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Biomedical subjects

S Kumar

Publications and source records attributed to S Kumar.

At least 1,693 records · Page 94Linked to original sources
PubMed1990

Effect of intraocular lens decentration on retinal image contrast.

We describe an optical model of the eye that allowed the effect of intraocular lens (IOL) decentration on retinal image contrast to be photographically studied. Decentrations of varying degrees of severity were modeled to correlate the amount of aphakic pupillary area with the contrast of the resulting images as measured by a digital photometer. Image contrast was found to decrease linearly as the proportion of aphakic pupillary area increased. Human clinical correlates are discussed.

Contrast Sensitivity↗
PubMed1990

Spinal stresses in simulated raking with various rake handles.

Five young male subjects performed a simulated raking task by pushing and pulling 14 different rake handles at 60 N and 110 N simulated soil resistance in a random order. The raking action was performed at a self-selected uniform pace over a 60 cm stroke length with initial, middle and final phases marked. During this action the raking force and angle of the rake was measured by a load cell and a potentiometer respectively. The posture was recorded with a video cassette recorder. The posture and force values were used for the determination of the spinal compression load. In rake pulling the 13 modified rake handles generated a spinal compression of only 20% to 50% of the straight handle, whereas in rake pushing the modified handles generated compression up to five times that of the straight handle. The compression generated with the straight handle never reached the action limit, whereas those of the 13 modified handles rarely stayed within the action limit. Therefore, a straight handle is considered the handle of choice.

Adult↗
PubMed1990

Effects of stimulus degradation on letter-matching performance of left and right hemispheric stroke patients.

Performance on a letter-matching task involving conditions of perceptual degradation was tested on 18 Right CVA patients, 18 Left CVA patients and 18 control subjects. Letter stimuli were presented in three conditions: Clear, Line-Masked, and Blurred. Subjects judged whether two letters of a pair were the same in name or different in name. Right CVA patients performed significantly less accurately than did Left CVA patients and control subjects when letters were perceptually degraded with a line mask overlay or by blurring. No significant differences were found between the two patients groups when the letters were presented without perceptual degradation (the Clear condition), but both patient groups were significantly less accurate than control subjects. The results are similar to findings reported in visual half-field studies with neurologically normal subjects and indicate right-hemisphere superiority for the processing of perceptually degraded visual information.

Adult↗
PubMed1990

Molecular recognition and binding of a GC site-avoiding thiazole-lexitropsin to the decadeoxyribonucleotide d-[CGCAATTGCG]2: 1H-NMR evidence for thiazole intercalation.

The structural and dynamic aspects of the interaction of the thiazole containing lexitropsin (1) with an oligodeoxyribonucleotide were studied by high field 1H-NMR spectroscopy. Complete assignment of the 1H-NMR resonances of lexitropsin 1 was accomplished by 2D-NMR techniques. The complexation-induced chemical shifts and NOE cross peaks in the NOESY map of the 1:1 complex of lexitropsin (1) and d-[CGCAATTGCG]2 reveal that the thiazole ring of the lexitropsin (1) intercalates between dA4.A5 bases and the rest of the ligand resides in the minor groove of the AT rich core of decamer, thus occupying the 5'-AATT sequence on the DNA. Intercalation of the thiazole moiety of the drug has been detected by the presence of intermolecular NOEs both in the major and the minor groove of the decamer helix. The absence of intranucleotide NOEs between base protons and H1'/H2' protons suggested local unwinding of the binding site on the DNA. From COSY and NOESY methods of 2D-NMR, it was established that the N-formyl (amino) terminus of the thiazole lexitropsin (1) is projecting into the major groove towards A5H8 while the amidinium terminus lies in the minor groove towards the T7G8 base pairs of the opposite strand. The expected intranucleotide NOEs confirmed that the decadeoxyribonucleotide in the 1:1 complex exists in a right handed B-conformation. The presence of exchange signals along the binding site 5'-AATT indicated an exchange of the bound drug process wherein the rate of exchange between the two equivalent sites was estimated to be congruent to 130 s-1 at 30 degrees C and with delta G degrees of 62.4 kJ mol-1. Force field and Pi calculations permitted a rationalization of the experimentally observed binding mode in terms of preferred conformation of the ligand and repeat length in lexitropsins compared with the DNA receptor.

Base Composition↗
PubMed1990

Sequence specific molecular recognition and binding by a GC recognizing Hoechst 33258 analogue to the decadeoxyribonucleotide d-[CATGGCCATG]2: structural and dynamic aspects deduced from high field 1H-NMR studies.

The non-exchangeable and imino proton NMR resonances have been assigned of the 1:1 complex of an analogue 2 of Hoechst 33258 1 bound to the decadeoxyribonuycleotide d-[CATGGCCATG]2 by a combination of NOE difference, COSY and NOESYPH techniques. In contrast to Hoechst 33258 which recognizes 5'-AATT sequences exclusively, analogue 2 possesses structural features designed to permit the recognition of GC sites. The NOESY and 1D-NOE experiments place the drug in the minor groove and it is located on the 5'-CCAT sequence. The orientation of the drug in the groove is such as to place the N-methylpiperazine terminus at a GC site. Cross-correlation peaks in the NOESY experiment show that the DNA duplex retains its right-handed B form, similar to that in the free decamer. Specific NOEs locate the benzoxazole moiety on the 5'-CCAT and are consistent with the pyridine nitrogen forming a new hydrogen bond to G(4)-2NH2 at 5'-CCAT. The drug appears to undergo rotation around the C9-C10 bond, at a rate comparable with NMR time scale, even after binding. Variable temperature 1H-NMR studies established that the DNA is thermally stabilized as a result of the drug binding. The drug binding is a dynamic process involving exchange between the equivalent 5'-CCAT sites at approximately 60s-1 with delta G degree of 65 kJ mol-1 at 308K. The experimental evidence is in accord with a slide-swing mechanism for this process.

Base Sequence↗
PubMed1990

A comparison of the sensitivity to photodynamic treatment of endothelial and tumour cells in different proliferative states.

Bovine aorta endothelial and human colon adenocarcinoma (WiDr) cells were exposed to haematoporphyrin derivative plus light. Cell survival was determined using a [3H]thymidine incorporation and a clonogenic assay for both cell types. The endothelial cells were more sensitive to photodynamic treatment. This could be explained in terms of increased drug uptake into the endothelial cells despite there being no difference in cell volume between the cells. For both tumour and endothelial cells, exponentially growing cells were more sensitive to photodynamic treatment than plateau-phase cells. This was associated with a reduction in drug uptake into plateau-phase endothelial cells. However, there was no difference in uptake into exponentially growing and plateau-phase WiDr cells.

Animals↗
PubMed1990

N,N-diethylphenylacetamide--a new repellent for Periplaneta americana (Dictyoptera: Blattidae), Blattella germanica, and Supella longipalpa (Dictyoptera: Blattellidae).

The residual repellency of N,N-diethylphenylacetamide (DEPA) was studied against American cockroach, Periplaneta americana (L.); German cockroach, Blattella germanica (L.); and brownbanded cockroach, Supella longipalpa (F.) at various concentrations. DEPA exhibited residual repellency for 4, 3, and 2 wk against American, German, and brownbanded cockroach, respectively, at a concentration of 0.5 mg/cm2.

Acetamides↗
PubMed1990

Cumulative load as a risk factor for back pain.

The association between cumulative load (biomechanic load and exposure time integral over the entire work experience) and back pain was investigated in a group of institutional aides with physically stressful jobs. A questionnaire/interview was conducted with 161 of these institutional aides. The point prevalence of back pain in this sample was 62%. Men had worked a mean duration of 14.3 years and women 11.6 years at the time of the onset of the first pain episode. Every job performed was analyzed by the use of a two-dimensional static mathematical model. The compression and shear at the thoracolumbar and lumbosacral discs were computed by the use of a biomechanic model. Cumulative compression and shear were significantly higher in institutional aides with pain compared with those without pain (P less than 0.05-0.01). The pain group was similar to the no-pain group in age, weight, and height.

Adult↗
PubMed1990

Molecular cloning and sequencing of an Australian isolate of proviral bovine leukaemia virus DNA: comparison with other isolates.

The molecular cloning and characterization of an EcoRI fragment, 8.26 kb in size, of an Australian isolate of bovine leukaemia virus (pBLV-A1) is described. This fragment includes most of the proviral genome as well as 340 bp of flanking bovine DNA sequence at the 5' end. Approximately 790 bp, including the 3' long terminal repeat, was missing from this clone. At the level of restriction enzyme mapping, this isolate could be distinguished from American, Belgian and Japanese isolates. DNA sequencing of the entire clone demonstrated some variation at the amino acid level between pBLV-A1 and the Japanese and Belgian isolates, particularly in the gag gene. In that gene there were 59 amino acid changes compared to the Japanese isolate and 24 compared to the Belgian isolate. The greater number in the case of the Japanese isolate was due to both single nucleotide changes and frameshift in a single region of the gene. This study also demonstrates that there are large tracts of amino acid sequence, particularly within the env and pol genes, that are highly conserved in different isolates. Some of these conserved sequences exist in regions containing epitopes important in virus infectivity.

Amino Acid Sequence↗
PubMed1990

Postoperative analgesia in children who have genito-urinary surgery. A comparison between caudal buprenorphine and bupivacaine.

A study conducted on 40 children, aged 1-11 years, who had genito-urinary surgery compared the quality and duration of analgesia after caudal blocks in two groups of patients. Group 1 (n = 20) received caudal bupivacaine 0.25% and group 2 (n = 20) caudal buprenorphine 4 micrograms/kg; each received 0.5 ml/kg body weight. Patients were operated on under general anaesthesia. Postoperative behaviour and severity of pain were measured on a 3-point scale. The results indicate that caudal buprenorphine provides excellent postoperative analgesia in children comparable to caudal bupivacaine in the early postoperative period. Buprenorphine proved better in the late postoperative period. Analgesia lasted from 20 hours to more than 24 hours after caudal buprenorphine with fewer side effects.

Analgesia↗
PubMed1990

A comparison of a short half-life marker (low-dose isoniazid), a long half-life pharmacological indicator (low-dose phenobarbitone) and measurements of a controlled release 'therapeutic drug' (metoprolol, Metoros) in reflecting incomplete compliance by volunteers.

1. Although, long half-life compounds appear to be more appropriate pharmacological indicators of compliance with treatment, short half-life markers or measurements of short half-life therapeutic drugs are frequently used. 2. We have compared the usefulness of low-dose phenobarbitone (a long half-life indicator), low dose isoniazid (a short half-life marker) and controlled release metoprolol (Metros) (a controlled release formulation of a short half-life 'therapeutic' drug) in seven volunteers with simulated partial (two thirds) compliance. 3. Detection of isoniazid metabolites in urine had an 83% sensitivity and 94% specificity for detecting ingestion within the previous 24 h and 100% sensitivity and 82% specificity for detecting ingestion within the past 6 h but gave no indication of the longer term pattern of compliance. 4. At 28 days (a time when steady-state would be obtained for all three drugs) phenobarbitone plasma levels were 70% (66-76%)--median and interquartile range--of the expected steady-state level if compliance had been complete. Corresponding figures for metoprolol were 82% (37-100%). 5. Measurement of phenobarbitone was much superior to isoniazid or metoprolol measurements in reflecting partial compliance over the previous 1 to 4 weeks.

Administration, Oral↗
PubMed1990

Effect of warfarin on plasma concentrations of vitamin K dependent coagulation factors in patients with stable control and monitored compliance.

There is a discrepancy in the results of reported studies of levels of vitamin K dependent coagulation factors in patients on warfarin therapy. This may have arisen partly because of the problem of assuring compliance with therapy in outpatients. The plasma concentrations of the vitamin K dependent clotting factors II, VII, IX and X were studied in 23 outpatients whose adherence to prescribed warfarin therapy was determined using a pharmacological indicator of compliance. In these patients, who were shown to have consistently good compliance and stable anticoagulant control over a period of 3-6 months, the activities in plasma of the four coagulation factors were not equally suppressed. Factor IX levels were significantly greater than those of factor VII (P less than 0.0001) which in turn were significantly greater than the levels of factor II (P less than 0.0001) or factor X (P less than 0.0001). There was no significant difference between the levels of factors II and X which were depressed to a similar extent. The proportion of variability of the International Normalized Ratio (INR) explained by linear regression was 51-77% and a model was derived to predict the INR from the mean of the levels of the four clotting factors. The concentrations of the coagulation factors II, VII, IX and X are likely to be highly dependent on the degree of compliance with warfarin therapy which should be taken into account when investigating the behaviour of these factors.

Aged↗
PubMed1990

Generation of a cytotoxic T-lymphocyte response using a Salmonella antigen-delivery system.

We have constructed a general-use vector for the cloning and stable expression of foreign genes in the chromosome of attenuated Salmonella typhimurium. Using this chromosomal expression vector (CEV), we expressed the circumsporozoite (CS) gene of the mouse malaria Plasmodium yoelii in an aroA S. typhimurium strain. Mice immunized with CS-expressing Salmonella recombinants mount a CS-specific cytotoxic T-lymphocyte (CTL) response. This is the first demonstration that attenuated Salmonella can elicit a specific CTL response to a foreign protein in mice. The ability to easily and stably express foreign genes from the Salmonella chromosome and the generation of specific CTL greatly expands the potential of Salmonella as an antigen-delivery system.

Amino Acid Sequence↗
PubMed1990

Effect of liver transplantation on the hypothalamic-pituitary-gonadal axis of chronic alcoholic men with advanced liver disease.

The hormones testosterone, follicle stimulating hormone (FSH), and luteinizing hormone (LH) were assayed in blood obtained from men with alcoholic liver disease before and after successful liver transplantation. The frequency and severity of self reported impotence, intercourse, and paternity were assessed before and 18 +/- 3 months post-transplantation. The results obtained were compared with those of age-matched males transplanted within the same month by the same surgical teams for advanced hepatocellular disease other than alcoholism. Little change for any parameter assessed pre- and post-transplantation was noted for the nonalcoholics. In contrast, the FSH, LH, and testosterone levels of the alcoholic men all increased significantly following successful transplantation. These data suggest that the liver disease associated with alcoholism contributes to some of the endocrine effects of alcohol-associated cirrhosis but not all. Because the transplanted alcoholics remain less adequate than controls, it is further suggested that some residual alcohol-induced injury to the hypothalamic-pituitary-gonadal axis persists despite successful liver transplantation.

Follicle Stimulating Hormone↗
PubMed1990

A quantitative animal model of traumatic iridodialysis.

The impact velocities and kinetic energies necessary to create a particular form of ocular injury, traumatic iridodialysis, were quantitatively studied by experimentally traumatizing enucleate porcine eyes. Thicknesses and tensile strengths of porcine and human iris tissue were measured in order to allow for predictions of human results to be made from the animal model. Application of blunt trauma at an impact angle of 30-35 degrees with respect to the iris plane with striking of the eye at the corneolimbal junction was found to optimize tearing of the iris from the root. Using this vector, the minimum velocity for the creation of an iridodialysis at least 6 mm in length in the human eye is predicted to be 14 m/sec for impact with a projectile of 13.4 g with a 6 mm diameter tip.

Animals↗