indicated faster aggregation in non-polar solvents. Aspect ratio, flow, compressibility and surface area of recrystallized products were also determined. Surface topography was determined by atomic force microscopy and the lath-shaped crystals (aspect ratio of 2-4) exhibited a roughness index of 1.79 in comparison with 2.92 for needles. Overall, the lath-shaped isomorphs exhibited improved flow and better compressibility.

Calorimetry, Differential Scanning↗
PubMed2005

Nanoparticle size-dependent lowering of temperature for phase transition from In(OH)3 to In2O3.

Phase transformation of In(OH)3 to In2O3 has been studied as a function of nanoparticle size without any alteration of nanoparticle size during transformation. Chemically capped In(OH)3 nanoparticles having sizes of 15, 11, and 8 nm transform to In2O3 at temperatures of 285, 272, and 255 degrees C, respectively. This first-time unambiguous observation of size-dependent lowering of transformation temperature represents a thermodynamic characteristic of the nanoparticle system. The results have been explained in terms of a lower cohesive energy of surface atoms and an increase in surface-to-volume ratio with a decrease in nanoparticle size.

Hydroxides↗
PubMed2005

Effect of nanoparticle nature on hydrogen concentration profiles and improved switching characteristics in Gd switchable mirrors.

A detailed elastic recoil detection analysis using 40 MeV 28Si5+ ions has been carried out to study the changes in the H concentration and concentration profiles during the hydrogenation/dehydrogenation process in polycrystalline and nanoparticle Gd layers formed using vacuum evaporation and inert gas evaporation techniques, respectively. Nanoparticle sample exhibits a larger difference in the [H]/[Gd] values (2.9 and 1.7) in comparison to polycrystalline sample (2.4 and 2.0) in the loaded and deloaded states. Hydrogenation/dehydrogenation activity is restricted to the top portion in case of polycrystalline sample. In contrast to this, size induced structural transformation; enhanced surface area and the presence of large number of inter particle boundaries due to nanoparticle character result in the complete Gd layer becoming active during switching.

Crystallization↗
PubMed2005

Size-induced changes in optical and X-ray photoelectron spectra of GaN nanoparticles deposited at lower substrate temperature.

This study reports the synthesis of GaN nanoparticles having hexagonal structure by a simple technique of activated reactive evaporation with substrates kept at comparatively lower temperatures than usually reported. By varying the substrate temperature from 30 degrees C to 350 degrees C, it is possible to vary nanoparticle sizes from 5-30 nm. X-ray diffraction and X-ray photoelectron spectroscopy analysis confirm the formation of GaN on quartz and silicon substrates at room temperature. The observed size dependent shift in energy position, large increase in full width at half maximum value of Ga 3d and N 1s X-ray photoelectron spectroscopy peaks and blue shift in the optical absorption edge are related to nanoparticle character.

Gallium↗
PubMed1984

Hyporeninemic hypoaldosteronism in a patient with multiple myeloma.

A patient with progressive renal failure due to multiple myeloma presented with a mixed acid-base disorder (non-anion gap acidosis and respiratory alkalosis) with persistent severe hyperkalemia. Studies revealed an intact ability to lower urine pH during acid loading, markedly decreased plasma renin and aldosterone concentrations despite volume depletion, and an inappropriately low fractional excretion of potassium. Renal biopsy demonstrated plasma cell infiltration of the renal interstitium and typical proteinaceous intratubular casts. Both proximal and distal renal tubular acidification defects have been described previously in patients with multiple myeloma, but this is the first report of hyporeninemic hypoaldosteronism, hyperkalemia, and hyperchloremic metabolic acidosis in association with renal involvement in multiple myeloma.

Acidosis↗
PubMed1983

Effects of acetate and bicarbonate hemodialysis on cardiac function in chronic dialysis patients.

Previous studies have suggested that acetate hemodialysis causes myocardial depression. This study examines the acute effects of hemodialysis using, alternately, bicarbonate and acetate in the dialysate, on cardiac function in ten patients. These patients were also studied during acetate dialysis using a large surface area (SA) dialyzer. Each patient was dialyzed for 4 hr with: (1) 1.0 m2 SA dialyzer and bicarbonate dialysate; (2) 1.0 m2 SA dialyzer and acetate bath, and; (3) 2.5 m2 SA dialyzer and acetate dialysate. All studies were performed during isovolemic dialysis to separate the effects of changes in cardiac filling volume with hemodialysis, from changes in myocardial contractility. Myocardial function, as assessed by pre- and postdialysis echocardiographically derived fractional shortening (Fs) and mean velocity of circumferential shortening (VCF), improved (P less than 0.05) to the same extent, after all three dialysis treatments. This occurred despite greater increases (P less than 0.002) in pH and bicarbonate after bicarbonate dialysis and decreases (P less than 0.05) in PO2, PCO2 and bicarbonate after acetate dialysis with 2.5 m2 SA dialyzer. These results indicate that diffusive dialysis with both acetate and bicarbonate dialysate improves myocardial function and do not support the view that acetate influx during dialysis can lead to myocardial depression.

Acetates↗
PubMed1983

Echocardiographic evaluation of cardiac size and function in dialysis patients.

M-mode echocardiography was performed on 43 maintenance hemodialysis patients and 3 patients on continuous ambulatory peritoneal dialysis (CAPD). Only seven patients had completely normal echocardiograms. Nine patients (20%) had pericardial effusions and 20 patients (44%) had left ventricular dilatation. Left ventricular hypertrophy was present in 26 patients (57%): in 18 patients this took the form of concentric hypertrophy and in 8 patients there was asymmetric septal hypertrophy. Left ventricular function was depressed in 12 patients (27%). Left ventricular dilatation was more common in patients with multiple vascular accesses, who also tended to have lower hematocrit values. Left ventricular hypertrophy tended to be more common in patients with prolonged hypertension and with excessive inter-dialytic weight gains. Younger patients and those who had been on dialysis for a longer period had less cardiac abnormalities, suggesting that chronic dialysis might reverse these changes. Echocardiography was more sensitive than chest X-ray and ECG in detecting clinically unsuspected abnormalities and provides useful information in the overall evaluation of maintenance dialysis patients.

Adolescent↗
PubMed1981

Acute effects of haemodialysis on left heart dimensions and left ventricular function: an echocardiographic study.

Carotid pulse tracings and M-mode echocardiography were recorded in 25 patients on maintenance haemodialysis pre- and post-dialysis. Myocardial function, as assessed by fractional shortening and velocity of circumferential fibre shortening, was depressed in 7 out of 25 patients pre-dialysis (28%). Acute Haemodialysis resulted in significant changes in body weight, mean arterial pressure, urea, creatinine and packed cell volumes in all patients. Left ventricular function, however, improved significantly only in that group of patients in which it was depressed prior to dialysis. Echocardiography provides a simple means for evaluating left ventricular function in patients on chronic haemodialysis and shows that cardiac performance improves with acute dialysis when it is depressed pre-dialysis.

Adolescent↗
PubMed1980

Lithium toxicity induced by triamterene-hydrochlorothiazide.

Two patients on long-term lithium therapy for manic-depressive psychosis developed serious toxicity within days of being prescribed a combination of triamterene (50 mg) and hydrochlorothiazide (25 mg) for mild symptomless hypertension. Reduced clearance of lithium has been reported to follow its concurrent administration with diuretics that deplete both sodium and potassium. A combination of triamterene with thiazide has not been shown previously to precipitate lithium toxicity.

Bipolar Disorder↗