Space-discretization error analysis and stabilization schemes for conduction velocity in cardiac electrophysiology.

In cardiac electrophysiology, the propagation of the action potential may be described by a set of reaction-diffusion equations known as the bidomain model. The shape of the solution is determined by a balance of a strong reaction and a relatively weak diffusion, which leads to steep variations in space and time. From a numerical point of view, the sharp spatial gradients may be seen as particularly problematic, because computational grid resolution on the order of 0.1 mm or less is required, yielding considerable computational efforts on human geometries. In this paper, we discuss a number of well-known numerical schemes for the bidomain equation and show how the quality of the solution is affected by the spatial discretization. In particular, we study in detail the effect of discretization on the conduction velocity (CV), which is an important quantity from a physiological point of view. We show that commonly applied finite element techniques tend to overestimate the CV on coarse grids, while it tends to be underestimated by finite difference schemes. Furthermore, the choice of interpolation and discretization scheme for the nonlinear reaction term has a strong impact on the CV. Finally, we exploit the results of the error analysis to propose improved numerical methods, including a stabilized scheme that tends to correct the CV on coarse grids but converges to the correct solution as the grid is refined. Copyright © 2016 John Wiley & Sons, Ltd.

Finite Element Estimation of Protein-Ligand Association Rates with Post-Encounter Effects: Applications to Calcium binding in Troponin C and SERCA.

We introduce a computational pipeline and suite of software tools for the approximation of diffusion-limited binding based on a recently developed theoretical framework. Our approach handles molecular geometries generated from high-resolution structural data and can account for active sites buried within the protein or behind gating mechanisms. Using tools from the FEniCS library and the APBS solver, we implement a numerical code for our method and study two Ca(2+)-binding proteins: Troponin C and the Sarcoplasmic Reticulum Ca(2+) ATPase (SERCA). We find that a combination of diffusional encounter and internal 'buried channel' descriptions provide superior descriptions of association rates, improving estimates by orders of magnitude.

Effect of aerobic exercise on tracking performance in elderly people: a pilot study.

BACKGROUND AND PURPOSE: Although much is known about the benefits of aerobic exercise on cardiovascular health, little research has been done on the effect of aerobic exercise on motor performance. This study examined whether aerobic exercise has an effect on visuospatial information processing during finger-movement tracking in elderly subjects. SUBJECTS: Fifteen elderly subjects (mean age=83.2 years, SD=5.7, range=72-91) from a senior housing complex were randomly assigned to a control group or an experimental (exercise) group. Twelve subjects completed the study, and data obtained for 10 subjects were used for data analysis (2 control subjects were eliminated to allow for matched-pairs analysis between the experimental and control groups). The control group (n=5) had a mean age of 80.2 years (SD=7.8). Subjects in the experimental group (n=5) had a mean age of 84.8 years (SD=2.5). METHODS: The intervention consisted of group exercise 3 times a week for 8 consecutive weeks, and included calisthenics (eg, marching in place, side stepping, mock boxing), stationary bicycling, and walking. A finger-movement tracking test and submaximal graded exercise tolerance step tests were performed before and after training to determine changes in finger-movement tracking and any aerobic training effects. RESULTS: Matched-pairs t tests showed a difference in tracking from pretest to posttest in the experimental group compared with the control group. Step test performance did not differ between the 2 groups. DISCUSSION AND CONCLUSION: The results of this small-scale study with a limited number of subjects indicate that, for elderly people, finger-movement tracking performance can improve with aerobic exercise, despite the absence of an aerobic training effect. Possible mechanisms for the treatment effect on information processing are discussed.

Time of drug elimination in chronic drug abusers. Case study of 52 patients in a "low-step" detoxification ward.

The elimination time of illicit drugs and their metabolites is of both clinical and forensic interest. In order to determine the elimination time for various drugs and their metabolites we recruited 52 volunteers in a protected, low-step detoxification program. Blood samples were taken from each volunteer for the first 7 days, daily, urine sample for the first 3 weeks, daily. Urine was analyzed using a fluorescence-polarization immunoassay (FPIA) and gas chromatography/mass spectrometry (GC/MS), serum using GC/MS. The elimination times of the drugs and/or their metabolites in urine and serum as well as the tolerance intervals/confidence intervals were determined. Due to the sometimes extremely high initial concentrations and low cut-off values, a few of the volunteers had markedly longer elimination times than those described in the literature. The cut-off values were as follows: barbiturates II (200ng/ml), cannabinoids (20ng/ml), cocaine metabolites (300ng/ml), opiates (200ng/ml). GC/MS detected the following maximum elimination times: total morphine in urine up to 270.3h, total morphine and free morphine in serum up to 121.3h, monoacetylmorphine in urine up to 34.5h, 11-nor-9-carboxy-delta-9-tetrahydrocannabinol (THC-COOH) in urine up to 433.5h, THC-COOH in serum up to 74.3h, total codeine in urine up to 123h, free codeine in urine up to 97.5h, total codeine in serum up to 29h, free codeine in serum up to 6.3h, total dihydrocodeine (DHC) in urine up to 314.8h, free DHC in urine up to 273.3h, total and free DHC in serum up to 50.1h. Cocaine and its metabolites were largely undetectable in the present study.

['Microbial air pollutants'. Emission sources and preventive measures]. / 'Mikrobielle Luftverunreinigungen'. Emissionsquellen und -minderungsmassnahmen.

Already in the planning or monitoring phase, measures have to be realized for the reduction in emissions of bio-aerosols in biological waste treatment plants. For this purpose, operation-related measures (in open and partially closed plants) and technology-related measures (in closed plants with automatic ventilation) can be taken. A survey on the currently feasible measures for reduction is submitted. The realization has to be adapted to the individual site and type of plant. An enormous demand for examinations is envisaged in order to enable a qualified assessment of the emission behaviour of diverse waste air systems or process steps.

Teaching occupational health to medical students.

Occupational and environmental disease and injury are both widespread and preventable, yet their study has been traditionally neglected in undergraduate medical education. Because family physicians will encounter many working patients who are subject to varying degrees of risk as a result of their job, home, or community environment, family practice faculty must play an important role in teaching occupational and environmental health to medical students. Goals for the longitudinal integration of occupational and environmental health over the four-year curriculum include sensitizing students to the relationship between work and health, introducing and reinforcing the importance of the occupational and environmental history in patient care, integrating occupational and environmental health principles and examples with existing course work, and providing appropriate clinical, research, and didactic activities for interested students. Goal achievement will vary with the availability of curricular time and teaching faculty. Strategies for implementing occupational and environmental health curriculum in the face of these two variables are discussed.