Shear Augmented Dispersion of a Solute in a Casson Fluid Flowing in a Conduit

The unsteady dispersion of a solute in a Casson fluid flowing in a conduit (pipe/channel) is studied using the generalized dispersion model of Gill and Sankarasubramanian. With this approach, the entire dispersion process is described appropriately in terms of a simple diffusion process with the effective diffusion coefficient as a function of time, in addition to its dependence on the yield stress of the fluid. The results are accurate up to a first approximation for small times, but verified with Sharp to be exact for large times. The model brings out mainly the effect of yield stress, or equivalently, the plug flow region on the overall dispersion process. It is found that the rate of dispersion is reduced (i.e., the effective diffusivity decreases) due to the yield stress of the fluid, or equivalently, the plug flow region in the conduit. Also, the effective diffusivity increases with time, but eventually attains its steady state value below a critical time [0.48(a²/D_m) for dispersion in a pipe and 0.55(a²/D_m) for dispersion in a channel—the critical transient time for a Newtonian fluid—where a is the radius of the pipe and D_m is the molecular diffusivity]. At steady state, for dispersion in a pipe with the plug flow radius one tenth of the radius of the pipe, the effective diffusivity is reduced to about 0.78 times of the corresponding value for a Newtonian fluid at equivalent flow rates; for dispersion in a channel, the reduction factor is about 0.73 confirming the earlier result of Sharp. Further, the location of the center of mass of a passive species over a cross section is found to remain unperturbed during the course of dispersion and for different values of the plug flow parameter (i.e., the yield stress of the fluid). The study can be used as a starting first approximate solution for studying the dispersion in the cardiovascular system or blood oxygenators. © 2000 Biomedical Engineering Society. PAC00: 8719Uv, 4760+i, 8350Nj, 8370Hq, 8715Vv, 8710+e, 4755Kf     

Ciliated metaplasia in a gastric adenoma in a Swedish patient

The second European case of ciliated gastric metaplasia is presented, this time in a Swedish patient. Cilia were found in cystically dilated glands underneath a gastric adenoma. The possibility that cilia represent adaptative metaplasia aimed at expelling the retained mucus within the cysts is discussed.     

Modelling a parasystolic rhythm in a heart-transplant patient

A parasystole from a heart-transplant patient is analysed using a beat-to-beat RR interval time series obtained from an electrocardiogram (ECG). The dysrhythmia, resulting from the co-existence of two pacemakers, the sinus node and an ectopic focus, presents distinctive regular patterns, with transitions from one pattern to another occurring abruptly. It is shown that the parasystolic rhythm can be simulated by a model involving two oscillators firing at fixed rates, under the restriction that neither is allowed to fire during the other's refractory period. It is found that the structure of the generated RR time series is essentially determined by the ratio of the periods of the two oscillators. In the case of a heart-transplant patient with a small heart-rate variability as a result of heart denervation, the model predicts the RR intervals with an error of less than 6% for an 80-beat sequence. From a physiological point of view, the results imply that the interaction between the two pacemakers in the heart is fairly weak, and hence the parasystole observed in the heart-transplant patient can be modelled as pure parasystole.     

Modelling a parasystolic rhythm in a heart-transplant patient

A parasystole from a heart-transplant patient is analysed using a beat-to-beat RR interval time series obtained from an electrocardiogram (ECG). The dysrhythmia, resulting from the co-existence of two pacemakers, the sinus node and an ectopic focus, presents distinctive regular patterns, with transitions from one pattern to another occurring abruptly. It is shown that the parasystolic rhythm can be simulated by a model involving two oscillators firing at fixed rates, under the restriction that neither is allowed to fire during the other's refractory period. It is found that the structure of the generated RR time series is essentially determined by the ratio of the periods of the two oscillators. In the case of a heart-transplant patient with a small heart-rate variability as a result of heart denervation, the model predicts the RR intervals with an error of less than 6% for an 80-beat sequence. From a physiological point of view, the results imply that the interaction between the two pacemakers in the heart is fairly weak, and hence the parasystole observed in the heart-transplant patient can be modelled as pure parasystole.     

Once in a lifetime: a case of a pineal tumour

This paper describes the case of a 14-year-old boy who presented to his general practitioner with a history of headaches and visual problems. Investigations subsequently revealed that he had a pineal tumour. The management of the patient is described and this rare condition discussed.     

Lipomedulloblastoma in a child: a controversial entity

Lipomedulloblastoma is regarded as a distinct entity that occurs exclusively in adults and has a low proliferative potential and a favorable outcome. We describe a rare case of lipomedulloblastoma in a 6-year-old female child showing a high labeling index that needs documentation. The various hypotheses of adiposal change are discussed.     

Identification of a novel astrovirus in a domestic pig in Hungary

The family Astroviridae consists of two genera, Avastrovirus and Mamastrovirus, whose members are associated with gastroenteritis in avian and mammalian hosts, respectively. We serendipitously identified a novel porcine astrovirus in a fecal specimen from a domestic pig (Sus scrofa domestica) in Hungary. Sequencing of a fragment indicated that it was an ORF1b/ORF2/3′UTR sequence, and it has been submitted to the database as porcine astrovirus type 2 (PAstV-2/Hungary/2007) with accession number GU562296. Its unique sequence characteristics and its phylogenetic position suggest that PAstV-2 could be an important link between previously reported astroviruses and that a genetically divergent lineage of astroviruses exist in piglets.     

Preventability of death in a medical intensive care unit at a university hospital in a developing country

Objective:

To determine the incidence and characteristics of preventable in-ICU deaths.

Materials and Methods:

A one-year observational study was conducted in a medical ICU of a teaching hospital. All patients who died in medical ICU beyond 24 h were analyzed and reviewed during daily medical meeting. A death was considered preventable when it would not have occurred if the patient had received ordinary standards of care appropriate for the time of study. Preventability of death was classified by using a 1-6 point preventability scale. The types of medical errors causing preventable in-ICU deaths and the contributory factors to deaths were identified.

Results:

120 deaths (47 ± 19 years, 57 months-63 weeks) were analyzed (mortality: 23%; 95% confidence interval (CI):15-31%). At admission, Acute Physiology and Chronic Health Evaluation (APACHE) II score was 18 ± 7.6 and Charlson comorbidity index was 1.3 ± 1.6. The main diagnosis was infectious disease (57%) and respiratory disease (23%). The median period between the ICU admission and death was 5 days. The rate of preventable in-ICU deaths was 14.1% (17/120). The most common medical errors related to occurrence of preventable in-ICU deaths were therapeutic error (52.9%) and inappropriate technical procedure (23.5%). The preventable in-ICU deaths were associated with inadequate training or supervision of clinical staff (58.8%), no protocol (47.1%), inadequate functioning of hospital departments (29.4%), unavailable equipment (23.5%), and inadequate communication (17.6%).

Conclusion:

According to our study, one to two in-ICU deaths would be preventable per month. Our results suggest that the implementation of supervision and protocols could improve outcomes for critically ill patients.     

Involvement of chromosome 22 in a Merkel cell carcinoma in a patient with a previous meningioma

The relatively simple cytogenetic findings in an aggressive metastatic Merkel cell carcinoma are reported. Deletion 2p was found in 100% of the cells. Nevertheless, this was considered a secondary (metastatic?) change because the same aberration has been found in several other kinds of malignancy. The involvement of chromosome 22 [del(22q) and -22] in 85% of the cells seemed more intriguing, considering the fact that the Merkel cell carcinoma followed a previous meningioma.     

Development of anuria after appendectomy in a patient with a distal ureteral stone in a single kidney

The development of anuria after appendectomy is usually related to complications associated with appendicitis or with the surgical sequelae of appendectomy. We report an unusual case of anuria after appendectomy in a 20-year-old woman. The patient was transferred to our hospital due to a sudden cessation of urine output just after appendectomy. We initially suspected that the anuria was caused by a complication of surgery. However, a review of her medical history and an abdominal computed tomography (CT) scan revealed that a distal ureteral stone in a single kidney had caused the anuria. There are few cases in the literature regarding a distal ureteral stone in a single kidney. This case indicates the importance of radiological evaluation in the differential diagnosis of acute appendicitis, especially in patients with unilateral renal agenesis.     

Growth in a Biofilm Induces a Hyperinfectious Phenotype in Vibrio cholerae

Biofilm formation plays a multifaceted role in the life cycles of a wide variety of microorganisms. In the case of pathogenic Vibrio cholerae, biofilm formation in its native aquatic habitats is thought to aid in persistence during interepidemic seasons and to enhance infectivity upon oral ingestion. The structure of V. cholerae biofilms has been hypothesized to protect the bacteria during passage through the stomach. Here, we directly test the role of biofilm architecture in the infectivity of V. cholerae by comparing the abilities of intact biofilms, dispersed biofilms, and planktonic cells to colonize the mouse small intestine. Not only were V. cholerae biofilms better able to colonize than planktonic cells, but the structure of the biofilm was also found to be dispensable: intact and dispersed biofilms colonized equally, and both vastly out-colonized planktonic cells. The infectious dose for biofilm-derived V. cholerae was orders of magnitude lower than that of planktonic cells. This biofilm-induced hyperinfectivity may be due in part to a higher growth rate of biofilm-derived cells during infection. These results suggest that the infectious dose of naturally occurring biofilms of V. cholerae may be much lower than previously estimated using cells grown planktonically in vitro. Furthermore, this work implies the existence of factors specifically induced during growth in a biofilm that augment infection by V. cholerae.Bacteria are often found in biofilms, surface-attached aggregates of microorganisms encased in an extracellular polysaccharide or protein matrix (14). Mature bacterial biofilms often assume a three-dimensional structure composed of pillars of bacteria separated by fluid-filled channels (15). Compared to their free-living, planktonic (PL) counterparts, biofilm-associated bacteria have been shown to be recalcitrant to a variety of stresses and antimicrobial agents, including chlorine, low pH, UV irradiation, antibiotics, host defenses, and more (4, 16, 21, 22, 39, 40, 44, 63, 72). The structure of the biofilm itself has been thought to physically protect the bacteria within. The decreased susceptibility of biofilms to antibiotics, for example, is understood to be due at least in part to decreased permeability of the biofilm to the antibiotic (20, 30, 60). However, growth rate and metabolic state have also been proposed to contribute to biofilm-related protection from certain antimicrobials and other stresses (5, 25, 59, 68). In addition, distinct genetic mechanisms of antibiotic resistance employed by biofilm microorganisms have been described (34, 41, 42).The ability to form biofilms is a virulence determinant of many microorganisms. Classic examples of biofilm infections include chronic infections of the cystic fibrosis lung by Pseudomonas aeruginosa, Haemophilus influenzae and Streptococcus pneumoniae in chronic otitis media, uropathogenic Escherichia coli in recurrent urinary tract infections, and disease caused by microbial biofilms on a variety of indwelling medical devices (27, 35, 36, 52, 56). The reduced susceptibility of in vivo biofilms to antimicrobials has a huge impact on human health due to the difficulty involved in their eradication.In other instances, biofilm formation contributes to a microorganism''s survival in an environmental niche, such as in water system piping or on other solid surfaces, and consequently affects the likelihood of contact with a host (24, 58, 69). Vibrio cholerae is the causative agent of cholera and is a natural inhabitant of freshwater, marine, and estuarine environments. In the aquatic environment, V. cholerae has been observed to form biofilms on abiotic and biotic surfaces, including those of zooplankton, phytoplankton, algae, and crustaceans (23, 33, 62). This surface-attached state is thought to be the primary means of persistence of V. cholerae in the environment, providing protection from a variety of stresses and, when the bacteria are attached to chitin, a source of nutrients and a forum for acquiring new genetic material (43, 45, 46, 50, 67, 71). Moreover, biofilms are likely a form in which pathogenic (toxigenic) V. cholerae is consumed by humans, and they provide a means by which humans can obtain a concentrated infective dose (13, 28, 32). Because chitin- and biofilm-associated V. cholerae is better able to survive acid exposure (50, 72), it has been hypothesized that V. cholerae biofilms are protected during transit through the gastric acid barrier of the stomach, thus allowing more bacteria to reach the small intestine colonization site. Yet the role of stomach acid in susceptibility to cholera is unclear in humans (26), and the infant mouse, with neutral pH in the stomach, may be an irrelevant model of this phenomenon.In this work, we test the hypothesis that the biofilm structure itself enhances colonization of the small intestine by V. cholerae. Instead, we found that V. cholerae bacteria dispersed from a biofilm are as infectious as those in an intact biofilm and that both are dramatically more infectious than free-living, planktonic cells in the infant mouse model. This work suggests that the physiological state of V. cholerae in biofilms, and not the biofilm structure, is the primary contributor to hyperinfectivity.     

Hantavirus infection during a stay in a mountain hut in Northern Slovakia

Hantaviruses in Europe cause human hemorrhagic fever with renal syndrome (HFRS) with various degree of severity. The most severe form is caused by the Dobrava/Belgrade virus (DOBV), associated with the rodent Apodemus flavicollis. During the last decade cases of infection caused by DOBV have been reported in Central Europe. The present study is a report on two Czech patients with severe HFRS who were infected during their stay in a mountain hut in Northern Slovakia. The two patients, combined with a third case observed in the same year in a nearby village in the Czech Republic, suggest that this region in Central Europe has to be considered as endemic for HFRS.     

Chondrocyte-seeded collagen matrices implanted in a chondral defect in a canine model

The objective of our study was to evaluate reparative tissues formed in chondral defects in an adult canine model implanted with cultured autologous articular chondrocytes seeded in type I and II collagen–GAG matrices. Two defects were produced in the trochlea grooves of the knees of 21 dogs, with cartilage removed down to the tidemark. This study includes the evaluation of 36 defects distributed among five treatment groups: Group A, type II collagen matrix seeded with autologous chondrocytes under a sutured type II collagen flap; Group B, type I collagen matrices seeded with chondrocytes under a sutured fascia flap; Group C, unseeded type I collagen matrix implanted under a sutured fascia flap; Group D, fascia lata flap alone; and Group E, untreated defects. All animals were killed 15 weeks after implantation. Six other defects were created at the time of death and evaluated immediately after production as ‘acute defect controls’. In three additional defects, unseeded matrices were sutured to the defect and the knee closed and reopened after 30 min to determine if early displacement of the graft was occurring; these defects served as ‘acute implant controls’. The areal percentages of four tissue types in the chondral zone of the original defect were determined histomorphometrically: fibrous tissue (FT); hyaline cartilage (HC); transitional tissue (TT, including fibrocartilage); and articular cartilage (AC). New tissue formed in the remodeling subchondral bone underlying certain defects was also assessed. Bonding of the repair tissue to the subchondral plate and adjacent cartilage, and degradation of the adjacent tissues were evaluated.

There were no significant differences in the tissues filling the original defect area of the sites treated with chondrocyte-seeded type I and type II matrices. Most of the tissue in the area of the original defect in all of the groups was FT and TT. The areal percentage of HC plus AC was highest in group E, with little such tissue in the cell-seeded groups, and none in groups C and D. The greatest total amount of reparative tissue, however, was found in the cell-seeded type II matrix group. Moreover, examination of the reparative tissue formed in the subchondral region of defects treated with the chondrocyte-seeded collagen matrices (Groups A and B) demonstrated that the majority of the tissue was positive for type II collagen and stained with safranin O. These results indicate an influence of the exogenous chondrocytes on the process of chondrogenesis in this site. In all groups with implants (A–D), 30–50% of the FT and TT was bonded to the adjacent cartilage. Little of this tissue (6–22%) was attached to the subchondral plate, which was only about 50% intact. Remarkable suture damage was found in sections from each group in which sutures were used. Harvest sites showed no regeneration of normal articular cartilage, 18 weeks after the biopsy procedure.

Future studies need to investigate other matrix characteristics, and the effects of cell density and incubation of the seeded sponges prior to implantation on the regenerative response.