Effects of Adsorbed Polymers on the Axisymmetric Motion of Two Colloidal Spheres

The effects of adsorbed polymer on the slow motion of two spherical particles along the line of their centers are examined semianalytically. The particles may have unequal radii, and their surface polymer layers are allowed to differ in characteristics. The surface polymer layer on each particle is assumed to be thin relative to the radius of the particle and to the surface-to-surface distance between the particles. A method of matched asymptotic expansions in small parameters lambdai (where i = 1 and 2) combined with a boundary collocation technique is used to find the solution for the creeping flow field within and outside the adsorbed polymer layers, where lambdai is the ratio of the polymer-layer length scale to the radius of particle i. The results for the hydrodynamic forces exerted on the particles in a resistance problem and for the particle velocities in a mobility problem are expressed in terms of the effective hydrodynamic thicknesses (Li) of the polymer layers, which are accurate to O(lambdai2). The O(lambdai) term for Li normalized by its value in the absence of the other particle is found to be independent of the polymer segment distribution, the hydrodynamic interactions among the segments, and the volume fraction of the segments. The O(lambdai2) term for Li, however, is a sensitive function of the polymer segment distribution and the volume fraction of the segments. In general, the effects of particle interactions on the motion of polymer-coated particles can be quite significant, especially when the particles are moving in the opposite directions. Copyright 1997 Academic Press. Copyright 1997Academic Press

Aortic and mitral valve replacement with reconstruction of the intervalvular fibrous body

OBJECTIVE

The intervalvular fibrous body between the aortic and mitral valves can be damaged by infective endocarditis, degenerative calcification, or multiple previous heart valve operations, making double valve replacement difficult. We have managed this problem by approaching the aortic and mitral valves through the aortic root and the dome of the left atrium. After excising the aortic valve, the diseased fibrous body, and the mitral valve, we suture a properly tailored patch of Dacron fabric or bovine pericardium to the lateral and medial fibrous trigones and to the aortic root, reestablishing the aortic and mitral anuli. A prosthetic mitral valve is implanted and a separate patch is used to close the left atriotomy before implantation of a prosthetic aortic valve. This study was undertaken to determine the efficacy of this operation.

METHODS

Forty-three patients underwent reconstruction of the intervalvular fibrous body during aortic and mitral valve replacement because of infective endocarditis with abscess in 14 patients, extensive calcification in 9, lack of fibrous tissue because of multiple previous operations in 10, and to enlarge the aortic and mitral anuli in 10. The group comprised 18 men and 25 women with a mean age of 58 +/- 12 years. Thirty-two patients had had one or more previous heart valve replacements. All patients were in New York Heart Association functional classes III and IV, and 9 patients were in shock before the operation.

RESULTS

Seven operative deaths occurred (16%). Early prosthetic valve endocarditis developed in two patients and necessitated reoperation. Follow-up extended from 4 to 108 months, with a mean of 38 months. No patient was lost to follow-up. Six late deaths occurred. The actuarial survival at 6 years was 56% +/- 6%. A Doppler echocardiographic study revealed normal prosthetic valve function and anatomically intact anuli in all 30 long-term survivors.

CONCLUSIONS

Reconstruction of the intervalvular fibrous body during aortic and mitral valve replacement is a satisfactory operative approach in patients with complex valve annular pathology.

Altered antigenicity of 'a' determinant variants of hepatitis B virus

The 'a' determinant of hepatitis B virus (HBV) surface antigen (HBsAg) is the most important target for diagnosis and immunoprophylaxis. Several HBV variants with point mutations within the 'a' determinant have been identified among fully vaccinated children in Taiwan. We investigated the effect of each of these mutations on the antigenic nature of the S protein by cloning and expression of the mutant S antigens in Pichia pastoris. Four variants, Ser-126, His-129, Arg-129 and Arg-145, all exhibited various degrees of altered binding of HBsAg to several monoclonal antibodies. Arg-145, a well-characterized immune escape mutant, and Arg-129 had the lowest binding capacities to all monoclonal antibodies as compared with other variants. Similar to Arg-145, the Arg-129 variant could be isolated from both vaccinated children and unvaccinated adults, thus representing a naturally occurring mutant with an altered 'a' determinant. Whether these 'a' determinant variants with altered antigenicity might gradually become major circulating strains, as a consequence of the immune pressure against the wild-type HBV created by vaccination, remains to be monitored.

Application of amplified restriction fragment length polymorphism for genetic characterization of colletotrichum pathogens of alfalfa

ABSTRACT Amplified restriction fragment length polymorphism (AFLP) was used to assess the levels of genomic variations among species and isolates of the genus Colletotrichum. Our objective was to characterize at the molecular level two alfalfa pathogens, isolates Arl-NW and 57RR, which are unusually aggressive to anthracnose-resistant alfalfa cultivars and whose taxa has been uncertain based on morphological criteria. The fingerprint patterns obtained were complex but did enable us to place these two isolates within the species C. trifolii and C. gloeosporioides, respectively. The diversity detected with AFLP among and within Colletotrichum species from alfalfa and other crops corroborated their published taxonomy based on morphology, ribosomal DNA sequence, and random amplified polymorphic DNA analyses. Similarity matrices generated with three primer pairs were highly correlated and, thus, were combined to determine the similarity among the fungal species and isolates that were analyzed. Analysis of the data generated with each of the primer pairs individually and application of either distance or parsimony methods supported the placement of these two isolates. The parsimony method of data analysis was more confirmatory in the placement of Phoma medicaginis as an out-group than the distance method, using either simple matching or Jaccard's coefficients to generate the similarity matrices. Our conclusion is that the AFLP technique will be useful for identification of individual isolates within complex genera such as Colletotrichum because of its ability to generate large numbers of polymorphisms and the consistency of polymerase chain reaction amplification.

Motion of a Colloidal Particle Coated with a Layer of Adsorbed Polymers in a Spherical Cavity

An analytical study is presented for the quasisteady translation and steady rotation of a spherical particle covered by a layer of adsorbed polymers located at the center of a spherical cavity that may also have an adsorbed polymer layer on its inside wall. The Reynolds number is assumed to be small, and the surface polymer layers are assumed to be thin with respect to the particle radius and the spacing between solid surfaces. To solve the Stokes flow equations within and outside the polymer layers a method of matched asymptotic expansions in small parameters lambda1 and lambda2 is used, where lambda1 and lambda2 are the ratios of the polymer-layer length scale to the radius of curvature at the particle surface and at the cavity wall, respectively. The results for the hydrodynamic force and torque exerted on the particle are expressed as an effective hydrodynamic thickness (L) of the adsorbed polymer layer surrounding the particle, which are accurate to O(lambda21). The O(lambda1) term for L normalized by its value in the absence of the cavity is found to be independent of the polymer segment distribution, the hydrodynamic interactions among the segments, and the volume fraction of the segments. The O(lambda21) term for L, however, is a sensitive function of the polymer segment distribution and the volume fraction of the segments. In general, the boundary effects on the motion of a polymer-coated particle can be quite significant in appropriate situations.

Speech-evoked brainstem frequency-following responses during verbal transformations due to word repetition

Speech-evoked brainstem frequency-following responses (FFRs) were recorded to repeated presentations of the same stimulus word. Word repetition results in illusory verbal transformations (VTs) in which word perceptions can differ markedly from the actual stimulus. Previous behavioral studies support an explanation of VTs based on changes in arousal or attention. Horizontal and vertical dipole FFRs were recorded to assess responses with putative origins in the auditory nerve and central brainstem, respectively. FFRs were recorded from 18 subjects when they correctly heard the stimulus and when they reported VTs. Although horizontal and vertical dipole FFRs showed different frequency response patterns, dipoles did not differentiate between perceptual conditions. However, when subjects were divided into low- and high-VT groups (based on percentage of VT trials), a significant Condition x Group interaction resulted. This interaction showed the largest difference in FFR amplitudes during VT trials, with the low-VT group showing increased amplitudes, and the high-VT group showing decreased amplitudes, relative to trials in which the stimulus was correctly perceived. These results demonstrate measurable subject differences in the early processing of complex signals, due to possible effects of attention on the brainstem FFR. The present research shows that the FFR is useful in understanding human language as it is coded and processed in the brainstem auditory pathway.

Partially Molten Middle Crust Beneath Southern Tibet: Synthesis of Project INDEPTH Results

INDEPTH geophysical and geological observations imply that a partially molten midcrustal layer exists beneath southern Tibet. This partially molten layer has been produced by crustal thickening and behaves as a fluid on the time scale of Himalayan deformation. It is confined on the south by the structurally imbricated Indian crust underlying the Tethyan and High Himalaya and is underlain, apparently, by a stiff Indian mantle lid. The results suggest that during Neogene time the underthrusting Indian crust has acted as a plunger, displacing the molten middle crust to the north while at the same time contributing to this layer by melting and ductile flow. Viewed broadly, the Neogene evolution of the Himalaya is essentially a record of the southward extrusion of the partially molten middle crust underlying southern Tibet.

A PCR-based DNA fingerprinting technique: AFLP for molecular typing of bacteria

Amplified restriction fragment polymorphism (AFLP) is a PCR-based DNA fingerprinting technique. In AFLP analysis, bacterial genomic DNA is digested with restriction enzymes, ligated to adapters, and a subset of DNA fragments are amplified using primers containing 16 adapter defined sequences with one additional arbitrary nucleotide. Polymorphisms of different Escherichia coli strains or Agrobacterium tumefaciens strains were demonstrated as distinct, unique bands in a denaturing sequencing gel using AFLP. The polymorphisms detected between BL21 and BL21F'IQ and between DH5 alpha and DH5 alpha F'IQ strains indicated that AFLP is able to resolve differences in F' episomal DNA (approximately 100 kb).

Dysrhythymia from an intrapericardial air gun pellet: a case report

We report a case of penetrating intrapericardial injury caused by an air gun pellet in which the onset of dysrhythmia suggested that the pericardium had been breached. Electrocardiographic changes appeared to be more useful in diagnosing pericardial penetration than transthoracic echocardiogram in this case.

Suture loop restriction of the medtronic hall valve: late presentation of a rare complication

Restriction of movement of the occluder of a single disc prosthetic valve is a serious and potentially fatal complication. We present a case in which the movement of the disc of a Medtronic Hall aortic valve was restricted by a loop of aortotomy closing suture inadvertently passed around the central guide of the valve.

A family cluster of an immune escape variant of hepatitis B virus infecting a mother and her two fully immunized children

A hepatitis B virus (HBV) immune escape variant which results from a substitution of glycine by arginine at position 145 (arginine-145) in the immunodominant neutralization epitope of the S protein was found to infect one child in a seroepidemiologic survey of 1,812 vaccinated children. The child's mother and a younger brother were also infected by the same HBV variant, despite a greater than accepted level of protective antibody (anti-HBV surface antigen) in both the index child (30 mIU/ml) and the brother (> 20,000 mIU/ml). Our findings suggest the perinatal or horizontal transmission of the arginine-145 HBV variant from mother to child, but the ability of this variant to propagate among the vaccinated children remains unknown.

Characterization of a recombinant pneumolysin and its use as a protein carrier for pneumococcal type 18C conjugate vaccines

Pneumolysin from Streptococcus pneumoniae was expressed in Escherichia coli as a glutathione S-transferase fusion protein and purified by affinity and hydroxylapatite chromatography. The purified recombinant pneumolysin (rPL), with a molecular mass of 53 kDa, had a specific activity of 3 x 10(5) hemolytic units per mg of protein on rabbit erythrocytes and reacted identically in immunodiffusion with the antisera against native pneumolysin. The rPL was used as a protein carrier to prepare conjugate vaccine with pneumococcal type 18C polysaccharide (PS18C). The PS18C was directly coupled to rPL by reductive animation or was indirectly coupled to rPL via a spacer molecule, adipic acid dihydrazide. The conjugates were nontoxic for mice and guinea pigs at 100 micrograms per dose. The immunogenicity and protective efficacy of both conjugates were tested in mice. A single dose of either of the vaccines elicited a rise in immunoglobulin G antibody production; after two booster injections of the vaccines, statistically significant booster responses (P < 0.001) to both rPL and PS18C were produced. The sera containing the antibodies to rPL were capable of neutralizing the hemolytic activity of rPL to rabbit erythrocytes and the cytotoxicity of rPL to bovine pulmonary endothelial cells. Immunization with the conjugate vaccines conferred statistically significant protection in mice against lethal challenge with type 18C pneumococci.

Resolution of isoforms of natural and recombinant fibrolase, the fibrinolytic enzyme from Agkistrodon contortrix contortrix snake venom, and comparison of their EDTA sensitivities

Fibrolase, the fibrinolytic enzyme from Agkistrodon contortrix contortrix snake venom, is a zinc metalloproteinase with a molecular mass of 23 kDa. We report a method to isolate two isoforms of natural fibrolase (fib1 and fib2) and three isoforms of recombinant fibrolase (r-fib1, r-fib2 and r-fib3) using CM 300 cation-exchange high-performance liquid chromatography. Utilizing mass spectrometry we characterized differences in molecular masses of the isoforms of r-fibrolase. These findings suggest that the isoforms differ by minor sequence variations at their amino-termini. Since the stability of fibrolase is exquisitely sensitive to the removal of zinc, we examined the EDTA sensitivity of the isoforms of fibrolase and r-fibrolase to determine if their different chromatographic behavior is related to differences in their zinc affinities. All of the isoforms examined appear to have similar zinc binding affinities. Thus, the IC50 (concentration of EDTA to produce 50% inhibition of enzymatic activity) for fib1 is 160 microM. For the closely related r-fib1, the IC50 is 180 microM. Similarly, r-fib3 has an IC50 of 140 microM.

SP-303, an antiviral oligomeric proanthocyanidin from the latex of Croton lechleri (Sangre de Drago)

SP-303, a large proanthocyanidin oligomer isolated from the latex of the plant species Croton lechleri (Eupborbiaceae) has demonstrated broad activity against a variety of DNA and RNA viruses. In cell culture, SP-303 exhibits potent activity against isolates and laboratory strains of respiratory syncytial virus (RSV), influenza A virus (FLU-A) and parainfluenza virus (PIV). Parallel assays of SP-303 and ribavirin showed comparable activity against these viruses. SP-303 also exhibits significant inhibitory activity against herpesvirus (HSV) types 1 and 2, including herpesviruses resistant to acyclovir and foscarnet. Inhibition was also observed against hepatitis A and B viruses. The antiviral mechanism of SP-303 seems to derive from its direct binding to components of the viral envelope, resulting in inhibition of viral attachment and penetration of the plasma membrane. Antiviral effects of SP-303 were measured by three distinct methods: CPE, MTT and precursor uptake/incorporation. Cytotoxicity endpoints were markedly greater than the respective antiviral endpoints. SP-303 exhibited activity in RSV-infected cotton rats and African green monkeys, PIV-3-infected cotton rats, HSV-2 infected mice and guinea pigs and FLU-A-infected mice. The most successful routes of SP-303 administration for producing efficacy were: topical application to HSV-2- genital lesions in mice and guinea pigs, aerosol inhalation to FLU-A-infected mice and PIV-3-infected cotton rats, and oral dosage to RSV-infected cotton rats. A variety of toxicological evaluations demonstrated the safety of SP-303, particularly orally, which was predictable, since condensed tannins are a common dietary component. It is notable that the larger proanthocyanidins as a class have high antiviral activity, whereas most of the monomers are inactive. Clinical trials are ongoing to evaluate SP-303 as a therapeutic antiviral agent.

Packing the chest: a useful technique for intractable bleeding after open heart operation

Mediastinal bleeding can be a problem after cardiac surgery, either as a result of coagulation derangements or technical problems. We evaluated 100 patients, treated with temporary chest packing for intractable bleeding, of 9,383 undergoing open heart operations during a 10-year period. Preoperatively, 60 of these patients had one or more predisposing factors for bleeding. There were four predominant sites of hemorrhage: general ooze, needle holes of the aortic and atrial suture lines, inaccessible origin, and another specific place. The chest was packed in the operating room in 84 patients and in the intensive care unit in 16. Four methods of temporary chest closure were used: the skin alone, partial sternal approximation plus skin closure, full closure, and the wound open and covered by a Steri-drape dressing. The bleeding was controlled in 65 patients who had been packed once, and in 29 patients after reexploration and multiple packings, for a total of 94 patients (94%). Sternal wound infection, generalized sepsis, and sternal dehiscence was present in 24 patients, 8 of whom died. The venue for inserting or removing the packs did not affect the incidence of infections. Our experience suggests that packing of the chest after cardiac procedures for intractable bleeding allows a reasonable patient salvage rate and complication risks.

Daily selenium intake estimates for residents of arsenic-endemic areas

The selenium in the diet of persons in arsenic-endemic areas, high levels of arsenic in the drinking water, was evaluated. The methodology used was that of 24-hr dietary recall. Daily selenium intakes of two rural towns in northern Mexico were found to be similar, approximating 72.9 and 60.6 micrograms. These values were similar to those of a previously arsenic-exposed area from California, Edison community. The Edison participants had a daily selenium intake of 61.8 micrograms. The possible negative effect of selenium to produce differences in reported geographical variation in disease could not be substantiated in this study. Other nutrient intakes, protein and energy were also found similar for communities. Differences were noted in vitamin A intake where one-third the daily requirement was experienced by Mexican participants compared to two-thirds the requirement being satisfied by those participants from Edison.

Myocardial infarction due to coronary artery compression by aortic root abscess

A 44-year-old man with aortic valve disease presented with myocardial ischaemia and ultimately infarction in the presence of suspected endocarditis. Thoracic computerised tomographic scan and coronary arteriography suggested the ischaemia was caused by external compression of the left coronary artery due to an aortic root abscess, later confirmed at surgery. Myocardial ischaemia is an infrequent accompaniment of infective endocarditis and is most commonly due to coexisting coronary disease. More rarely, emboli from vegetations may give rise to infarction. Although aortic root abscess is a well recognised complication of aortic valve endocarditis, coronary artery compression is an unusual mode of presentation and we believe this to be the first reported case of myocardial infarction resulting from external compression in this setting.

Microanalytical studies of metal localization in biological tissues by environmental SEM

The presence and distribution of Al and Mn in floral and seed tissues of eucalypts from Al-contaminated soils was analyzed using energy-dispersive X-ray microanalysis (EDS) in an environmental scanning electron microscope (ESEM). EDS by ESEM determined the distribution of elements between tissue types was suitable for intact samples or those with lower available moisture or intact specimens. The analytical technique was not appropriate for highly vascular samples. Other factors influencing the detection of elements by ESEM-EDS were electron scattering and the relative concentration and localization of elements within the tissues. EDS-detectable levels were significantly correlated with tissue concentrations determined by atomic absorption spectrophotometry for Mn but not for Al.

Effect of vascular clamp on endothelial integrity of the internal mammary artery

The preservation of endothelial integrity is essential for maintaining patency of vascular grafts. The internal mammary artery flow is often interrupted with the application of a soft vascular clamp to achieve a bloodless field during the anastomosis. We investigated the effect of the vascular clamp on the internal mammary artery endothelium using the scanning electron and light microscope. The endothelium was examined before and at 15 and 30 minutes after clamping in both the pedicled and the skeletonized arteries. Endothelial integrity was breached by clamping with early evidence of platelet adhesion to the damaged areas. The severity of the endothelial damage was related to the clamp time, but there was no difference in the degree of damage between the pedicled and the skeletonized arteries. We conclude that the vascular clamp causes injury to the internal mammary artery endothelium and may be implicated in early postoperative graft failure.

Microscopic evidence on how iron deficiency limits nodule initiation in Lupinus angustifolius L

Lupins (Lupinus angustifolius L. ev. Yandee), grown in solution culture, have been used to study the sites and process of infection by Bradyrhizobium sp. (Lupinus) and the impairment of nodulation by iron deficiency. Infection leading to nodulation occurred in an area of epidermal cells either lacking root hairs or with very young root hairs at the time of inoculation. Cells aged 13 h or over appeared not to be infected. Infection was initiated in the outer cortex. Rare, short infection threads were evident on day 4 after inoculation, 2 d after the initial division of cortical cells resulting from the bradyrhizobial inoculation. Bacteria had been released into the cytoplasm of cortical cells within 5 d after inoculation. Bacteroids multiplied in the cytoplasm, segregated passively and spread in the infection zones by repeated division of the invaded cells. Under iron deficiency, initial cell division occurred in the outer cortex of host roots, as in iron-sufficient plants after inoculation. Iron deficiency then limited further division of cortical cells. Only a few surviving infection sites developed nodules with normal structure but development was much slower than in iron-sufficient plants.

Oesophageal erosion of an Angelchik prosthesis: surgical management using fundoplication

Complications following insertion of the Angelchik prosthesis are becoming increasingly recognised. We report a 35-year-old patient with both mediastinal migration and intraluminal oesophageal erosion of a prosthesis. Successful management included transthoracic removal combined with a modified onlay fundoplication over the oesophageal defect to prevent gastro-oesophageal reflux.

Initial evaluation of an intracorporeal oxygenation device

We describe a recently developed intracorporeal gas transfer device, its potential applications and hazards. To date, patients with potentially reversible respiratory failure have been treated with controlled oxygen therapy and positive pressure ventilation, but this treatment may itself contribute to lung parenchymal damage from barotrauma and oxygen toxicity. Total or partial extracorporeal gas exchange can be used to reduce these risks, but this treatment is complex and has significant morbidity and mortality. This gas exchange device has been designed to provide partial gas transfer with simplicity of insertion and use. The oxygenator lies in the vena cava to provide prepulmonary gas exchange. In preliminary studies with three calves we have shown that the device increases both mean mixed venous and arterial oxygen content and reduces mean arterial carbon dioxide tension.

Genetic evidence against intramolecular rejoining of the donor DNA molecule following IS10 transposition

Tn10 and IS10 transpose by a nonreplicative mechanism in which the transposon is excised from the donor molecule and integrated into a target DNA site, leaving behind a break at the original donor site. The fate of this broken donor DNA molecule is not known. We describe here two experiments that address this issue. One experiment demonstrates that a polar IS10 element gives rise to polarity-relief revertants at less than 1% the frequency of transposition of the same element in the same culture. In a second experiment, transpositions of an IS10 element from one site in the bacterial genome to another are selected and the resulting isolates examined for alterations at the donor site; none of 1088 such isolates exhibited a detectable change at the donor locus. These results are compatible with two possible fates of the transposon donor molecule: degradation ("donor suicide"), or restoration of the original information at the donor site by a recombinational repair mechanism analogous to double-strand break repair. These results argue against the possibility that the donor molecule gap is simply resealed by intramolecular rejoining.