Numerical simulations of pulsatile blood flow using a new constitutive model

In the present paper we use a new constitutive equation for whole human blood [R.G. Owens, A new microstructure-based constitutive model for human blood, J. Non-Newtonian Fluid Mech. (2006), to appear] to investigate the steady, oscillatory and pulsatile flow of blood in a straight, rigid walled tube at modest Womersley numbers. Comparisons are made with the experimental results of Thurston [Elastic effects in pulsatile blood flow, Microvasc. Res. 9 (1975), 145-157] for the pressure drop per unit length against volume flow rate and oscillatory flow rate amplitude. Agreement in all cases is very good. In the presentation of the numerical and experimental results we discuss the microstructural changes in the blood that account for its rheological behaviour in this simple class of flows. In this context, the concept of an apparent complex viscosity proves to be useful.     

Effect of local aromatase inhibition in endometriosis using a new chick embryo chorioallantoic membrane model

Endometriosis is an oestrogen‐dependent, inflammation‐driven gynaecologic disorder causing severe disability. Endometriosis implants are characterized by unbalanced local oestrogen metabolism leading to hyperoestrogenism and aromatase up‐regulation is one of main mechanism involved. Aromatase inhibitors such as letrozole or anastrozole use in young women are associated with severely side effects limiting their long‐term clinical use. An endometriosis‐targeted inhibition of local aromatase could be a viable alternative, although the role of the local inhibition of this enzyme is still unclear. Using a new chick embryo allantoic membrane (CAM) model incorporating xenografted human endometriosis cyst, we showed that topical treatment with anastrozole reduced lesion size, although oestrogens produced by CAM female embryo blunted this effect. Xenografted human endometriosis CAM is a new efficient model for the screening of new drugs targeting endometriosis tissue.     

Nidogen: a new, self-aggregating basement membrane protein

Nidogen was purified from a mouse tumor basement membrane where it accounted for 2-3% of the total proteins. It was isolated as two forms (A and B) of a monomer (Mr = 80000) each consisting of a single polypeptide chain folded into a globular head connected to a small tail. The B form of the monomer was shown to be capable of aggregating into a nest-like structure (Mr greater than 250000). A smaller form (Mr = 45000) was observed in some of the extracts. The amino acid composition of nidogen was different to that of other basement membrane proteins. It contained about 10% carbohydrate, with N-linked and O-linked oligosaccharide chains in similar proportions. Isoelectrofocussing demonstrated a limited heterogeneity of nidogen with pI in the range 6.5 - 7. Monomeric nidogen failed to interact with other basement membrane components and heparin. Aggregation could be induced by limited proteolysis and was reversed by detergents or high salt concentrations. Together with the observation that most of the nidogen could be solubilized only after destroying the collagenous matrix, the data indicate that aggregation of nidogen reflects an activity involved in matrix assembly. Specific antibodies raised against nidogen did not distinguish between the monomeric and aggregated form of the protein but showed that the fragment was antigenically deficient. These antibodies did not cross-react with collagen type IV, laminin, entactin and heparansulfate proteoglycan. Immunofluorescence staining and absorption studies demonstrated that nidogen is a common component of authentic basement membranes. Larger forms of nidogen (Mr about 100000 and 150000) were found in organ cultures of Reichert's membrane suggesting that it is synthesized in precursor forms.     

The adductor flap: a new method for transferring posterior and medial thigh skin

Skin flaps from the medial aspect of the thigh have traditionally been based on the gracilis musculocutaneous unit. This article presents anatomic studies and clinical experience with a new flap from the medial and posterior aspects of the thigh based on the proximal musculocutaneous perforator of the adductor magnus muscle and its venae comitantes. This cutaneous artery represents the termination of the first medial branch of the profunda femoris artery and is consistently large enough in caliber to support much larger skin flaps than the gracilis musculocutaneous flap. In all 20 cadaver dissections, the proximal cutaneous perforator of the adductor magnus muscle was present and measured between 0.8 and 1.1 mm in diameter, making it one of the largest skin perforators in the entire body. Based on this anatomic observation, skin flaps as large as 30 x 23 cm from the medial and posterior aspects of the thigh were successfully transferred. Adductor flaps were used in 25 patients. On one patient the flap was lost, in one the flap demonstrated partial survival, and in 23 patients the flaps survived completely. The flap was designed as a pedicle island flap in 14 patients and as a free flap in 11.When isolating the vascular pedicle for free tissue transfer, the cutaneous artery is dissected from the surrounding adductor magnus muscle and no muscle is included in the flap. Using this maneuver, a pedicle length of approximately 8 cm is isolated. In addition to ample length, the artery has a diameter of approximately 2 mm at its origin from the profunda femoris artery. The adductor flap provides an alternative method for flap design in the posteromedial thigh. Because of the large pedicle and the vast cutaneous territory that it reliably supplies, the authors believe that the adductor flap is the most versatile and dependable method for transferring flaps from the posteromedial thigh region.     

Magnetic drug targeting through a realistic model of human tracheobronchial airways using computational fluid and particle dynamics

Biomechanics and Modeling in Mechanobiology - Magnetic drug targeting (MDT) is a local drug delivery system which aims to concentrate a pharmacological agent at its site of action in order to...     

Measured effects of user and clinical engineer training using a queuing model

This article puts forward a new proposal to calculate count, turnaround, response, and service time of work orders in a clinical engineering (CE) department. These are calculated by means of a queuing model as a measurement tool. This proposal was tested in a 600-bed hospital with an inventory of 1094 medical devices and with 6 full-time clinical engineers. In April 1999, a simulation (with ARENA 3.01 developed by System Modeling Corporation) of the working of this proposal was performed with desired values being applied to the queuing model. At the end of 2002, real work order data from the database was recorded. As predicted, the results showed that all the indicators of nonscheduled work orders decreased. Response and turnaround time were reduced from 27 to 0.56 hours and 27.48 to 1.13 hours, respectively. From a backlog of 22 outstanding repair orders per month between April 1999 and January 2000, the number was reduced to 4 in December 2002. The queuing model also helped to measure the positive effects on arrival and service rates when users and CE were trained. The difference between simulated and real values was under 5%.     

Milligram scale parallel purification of plasmid DNA using anion-exchange membrane capsules and a multi-channel peristaltic pump

A parallel chromatographic procedure for the purification of milligram amounts of plasmid DNA was developed. Initial studies showed that ion-exchange membrane capsules displayed high capacity for plasmid DNA. Interestingly, a weak anion exchanger (DEAE) proved to be superior to the strong quarternary ammonium group with respect to elution and regeneration properties and the 75 cm(2) Sartobind D membrane capsule (MA75D, Sartorius) was selected for further studies. A method for reducing endotoxin levels by using CTAB as a precipitant was optimised. By introducing this step into the protocol, endotoxin levels could be reduced approximately 100-fold to 相似文献   

Osmotic hemolysis and fragility A new model based on membrane disruption,and a potential clinical test

Red cell osmotic hemolysis has traditionally been defined by the loss of hemoglobin, in response to reduced osmotic pressure, as measured spectroscopically. Previous work from this laboratory using resistive pulse spectroscopy (RPS) has shown that in a mixed population of hemolyzing cell, ghosts can be detected as being more deformable, and hence appearing distinctly smaller, than the remaining intact cells. Other researchers using similar methods have reported detection of ghosts as apparently smaller objects, resulting from their greater sensitivity to dielectric breakdown. We now confirm both of these results, and demonstrate by kinetic studies that changes which occur in the rheological and electrical properties of ghosts are independent phenomena. We include in our analysis the explicit calculation of ghost and intact spherocyte resistivity after dielectric breakdown. The two different characterizations for ghosts are integrated into a proposed model of osmotic hemolysis based on known red blood cell membrane and cytoplasmic properties. This work provides both a theoretical and a practical foundation for RPS-based measures of osmotic fragility, including a potential new clinical test, measures which provide very early detection of the ultimate fate of osmotically stressed red cells.     

Mitochondrial membrane potential probes and the proton gradient: a practical usage guide

Fluorescent probes for monitoring mitochondrial membrane potential are frequently used for assessing mitochondrial function, particularly in the context of cell fate determination in biological and biomedical research. However, valid interpretation of results obtained with such probes requires careful consideration of numerous controls, as well as possible effects of non-protonic charges on dye behavior. In this context, we provide an overview of some of the important technical considerations, controls, and parallel complementary assays that can be employed to help ensure appropriate interpretation of results, thus providing a practical usage guide for monitoring mitochondrial membrane potentials with cationic probes. In total, this review will help illustrate both the strengths and potential pitfalls of common mitochondrial membrane potential dyes, and highlight best-usage approaches for their efficacious application in life sciences research.     

Magnetically aligned phospholipid bilayers with positive ordering: a new model membrane system.

A stable smectic phospholipid bilayer phase aligned with the director parallel to the magnetic field can be generated by the addition of certain trivalent paramagnetic lanthanide ions to a bicellar solution of dimyristoylphosphatidylcholine (DMPC) and dihexanoylphosphatidylcholine (DHPC) in water. Suitable lanthanide ions are those with positive anisotropy of their magnetic susceptibility, namely Eu3+, Er3+, Tm3+, and Yb3+. For samples doped with Tm3+, this phase extends over a wide range of Tm3+ concentrations (6-40 mM) and temperatures (35-90 degrees C) and appears to undergo a transition from a fluid nematic discotic to a fluid, but highly ordered, smectic phase at a temperature that depends on the thulium concentration. As a membrane mimetic, these new, positively ordered phospholipid phases have high potential for structural studies using a variety of techniques such as magnetic resonance (EMR and NMR), small-angle x-ray and neutron diffraction, as well as optical and infrared spectroscopy.     

Dominant ionic mechanisms explored in spiking and bursting using local low-dimensional reductions of a biophysically realistic model neuron

The large number of variables involved in many biophysical models can conceal potentially simple dynamical mechanisms governing the properties of its solutions and the transitions between them as parameters are varied. To address this issue, we extend a novel model reduction method, based on “scales of dominance,” to multi-compartment models. We use this method to systematically reduce the dimension of a two-compartment conductance-based model of a crustacean pyloric dilator (PD) neuron that exhibits distinct modes of oscillation—tonic spiking, intermediate bursting and strong bursting. We divide trajectories into intervals dominated by a smaller number of variables, resulting in a locally reduced hybrid model whose dimension varies between two and six in different temporal regimes. The reduced model exhibits the same modes of oscillation as the 16 dimensional model over a comparable parameter range, and requires fewer ad hoc simplifications than a more traditional reduction to a single, globally valid model. The hybrid model highlights low-dimensional organizing structure in the dynamics of the PD neuron, and the dependence of its oscillations on parameters such as the maximal conductances of calcium currents. Our technique could be used to build hybrid low-dimensional models from any large multi-compartment conductance-based model in order to analyze the interactions between different modes of activity.     

Teaching technical skills: training on a simple, inexpensive, and portable model.

The purpose of this study was to determine whether surgical residents could significantly improve their performance on a specific surgical procedure after a brief practice session with feedback. Attending plastic surgeons, using valid and reliable checklists and global rating scales, objectively assessed 37 junior surgical residents while performing two-flap Z-plasties on pig thighs (one before and one after a one-on-one, 5-minute practice session with feedback). The total cost per resident was $1.00 (Canadian currency). After the practice session, total checklist scores improved from 7.3 (range, 1 to 9) to 7.9 (range, 5 to 9), and the total global rating scores improved from 29.1 (range, 13 to 41) to 31.9 (range, 19 to 43). Paired Student's t tests revealed significant improvement in both the mean total checklist scores (p < 0.05) and mean total global rating scores (p < 0.01). Also, the global rating score for appearance and quality of the final surgical product significantly improved from 2.7 to 3.3 after the practice session (p < 0.01). There were no significant differences in performance scores between men and women, between first-year and second-year residents, with residents' previous experience with the Z-plasty procedure, or with resident's base surgical specialties. The results of this prospective study indicate that training on a simple and portable model with very brief individualized practice and feedback is an effective and inexpensive way of improving resident performance. A 5-minute practice session with a surgical trainee before performing a procedure on a living patient may significantly improve the patient's surgical performance and produce a superior result.