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Biomedical subjects

G Das

Publications and source records attributed to G Das.

At least 73 records · Page 4Linked to original sources
PubMed1993

Chemical analysis of post-lithotripsy stone fragments: a critical evaluation.

A scheme for the chemical microanalysis of renal stone fragments recovered from urine voided immediately after lithotripsy has been developed and evaluated. The analytical procedure includes assay of calcium, magnesium, phosphate, oxalate and urate and has been applied to 78 such urine samples. Problems relating to co-existing crystalluria and blood and urine contaminants have been recognised and overcome. However, significant loss of all stone components due to fragment dissolution in urine prior to recovery was found to occur and was investigated. The distribution of stone components found in these analyses was similar to that seen in previous surveys of intact stones.

Calcium↗
PubMed1993

Cocaine: friend or foe? (Part 1).

The history of cocaine use goes back a long time. Initially, cocaine was used as a medicine by physicians and as a pleasure agent in over-the-counter preparations. The significance and intensity of cocaine use and abuse became well known soon thereafter and resulted in extensive regulations to curb its use. Cocaine is a powerful anesthetic agent with powerful vasoconstrictive properties. It can be absorbed from all mucous membrane sites and results in severe cardiovascular complications. The effects of cocaine on various organ systems are presented here.

Brain↗
PubMed1993

Cocaine: friend or foe? (Part 2).

The cocaine epidemic is growing at an alarming rate in the United States. Medical and social implications of cocaine abuse are many and include such aspects as intoxication, personal, financial and moral ruin. Complications associated with cocaine use more commonly involve the cardiovascular, central nervous system and the reproductive systems. One of the major concerns regarding cocaine abuse goes far beyond its ill effects on the user. High incidence of congenital malformations and the learning and behavioral disorders in the infants results in a growing number of "misfit" or "undesirable" citizens in the country. Hence, the healthcare providers, the politicians and the legal system must intensely direct their efforts at eradicating this menace.

Arrhythmias, Cardiac↗
PubMed1993

Cardiovascular effects of cocaine abuse.

Cocaine abuse is widespread in North America. It is estimated that almost one in every four Americans has used cocaine at least once in his/her lifetime. In the past two decades, cocaine related cardiovascular complications have mushroomed because cocaine has become cheaper and more readily available. The fundamental effects of cocaine on cardiovascular system are similar to those observed following an intense, sympathetic stimulation. Cocaine intake results in marked increase in blood pressure, myocardial oxygen demand and heart rate. Coronary blood flow, which increases in response to exercise (endogenous sympathetic stimulation) however, is decreased by cocaine intake. Increased demand of oxygen by the myocardium in the face of decreased supply in subjects with cocaine use, leads to myocardial ischemia, which in turn forms a substrate for most of the cardiovascular complications, namely, myocardial infarction, cardiac arrhythmias and acute pulmonary edema. Hypertension related complications, dissection and rupture of aortic aneurysm, hemorrhagic stroke, in addition to infective endocarditis, myocarditis, cardiomyopathy all occur more frequently in cocaine addicts. In this review, pertinent clinical pharmacology and cardiovascular risks associated with cocaine abuse are presented.

Cardiovascular Diseases↗
PubMed1993

Cocaine and the nervous system.

Cocaine abuse today has reached greater heights than it did during the first cocaine epidemic in the late nineteenth century. It is estimated that one out of every four Americans has used cocaine and some six million people in the US use it regularly. Although cocaine affects all systems in the body, the central nervous system (CNS) is the primary target. Cocaine blocks the reuptake of neurotransmitters in the neuronal synapses. Almost all CNS effects of cocaine can be attributed to this mechanism. Euphoria, pharmacological pleasure and intense cocaine craving share basis in this system. The effects of cocaine on other organ systems, in addition to its effects on the CNS, account for the majority of the complications associated with cocaine abuse. In this paper, the CNS effects following cocaine administration and their treatment are discussed.

Acute Disease↗
PubMed1991

Enhanced thermodynamic stabilities of yeast iso-1-cytochromes c with amino acid replacements at positions 52 and 102.

We have determined the structures and thermodynamic stabilities of the wild type Asn-52 and unusually thermostable mutant Ile-52 yeast iso-1-cytochromes c (Das, G., Hickey, D. R. McLendon, D., McLendon, G., and Sherman, F. (1989) Proc. Natl. Acad. Sci. U.S.A. 86, 496-499). Although both structures were similar, Water-166, buried within the wild type protein, is excluded from the Ile-52 mutant, which substantially reorganizes the local hydrogen bonding. Wild type Cys-102 was replaced with alanine or serine to eliminate dimerization in vitro. The Cys-102 (wild type), Ala-102, and Ser-102 proteins were equally stable, whereas the chemically modified Cys-102-SCH3 was less stable. The order of stability observed with replacements at positions 52 and 102 was as follows: Ile-52 Ala-102 greater than Ala-52 Ala-102 greater than Asn-52 Ala-102 ("normal") greater than Gly-52 Ala-102. No significant stabilization was attributed to potential energy interactions expressed as helix-forming propensities of replacements at position 52. A high correlation between differences in free energy changes and transfer free energies suggests hydrophobic interactions are the main factor for enhancing stability in the Ile-52 mutant. Additional possible contributions to the thermostability of the Ile-52 variant are energetic effects due to packing and hydrogen bonding changes surrounding position 52.

Amino Acids↗
PubMed1991

Percutaneous balloon mitral valvuloplasty in rheumatic mitral stenosis: an experience of 50 patients in India.

We attempted percutaneous balloon mitral valvuloplasty in 50 patients (27 female and 23 male, age 10-38 years) with rheumatic mitral stenosis. The procedure could be completed in 40 patients. The failures were caused by problems related to transseptal puncture in eight cases and inability to cross the mitral valve in two cases. Immediately after valvuloplasty there was a remarkable reduction in the mean pulmonary artery pressure, left atrial mean pressure, mean diastolic gradient across the mitral valve, and the calculated pulmonary vascular resistance. The calculated mitral valve area increased and the cardiac index increased marginally. Inadequate results with a post valvuloplasty mitral valve area of 0.9 cm2 were seen in only one patient. Repeat hemodynamic evaluation in 25 patients within two weeks of valvuloplasty showed persistent benefit in all except one patient, who showed partial restenosis. Follow-up cardiac catheterization at 3-6 months in 13 patients showed evidence of restenosis (mitral valve area less than 1.0 cm2 and mean diastolic gradient of greater than 10 mmHg) in one patient, while all others maintained hemodynamic benefit. Repeat hemodynamic evaluation at 9-18 months after valvuloplasty in eight patients showed evidence of restenosis in an additional two cases. The patients in our series are young (28 patients less than 20 years), small body surface area (1.35-0.2 m2), and have high left atrial and pulmonary arterial pressures.

Adolescent↗
PubMed1990

QT interval and repolarization time in patients with intraventricular conduction delay.

A prolonged QT interval is an important prognostic indicator for cardiac arrhythmias and sudden death. The conventional QT interval measurement, however, includes in its measure the cardiac depolarization (QRS) as well as the cardiac repolarization (JT) intervals. To evaluate the relative contribution of the depolarization and the repolarization time prolongation to the prolonged QT interval in patients with intraventricular conduction delay (IVCD), the QRS, QT, and JT intervals were measured in 72 subjects with various types of IVCD. The observed intervals in IVCD subjects were compared to similar intervals in 33 healthy individuals in whom there was no evidence for intraventricular conduction abnormalities. The QTc (QT interval corrected for heart rate) in subjects with IVCD were 445 +/- 6.8 msec (mean +/- SEM) in those with LAD, 470 +/- 9.1 msec with RBBB, and 489 +/- 6.9 msec with LBBB. All of these intervals were significantly prolonged compared to 430 +/- 4.3 msec in the control group. The prolongation of QTc interval in each category of IVCD subjects was entirely secondary to a prolonged depolarization time, as the repolarization intervals were not significantly different from those observed in the control group (F = 0.5, p = NS). These observations may provide an explanation for the differential prognosis for subjects with prolonged QT interval with prolonged repolarization time as compared to those with prolonged QT interval with prolonged depolarization time.

Adult↗
PubMed1990

Multicentre controlled trial of indoramin in the symptomatic relief of benign prostatic hypertrophy.

A group of 139 patients with symptoms of bladder outflow obstruction due to benign prostatic hypertrophy were entered into a double-blind, parallel group, multicentre study of 2 doses of indoramin versus placebo. There were 18 withdrawals or exclusions, leaving 121 patients for analysis. After 8 weeks, mean peak flow rates increased more in patients treated with indoramin 20 mg bd than in those with placebo. The difference between indoramin 20 mg nocte and placebo was not significant. The change in mean peak flow rate for the higher dose of indoramin represented an increase of 50%. Both patients and investigators reported that the patients' symptoms had improved significantly on both indoramin 20 mg bd and 20 mg nocte; 9 patients were withdrawn because of adverse events, 5 taking placebo and 2 in each of the treatment groups. It was concluded that indoramin 20 mg bd was both effective and well tolerated in the management of symptomatic benign prostatic hypertrophy.

Aged↗
PubMed1990

Artificial cardiac pacemakers.

Artificial pacemakers are electronic devices used primarily to control cardiac rate in patients in whom the intrinsic heart rate is inadequate for a normal life style. These devices automatically and rhythmically provide electrical impulses to stimulate the heart. Electrical stimulation of various organs of the human body was already in practice more than two centuries ago. These applications, however, were in experimental stages until recently when electrical stimulation of the heart has emerged as a new therapy. In view of the astonishing progress made in the field of pacemaker technology and the current indications for the specific types of pacing systems, it behooves physicians caring for patients with heart disease to become familiar with the use of cardiac pacemakers and the not infrequent problems associated with their use. The primary purpose of this review is to present fundamental knowledge in the electrical stimulation of the heart and the various pacing systems available.

Cardiac Output↗
PubMed1990

Cocaine and the cardiovascular system.

Cocaine abuse is widespread and increasing in North America. One in every four Americans has used cocaine for its euphorogenic properties. The cardiovascular actions of cocaine are similar to those observed following intense sympathetic stimulation. Cocaine increases heart rate, blood pressure and myocardial oxygen demand. Yet, paradoxically it decreases oxygen supply by inducing coronary vasoconstriction, leading to myocardial ischemia. This myocardial ischemia undoubtedly forms the substrate for most of the cardiovascular complications observed with cocaine use. In this article, the history, clinical pharmacology and complications of cocaine abuse are reviewed.

Cardiovascular System↗
PubMed1989

Esmolol versus verapamil in the acute treatment of atrial fibrillation or atrial flutter.

The effects of esmolol, an ultrashort-acting beta blocker, and verapamil were compared in controlling ventricular response in 45 patients with atrial fibrillation or atrial flutter, in a randomized, parallel, open-label study. Patients with either new onset (less than 48 hours, n = 31) or old onset (greater than 48 hours, n = 14) of atrial fibrillation or flutter with rapid ventricular rate were stratified to receive esmolol (n = 21) or verapamil (n = 24). Drug efficacy was measured by ventricular rate reduction and conversion to sinus rhythm. The heart rate declined with esmolol from 139 to 100 beats/min (p less than 0.001) and with verapamil from 142 to 97 beats/min (p less than 0.001). Fifty percent of esmolol-treated patients with new onset of arrhythmias converted to sinus rhythm, whereas only 12% of those who received verapamil converted (p less than 0.03). Mild hypotension was observed in both treatment groups. Esmolol compares favorably with verapamil with respect to both efficacy and safety in acutely decreasing ventricular response during atrial fibrillation or flutter. Moreover, conversion to sinus rhythm is significantly more likely with esmolol.

Adrenergic beta-Antagonists↗
PubMed1989

Dramatic thermostabilization of yeast iso-1-cytochrome c by an asparagine----isoleucine replacement at position 57.

Two Saccharomyces cerevisiae yeast mutants, cyc1-73 and cyc1-190, contain nonfunctional and presumably unstable forms of iso-1-cytochrome c due to Gly-34----Ser and His-38----Pro replacements, respectively. Second-site reversions that produced Asn-57----Ile replacements at least partially restored function, presumably by alleviating the instability of these two altered iso-1-cytochromes c. Introduction of the Ile-57 replacement by site-directed mutagenesis in an otherwise normal protein resulted in a 17 degrees C increase in the transition temperature (Tm), corresponding to over a 2-fold increase in the free energy change (delta G degrees) for thermal unfolding.

Amino Acid Sequence↗