[Pain management of cognitively impaired patients]

Pain is a significant problem in clinical practice and its control is one of the most important challenging aspects as pain has a major impact on patients' quality of life and health care costs. Particularly vulnerable persons, like cognitively impaired patients are challenging for pain management and underline its increasing relevance.National and international studies showed significant differences concerning pain therapy between cognitively impaired and cognitively intact patients. A possible cause of this may be that patients who are cognitively impaired are only in a restricted way able to express their pain. Furthermore, knowledge gaps and reservations concerning the effect and dosage of analgesics among cognitively impaired patients could be identified on the involved professions.Further investigations in Germany are needed as deficient treatment remains a persistent problem and evidence-based data are missing. These investigations should describe the status quo of pain management for cognitively impaired patients and provide information which processes have to be adapted to the needs of these vulnerable patients.

A novel approach to temporary stenting: degradable cardiovascular stents produced from corrodible metal-results 6-18 months after implantation into New Zealand white rabbits

OBJECTIVE

To determine whether corrodible materials may be safely used as biodegradable cardiovascular implants.

DESIGN

Corrodible iron stents (> 99.8% iron) were produced from pure iron and laser cut with a stent design similar to a commercially available permanent stent (PUVA-AS16). A total of 16 NOR-I stents were implanted into the native descending aorta of 16 New Zealand white rabbits (mean luminal diameter at the implantation site 3.4 mm, balloon diameter to vessel diameter ratio 1.13).

RESULTS

No thromboembolic complications and no adverse events occurred during the follow up of 6-18 months. All stents were patent at repeat angiography after 6 (n = 9), 12 (n = 5), and 18 months (n = 2) with no significant neointimal proliferation, no pronounced inflammatory response, and no systemic toxicity.

CONCLUSIONS

This initial in vivo experience suggests that degradable iron stents can be safely implanted without significant obstruction of the stented vessel caused by inflammation, neointimal proliferation, or thrombotic events.

[Metallic biomaterials for coronary stents]

The introduction of coronary stents is a milestone in interventional cardiology. Two landmark studies have shown that stainless steel stents significantly decrease the restenosis rate as compared to balloon angioplasty. This fact led to a marked increase of stent implantation since the first stent implantation by Jacques Puel in 1986. Although the concept of coronary stenting significantly improved the interventional therapy of coronary artery disease, restenosis remains a major unsolved drawback of this technique. In addition to procedure and disease related factors like implantation pressure and plaque burden, data suggest that the stent as a medical implant plays a crucial role in the process of neointima formation. Since its introduction in cardiology, more than 50 different stents of different configuration and material have been developed. Although recent publications report of promising results using biodegradable materials, almost all coronary stents commercially available at the moment are made of metallic alloys. Whereas first generation stents were made exclusively from stainless steel and only minor interest was focussed on the stent material in the manufacture of coronary stents, recent studies strongly suggest that the metallic alloy used has a direct impact on the extent of neointima formation. Thus, metallic alloys differ not only with respect to mechanical features, but also by their biocompatible properties. These two factors are of major importance in the induction of vessel wall injury, inflammatory processes and cell proliferation. In the first part, the present paper reviews the metallurgic characteristics of metallic materials, which are currently used or under investigation in the production of coronary stents. In the second part, clinical and experimental results are summarized with respect to their biocompatibility and impact on the process of restenosis formation.

The influence of local tissue conductivity changes on the magnetoencephalogram and the electroencephalogram

We examined the influence of local tissue conductivity changes in the vicinity of a dipolar source on the neuromagnetic field and the electric scalp potential using a high resolution finite element method model of the human head. We found that the topology of both the electric scalp potential and the neuromagnetic field (and consequently dipole localization) is influenced significantly by conductivity changes only in voxels adjacent to the source. Conductivity changes in these voxels yield a greater change in the amplitude of the magnetic field (and consequently in the dipole strength) than in the amplitude of the electric potential.

[Biophysical study of coronary stents: which factors influence the dilatation and recoil behavior?]

In Europe more than fifty stents are currently available for the therapy of coronary artery disease. Nonetheless it is unknown whether material and design influence the stent's behavior. We have studied the recoil and dilatation behavior of five currently available stainless steel (316L) stents compared to stent prototypes made of pure titanium. Furthermore we have investigated how the behavior is influenced by the process of crimping. The aim of this work was to determine material and design characteristics, which influence the recoil and dilatation behavior. The 316L stents showed a homogeneous behavior (plateau pressure min. 1.15 +/- 0.01 atm, max. 0.26 +/- 0.03 atm, recoil min. 0.15 +/- 0.03%, max. 0.26 +/- 0.03%). The titanium stent showed a linear response to the balloon expansion. This was seen in a significantly lower plateau pressure (0.43 +/- 0.15 atm, p < 0.001). Despite the material characteristics of titanium, there were no significant differences in the recoil behavior (0.28 +/- 0.02%). Crimping leads to stent alterations which result in a significantly higher plateau pressure (1.9 +/- 0.07 atm vs. 2.7 +/- 0.58 atm, p < 0.001) and a reduced end-diameter (3.6 +/- 0.02 mm vs. 3.54 +/- 0.05 mm, p < 0.005). The presented data show that the dilatation behavior is relying on the stent material while the recoil is strongly influenced by the stent design.

Source localization in an inhomogeneous physical thorax phantom

The influence of lung inhomogeneities on focal source localizations in electrocardiography (ECG) and magnetocardiography (MCG) is investigated. A realistically shaped physical thorax phantom with cylindrical lung inhomogeneities is used for electric and magnetic measurements. The lungs are modelled with a special ionic exchange membrane which allows different conductivity compartments without influencing the free ionic current flow. The dipolar current sources are composed of platinum wire and located at different depths and directions between the lung inhomogeneities. We localized the current dipoles with different boundary element method (BEM) models, based on electrical data and simultaneous electrical and magnetic data. Our results indicate the possibility of superadditive information gain by combining electrical and magnetic data for source reconstructions. We found a significant influence of the inhomogeneities on both the calculated source location and the calculated source strength. Mislocalizations of up to 16 mm and wrong dipole strengths of up to 52% were obtained when the lung inhomogeneities were not taken into account for source localization. Dipoles parallel to the lungs showed a larger localization error in depth than dipoles perpendicular to the lungs. We conclude that the incorporation of lung inhomogeneities will improve source localization accuracy in ECG and MCG.

The influence of conductivity changes in boundary element compartments on the forward and inverse problem in electroencephalography and magnetoencephalography

Source localization based on magnetoencephalographic and electroencephalographic data requires knowledge of the conductivity values of the head. The aim of this paper is to examine the influence of compartment conductivity changes on the neuromagnetic field and the electric scalp potential for the widely used three compartment boundary element models. Both the analysis of measurement data and the simulations with dipoles distributed in the brain produced two significant results. First, we found the electric potentials to be approximately one order of magnitude more sensitive to conductivity changes than the magnetic fields. This was valid for the field and potential topology (and hence dipole localization), and for the amplitude (and hence dipole strength). Second, changes in brain compartment conductivity yield the lowest change in the electric potentials topology (and hence dipole localization), but a very strong change in the amplitude (and hence in the dipole strength). We conclude that for the magnetic fields the influence of compartment conductivity changes is not important in terms of dipole localization and strength estimation. For the electric potentials however, both dipole localization and strength estimation are significantly influenced by the compartment conductivity.

Multichannel magnetocardiographic measurements with a physical thorax phantom

Artificial dipolar sources were applied inside a physical thorax phantom to experimentally investigate the accuracy obtainable for non-invasive magnetocardiographic equivalent current dipole localisation. For the measurements, the phantom was filled with saline solution of electrical conductivity 0.21 S m-1. A multichannel cardiomagnetometer was employed to record the magnetic fields generated by seven dipolar sources at distances from 25 mm to 145 mm below the surface of the phantom. The inverse problem was solved using an equivalent current dipole in a homogeneous boundary element torso model. The dipole parameters were determined with a non-linear least squares fitting algorithm. The signal-to-noise ratio (SNR) and the goodness of fit of the calculated localisations were used in assessing the quality of the results. The dependence between the SNR and the goodness of fit was derived, and the results were found to correspond to the model. With SNR between 5 and 10, the average localisation error was found to be 9 +/- 8 mm, while for SNR between 30 and 40 and goodness of fit between 99.5% and 100%, the average error reduced to 3.2 +/- 0.3 mm. The SNR values obtained in this study were also compared with typical clinical values of SNR.

[Effect of boundary element discretization on forward calculation and the inverse problem in electroencephalography and magnetoencephalography]

Modelling in magnetoencephalography (MEG) and electroencephalography (EEG) is increasingly based on the boundary element method (BEM). We quantify the influence of boundary element discretization on the neuromagnetic and neuroelectric forward and inverse problem for different dipole depths, brain regions and the quasispherical correction. In particular we derive standards for the general use of BEM models in MEG/EEG source localization. For this purpose simulation with single current dipoles, and source reconstructions from somatosensory evoked potentials and magnetic fields were employed. It was found that both local and global discretization influence source reconstruction. Only at a minimum triangle side length of 10 mm was it possible to achieve stable results for MEG and EEG. In order to obtain acceptable errors within the stable region, the ratio of dipole depth to triangle side length must not be less than 0.5. The results obtained from a comparison of the different brain regions indicate that the similarity to spherical geometry might well have an influence on the estimated dipole location, but not so much on its strength. Source reconstruction employing quasispherical correction was found to be the most stable, in particular in the case of coarse BEM discretization.

Influence of tissue resistivities on neuromagnetic fields and electric potentials studied with a finite element model of the head

Modeling in magnetoencephalography (MEG) and electroencephalography (EEG) requires knowledge of the in vivo tissue resistivities of the head. The aim of this paper is to examine the influence of tissue resistivity changes on the neuromagnetic field and the electric scalp potential. A high-resolution finite element method (FEM) model (452,162 elements, 2-mm resolution) of the human head with 13 different tissue types is employed for this purpose. Our main finding was that the magnetic fields are sensitive to changes in the tissue resistivity in the vicinity of the source. In comparison, the electric surface potentials are sensitive to changes in the tissue resistivity in the vicinity of the source and in the vicinity of the position of the electrodes. The magnitude (strength) of magnetic fields and electric surface potentials is strongly influenced by tissue resistivity changes, while the topography is not as strongly influenced. Therefore, an accurate modeling of magnetic field and electric potential strength requires accurate knowledge of tissue resistivities, while for source localization procedures this knowledge might not be a necessity.

Cardiorespiratory and renal responses to arterial chemoreceptor stimulation by hypoxia or almitrine in men

1. The cardiorespiratory and renal responses to 3 h of normobaric whole-body hypoxic hypoxia (FiO2 = 0.12) as well as to arterial chemoreceptor stimulation by the oral administration of 100 mg almitrine bismesylate during normoxia were measured in 12 normotensive young men undergoing water diuresis. A third series of responses obtained under comparable conditions in the same subjects served as time controls. 2. No significant changes could be detected over time in the parameters measured in control experiments. The subjects reacted to both whole-body hypoxic hypoxia and to pharmacological chemoreceptor stimulation with significant increases in heart rate, tidal volume, minute ventilation and filtration-fraction. Overall renal vascular resistance rose significantly in hypoxia; increases in renal vascular resistance in almitrine experiments were not significant. 3. Renal fractional lithium excretion decreased significantly in response to whole-body hypoxic hypoxia and increased slightly in response to almitrine. Fractional urine and sodium excretion showed negligible changes. 4. The data indicate that, in humans, both almitrine and whole-body hypoxic hypoxia affect not only alveolar ventilation but also renal haemodynamics. 5. The renal electrolyte excretion pattern suggests that under certain circumstances (e.g. dilated renal vascular bed) acute, but well-tolerated, whole-body hypoxic hypoxia can simultaneously stimulate renal proximal tubular sodium reabsorption and inhibit distal tubular sodium reabsorption. The renal tubular responses also indicate that almitrine may influence renal tubular lithium reabsorption by, thus far, unknown mechanisms.