Emergent ordering of microswimmers in smectic liquid crystals

Self-propelled agents can interact in many different ways, including by perturbing a shared physical environment, e.g, hydrodynamic interactions. We study motile particles that are embedded into a smectic liquid crystal, locally distorting the smectic layer spacing. This results in interactions mediated by a smectic liquid crystal distortion field and corresponds to a form of “active smectic” liquid crystal. We identify several dynamical phases that emerge in different regimes of the smectic stiffness and particle reorientation time. We characterise these as (i) ballistic motion, (ii) clustering and (iii) collective motion where orientational order emerges even thought the system lacks explicit co-alignment. We further identify an order-to-disorder transition on the addition of angular noise.

The design and use of a simple device for the MRI assessment of changes in cardiovascular function by lower-body negative-pressure-simulated reduction of central blood volume

AIM

To use a locally designed and simple lower-body negative-pressure (LBNP) device and 1.5 T magnetic resonance imaging (MRI) to demonstrate the ability to assess changes in cardiovascular function during preload reduction. These effects were evaluated on ventricular volumes and great vessel flow in healthy volunteers, for which there are limited published data.

MATERIAL AND METHODS

After ethical review, 14 volunteers (mean age 33.9 ± 7 years, mean body mass index [BMI] 23.1 ± 2.5) underwent LBNP prospectively at 0, -5, -10, and -20 mmHg pressure, using a locally designed LBNP box. Expiratory breath-hold biventricular volumes, and free-breathing flow imaging of the ascending aorta and main pulmonary artery were acquired at each level of LBNP.

RESULTS

At -5 mmHg, there was no change in aortic flow or left ventricular volumes versus baseline. Right ventricular output (p=0.013) and pulmonary net flow (p=0.026) decreased. At -20 mmHg, aortic and pulmonary net flow (p<0.001) decreased, as were left and right ventricular end diastolic volume (p<0.001) and left and right end systolic volumes (p=0.038 and p=0.003 respectively).

CONCLUSIONS

Use of a MRI-compatible LBNP device is feasible to measure changes in ventricular volume and great arterial flow in the same experiment. This may enhance further research into the effects of preload reduction by MRI in a wide range of important cardiovascular pathologies.

Emergent behavioural phenotypes of swarming models revealed by mimicking a frustrated anti-ferromagnet

Self-propelled particle (SPP) models are often compared with animal swarms. However, the collective animal behaviour observed in experiments often leaves considerable unconstrained freedom in the structure of a proposed model. Essentially, multiple models can describe the observed behaviour of animal swarms in simple environments. To tackle this degeneracy, we study swarms of SPPs in non-trivial environments as a new approach to distinguish between candidate models. We restrict swarms of SPPs to circular (periodic) channels where they polarize in one of two directions (like spins) and permit information to pass through windows between neighbouring channels. Co-alignment between particles then couples the channels (anti-ferromagnetically) so that they tend to counter-rotate. We study channels arranged to mimic a geometrically frustrated anti-ferromagnet and show how the effects of this frustration allow us to better distinguish between SPP models. Similar experiments could therefore improve our understanding of collective motion in animals. Finally, we discuss how the spin analogy can be exploited to construct universal logic gates, and therefore swarming systems that can function as Turing machines.

Two-point heterogeneous connections in a continuum neural field model

We examine a novel heterogeneous connection scheme in a 1D continuum neural field model. Multiple two-point connections are added to a local connection function in order to model the "patchy" connections seen in, for example visual cortex. We use a numerical approach to solve the equations, choosing the locations of the two-point connections stochastically. We observe self-sustained persistent fluctuations of activity which can be classified into two types (one of which is similar to that seen in network models of discrete excitable neurons, the other being particular to this model). We study the effect of parameters such as system size and the range, number and strength of connections, on the probability that a particular realisation of the connections is able to exhibit persistent fluctuations.

Persistent fluctuations of activity in undriven continuum neural field models with power-law connections

We study the effect of random inhomogeneous connections on a continuous field description of neural tissue. We focus on a regime in which persistent random fluctuations in activity arise spontaneously in the absence of either time-varying or spatially inhomogeneous input. While present in real tissue and network models of discrete neurons, such behavior has not been reported in continuum models of this type. The activity contains frequencies similar to those seen experimentally. We consider a power-law envelope r(-alpha) for the inhomogeneity and present evidence that the statistical coherence (a measure of two-point correlation) rapidly percolates across the system as alpha is reduced below alphac approximately 1,2 in one and two dimensions, respectively.

Deforming biological membranes: how the cytoskeleton affects a polymerizing fiber

We give a theoretical treatment of the force exerted by a fluctuating membrane on a polymer rod tip, taking into account the effects of an underlying biological cytoskeleton by way of a simple harmonic dependence on displacement. We also consider theoretically and experimentally the dynamics of a growing fiber tip under the influence of such a fluctuation-induced membrane force, including the effects of an underlying cytoskeletal network. We compare our model with new experimental data for the growth of hemoglobin fibers within red blood cells, revealing a good agreement. We are also able to estimate the force and membrane/cytoskeletal displacement required to stall growth of, or buckle, a growing fiber. We discuss the significance of our results in a biological context, including how the properties of the membrane and cytoskeleton relate to the thermodynamics of rod polymerization.

Diffusion on membrane tubes: a highly discriminatory test of the Saffman-Delbruck theory

The efficient transport of membrane proteins is vital in maintaining life. In this work, we investigate the transport of such membrane proteins along long thin membrane tubes or tethers. We calculate the diffusion constant to leading order in the low Reynolds number regime to be D = (4 pi eta)-1 log(r/a), with r and a being the tube and protein radii, respectively, and eta being the membrane viscosity. Thus we propose an exact limiting form for the controversial logarithmic correction, such as originally introduced by Saffman and Delbruck, that involves the tube radius rather than some "frame size". Our work suggests a test of this logarithmic correction could be achieved by measuring diffusion on membrane tubes, exploiting the fact that the equilibrium tube radius can be controlled by the membrane tension and varied over several orders of magnitude. We analyze the time taken for a protein to transit a membrane tube between cells and find that this can vary by an order of magnitude over physiological tensions. This is a strong effect in biological terms and suggests a possible regulatory coupling between membrane tension and signaling.

Random fluctuations of the firing rate function in a continuum neural field model

We incorporate a source of noise into a continuum neural field model by allowing the firing threshold to fluctuate noisily about a mean value, and examine traveling wave front solutions. Under certain conditions we are able to calculate the first and second moments of the distributions of the resulting time varying front speed and shape. This is then compared with more complete numerical solutions. Fluctuations in the wave front speed and in the shape (i.e., fluctuations in activity at particular coordinate positions across the wave front) were found to increase as the magnitude of the fluctuations in firing threshold increased. The mean speed was found to increase as the magnitude of the fluctuations increases. The role of the correlation time for the threshold variation is also investigated. We also study the role of threshold fluctuations in the failure of front propagation, both in the fast and slow varying noise limits.

Clinical impact of selective serotonin reuptake inhibitors therapy with bleeding risks

The selective serotonin reuptake inhibitors (SSRIs) are extensively used for the treatment of multiple psychiatric conditions. In vitro and ex vivo data with these agents indicate they may have varying degrees of antiplatelet activity via multiple receptors. Reports of bleeding in patients receiving SSRIs appeared soon after their introduction. A review of the literature suggests SSRI therapy may increase the risk of bleeding especially with concomitant aspirin or nonsteroidal anti-inflammatory agents. Clinicians should exercise caution when prescribing these agents in high risk patients and maintain awareness of the potential contribution of SSRIs to unexplained bleeding episodes.

Stall, spiculate, or run away: The fate of fibers growing towards fluctuating membranes

We study the dynamics of a growing semiflexible fiber approaching a membrane at an angle. At late times we find three regimes: fiber stalling, when growth stops, runaway, in which the fiber bends away from the membrane, and another regime in which spicules form. We discuss which regions of the resulting "phase diagram" are explored by (i) single and bundled actin fibers in living cells, (ii) sickle hemoglobin fibers, and (iii) microtubules inside vesicles. We complement our analysis with 3D stochastic simulations.

Fiber depolymerization

Depolymerization is, by definition, a crucial process in the reversible assembly of various biopolymers. It may also be an important factor in the pathology of sickle cell disease. If sickle hemoglobin fibers fail to depolymerize fully during passage through the lungs then they will reintroduce aggregates into the systemic circulation and eliminate or shorten the protective delay (nucleation) time for the subsequent growth of fibers. We study how depolymerization depends on the rates of end- and side-depolymerization, k(end) and k(side), which are, respectively, the rates at which fiber length is lost at each end and the rate at which new breaks appear per unit fiber length. We present both an analytic mean field theory and supporting simulations showing that the characteristic fiber depolymerization time tau= square root 1/k(end)k(side) depends on both rates, but not on the fiber length L, in a large intermediate regime 1 << k(side)L(2)/k(end) << (L/d)(2), with d the fiber diameter. We present new experimental data which confirms that both mechanisms are important and shows how the rate of side depolymerization depends strongly on the concentration of CO, acting as a proxy for oxygen. Our theory remains rather general and could be applied to the depolymerization of an entire class of linear aggregates, not just sickle hemoglobin fibers.

Anisotropy in Sickle Hemoglobin Fibers from Variations in Bending and Twist

We have studied the variations of twist and bend in sickle hemoglobin fibers. We find that these variations are consistent with an origin in equilibrium thermal fluctuations, which allows us to estimate the bending and torsional rigidities and effective corresponding material moduli. We measure bending by electron microscopy of frozen hydrated fibers and find that the bending persistence length, a measure of the length of fiber required before it starts to be significantly bent due to thermal fluctuations, is 130microm, somewhat shorter than that previously reported using light microscopy. The torsional persistence length, obtained by re-analysis of previously published experiments, is found to be only 2.5microm. Strikingly this means that the corresponding torsional rigidity of the fibers is only 6x10(-27)Jm, much less than their bending rigidity of 5x10(-25)Jm. For (normal) isotropic materials, one would instead expect these to be similar. Thus, we present the first quantitative evidence of a very significant material anisotropy in sickle hemoglobin fibers, as might arise from the difference between axial and lateral contacts within the fiber. We suggest that the relative softness of the fiber with respect to twist deformation contributes to the metastability of HbS fibers: HbS double strands are twisted in the fiber but not in the equilibrium crystalline state. Our measurements inform a theoretical model of the thermodynamic stability of fibers that takes account of both bending and extension/compression of hemoglobin (double) strands within the fiber.

Spicules and the effect of rigid rods on enclosing membrane tubes

Membrane tubes (spicules) arise in cells, or artificial membranes, in the nonlinear deformation regime due to, e.g., the growth of microtubules, actin filaments, or sickle hemoglobin fibers towards a membrane. We calculate the axial force f exerted by the tube, and its average radius, taking into account steric interactions between the fluctuating membrane and the enclosed rod. We find a smooth crossover of the axial force between f approximately square root of (sigma) and f approximately sigma as the membrane tension sigma increases and the tube radius shrinks. This crossover occurs around the most physiologically relevant membrane tensions. Our work may be important in (i) interpreting experiments in which axial force is related to the tube radius or membrane tension, and (ii) constructing dynamical theories for biopolymer growth in narrow tubes where these fluctuation effects control the tube radius.

Modelling genetic networks with noisy and varied experimental data: the circadian clock in Arabidopsis thaliana

Circadian clocks in all organisms include feedback loops that generate rhythmic expression of key genes. We model the first such loop proposed for the clock of Arabidopsis thaliana, the experimental model species for circadian timing in higher plants. As for many biological systems, there are no experimental values for the parameters in our model, and the data available for parameter fitting is noisy and varied. To tackle this we constructed a cost function, which quantifies the agreement between our model and various key experimental features. We then undertook an efficient global search of parameter space, to test whether the proposed circuit can fit the experimental data. Using this approach we show that circadian clock models can function well with low cooperativity in transcriptional regulation, whereas high cooperativity has been a feature of previous (hand-fitted) clock models in other species. Our optimized solution for the Arabidopsis clock model fits several, but not all, of the key experimental features. We test the predicted effects of well-characterized mutations in the clock circuit and show the phases of the circadian cycle where additional components that are yet to be identified experimentally must be present to complete the circadian feedback loop.

Measuring forces between protein fibers by microscopy

We propose a general scheme for measuring the attraction between mechanically frustrated semiflexible fibers by measuring their thermal fluctuations and shape. We apply this analysis to a system of sickle hemoglobin (HbS) fibers that laterally attract one another. These fibers appear to "zip" together before reaching mechanical equilibrium due to the existence of cross-links into a dilute fiber network. We are also able to estimate the rigidities of the fibers. These rigidities are found to be consistent with sickle hemoglobin "single" fibers 20 nm in diameter, despite recent experiments indicating that fiber bundling sometimes occurs. Our estimate of the magnitude of the interfiber attraction for HbS fibers is in the range 8 +/- 7 kBT/microm, or 4 +/- 3 k(B)T/microm if the fibers are assumed, a priori to be single fibers (such an assumption is fully consistent with the data). This value is sufficient to bind the fibers, overcoming entropic effects, although extremely chemically weak. Our results are compared to models for the interfiber attraction that include depletion and van der Waals forces. This technique should also facilitate a similar analysis of other filamentous protein assembles in the future, including beta-amyloid, actin, and tubulin.

The wild-type circadian period of Neurospora is encoded in the residual network of the null frq mutants

We model theoretically the response of the widely studied circadian oscillator of Neurospora crassa to inactivation of the frq gene. The resulting organism has been termed "arrhythmic" under constant conditions. Under entrainment to periodic temperature cycles Roenneberg, Merrow and coworkers have shown that the phase angle at which spore formation occurs depends on the entrainment period, curiously even in the null frq mutants (frq9 and frq10). We show that such a response does not imply the presence of a self-sustained free-running oscillator. We derive a simple candidate model (a damped harmonic oscillator) for the null frq mutants that successfully reproduces the observed phase angle response. An endogenous period of 21 h for the damped harmonic oscillator coincides with the endogenous period of wild-type Neurospora. This suggests that the (noise driven) "residual system" present in the mutants may have a significant timekeeping role in the wild-type organism. Our model (with no change of parameters) was then used to investigate spore formation patterns under constant conditions and reproduces the corresponding experimental data of Aronson et al. (Proc. Natl. Acad. Sci. USA 91 (1994) 7683.)

Left Ventricular Pacing Minimizes Diastolic Ventricular Interaction, Allowing Improved Preload-Dependent Systolic Performance

Background— Left ventricular (LV) pacing improves hemodynamics in patients with heart failure. We hypothesized that at least part of this benefit occurs by minimization of external constraint to LV filling from ventricular interaction.

Methods and Results— We present median values (interquartile ranges) for 13 heart failure patients with LV pacing systems implanted for New York Heart Association class III/IV limitation. We used the conductance catheter method to measure LV pressure and volume simultaneously. External constraint was measured from the end-diastolic pressure-volume relation recorded during inferior vena caval occlusion, during LV pacing, and while pacing was suspended. External constraint to LV filling was reduced by 3.0 (4.6 to 0.6) mm Hg from 4.8 (0.6 to 7.5) mm Hg ( P <0.01) in response to LV pacing; effective filling pressure (LV end-diastolic pressure minus external constraint) increased by 4.0 (2.2 to 5.8) mm Hg from 17.7 (13.3 to 22.6; P <0.01). LV end-diastolic volume increased by 10 (3 to 11) mL from 238 (169 to 295) mL ( P =0.01), whereas LV end-systolic volume did not change significantly (−1 [−2 to 3] mL from 180 [124 to 236] mL, P =0.97), which resulted in an increase in stroke volume of 11 (5 to 13) mL from 49 (38 to 59) mL ( P <0.01). LV stroke work increased by 720 (550 to 1180) mL · mm Hg from 3400 (2110 to 4480) mL · mm Hg ( P =0.01), and maximum dP/dt increased by 120 (2 to 161) mm Hg/s from 635 (521 to 767) mm Hg/s ( P =0.03).

Conclusions— This study suggests a potentially important mechanism by which LV pacing may produce hemodynamic benefit. LV pacing minimizes external constraint to LV filling, resulting in an increase in effective filling pressure; the consequent increase in LV end-diastolic volume increases stroke volume via the Starling mechanism.

The force generated by biological membranes on a polymer rod and its response: Statics and dynamics

We propose a theory for the force exerted by a fluctuating membrane on a polymer rod tip. Using statistical mechanical methods, the expression for the generated force is written in terms of the distance of the rod tip from the membrane "frame." We apply the theory in calculating the stall force and membrane displacement required to cease the growth of a growing fiber induced by membrane fluctuations, as well as the membrane force and membrane displacement required for rod/fiber buckling. We also consider the dynamics of a growing fiber tip under the influence of a fluctuation-induced membrane force. We discuss the importance of our results in various biological contexts. Finally, we present a method to simultaneously extract both the rigidity of the semiflexible rod and the force applied by, e.g., the membrane from the measurements of the bending fluctuations of the rod. Such a measurement of the force would give information about the thermodynamics of the rod polymerization that involves the usual Brownian ratchet mechanism.

Possible therapeutic targets in cardiac myocyte apoptosis

Since Kerr described programmed cell death (apoptosis) as a process distinct from necrosis, there have been many studies of apoptosis in disease, especially of immunological origin. Because cardiac myocytes are terminally differentiated cells, they have typically been assumed to die exclusively by necrosis. However, during the last decade this view has been challenged by several studies demonstrating that a significant number of cardiac myocytes undergo apoptosis in myocardial infarction, heart failure, myocarditis, arrhythmogenic right ventricular dysplasia, and immune rejection after cardiac transplantation, as well as in other conditions of stress. These are potentially relevant observations, because apoptosis--unlike necrosis--can be blocked or reversed at early stages. Specific inhibition of this process may confer a considerable degree of cardioprotection, but requires a thorough understanding of the underlying mechanisms. Recent progress includes a better understanding of the importance of mitochondria-initiated events in cardiac myocyte apoptosis, of factors inducing apoptosis in heart failure and during hypoxia, and of the dual pro-apoptotic and anti-apoptotic effects of hypertrophic stimuli such as beta-adrenoceptor agonists, angiotensin converting enzyme inhibitors, nitric oxide and calcineurin. The investigation of cytoprotective and apoptotic signal transduction pathways has revealed important new insights into the roles of the mitogen-activated protein kinases p38, extracellular signal regulated kinase and c-Jun N-terminal kinase in cardiac cell fate. Our present review focuses on the intracellular signal transduction pathways of cardiac myocyte apoptosis and the possibility of specific inhibition of the process.

Left ventricular pacing improves haemodynamic variables in patients with heart failure with a normal QRS duration

OBJECTIVES

To assess whether patients with congestive heart failure (CHF) and a normal QRS duration can benefit from left ventricular (VDD-LV) pacing.

DESIGN

Cardiac resynchronisation is reserved for patients with a broad QRS duration on the premise that systolic resynchronisation is the mechanism of benefit, yet improvement from pacing correlates poorly with QRS duration. In CHF patients with a broad QRS duration, those with a high resting pulmonary capillary wedge pressure (PCWP) > 15 mm Hg benefit. In this acute haemodynamic VDD-LV pacing study, patients with CHF with a normal QRS duration were divided into two groups--patients with a resting PCWP > 15 mm Hg and patients with a resting PCWP < 15 mm Hg--to determine whether benefit is predicted by a high resting PCWP.

PATIENTS

20 patients with CHF, New York Heart Association functional class IIb-IV, all with a normal QRS duration (< or = 120 ms).

INTERVENTIONS

Temporary pacing wires were positioned to enable VDD-LV pacing and a pulmonary artery catheter was inserted for measurement of PCWP, right atrial pressure, and cardiac output.

RESULTS

In patients with a PCWP > 15 mm Hg (n = 10), cardiac output increased from 3.9 (1.5) to 4.5 (1.65) l/min (p < 0.01), despite a fall in PCWP from 24.7 (7.1) to 21.0 (6.2) mm Hg (p < 0.001). In patients with a PCWP < 15 mm Hg there was no change in PCWP or cardiac output. Combined data showed that PCWP decreased from 17.0 (9.1) to 15.3 (7.7) mm Hg during VDD-LV pacing (p < 0.014) and cardiac output increased non-significantly from 4.7 (1.5) to 4.9 (1.5) (p = 0.125).

CONCLUSIONS

Patients with CHF with a normal QRS duration and PCWP > 15 mm Hg derive acute haemodynamic benefit from VDD-LV pacing.

Interactions between proteins bound to biomembranes

We study a physical model for the interaction between general inclusions bound to fluid membranes that possess finite tension gamma, as well as the usual bending rigidity kappa. We are motivated by an interest in proteins bound to cell membranes that apply forces to these membranes, due to either entropic or direct chemical interactions. We find an exact analytic solution for the repulsive interaction between two similar circularly symmetric inclusions. This repulsion extends over length scales approximately sqrt[kappa/gamma] and contrasts with the membrane-mediated contact attraction for similar inclusions on tensionless membranes. For noncircularly symmetric inclusions we study the small, algebraically long-ranged, attractive contribution to the force that arises. We discuss the relevance of our results to biological phenomena, such as the budding of caveolae from cell membranes and the striations that are observed on their coats. These, and other, "gnarly buds" may prove fascinating to study further.

Twisted protein aggregates and disease: the stability of sickle hemoglobin fibers

We describe how twist could play an essential role in stabilizing 20 nm diameter sickle hemoglobin fibers. Our theory successfully reproduces the observed variation of helical pitch length with fiber diameter. With no remaining adjustable parameters it also yields a prediction for the torsional rigidity of sickle hemoglobin fibers that is in good agreement with experiment and hence retains the striking feature that such fibers can be highly mechanically anisotropic, even with a ratio of bending to torsional rigidity of about 50. We discuss how our study might be relevant to the development of treatment strategies.

Intrathecal drug delivery 2002

BACKGROUND

Intrathecal drug delivery has been used clinically since the 1970's. Significant clinical advances have been made combining new technology with pharmacology and surgery. Continuous infusion of medication for both analgesia and spasticity has become a part of the armamentarium for specialists in these areas. Significant recent advances in technology promise further enhancements and improvements for intrathecal therapy.

METHODS

A review of the literature combined with 20 years personal experience with intrathecal drug delivery.

FINDINGS/DISCUSSION

Intrathecal therapy has established a role in the treatment of malignant pain, benign pain and severe spasticity. Significant literature and the current state of practice in the United States are reviewed. Recent therapeutic enhancements are discussed, and a wish list of future technological enhancements presented.

Early use of intrathecal baclofen in brain injury in pediatric patients

BACKGROUND

The Food and Drug Administration (FDA) approved the use of intrathecal Baclofen for spasticity from traumatic brain injury in June of 1996 based on a Phase III clinical trial that documented efficacy in patients one year post injury. The FDA approval is only for patients who are one year post injury based on the Phase III study. We have found use of ITB in the first few months after injury very effective in a subgroup of severe traumatic brain injury (TBI) pediatric patients with spasticity, dystonia and autonomic storming following brain injury.

METHOD

The author's database of over 250 patients receiving intrathecal baclofen was reviewed. Retrospective chart review was undertaken of the 6 patients identified with brain injuries over a three year period that were given ITB less than one year post injury. The patients' diagnosis included asphyxia, traumatic brain injury and stroke. The ages were one year to fourteen years of age. ITB was offered after all conventional therapy had been exhausted and the patient's spasticity remained intractable. These patients also all experienced autonomic dysfunction with severe autonomic storms.

FINDINGS

All of the patients had a decrease in their spasticity of at least 2 points on the Ashworth score. The autonomic storms ceased in all 6 patients when adequate dosages of ITB were reached. The patients could be weaned from all oral and intravenous medications for tone, storming and fever. Many of the patients became much more alert and interactive when the medications were stopped. Five of the six are still using their pump for their tone one to five years post implant, the sixth had the pump stopped at the parents' request for religious reasons.

INTERPRETATION

Early use of ITB can play a significant role in the rehabilitation of brain injury in children.

Solid-phase amplification for detection of C282y and H63D hemochromatosis (HFE) gene mutations

BACKGROUND

There is a need for simple, rapid, and inexpensive methods for the detection of single-nucleotide polymorphisms. Our aim was to develop a single-tube ELISA-like PCR assay and evaluate it by detecting the common C282Y and H63D mutations found in the hemochromatosis gene (HFE) by use of clinical samples.

METHODS

The method, termed solid-phase amplification (SPA), involves dual liquid- and solid-phase amplification of a target sequence by the use of two PCR primers, one of which is in two forms: the first is covalently immobilized to the wall of a microwell, and the second is free in solution. During allele-specific amplification, both the free and solid-phase amplicons are labeled by incorporation of digoxigenin (DIG)-dUTP. The amount of surface-bound amplicon is determined colorimetrically by the use of an alkaline phosphatase-anti-DIG-Fab conjugate and p-nitrophenyl phosphate.

RESULTS

Two different amplicon-labeling methods were evaluated. Analysis of 173 clinical samples for the C282Y and H63D HFE point mutations with SPA revealed that only one sample was incorrectly diagnosed, apparently because of operator error, when compared with conventional restriction fragment length polymorphism assay results.

CONCLUSIONS

The SPA assay has potential for medium-scale mutation detection, having the advantage of being manipulatively simple and immediately adaptable for use in clinical laboratories with existing ELISA instrumentation.

The reversal exchange technique of total calvarial reconstruction for sagittal synostosis

The role of total calvarial reconstruction in the treatment of sagittal synostosis remains controversial, especially in patients younger than 1 year of age. The purpose of this study was to prospectively evaluate the efficacy of a single surgical technique for total calvarial reconstruction (the reversal exchange technique) in patients younger than 1 year of age who had a radiographically confirmed diagnosis of sagittal synostosis. Twenty-three consecutive patients underwent the reversal exchange technique of total calvarial reconstruction at a median age of 3 months (age range, 6 weeks to 10 months). Quantitative assessments were performed on the basis of preoperative and postoperative (minimum, 6 months) measurements of the cephalic index (cranial width/cranial length x 100) taken from three-dimensional computed tomography scans, which were obtained in 18 of 23 patients. Aesthetic assessments were performed on the basis of the grading of preoperative and postoperative photographs, obtained in 17 of 23 patients, by three independent raters who were blinded as to the surgical technique. The mean preoperative cephalic index was 65.0, and the mean postoperative index was 76.4, yielding a mean improvement of 11.4 (17.5 percent). By photographic evaluation, 12 of 17 patients (70.6 percent) were classified as having a normal head shape (grade 4) and five of 17 (29.4 percent) as having minor residual deformities (grade 3). No patients were identified as having significant residual deformities (grades 1 or 2). There were two intraoperative complications and one postoperative complication, none of which resulted in permanent morbidity. It was concluded that the reversal exchange technique of total calvarial reconstruction provided significant improvement in head shape on the basis of quantitative measurements (cephalic index) and independent evaluations of aesthetic improvement.

Regulation of limbic information outflow by the subthalamic nucleus: excitatory amino acid projections to the ventral pallidum

The subthalamic nucleus (STN), a component of the basal ganglia motor system, sends an excitatory amino acid (EAA)-containing projection to the ventral pallidum (VP), a major limbic system output region. The VP contains both NMDA and AMPA subtypes of EAA receptors. To characterize the physiology of the subthalamic pathway to the VP, and to determine the influence of EAA receptor subtypes, in vivo intracellular recordings, and in vivo extracellular recordings combined with microiontophoresis, were made from VP neurons in anesthetized rats. Of the intracellularly recorded neurons, 86% responded to STN stimulation, and these displayed EPSPs with an onset of 8.7 msec, consistent with a monosynaptic input. The EPSPs evoked in spontaneously firing neurons were nearly twice the amplitude of those in nonfiring cells (13.1 vs 6.8 mV, respectively). As neurons were depolarized by current injection, the latency for spiking decreased from 24.2 to 14.2 msec, although EPSP latency was unaffected. Eighty-seven percent of the extracellularly recorded VP neurons responded to STN stimulation with a rapid and robust enhancement of spiking; the response onset, like the EPSP onset, equaled 8.7 msec. Firing rate was enhanced by NMDA in 94% of the STN-excited cells, and AMPA increased firing in 94% as well. The NMDA-selective antagonist AP-5 attenuated 67% of the STN-evoked excitatory responses, and the AMPA-selective antagonist CNQX attenuated 52%. Both antagonists attenuated 33% of responses, and 78% were attenuated by at least one. This evidence suggests that a great majority of VP neurons are directly influenced by STN activation and that both NMDA and non-NMDA receptors are involved. Moreover, the VP response to STN stimulation appears to be strongly dependent on the depolarization state of the neuron.

Reduction in episodes of self harm/harm to others in severely mentally ill population through assertive outreach

This article aims to apply the process of clinical governance to the management of patients with a major mental illness, living in the community, with a history of self harm and/or harm to others; and to design an early warning system to drive rapid intervention if patients miss a clinic appointment. This follows the recommendations of good clinical practice for this vulnerable group.

Precision cosmology and the density of baryons in the universe

Big-bang nucleosynthesis (BBN) and cosmic microwave background (CMB) anisotropy measurements give independent, accurate measurements of the baryon density and can test the framework of the standard cosmology. Early CMB data are consistent with the long-standing conclusion from BBN that baryons constitute a small fraction of matter in the Universe, but may indicate a slightly higher value for the baryon density. We clarify precisely what the two methods determine and point out that differing values for the baryon density can indicate either an inconsistency or physics beyond the standard models of cosmology and particle physics. We discuss other signatures of the new physics in CMB anisotropy.

The use of plasmapheresis and immunosuppression in the treatment of pemphigus vulgaris

BACKGROUND

Pemphigus vulgaris is an autoimmune blistering disease for which the mainstay of treatment is systemic corticosteroids and immunosuppressants. This therapy had reduced the mortality of pemphigus; however, it is associated with significant morbidity.

OBJECTIVE

The objective of this study was to assess the group's experience with plasmapheresis in the treatment of pemphigus vulgaris and report on its utility.

METHODS

Seven patients with severe or resistant pemphigus vulgaris underwent a series of 5 plasma exchanges over an average of 8 days. Immunosuppressive drugs were administered immediately after plasmapheresis to prevent the "rebound" flare of disease that can occur after plasmapheresis.

RESULTS

Remission was induced in 4 patients, partial remission was induced in 2 patients, and 1 patient continues to have active disease.

CONCLUSION

This study suggests that plasmapheresis is a useful intervention in patients with pemphigus vulgaris who are not responding to standard therapy or who require unacceptably high doses of steroids or immunosuppressants.

Annihilating cold dark matter

Structure formation with cold dark matter (CDM) predicts halos with a central density cusp, which are observationally disfavored. If CDM particles have an annihilation cross section sigmav approximately 10(-29)(m/GeV) cm(2), then annihilations will soften the cusps. We discuss plausible scenarios for avoiding the early Universe annihilation catastrophe that could result from such a large cross section. The predicted scaling of core density with halo mass depends upon the velocity dependence of sigmav, and s-wave annihilation leads to a core density nearly independent of halo mass, which seems consistent with observations.

Pacing in heart failure: improved ventricular interaction in diastole rather than systolic re-synchronization

AIMS

To determine the mechanism by which left ventricular and biventricular pacing works.

BACKGROUND

Pacing for congestive heart failure patients is employed in those with left bundle branch block on the basis that it will improve discoordinated contraction; however, the response is unpredictable. The authors propose that the mechanism of benefit is rather related to improvement of ventricular interaction in diastole (VID). VID is found in patients with a high left ventricular end-diastolic pressure (> 15 mmHg). Left ventricular pacing in these patients will delay right ventricular filling and allow greater left ventricular filling before the onset of VID.

METHODS

The study group consisted of 18 congestive heart failure patients with an ejection fraction < 30% and with no more than Grade 1 mitral regurgitation. Group I comprised 10 patients with pulmonary capillary wedge pressure > 15 mmHg, four patients had a normal QRS duration and six had left bundle branch block. Group II comprised eight patients with pulmonary capillary wedge pressure < 15 mmHg, of whom five had a normal QRS duration. Haemodynamics were measured at baseline and during VDD pacing from either the left ventricle or right ventricle.

RESULTS

The ratio of stroke volume/pulmonary capillary wedge pressure was calculated as an index of the relationship between left ventricular end-diastolic pressure and contractile function. This ratio was lower in group I than in group II patients (P = 0.005). In group I, haemodynamics were improved with left ventricular pacing (stroke volume/pulmonary capillary wedge pressure increased from 2.2 +/- 0.9 to 4.4 +/- 3.6, P = 0.03). In group II there was no response to either left ventricular or right ventricular pacing. The improvement with left ventricular pacing was unrelated to QRS duration (r = 0.09).

CONCLUSIONS

Left ventricular pacing acutely benefits congestive heart failure patients with pulmonary capillary wedge pressure > 15 mmHg irrespective of left bundle branch block. The present data suggest that the mechanism of response may be an improvement in left ventricular filling rather than ventricular systolic re-synchronization.

Mutations in multidrug efflux homologs, sugar isomerases, and antimicrobial biosynthesis genes differentially elevate activity of the sigma(X) and sigma(W) factors in Bacillus subtilis

The sigma(X) and sigma(W) extracytoplasmic function sigma factors regulate more than 40 genes in Bacillus subtilis. sigma(W) activates genes which function in detoxification and the production of antimicrobial compounds, while sigma(X) activates functions that modify the cell envelope. Transposon mutagenesis was used to identify loci which negatively regulate sigma(W) or sigma(X) as judged by up-regulation from the autoregulatory promoter site P(W) or P(X). Fourteen insertions that activate P(W) were identified. The largest class of insertions are likely to affect transport. These include insertions in genes encoding two multidrug efflux protein homologs (yqgE and yulE), a component of the oligopeptide uptake system (oppA), and two transmembrane proteins with weak similarity to transporters (yhdP and yueF). Expression from P(W) is also elevated as a result of inactivation of at least one member of the sigma(W) regulon (ysdB), an ArsR homolog (yvbA), a predicted rhamnose isomerase (yulE), and a gene (pksR) implicated in synthesis of difficidin, a polyketide antibiotic. In a parallel screen, we identified seven insertions that up-regulate P(X). Remarkably, these insertions were in functionally similar genes, including a multidrug efflux homolog (yitG), a mannose-6-phosphate isomerase gene (yjdE), and loci involved in antibiotic synthesis (srfAB and possibly yogA and yngK). Significantly, most insertions that activate P(W) have little or no effect on P(X), and conversely, insertions that activate P(X) have no effect on P(W). This suggests that these two regulons respond to distinct sets of molecular signals which may include toxic molecules which are exported, cell density signals, and antimicrobial compounds.

Reducing time in bed after percutaneous transluminal coronary angioplasty (TIBS III)

BACKGROUND: This study is the third in a series of investigations on the requisite length of time that patients should be restricted to bed after coronary arteriography or percutaneous transluminal coronary angioplasty using a femoral artery approach. METHODS: A prospective, experimental-control group design with randomization was used initially to compare the incidence of bleeding between patients who remained in bed for 4 hours and patients who remained in bed for 6 hours after sheath removal following percutaneous transluminal coronary angioplasty. RESULTS: Rapid changes in the healthcare environment led to nurses collecting complete data sets for the experimental group only. The experimental group (n = 51) was 73% male and 27% female; mean age was 57 years (SD = 11.4 years). Mean time in bed was 4.1 hours (SD = 0.27 hours). Most patients (98%) did not bleed from the femoral artery access site after remaining in bed for 4 hours following sheath removal. Ninety-two percent of patients required analgesics while in bed. Mean length of stay after the angioplasty was 1.4 days (SD = 0.79 days). Bleeding occurred in one subject and was related to multiple invasive procedures and an activated clotting time of greater than 200 seconds. CONCLUSIONS: Requisite time in bed after percutaneous transluminal coronary angioplasty has been reduced to 4 hours at the University of Virginia Medical Center, the same time required for patients undergoing cardiac catheterization. Discomfort after the procedure remains to be addressed.

Reducing time in bed after percutaneous transluminal coronary angioplasty (TIBS III)

BACKGROUND

This study is the third in a series of investigations on the requisite length of time that patients should be restricted to bed after coronary arteriography or percutaneous transluminal coronary angioplasty using a femoral artery approach.

METHODS

A prospective, experimental-control group design with randomization was used initially to compare the incidence of bleeding between patients who remained in bed for 4 hours and patients who remained in bed for 6 hours after sheath removal following percutaneous transluminal coronary angioplasty.

RESULTS

Rapid changes in the healthcare environment led to nurses collecting complete data sets for the experimental group only. The experimental group (n = 51) was 73% male and 27% female; mean age was 57 years (SD = 11.4 years). Mean time in bed was 4.1 hours (SD = 0.27 hours). Most patients (98%) did not bleed from the femoral artery access site after remaining in bed for 4 hours following sheath removal. Ninety-two percent of patients required analgesics while in bed. Mean length of stay after the angioplasty was 1.4 days (SD = 0.79 days). Bleeding occurred in one subject and was related to multiple invasive procedures and an activated clotting time of greater than 200 seconds.

CONCLUSIONS

Requisite time in bed after percutaneous transluminal coronary angioplasty has been reduced to 4 hours at the University of Virginia Medical Center, the same time required for patients undergoing cardiac catheterization. Discomfort after the procedure remains to be addressed.

Analysis of promoter sequences from Lactobacillus and Lactococcus and their activity in several Lactobacillus species

Promoter-active fragments were isolated from the genome of the probiotic organism Lactobacillus rhamnosus strain GG using the promoter-probe vector pNZ272. These promoter elements, together with a promoter fragment isolated from the vaginal strain Lactobacillus fermentum BR11 and two previously defined promoters (Lactococcus lactis and Lactobacillus acidophilus ATCC 4356 slpA), were introduced into three strains of Lactobacillus. Primer-extension analysis was used to map the transcriptional start site for each promoter. All promoter fragments tested were functional in each of the three lactobacilli and a purine residue was used to initiate transcription in most cases. The promoter elements encompassed a 52- to 1,140-fold range in promoter activity depending on the host strain. Lactobacillus promoters were further examined by surveying previously mapped sequences for conserved base positions. The Lactobacillus hexamer regions (-35: TTgaca and -10: TAtAAT) closely resembled those of Escherichia coli and Bacillus subtilis, with the highest degree of agreement at the -10 hexamer. The TG dinucleotide upstream of the -10 hexamer was conserved in 26% of Lactobacillus promoters studied, but conservation rates differed between species. The region upstream of the -35 hexamer of Lactobacillus promoters showed conservation with the bacterial UP element.

Changes in hemoglobin values in elite cross-country skiers from 1987-1999

Hemoglobin data have been available from ski teams beginning from 1987, and from 1989 to 1999 we have followed hemoglobin values in elite cross-country skiers in international competitions. The mean values at the 1989 World Nordic Ski Championships were lower than population reference values, as would be expected from plasma volume expansion associated with endurance training. However, an increase, particularly in the maximal values, became obvious in 1994 and rose further in 1996. These extreme values provide both a health risk to the individual athlete and unfair competition. After a rule limiting hemoglobin values was introduced, the drop of the highest values was remarkable: among men 15 g/l (0.23 mmol/l) and among women 42 g/l (0.65 mmol/l). It would appear that the rule had achieved its goal of limiting extreme hemoglobin values. Yet the mean hemoglobin concentrations in men and women have continued to rise, suggesting the continued use of artificial methods to increase total hemoglobin mass.

Two time constants for the binding of proteins to DNA from micromechanical data

Recent experimental advances allow the direct measurement of the force/extension behavior for DNA in the presence of strongly binding proteins. Such experiments reveal information about the cooperative mechanism of protein binding. We have studied the irreversible binding of such proteins to DNA using a simple simulation and present a method for estimating quantitative rate constants for the nucleation and growth of linear domains of proteins bound to DNA. Such rate constants also give information about the relative energetics of the two binding processes. We discuss our results in the context of recent data for the DNA-recA-ATPgammas system, for which the nucleation time is 4.7 x 10(4) min per recA binding site and the total growth rate of each domain is 1400 recA/min.

Within-center correlation in dialysis adequacy

The purpose of this study was to determine whether patients with end stage renal disease treated with hemodialysis were correlated in dialysis adequacy within facilities. This was a retrospective analysis of dialysis adequacy based on urea reduction ratio (URR) values from 6969 patients dialyzed at 154 facilities. The within-center correlation was quantified using the between-center variation and the parameter p that was derived using ANOVA tables and mixed effects models. The variation in center means for URR was wider than expected for independent observations (52.9-76.1 versus 60.7-73.8, respectively). Furthermore, there was a significant within-center correlation in URR values across all facilities (p = 0.136, P<0.0001), which persisted after adjusting for patient specific covariates, facility characteristics, and state. In conclusion, there was a substantial within-center correlation in dialysis adequacy that reflected important center effects on the outcome of ESRD patients.