Human erythrocyte filterability at low driving pressure

In this study, the human RBC capillary flow has been modeled by passing 11 microl of RBC suspension (Hematocrit = 6%) in phosphate buffer solution (PBS) of a viscosity of 1 and 2.6 cP (in the presence of 2% Dextran) through 5 microm pore diameter polycarbonate Nuclepore filters. We have developed a digitally controlled experimental system for measuring the RBC filterability at a constant driving pressure, in the range of 10-400 Pa, producing a wall shear stress range of 1-50 Pa. The RBC filterability was evaluated by measuring the cell suspension flow rate normalized by the PBS flow rate. The RBC filterability has been found to be a nonlinear function of the driving pressure, having a single minimum locus at 25 Pa. Lowering the driving pressure below 25 Pa revealed an unexpected increase of the RBC filterability.The maximal RBC filterability (near unity) was detected at the lowest driving pressure (10 Pa) and the corresponding estimated RBC linear velocity while traveling through the capillary pore was as high as 800 microm/s. Increasing the driving pressure above 25 Pa confirmed previous results, where RBC filterability is monotonically and asymptotically increasing. Increasing the PBS medium viscosity from 1 to 2.26 cP significantly attenuated the RBC filterability and led to the anomalous increase of RBC deformability at the 10 Pa pressure range. We propose that the anomalous increase in RBC deformability was caused by RBCs undergoing spontaneous mechanical fluctuations.

Reverse engineering of the spindle assembly checkpoint

The Spindle Assembly Checkpoint (SAC) is an intracellular mechanism that ensures proper chromosome segregation. By inhibiting Cdc20, a co-factor of the Anaphase Promoting Complex (APC), the checkpoint arrests the cell cycle until all chromosomes are properly attached to the mitotic spindle. Inhibition of Cdc20 is mediated by a conserved network of interacting proteins. The individual functions of these proteins are well characterized, but understanding of their integrated function is still rudimentary. We here describe our attempts to reverse-engineer the SAC network based on gene deletion phenotypes. We begun by formulating a general model of the SAC which enables us to predict the rate of chromosomal missegregation for any putative set of interactions between the SAC proteins. Next the missegregation rates of seven yeast strains are measured in response to the deletion of one or two checkpoint proteins. Finally, we searched for the set of interactions that correctly predicted the observed missegregation rates of all deletion mutants. Remarkably, although based on only seven phenotypes, the consistent network we obtained successfully reproduces many of the known properties of the SAC. Further insights provided by our analysis are discussed.

Cellular Alterations in Cultured Endothelial Cells Exposed to Therapeutic Ultrasound Irradiation

Restoration of blood supply to tissue with impaired perfusion depends on spontaneous or mediated angiogenesis, which among other mechanisms includes stimulation, migration, and proliferation of endothelial cells (ECs). Therapeutic ultrasound (US) irradiation is known as an inducer of cellular modifications and is used to accelerate wound healing. An in vitro setup was developed in order to allow for a comprehensive investigation of cellular alterations induced in cultured ECs after exposure to different modes of therapeutic US irradiation. Viability assays revealed a higher rate of proliferation in the sonicated groups, although cell death was not observed. Visualization of actin stress fibers demonstrated partial disassembly of the fibers immediately after US sonication, with a maximum after about 2 h. However, 24 h following sonication the fibers regain normal appearance. A similar behavior was observed with the microtubules and focal adhesion complexes. Utilizing a wound healing assay revealed that migration rate of ECs is enhanced by US irradiation. These findings hint that therapeutic US sonication of ECs results in temporarily cellular alterations, which may induce tissue remodeling via stimulation of EC proliferation and migration.

Does the chromatic Mach bands effect exist?

The achromatic Mach bands effect is a well-known visual illusion, discovered over a hundred years ago. This effect has been investigated thoroughly, mainly for its brightness aspect. The existence of Chromatic Mach bands, however, has been disputed. In recent years it has been reported that Chromatic Mach bands are not perceived under controlled iso-luminance conditions. However, here we show that a variety of Chromatic Mach bands, consisting of chromatic and achromatic regions, separated by a saturation ramp, can be clearly perceived under iso-luminance and iso-brightness conditions. In this study, observers' eye movements were recorded under iso-brightness conditions. Several observers were tested for their ability to perceive the Chromatic Mach bands effect and its magnitude, across different cardinal and non-cardinal Chromatic Mach bands stimuli. A computational model of color adaptation, which predicted color induction and color constancy, successfully predicts this variation of Chromatic Mach bands. This has been tested by measuring the distance of the data points from the "achromatic point" and by calculating the shift of the data points from predicted complementary lines. The results suggest that the Chromatic Mach bands effect is a specific chromatic induction effect.

Abdominal aortic aneurysm risk of rupture: patient-specific FSI simulations using anisotropic model

Abdominal aortic aneurysm (AAA) rupture represents a major cardiovascular risk, combining complex vascular mechanisms weakening the abdominal artery wall coupled with hemodynamic forces exerted on the arterial wall. At present, a reliable method to predict AAA rupture is not available. Recent studies have introduced fluid structure interaction (FSI) simulations using isotropic wall properties to map regions of stress concentrations developing in the aneurismal wall as a much better alternative to the current clinical criterion, which is based on the AAA diameter alone. A new anisotropic material model of AAA that closely matches observed biomechanical AAA material properties was applied to FSI simulations of patient-specific AAA geometries in order to develop a more reliable predictor for its risk of rupture. Each patient-specific geometry was studied with and without an intraluminal thrombus (ILT) using two material models-the more commonly used isotropic material model and an anisotropic material model-to delineate the ILT contribution and the dependence of stress distribution developing within the aneurismal wall on the material model employed. Our results clearly indicate larger stress values for the anisotropic material model and a broader range of stress values as compared to the isotropic material, indicating that the latter may underestimate the risk of rupture. While the locations of high and low stresses are consistent in both material models, the differences between the anisotropic and isotropic models become pronounced at large values of strain-a range that becomes critical when the AAA risk of rupture is imminent. As the anisotropic model more closely matches the biomechanical behavior of the AAA wall and resolves directional strength ambiguities, we conclude that it offers a more reliable predictor of AAA risk of rupture.

Walking reduces the post-void residual volume in parturients with epidural analgesia for labor: a randomized-controlled study

BACKGROUND

The post-void residual volume is higher among parturients who received epidural analgesia than those who received no or alternative analgesia.

METHODS

This prospective, randomized, controlled, non-blinded study was performed in a tertiary referral center labor suite. The post-void residual volume was measured by a transabdominal ultrasound following a voiding attempt. Healthy parturients with low-dose epidural analgesia in active labor were randomized either to walk to the toilet or to use a bedpan for voiding. The primary outcome measure (post-void residual volume in labor) was compared between the study groups.

RESULTS

The toilet group (n=34) and the bedpan group (n=28) demonstrated similar post-void residual volumes (212 +/- 100 vs. 168 +/- 93 ml, P=0.289). Twenty patients (59%) randomized to the toilet group were unable to walk and actually voided in a bedpan. A secondary analysis was performed analyzing the groups as treated. The post-void residual volume was significantly lower in the actual toilet group (n=14, 63 +/- 24 ml) vs. the bedpan group (n=48, 229 +/- 200 ml), P=0.0052. Thirteen (93%) women who walked to the toilet managed to void before the ultrasound measurement vs. 20/48 (42%) using the bedpan, P=0.001. Fewer women who managed to walk to the toilet required urinary bladder catheterization during the labor than women who used the bedpan (6/14, 43% vs. 36/48, 75%) P=0.028.

CONCLUSION

Women who were randomized to walk to the bathroom with epidural analgesia and were able to do so during labor had a significantly reduced post-void residual volume and a reduced requirement for urinary catheterization.

Cardiovascular disease management: the need for better diagnostics

Current diagnostic testing for cardiovascular pathology usually rests on either physiological or anatomic measurement. Multiple tests must then be combined to arrive at a conclusion regarding treatment of a specific pathology. Much of the diagnostic decisions currently made are based on rough estimates of outcomes, often derived from gross anatomic observations or extrapolation of physical laws. Thus, intervention for carotid and coronary disease is based on estimates of diameter stenosis, despite data to suggest that plaque character and lesion anatomy are important determinants of outcome. Similarly, abdominal aortic aneurysm (AAA) intervention is based on maximal aneurysm diameter without regard for arterial wall composition or individual aneurysm geometry. In other words, our current diagnostic tests do not reflect the sophistication of our current knowledge of vascular disease. Using a multimodal approach, computer modeling has the potential to predict clinical outcomes based on a variety of factors including arterial wall composition, surface anatomy and hemodynamic forces. We term this more sophisticated approach "patient specific diagnostics", in which the computer models are reconstructed from patient specific clinical visualizing modalities, and material properties are extracted from experimental measurements of specimens and incorporated into the modeling using advanced material models (including nonlinear anisotropic models) and performed as dynamic simulations using the FSI (fluid structure interaction) approach. Such an approach is sorely needed to improve the effectiveness of interventions. This article will review ongoing work in "patient specific diagnostics" in the areas of carotid, coronary and aneurismal disease. We will also suggest how this approach may be applicable to management of aortic dissection. New diagnostic methods should allow better patient selection, targeted intervention and modeling of the results of different therapies.

Brightness contrast-contrast induction model predicts assimilation and inverted assimilation effects

In classical assimilation effects, intermediate luminance patches appear lighter when their immediate surround is comprised of white patches and appear darker when their immediate surround is comprised of dark patches. With patches either darker or lighter than both inducing patches, the direction of the brightness effect is reversed and termed as "inverted assimilation effect." Several explanations and models have been suggested, some are relevant to specific stimulus geometry, anchoring theory, and models that involve high level cortical processing (such as scission, etc.). None of these studies predicted the various types of assimilation effects and their inverted effects. We suggest here a compound brightness model, which is based on contrast-contrast induction (second-order adaptation mechanism). The suggested model predicts the various types of brightness assimilation effects and their inverted effects. The model is composed of three main stages: (1) composing post-retinal second-order opponent receptive fields, (2) calculations of local and remote contrast, and (3) adaptation of the second-order (contrast-contrast induction). We also utilize a variation of the Jacobi iteration process to enable elegant edge integration in order to evaluate the model is performance.

Controlling cardiac transport and plaque formation

Macro-particles transported in the bloodstream, such as LDL particles and macrophages, are considered to be one of the initiating factors of atherosclerotic plaque development. LDL infiltration from the bloodstream into a blood vessel's wall, whether the coronary, peripheral, or carotid arteries, is considered a major inflammatory factor, recruiting macrophages from the blood flow and leading to the formation of vulnerable atherosclerotic plaques. Infiltration sites are influenced by patterns of blood flow, as regions of lower shear stresses and high oscillations may give rise to higher infiltration rates through the endothelium, exacerbating the growth of a plaque and its tendency to rupture. Previous studies demonstrated a high prevalence of rupture sites proximal to the minimum lumen area, which raised the question of whether the existence of two distinct adjacent plaques, in which the distal plaque is more severe, can give rise to hemodynamic forces that can push the non-stenotic plaque to rupture. Models of the coronary arteries with one and two eccentric and concentric stenotic narrowings were built into a closed flow loop. The single stenosis model had a 75% area reduction narrowing (representing the vunerable atherosclerotic plaque) with relevant elastic properties. The double stenosis model included an additional distal 84% area reduction narrowing. The flow in the area between the two stenoses was recorded and analyzed using continuous doppler particle image velocimetry (CDPIV), together with the hydrostatic pressure acting on the proximal plaque. Results indicated that the combined shear rates and pressure effects in a model with a significant distal stenosis can contribute to the increase in plaque instability by LDL and enhanced macrophage uptake. The highly oscillatory nature of the disturbed flow near the shoulder of the vulnerable atherosclerotic plaque enriches its lipid soft core, and the high hydrostatic pressures acting on the same lesion in this geometry induce high internal maximal stresses that can trigger the rupture of the plaque.

DPIV prediction of flow induced platelet activation-comparison to numerical predictions

Flow induced platelet activation (PA) can lead to platelet aggregation, deposition onto the blood vessel wall, and thrombus formation. PA was thoroughly studied under unidirectional flow conditions. However, in regions of complex flow, where the platelet is exposed to varying levels of shear stress for varying durations, the relationship between flow and PA is not well understood. Numerical models were developed for studying flow induced PA resulting from stress histories along Lagrangian trajectories in the flow field. However, experimental validation techniques such as Digital Particle Image Velocimetry (DPIV) were not extended to include such models. In this study, a general experimental tool for PA analysis by means of continuous DPIV was utilized and compared to numerical simulation in a model of coronary stenosis. A scaled up (5:1) 84% eccentric and axisymetric coronary stenosis model was used for analysis of shear stress and exposure time along particle trajectories. Flow induced PA was measured using the PA State (PAS) assay. An algorithm for computing the PA level in pertinent trajectories was developed as a tool for extracting information from DPIV measurements for predicting the flow induced thrombogenic potential. CFD, DPIV and PAS assay results agreed well in predicting the level of PA. In addition, the same trend predicted by the DPIV was measured in vitro using the Platelet Activity State (PAS) assay, namely, that the symmetric stenosis activated the platelets more as compared to the eccentric stenosis.

A hypothesis for vulnerable plaque rupture due to stress-induced debonding around cellular microcalcifications in thin fibrous caps

In this article, we advance a hypothesis for the rupture of thin fibrous cap atheroma, namely that minute (10-mum-diameter) cellular-level microcalcifications in the cap, which heretofore have gone undetected because they lie below the visibility of current in vivo imaging techniques, cause local stress concentrations that lead to interfacial debonding. New theoretical solutions are presented for the local stress concentration around these minute spherical inclusions that predict a nearly 2-fold increase in interfacial stress that is relatively insensitive to the location of the hypothesized microinclusions in the cap. To experimentally confirm the existence of the hypothesized cellular-level microcalcifications, we examined autopsy specimens of coronary atheromatous lesions using in vitro imaging techniques whose resolution far exceeds conventional magnetic resonance imaging, intravascular ultrasound, and optical coherence tomography approaches. These high-resolution imaging modalities, which include confocal microscopy with calcium-specific staining and micro-computed tomography imaging, provide images of cellular-level calcifications within the cap proper. As anticipated, the minute inclusions in the cap are very rare compared with the numerous calcified macrophages observed in the necrotic core. Our mathematical model predicts that inclusions located in an area of high circumferential stress (>300 kPa) in the cap can intensify this stress to nearly 600 kPa when the cap thickness is <65 microm. The most likely candidates for the inclusions are either calcified macrophages or smooth muscle cells that have undergone apoptosis.

The hemodynamics of the Berlin pulsatile VAD and the role of its MHV configuration

The 3D flow in a model of the Berlin ventricular assist device (VAD) chamber with monoleaflet valves placed in S-shape conduits was simulated numerically. The blood flow dynamics were described in terms of flow patterns, velocity, pressure, and shear stress. The hemodynamic properties and the VAD's potential risk for thrombosis were evaluated in terms of mixing and washout properties, and global estimations of platelet level of activation (LOA). In order to evaluate the role of valves on the flow in the chamber, the flow in a model with bileaflet valves in straight conduits was simulated and compared with the original case. The results showed that in both models a large rotating flow was developed in the chamber during filling. This vortex filled the entire chamber and moved constantly up to the peak ejection phase, resulting in relatively low shear stress (up to 0.4 Pa) and no lasting stagnation regions. Significant shear stresses were found near the valves with higher values near the outlet valve in both models. The configuration of valves and conduits had a large effect on VAD washout and mixing properties, with advantage to the bileaflet model. However, since the bileaflet valves exhibited higher shear stresses, higher LOA were found for the bileaflet model.

Numerical Model of Flow in a Sac-Type Ventricular Assist Device

This article addresses the growing need for comprehensive tools to investigate the hemodynamics of ventricular assist devices (VADs) in general and sac-type VADs in particular. Numerical simulations can be very helpful in these efforts. However, full simulation of flow inside sac-type VADs poses several key problems, among them simulation of the mechanical heart valves and calculation of the motion of flexible walls. We present a simplified three-dimensional (3D) numerical model of a sac-VAD chamber. The walls in the simplified model are defined to move according to experimental measurements, and the valves are modeled in fully open or fully closed positions. The model is validated by comparison to a fully coupled fluid-structure interaction numerical simulation and to experimental measurements using continuous digital particle image velocimetry. Our results demonstrate that the flexible wall motion is sensitive to changes in pressure distribution inside the chamber. However, small variations in wall motion do not significantly affect the global features of flow inside the chamber. Therefore, the simplified model can be used to predict the 3D time-dependent flow field in the VAD.

Attitudes of medical practitioners towards "Do Not Resuscitate" orders

When the desires of a patient are unknown or cannot be ascertained, cardio-pulmonary resuscitation (CPR) is the default procedure. Explicit, Do Not Resuscitate (DNR), orders are required to prevent implementation of CPR. We studied the response of general medical internists in specific clinical situations demanding consideration of DNR orders and respect for patient preferences; their current practice regarding slow codes and participation in CPR attempts considered futile provide information as to how often they discuss DNR issues with patients or families. Eighty-five internists attending the monthly meeting of the Internal Medicine Forum participated in the study. The physicians demonstrated their consent to participate by accepting a remote transmitter that elicited a response 2-3 minutes following the presentation of case vignettes or practice-related questions. The survey showed that 73% of the physicians agreed to assign a DNR order for a terminally ill patient unable to express her preferences. Only 55% agreed to do the same for a competent patient who specifically requested that CPR be withheld in the event of a cardiopulmonary arrest (p<0.05). 77% reported to have performed CPR, at least three times, in situations where they expected no benefit. 59% affirmed that their team had performed a partial CPR (slow code) at least once. Only 28% discussed the subject of DNR with patients or family more than 5 times a year. Paternalism, disregard for patients' preferences and poor communication skills influence normative behaviour in end-of-life decision-making.

Molecular and cellular characterization of mesenchymal progenitors for skeletal biomedical devices

Mesenchymal cells are successfully used to create cell-loaded devices in tissue engineering. Molecular properties of the cells and interaction with polymer scaffolds regulate the development of desired tissues. The present study compared the molecular markers in mesenchymal pleuripotent C3H10T1/2 and osteogenic MBA-15 cells. The cells express transcription factors (TF) of chondro-ostegenic pathway (cbfa-1 and c-fos) and MyoD - TF of muscle differentiation pathway, but not myogenin. Analyzed cells expressed receptors for glucocorticoids, growth hormone, prolactin, and PTH, which indicates their potential responsiveness to systemic signals. Analysis of mRNA encoding for receptors of TGFbeta, TNF, and various interleukins revealed differential expression of IL-2r and TGFbeta-1r receptors, which were expressed by MBA-15 but not by C3H10T1/2 cells. Expression of functional genes indicates differences in the stages of cell differentiation: ALK was present in MBA-15 only, while both cell types expressed collagen-I. Furthermore, we evaluated the expression of adhesion proteins that mediate cell-polymer interactions by flow cytometry analysis. Cell adhesion molecules (CAMs) analyzed were integrinalpha-M (CD11b), selectin-E (CD62E), and PECAM-1 (CD31), which have shown differential expression on cells cultured on plastic, poly(L-lactic acid) (PLLA) or poly(DL-lactide-glycolide acid) (PDLGA) polymer films. Detailed molecular characterization of mesenchymal cells will enable optimization of culture conditions for successful creation of implantable cell-loaded constructs.