Characteristics of improvements in balance control using vibro-tactile biofeedback of trunk sway for multiple sclerosis patients.

BACKGROUND AND AIMS: Previously, we determined that training with vibrotactile feedback (VTfb) of trunk sway improves MS patients' balance impairment. Here, we posed 5 questions: 1) How many weeks of VTfb training are required to obtain the best short-term carry over effect (CoE) with VTfb? 2) How long does the CoE last once VTfb training terminates? 3) Is the benefit similar for stance and gait? 4) Is position or velocity based VTfb more effective in reducing trunk sway? 5) Do patients' subjective assessments of balance control improve? METHODS: Balance control of 16 MS patients was measured with gyroscopes at the lower trunk. The gyroscopes drove directionally active VTfb in a head-band. Patients trained twice per week with VTfb for 4 weeks to determine when balance control with and without VTfb stopped improving. Thereafter, weekly assessments without VTfb over 4 weeks and at 6 months determined when CoEs ended. RESULTS: A 20% improvement in balance to normal levels occurred with VTfb. Short term CoEs improved from 15 to 20% (p ≤ 0.001). Medium term (1-4 weeks) CoEs were constant at 19% (p ≤ 0.001). At 6 months improvement was not significant, 9%. Most improvement was for lateral sway. Equal improvement occurred when angle position or velocity drove VTfb. Subjectively, balance improvements peaked after 3 weeks of training (32%, p ≤ 0.05). CONCLUSIONS: 3-4 weeks VTfb training yields clinically relevant sway reductions and subjective improvements for MS patients during stance and gait. The CoEs lasted at least 1 month. Velocity-based VTfb was equally effective as position-based VTfb.

The effect of vibrotactile biofeedback of trunk sway on balance control in multiple sclerosis.

BACKGROUND: Patients with multiple sclerosis (MS) suffer from diminished balance control due to slowed sensory conduction and possibly delayed central processing. Vibrotactile biofeedback of trunk sway has been shown to improve balance control in patients with peripheral and central vestibular disorders. Here, the effects of vibrotactile feedback training on trunk sway and a possible carry-over effect was measured in MS patients during stance and gait. METHODS: Ten MS patients (mean age 46.8±7.7 years, 40% male) participated in a crossover study in which 7 different stance and gait tasks were trained with and without angle feedback for stance and angular velocity feedback for gait. An assessment sequence of 12 tasks was performed once before and twice after the training sequence. Trunk sway was measured with body-worn gyroscopes. Head mounted vibrotactile biofeedback of trunk sway was provided during one crossover training arm and the following second assessment sequence. RESULTS: Biofeedback generally leads to a decrease in sway but an increase in sway angular velocities during some stance tasks compared to training without biofeedback. Biofeedback while walking eyes open resulted in a decreased sway angular velocity. The greatest changes were found in the pitch direction of trunk sway. Effects diminished after biofeedback was removed. CONCLUSIONS: This study showed that vibrotactile biofeedback of trunk sway beneficially effects stance and provides significant improvement in gait compared to training without biofeedback in MS patients.

A portable microevaporator for low temperature single atom studies by scanning tunneling and dynamic force microscopy.

Here, we present a microevaporator setup for single adatom deposition at low temperature, which is a prerequisite for most single atom studies with scanning probe techniques. The construction of the microevaporator is based on the tungsten filament of a modified halogen lamp, covered with the required adsorbate. Very stable evaporation conditions were obtained, which were controlled by the filament current. The installation of this microevaporator on a manipulator enabled its transportation directly to the sample at the microscope kept at 5 K. In this way, the controlled deposition of Li onto Ag(100), Li, Pd, and Au onto MgO/Ag(001) as well as Au onto alumina/NiAl(110) at low temperature has been performed. The obtained images recorded after the deposition show the presence of single Li/Au atoms on the sample surfaces as a prove for successful dispersion of single atoms onto the sample surface using this technique.

Measuring the charge state of point defects on MgO/Ag(001).

A detailed understanding of surface defects is highly desirable, e.g. to clarify their role as active sites in catalysis. Here localized defects on the surface of MgO films deposited on Ag(001) are investigated. Since the electronic structure of color centers depends on their local position, spectroscopic signals are highly convoluted and often difficult to disentangle. In this study we aimed to obtain morphological and spectroscopic information on single color centers at a microscopic level with frequency modulated dynamic force microscopy (FM-DFM) and scanning tunneling microscopy (STM) in an ultrahigh vacuum and at low temperature. Four of the major and in literature mostly discussed defect types on MgO have been characterized by their charge state and finally identified by the complementary application of FM-DFM and STM in combination with density functional theory results.

Au dimers on thin MgO(001) films: flat and charged or upright and neutral?

A combination of low temperature scanning tunneling microscopy (STM) and theoretical calculations is used to investigate Au dimers, supported on thin MgO(001) films, whose thickness was chosen such that charge transfer from the Ag substrate to the deposited Au is possible. Au dimers exist not only in an upright geometry--as theoretically predicted to be the most stable configuration--but also as flat lying dimers which populate a manifold of different azimuthal orientations. Apart from the difference in adsorption configurations, these two isomers exhibit rather different electronic structures: while upright dimers are neutral, flat ones are charged.

Oxygen-deficient line defects in an ultrathin aluminum oxide film.

A model for the straight antiphase domain boundary of the ultrathin aluminum oxide film on the NiAl(110) substrate is derived from scanning tunneling microscopy measurements and density-functional theory calculations. Although the local bonding environment of the perfect film is maintained, the structure is oxygen deficient and possesses a favorable adsorption site. The domain boundary exhibits a downwards band bending and three characteristic unoccupied electronic states, in excellent agreement with scanning tunneling spectroscopy measurements.

Bulk electronic structure of metals resolved with scanning tunneling microscopy.

We demonstrate that bulk band structure can have a strong influence in scanning tunneling microscopy measurements by resolving electronic interference patterns associated with scattering phenomena of bulk states at a metal surface and reconstructing the bulk band topology. Our data reveal that bulk information can be detected because states at the edge of the surface-projected bulk band have a predominant role on the scattering patterns. With the aid of density functional calculations, we associate this effect with an intrinsic increase in the projected density of states of edge states. This enhancement is characteristic of the three-dimensional bulk band curvature, a phenomenon analog to a van Hove singularity.

Frequency modulated atomic force microscopy on MgO(001) thin films: interpretation of atomic image resolution and distance dependence of tip-sample interaction.

Atomically resolved images on a MgO(001) thin film deposited on Ag(001) obtained in ultrahigh vacuum by frequency modulated atomic force microscopy at low temperature are presented and analysed. Images obtained in the attractive regime show a different type of contrast formation from those acquired in the repulsive regime. For the interpretation of the image contrast we have investigated the tip-sample interaction. Force and energy were recovered from frequency shift versus distance curves. The derived force curves have been compared to the force laws of long-range, short-range and contact forces. In the attractive regime close to the minimum of the force-distance curve elastic deformations have been confirmed. The recovered energy curve has been scaled to the universal Rydberg model, yielding a decay length of l = 0.3 nm and ΔE = 4.2 aJ (26 eV) for the maximum adhesion energy. A universal binding-energy-distance relation is confirmed for the MgO(001) thin film.

Role of spin in quasiparticle interference.

Quasiparticle interference patterns measured by scanning tunneling microscopy can be used to study the local electronic structure of metal surfaces and high-temperature superconductors. Here, we show that even in nonmagnetic systems the spin of the quasiparticles can have a profound effect on the interference patterns. On Bi(110), where the surface state bands are not spin degenerate, the patterns are not related to the dispersion of the electronic states in a simple way. In fact, the features which are expected for the spin-independent situation are absent and the observed interference patterns can be interpreted only by taking spin-conserving scattering events into account.

Mesoscopic chiral reshaping of the Ag(110) surface induced by the organic molecule PVBA.

We report scanning tunneling microscopy observations on the restructuring of a Ag(110) surface induced by the molecule 4-[trans-2-(pyrid-4-yl-vinyl)]benzoic acid (PVBA). Our data reveal that the surface undergoes a mesoscopic step faceting following exposure to submonolayer coverages and thermal activation. A sawtooth arrangement evolves implying long-range mass transport of substrate atoms and forming a regular arrangement of kink sites. Its formation is associated with the molecules' functional headgroups forming carboxylates with [100] Ag microfacets at step edges, and eventually operating to reshape the surface morphology. Interestingly, the resulting microfacets act as chiral templates for the growth of supramolecular PVBA structures. Theoretical modeling based on ab initio results indicates that chiral recognition processes discriminating between the two enantiomers of adsorbed PVBA molecules occur in this process.

Selectivity in vibrationally mediated single-molecule chemistry.

The selective excitation of molecular vibrations provides a means to directly influence the speed and outcome of chemical reactions. Such mode-selective chemistry has traditionally used laser pulses to prepare reactants in specific vibrational states to enhance reactivity or modify the distribution of product species. Inelastic tunnelling electrons may also excite molecular vibrations and have been used to that effect on adsorbed molecules, to cleave individual chemical bonds and induce molecular motion or dissociation. Here we demonstrate that inelastic tunnelling electrons can be tuned to induce selectively either the translation or desorption of individual ammonia molecules on a Cu(100) surface. We are able to select a particular reaction pathway by adjusting the electronic tunnelling current and energy during the reaction induction such that we activate either the stretching vibration of ammonia or the inversion of its pyramidal structure. Our results illustrate the ability of the scanning tunnelling microscope to probe single-molecule events in the limit of very low yield and very low power irradiation, which should allow the investigation of reaction pathways not readily amenable to study by more conventional approaches.

Atomic structure of antiphase domain boundaries of a thin Al2O3 film on NiAl(110).

Line defects of a thin alumina film on NiAl(110) have been studied on the atomic level with scanning tunneling microscopy at 4 K. While boundaries between two reflection domains do not expose a characteristic structure, antiphase domain boundaries are well ordered. The latter boundaries result from the insertion of a row of O atoms, as atomically resolved images of the topmost oxygen layer show. The insertion occurs only in two of the three characteristic directions of the quasihexagonal O lattice. Depending on the direction, either straight or zigzagged boundaries form. An atomic characterization of line defects on the oxide surface is a first step to correlate their topographic structure and chemical activity.

Adsorbate-substrate vibrational modes of benzene on Ag(110) resolved with scanning tunneling spectroscopy.

Using a low temperature scanning tunneling microscope, we have detected low energy adsorbate-substrate (external or frustrated) vibrational modes of benzene molecules adsorbed on a Ag(110) surface. We demonstrate that such vibrations represent a fingerprint of the molecules' chemical state and environment; two different vibrational spectra are measured on molecules populating two different adsorption states. We also find that the distortion of the adsorption geometry of the molecules may give rise to the excitation of additional (initially hidden) modes. Important differences in the spatial distribution of the inelastic signal are also observed for these external modes.

Valsartan for prevention of restenosis after stenting of type B2/C lesions: the VAL-PREST trial.

The following study was performed to evaluate the effects of chronic 6-month administration of the angiotensin I receptor antagonist valsartan on restenosis rate after stenting of type B2/C lesions in comparison to placebo. Despite encouraging results of the BENESTENT and STRESS trials, stenting of complex coronary lesions leads to an in-stent restenosis rate of up to 40%. Several attempts at systematic medical therapy (e.g., ACE inhibitors) have not improved these results. Because of the important role of angiotensin in endothelial function, the hypothesis that angiotensin I receptor antagonists after stent implantation lead to a reduction of the in-stent restenosis rate should be tested in a single-center trial. Two hundred and fifty patients with type B2/C coronary lesions were randomized in an open-label study with respect to age, gender, lesion type and indication of percutaneous coronary intervention to a chronic administration of 80 mg valsartan or placebo (beta-blocking agents and/or ACE inhibitors). In-stent restenosis rate according to quantitative coronary angiography (QCA) and need for reintervention as primary and secondary endpoints were analyzed after a repeat angiogram at 6 months in 99 patients with 80 mg valsartan and 101 patients with placebo. Chronic administration of 80 mg valsartan reduced the in-stent restenosis rate to 19.2% (n = 19/99) in comparison to placebo with an in-stent restenosis rate of 38.6% (n = 39/101) (p < 0.005). Reintervention rate was 28.7% (n = 29/101) in the placebo group and only 12.1% (n = 12) in the valsartan group (p < 0.005). QCA analysis of stented coronary segments disclosed no differences in reference vessel diameter (2.68 +/- 0.26 mm in the valsartan group versus 2.71 +/- 0.24 mm in the placebo group) but significant differences in stented vessel diameter (2.17 +/- 0.27 mm in the valsartan group and 1.60 +/- 0.20 mm in the placebo group) (p < 0.000001).

Familial hypertrophic cardiomyopathy associated with prolongation of the QT interval.

In a 61 year old female patient who suffered from atypical chest pain we diagnosed long QT syndrome by QTc duration of 467 ms, macroscopic T wave alternans and notched T waves in three leads and hypertrophic cardiomyopathy with asymmetric thickening of basal parts of the septum (2.0 cm) without relevant outflow tract obstruction by echocardiography. Coronary angiography could exclude coronary artery disease. In a systematic family screening two sons of the patient could also be diagnosed as having long QT syndrome with QTc durations of 472 and 496 ms and asymmetric septal thickening (1.8 and 2.1 cm, respectively). One of these two sons suffered from pre-syncope, the other was asymptomatic despite maximum sports activity. In the third son, LQTS and hypertrophic cardiomyopathy could be excluded.