Impact of an irreversibly adsorbed layer on local viscosity of nanoconfined polymer melts

We report the origin of the effect of nanoscale confinement on the local viscosity of entangled polystyrene (PS) films at temperatures far above the glass transition temperature. By using marker x-ray photon correlation spectroscopy with gold nanoparticles embedded in the PS films prepared on solid substrates, we have determined the local viscosity as a function of the distance from the polymer-substrate interface. The results show the impact of a very thin adsorbed layer (~7 nm in thickness) even without specific interactions of the polymer with the substrate, overcoming the effect of a surface mobile layer at the air-polymer interface and thereby resulting in a significant increase in the local viscosity as approaching the substrate interface.

Comparison between acetylator phenotype and genotype polymorphism of n-acetyltransferase-2 in tuberculosis patients

BACKGROUND

Isoniazid (INH) is one of the most important drugs of antitubercular treatment regime, and in some cases it causes hepatotoxicity. It is metabolized by hepatic N-acetyltransferase-2 (NAT2).

AIM

To compare whether both methods, i.e., genotype NAT2 and phenotype test of measuring serum INH levels, are useful to identify acetylator status of patients on antitubercular treatment (ATT).

METHODS

A total of 251 tuberculosis (TB) patients on standard treatment were followed up to 6 months for this study. NAT2 genotype was assessed by PCR with restriction fragment length polymorphism (RFLP) whereas serum INH levels were measured by fluorometry.

RESULTS

Of the 251 patients, 50 (19.9%) developed ATT-induced hepatotoxicity. By phenotypic estimation, in the hepatotoxicity group, 17/50 (34%) were slow acetylators whereas 33/50 (66%) were fast acetylators. Genotypically, 19/50 (38%) were slow acetylators and 31/50 (62%) fast acetylators. By phenotypic analysis, in non-hepatotoxicity group, 46/201 (22.9%) were slow acetylators and 155/201 (77.1%) fast acetylators. By genotypic analysis, 30/201 (14.9%) were slow acetylators and 171/201 (85%) fast acetylators. Overall, slow acetylators (25.1%) measured phenotypically were not significantly different from slow acetylators (19.5%) measured genotypically.

CONCLUSION

This study suggests that the acetylator status of TB patients can be detected by phenotypic method as efficaciously as by genotypic method. Therefore, phenotypic method can replace genotypic method to determine acetylating status as phenotypic method is simple and inexpensive.

Evaluation of the effectiveness of ophthalmic assistants as screeners for glaucoma in North India

AIM

To assess whether ophthalmic assistants are effective in screening people for glaucoma in India.

METHODOLOGY

The study subjects were examined by both trained ophthalmic assistants and an ophthalmologist in both hospital and community settings. Specific tests for the diagnosis of glaucoma suspects included visual field examination using frequency doubling technology perimetry, intraocular pressure measurement (Tonopen), A-scan central anterior chamber depth measurement and dilated optic disc examination. The findings recorded by the ophthalmic assistants were masked to the ophthalmologist to avoid measurement bias.

RESULTS

In the hospital setting, there was a substantial level of agreement between the ophthalmic assistants and the ophthalmologist in the diagnosis of glaucoma suspects (89.29%, k=0.7, 95% confidence interval (CI)=0.54-0.86). The diagnostic accuracy of the ophthalmic assistants in detecting glaucoma suspects was high for sensitivity (95.2%, 95% CI=91.4-97.7%) but lower for specificity at 71.4% (95% CI=60.0-78.7%).In the community setting, there was a moderate level of agreement between the ophthalmic assistants and the ophthalmologist in the diagnosis of glaucoma suspects (78.23%, k=0.50, 95% CI=0.37-0.64). The diagnostic accuracy of the ophthalmic assistants in detecting glaucoma suspects was moderate for sensitivity (82.9, 95% CI=69.7-91.5%) but lower for specificity at 76.8% (95% CI=72.7-79.5%).

CONCLUSION

Ophthalmic assistants can be used for opportunistic case detection of glaucoma suspects in the community. Structured training of the ophthalmic assistants together with enhanced clinical experience would improve their performance in detecting glaucoma suspects in the community.

Pseudothrombocytopenia -- a caveat

Pseudothrombocytopenia is an ex vivo thrombocytopenia, counted by an automated cell counter, but not configured by microscopic examination of a well prepared blood smear. Incidences of pseudothrombocytopenia reported in different studies range from 0.09-0.21%, which could account for 15-30% of all cases of thrombocytopenla. Failure to identify pseudothrombocytopenia has led to a lot of clinical problems like unnecessary platelet transfusion, glucocorticoid therapy and so on. Haematological cell counters count platelets as particles with volume between 2 and 20fl. Thus platelet clumps are counted as leucocytes while fragmented RBCs as platelets. This study found pseudothrombocytopenia due to causes like EDTA blood stored at less than 32 degrees C for more than 2 hours (35%), excess EDTA in sample (10.7%), hyperlipidaemia, auto-immune disease, pregnancy, etc. No apparent cause could be found in 52% of cases. Hence it is emphasised that direct microscopic examination of a well stained blood smear from EDTA-venous blood (within 1hour) and or direct counting under Neubauer chamber with 1% ammonium oxalate (in special cases) is almost mandatory before releasing a report of platelet count. Also factors related to ratio and storage of EDTA-blood, calibration of instruments, proper selection of reagents, supervision of laboratory staff are essential to rule out any error of report including pseudothrombocytopenia.

Molecular simulation of the frictional behavior of polymer-on-polymer sliding

Molecular simulations of the sliding processes of polymer-on-polymer systems were performed to investigate the surface and subsurface deformations and how these affect tribological characteristics of nanometer-scale polymer films. It is shown that a very severe deformation is localized to a band of material about 2.5 nm thick at the interface of the polymer surfaces. Outside of this band, the polymer films experience a uniform shear strain that reaches a finite steady-state value of close to 100%. Only after the polymer films have achieved this steady-state shear strain do the contacting surfaces of the films show significant relative slippage over each other. Because severe deformation is limited to a localized band much thinner than the polymeric films, the thickness of the deformation band is envisaged to be independent of the film thickness and hence frictional forces are expected to be independent of the thickness of the polymer films. A strong dependency of friction on interfacial adhesion, surface roughness, and the shear modulus of the sliding system was observed. Although the simulations showed that frictional forces increase linearly with contact pressure, adhesive forces contribute significantly to the overall friction and must therefore be accounted for in nanometer-scale friction. It is also shown that the coefficient of friction is lower for lower-density polymers as well as for polymers with higher molecular weights.

Measurement of the interior structure of thin polymer films using grazing incidence diffuse x-ray scattering

A method is developed for calculating the small-angle x-ray scattering originating from within the interior of a thin film under grazing incidence illumination. This offers the possibility of using x-ray scattering to probe how the structure of polymers is modified by confinement. When the diffuse scattering from a thin film is measured over a range of incident angles, it is possible to separate the contributions to scattering from the interfaces and the contribution from the film interior. Using the distorted-wave Born approximation the structure factor, S(q), of the film interior can then be obtained. We apply this method to analyze density fluctuations from within the interior of a silicon supported molten polystyrene (PS) film. Measurements were made as a function of film thickness ranging from one to ten times the polymer radius of gyration (Rg). The compressibility, calculated by extrapolating the measured S(q) to q=0, agrees well with that of bulk PS for thick films, but thinner films exhibit a peak in S(q) near q=0. This peak, which grows with decreasing thickness, is attributed to a decreased interpenetration of chains and a consequent enhanced compressibility.

Reduced viscosity of the free surface in entangled polymer melt films

By embedding "dilute" gold nanoparticles in single polystyrene thin films as "markers", we probe the local viscosity of the free surface at temperatures far above the glass transition temperature (T(g)). The technique used was x-ray photon correlation spectroscopy with resonance-enhanced x-ray scattering. The results clearly showed the surface viscosity is about 30% lower than the rest of the film. We found that this reduction is strongly associated with chain entanglements at the free surface rather than the reduction in T(g).

Long term follow-up of very low birthweight infants from a neonatal volume versus pressure mechanical ventilation trial

BACKGROUND

A previous randomised trial showed volume controlled ventilation (VCV) was efficacious in ventilating very preterm and extremely low birthweight babies.

OBJECTIVE

To compare long term survival, pulmonary morbidities and gross neurodevelopmental outcomes of babies randomised to either VCV or pressure limited ventilation (PLV) for treatment of respiratory distress syndrome.

DESIGN/METHODS

Masked evaluation of health status, including frequency of respiratory illness, use of medications, hospital admissions, and gross neurodevelopmental status were obtained using a structured parental questionnaire and verification from medical records.

RESULTS

94 of 109 children (86%) survived to discharge. Three died after discharge (2 VCV, 1 PLV). Modality of ventilation did not affect overall mortality; seven VCV children died (12%) versus 11 PLV (21%) (OR 0.5 (95% CI 0.1 to 1.4), p = 0.13). Respiratory abnormalities were present in 32 (37%), and 26 (30%) required hospital readmission. There was no significant difference in readmission rates between the two groups: VC 13/45 (29%) and PLV 19/40 (47%) (OR 0.4 (0.1 to 1.1), p = 0.07). Modality of ventilation did not affect frequency of respiratory illness: VC 12 (27%) and PLV 14 (35%) (OR 0.46 (0.1 to 1.1), p = 0.09). However, significantly fewer VCV children (13%, n = 6) compared to PLV children (32%, n = 13) required treatment with inhaled steroids/bronchodilators (OR 0.3 (0.1 to 0.9), p = 0.04). Nine children had severe neurodevelopmental disability (cerebral palsy, blindness, deafness) (9.8%; 3 VCV, 6 PLV 6) (OR 0.4 (0.09 to 1.7)).

CONCLUSIONS

The efficacy of VCV in very preterm and low birth babies appears to be maintained on longer term evaluation.

Effect of predominant methanogenic flora on outcome of lactose hydrogen breath test in controls and irritable bowel syndrome patients of north India

The relationship between methanogenic flora and hydrogen (H(2)) production is considered to be a possible confounding factor in the interpretation of hydrogen breath tests (H(2)BT). Therefore, the present study was conducted prospectively and included 154 IBS patients (fulfilling Rome II criteria) and 286 age-and-sex-matched apparently healthy controls. Each subject underwent H(2)BT after overnight fasting using 25 g lactose. Methane and H(2) were measured using an SC Microlyser from Quintron, USA, at baseline and every 30 min for a total of 4 h. Subjects with fasting methane concentration <10 ppm were labeled as low methane producers (LMP) and >10 ppm as predominant methane producers (PMP). A rise >20 ppm over base line in hydrogen concentration was taken as +ve hydrogen breath test. IBS and control groups included 66.78% and 67.53% males, respectively. Mean age in the two groups were 48.52 +/- 30.54 years (range 15-68 years) and 45.67 +/- 30.54 years (range 15-78 years), respectively. Hydrogen breath test was +ve in 77/154 (50%) IBS patients and in 142/286 (49.65%) in controls (P > 0.05). It was also observed that the hydrogen breath test was -ve due to PMP in 5/77 (6.49%) of IBS patients and in 29/154 (20.14%) in controls. PMP affected lactose hydrogen breath tests in 6.49-20.14% subjects. This effect is more apparent in apparently healthy subjects as compared to patients with IBS.

Influence of previously ingested wheat on fasting breath hydrogen in celiac patients

The excretion of hydrogen in breath commonly persists, despite an overnight fast. Although the elevation of hydrogen concentration above the fasting value after the administration of a test sugar is evidence of malabsorption, the level of the fasting value itself in untreated celiac patients is unknown. Therefore, we studied the fasting breath hydrogen (FBH(2)) concentration in 40 healthy controls, 35 subjects with functional bowel disorders, and 30 patients of untreated celiac disease with and without bread or wheat diet one day before the test. The fasting level of hydrogen concentration in untreated celiac patients (28.7 +/- 19.5 ppm) was significantly higher than those in healthy volunteers (9.5 +/- 3.4 ppm) and subjects with functional bowel disorders (10.6 +/- 4.5 ppm). The percentage of patients with elevated H(2) fasting levels in untreated celiac disease (82.5%) was significantly higher than that in healthy controls (10%) and subjects with functional bowel disorders (17.1%). In 30 celiac patients, studied with and without wheat-free diet one day before the test, the fasting hydrogen levels decreased from 28.7 +/- 19.5 ppm to 10.6 +/- 3.5 ppm, and becoming normal in all patients of celiac disease. Our results show that the patients of untreated celiac disease should be instructed not to eat things made up of wheat one day before hydrogen breath testing so that the normal fasting hydrogen concentration can be obtained and false-negative hydrogen breath test results can be avoided.

The effect of two levels of pressure support ventilation on tidal volume delivery and minute ventilation in preterm infants

OBJECTIVE

To study the effect of different levels of pressure support ventilation (PSV) on respiratory parameters in preterm infants during the weaning phase of mechanical ventilation.

DESIGN/METHODS

In this quasi-experimental crossover study, a total of 19 154 breaths were analysed from 10 ventilated infants of <32 weeks' gestation. Breath-to-breath data on minute ventilation, tidal volume, respiratory rate, peak inspiratory pressure and mean airway pressure were collected during three study epochs: synchronised intermittent mandatory ventilation (SIMV) alone, SIMV with partial PSV (PS(min)), and SIMV with full PSV (PS(max)). PS(min) was set to provide an exhaled tidal volume (V(Te)) between 2.5-4 ml/kg and PS(max) 5-8 ml/kg V(Te). Statistical analyses were performed using analysis of variance (ANOVA) for repeated measures.

RESULTS

The addition of full PSV (PS(max)) was associated with a significant increase in total minute ventilation as compared with SIMV alone (392 ml/kg/min vs 270 ml/kg/min, respectively; p<0.05). This difference in minute ventilation was still present when PS(min) was used (332 ml/kg/min as compared with 270 ml/kg/min in SIMV; p<0.05). There was also a concomitant decrease in the respiratory rate with both PS(max) (59 breaths per minute) and PS(min) (65 breaths per minute) compared with SIMV alone (72 breaths per min) (p<0.05).

CONCLUSIONS

Pressure support ventilation increases total minute ventilation and stabilises breathing in proportion to the level of pressure support used. This may be advantageous and provide a useful ventilation strategy for use during weaning stages of mechanical ventilation in preterm infants.

Complex dynamics in polymer nanocomposites

Polymer nanocomposites offer the potential to create a new type of hybrid material with unique thermal, optical, or electrical properties. Understanding their structure, phase behavior, and dynamics is crucial for realizing such potentials. In this work we provide an experimental insight into the dynamics of such composites in terms of the temperature, wave vector, and volume fraction of nanoparticles, using multispeckle synchrotron x-ray photon correlation spectroscopy measurements on gold nanoparticles embedded in polymethylmethacrylate. Detailed analysis of the intermediate scattering functions reveals possible existence of an intrinsic length scale for dynamic heterogeneity in polymer nanocomposites similar to that seen in other soft materials like colloidal gels and glasses.

Thickness induced structural changes in polystyrene films

Changes to the structure of polystyrene melt films as measured through the spectrum of density fluctuations have been observed as a function of film thickness down to the polymer radius of gyration (Rg). Films thicker than 4Rg show bulklike density fluctuations. Thinner films exhibit a peak in S(q) near q=0 which grows with decreasing thickness. This peak is attributed to a decreased interpenetration of chains resulting in an enhanced compressibility. Measurements were made using small angle x-ray scattering in a standing wave geometry designed to enhance scattering from the interior of the film compared to interface scattering.

Orocecal transit time in patients with celiac disease from North India: a case control study

AIM

The mechanisms responsible for bowel disturbances in celiac disease are still unknown. Small bowel motor abnormalities may be involved in this pathological condition; however, there is no study addressing small bowel transit in patients of celiac disease from Northern India.

METHOD

The mouth-to-cecum transit time was studied in 80 celiac patients and 80 age and sex matched apparently healthy controls.

RESULTS

Orocecal transit time in celiac patients was significantly delayed being 180+/-10.6 minutes (Mean+/-SE) as compared to 105+/-12.4 minutes in apparently healthy controls.

CONCLUSION

This prolonged orocecal transit time could be due to impaired small bowel function (deranged motility) in patients with celiac disease.

Squeeze-out of branched alkanes on graphite

We study squalane and heptamethylnonane (HMN) confined between a conducting atomic force microscope tip and a graphite surface. Solvation layering occurs for both liquids but marked differences in the squeeze out mechanics are observed for ordered or disordered monolayers. The squalane monolayer at 25 degrees C is an ordered solid, as verified by direct imaging, and the squeeze out can be modeled using elastic continuum mechanics. HMN is in a disordered state at 25 degrees C and cannot be modeled as a single elastic asperity even in solid-solid contact because HMN liquid is trapped in the contact zone.

Study of small intestinal bacterial overgrowth in North Indian patients with irritable bowel syndrome: a case control study

BACKGROUND

Approximately 20% of the general population has irritable bowel syndrome. Despite this high prevalence, the cause of irritable bowel syndrome is unknown. There is no data available concerning the prevalence of small intestinal bacterial overgrowth in North Indian patients with irritable bowel syndrome.

AIM

This study evaluated the prevalence of small intestinal bacterial overgrowth in patients with irritable bowel syndrome compared with healthy controls.

METHODS

This study included 225 consecutive patients of irritable bowel syndrome between the ages 20 and 65 years attending the gastroenterology clinics. Diagnosis of irritable bowel syndrome was made according to the Rome II criteria. Small intestinal bacterial overgrowth was estimated by using the non-invasive glucose hydrogen breath test.

RESULTS

Of 225 patients of irritable bowel syndrome, 160 (71.1%) were male and 65 (28.9%) were female. Of 100 controls, 65 (65%) were male and 35 (35%) female. The prevalence of small intestinal bacterial overgrowth was 25 of 225 (11.1%) patients with irritable bowel syndrome and 1 of 100 (1%) in apparently healthy controls. This difference was statistically significant. The prevalence of small intestinal bacterial overgrowth in male and female patients was not significantly different.

CONCLUSION

This study indicates that the prevalence of small intestinal bacterial overgrowth in irritable bowel syndrome patients from North India is approximately 11.1%, which is lower than the reported prevalence.

Traumatic orbitomaxillary encephalocele

A rare case of occult traumatic intramaxillary encephalocele and intraorbital encephalocele without obvious connection to exterior is described

Small intestinal bacterial overgrowth in North Indian patients with celiac disease

BACKGROUND

Occasionally celiac patients continue to experience gastro-intestinal symptoms even with a gluten free diet. In these cases, small intestinal bacterial overgrowth may be one of the causes of the lack of response. Therefore, this prospective study was planned to determine the prevalence of small intestinal bacterial overgrowth in celiac patients.

MATERIALS AND METHODS

We studied 87 confirmed cases of celiac disease from North India and 87 age and sex matched controls. Celiac disease was confirmed by positive IgA antitissue transglutaminase on ELISA. 80 g glucose hydrogen breath test (non-invasive test) was performed to establish small intestinal bacterial overgrowth. Rise of more than 10 ppm in hydrogen concentration over baseline value within two hours was considered suggestive of small intestinal bacterial overgrowth.

RESULTS

Out of 87 patients with celiac disease, 49 were male and 38 were female. The mean (+/-SD) age for male patients was 26.3 +/- 16.3 years (range 14-59 years) and for female patients was 28.4 +/- 15.6 years (range 16-58 years). Amongst the controls, 52 (59.8%) were male and 35 (40.2%) were female. The mean (+/- SD) age for male controls was 27.6 +/- 14.5 years (range 15-57 years) and for female controls was 29.3 +/- 16.5 years (range 18-59 years). Hydrogen breath test was suggestive of bacterial overgrowth in 18 of the 87 (20.7%) celiac disease patients but not in any of the apparently healthy controls.

CONCLUSION

This study indicates that a large number of celiac patients from North India suffer from bacterial overgrowth which can be accordingly treated with antibiotics.

Partially wetting thin liquid films: structure and dynamics studied with coherent x rays

We studied the surface structure of thin liquid films vapor deposited on solid substrates in a partial wetting situation by means of coherent x-ray scattering. No dynamics has been observed showing the absence of capillary waves on liquid films partially wetting a substrate. Instead an exponential form of the height-height correlation function has been found pointing toward a solidlike behavior of the thin liquid films at large length scales. The exact surface structure and degree of replication with the substrate depend on the deposition rate of the molecules.

Solvation and squeeze out of hexadecane on graphite

We have performed simultaneous force and conductivity measurement of hexadecane liquid confined between a conducting atomic force microscope tip and a graphite surface. Both the current and the force data reveal discrete solvation layering of the hexadecane near the surface. We typically observe that the current does not vary with load in a simple way as the layer closest to the surface is compressed, but increases markedly prior to the expulsion of material from the tip-sample gap. We infer that even for a nanoscale asperity there is conformation change of the confined hexadecane under the tip apex prior to squeeze out of the molecules.

Evidence for viscoelastic effects in surface capillary waves of molten polymer films

The surface dynamics of supported ultrathin polystyrene films with thickness comparable to the radius of gyration were investigated by surface sensitive x-ray photon correlation spectroscopy. We show for the first time that the conventional model of capillary waves on a viscous liquid has to be modified to include the effects of a shear modulus in order to explain both static and dynamic scattering data from ultrathin molten polymer films.

Isolation and characterization of microsomal omega-6-desaturase gene (fad2-1) from soybean

A genomic DNA sequence (fad2-1) encoding seed specific microsomal 0-6 desaturase was isolated from soybean (Glycine max. L cv. Pusa-9702). A positive genomic clone of 1852 nucleotides containing a single uninterrupted 3' end exonic region with an ORF of 1140 bp encoding a peptide of 379 amino acids, a complete 3' UTR of 206 bp and 86 bp of 5' UTR interrupted by a single intron of 420 bp was obtained on screening the sub-genomic library of soybean. Southern blots revealed at least two copies of the gene per haploid genome. Analysis of the translated product showed the presence of three histidine boxes, with the general sequence HXXXH and five probable transmembrane segments reported to be involved in substrate specificity.

Minimising ventilator induced lung injury in preterm infants

Ventilator induced lung injury continues to occur at an unacceptably high rate, which is inversely related to gestational age. Although the "new BPD" may not be entirely avoidable in the extremely premature infant, recognition of risk factors and adoption of an appropriate ventilatory strategy, along with continuous real time monitoring, may help to minimise lung damage. This paper will review the pathogenesis of ventilator induced lung injury and strategies that may mitigate it.