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BACKGROUND: It has been shown that cold caloric irrigation decreases the vestibulo-ocular reflex (VOR) gain in the vertically positioned lateral canal as measured by head impulse testing. This effect is most probably caused by a sustained deflection of the cupula in the inhibitory direction. OBJECTIVE: The aim of the present experiment was to answer the question if a sustained excitatory deflection increases the gain of the reflex in healthy volunteers. METHODS: In order to deflect the cupula, cold caloric irrigation was applied in prone (forward head hanging) position. In this position cold thermal irrigation elicited an excitatory caloric nystagmus with an ipsilateral fast phase. RESULTS: When head impulses were applied immediately after cold caloric irrigation, the gain of the VOR decreased in comparison to the values measured before irrigation. CONCLUSIONS: Together with the previous results cited above, these data show that biasing the cupula in either direction decreases its sensitivity with respect to high acceleration stimuli. This might occur because the deviation elicits a partial mechanical and electrophysiological saturation of the cupula. [ABSTRACT FROM AUTHOR]

Objective: A new generation of leadless cardiac pacemakers effectively overcomes the main limitations of conventional devices, but only offer single-chamber pacing, although dual-chamber or multisite pacing is highly desirable for most patients. The combination of several leadless pacemakers could facilitate a leadless multisite pacemaker but requires an energy-efficient wireless communication for device synchronization. This study investigates the characteristics of conductive intracardiac communication between leadless pacemakers to provide a basis for future designs of leadless multisite pacemaker systems. Methods: Signal propagation and impedance behavior of blood and heart tissue were examined by in vitro and in vivo measurements on domestic pig hearts and by finite-element simulations in the frequency range of 1 kHz to 1 MHz. Results: A better signal transmission was obtained for frequencies higher than 10 kHz. The influence of a variety of practical parameters on signal transmission could be identified. A larger distance between pacemakers increases signal attenuation. A better signal transmission is obtained through larger inter-electrode distances and a larger electrode surface area. Furthermore, the influence of pacemaker encapsulation and relative device orientation was assessed. Conclusion: This study suggests that conductive intracardiac communication is well suited to be incorporated in leadless pacemakers. It potentially offers very low power consumption using low communication frequencies. Significance: The presented technique enables highly desired leadless multisite pacing in near future. [ABSTRACT FROM AUTHOR]

Aims: To explore the feasibility of minimally invasive catheter‐based electrophysiology studies in the urinary tract. This is a well‐known method used in cardiology to investigate and treat arrhythmias. Methods: We developed an experimental platform which allows electrophysiological recordings with cardiac catheters and conventional needle electrodes in ex vivo pig ureters. The action potential was triggered by a stimulating electrode. We considered 13 porcine ureters (freshly collected and harvested in organ bath), 7 of which were used to optimize the setup and define the stimulation parameters; we performed the recordings in the remaining six ureters. The electrical propagation of the generated action potential was tracked with multiple sensing electrodes, from which propagation directions, velocities, refractory periods, and pacing thresholds were extracted. Results: We recorded propagating electrical activity in four ureters using needle electrodes and in two ureters using cardiac catheters. Propagation velocities for forward direction (from kidney to bladder) derived by the two methods were similar (15.1 ± 2.6 mm/s for cardiac catheters, 15.6 ± 2.3 mm/s for needle recordings). Pacing thresholds, activation patters, and refractory times were provided for the ureteric smooth muscle. Retrograde propagations and corresponding velocities were also observed and measured. Conclusions: This study is a proof‐of‐concept showing that electrical activity can be measured "from the inside" of urinary cavities using catheters and that obtained results are comparable with the more invasive needle recordings. Catheter‐based electrophysiology may allow, in the clinical setting, for: i) a more differentiated understanding of urological disorders such as overactive bladder and ii) new therapeutic approaches (e.g., targeted tissue ablation). [ABSTRACT FROM AUTHOR]

Aims: To explore the use of time‐frequency analysis as an analytical tool to automatically detect pattern changes in bladder pressure recordings of patients with overactive bladder (OAB). To provide quantitative data on the bladder's non‐voiding activity which could improve the current diagnosis and potentially the treatment of OAB. Methods: We developed an algorithm, based on time‐frequency analysis, to analyze bladder pressure during the filling phase of urodynamic studies. The algorithm was used to generate a bladder overactivity index (BOI) for a quantitative estimation of the average bladder non‐voiding‐activity. We tested the algorithm with one control group and two groups of patients with OAB symptoms: one group with detrusor overactivity (DO), assessed by an experienced urologist (OAB‐with‐DO group), and another group for which detrusor overactivity was not diagnosed (OAB‐without‐DO group). Results: The algorithm identified diagnostically significant data on the bladder non‐voiding activity in a specified frequency range. BOI was significantly higher for both OAB groups compared to the control group: the median value of BOI was twice as big in OAB‐without‐DO and more than four times higher in OAB‐with‐DO compared to control group. Moreover the algorithm was successfully tested to detect episodes of detrusor overactivity. Conclusions: We have shown that a simple algorithm, based on time‐frequency analysis of bladder pressure, may be a promising tool in the clinical setting. The algorithm can provide quantitative data on non‐voiding bladder activity in patients and quantify the changes according to phenotype. Moreover the algorithm can detect DO, showing potential for triggering conditional bladder stimulation. [ABSTRACT FROM AUTHOR]

The Lapeyre-Triflo FURTIVA valve aims at combining the favorable hemodynamics of bioprosthetic heart valves with the durability of mechanical heart valves (MHVs). The pivoting region of MHVs is hemodynamically of special interest as it may be a region of high shear stresses, combined with areas of flow stagnation. Here, platelets can be activated and may form a thrombus which in the most severe case can compromise leaflet mobility. In this study we set up an experiment to replicate the pulsatile flow in the aortic root and to study the flow in the pivoting region under physiological hemodynamic conditions (CO = 4.5 L/min / CO = 3.0 L/min, f = 60 BPM). It was found that the flow velocity in the pivoting region could reach values close to that of the bulk flow during systole. At the onset of diastole the three valve leaflets closed in a very synchronous manner within an average closing time of 55 ms which is much slower than what has been measured for traditional bileaflet MHVs. Hot spots for elevated viscous shear stresses were found at the flanges of the housing and the tips of the leaflet ears. Systolic VSS was maximal during mid-systole and reached levels of up to 40 Pa. [ABSTRACT FROM AUTHOR]

Patients with superior canal dehiscence (SCD) suffer from events of dizziness and vertigo in response to sound, also known as Tullio phenomenon (TP). The present work seeks to explain the fluid-dynamical mechanisms behind TP. In accordance with the so-called third window theory, we developed a computational model for the vestibular signal pathway between stapes and SCD. It is based on first principles and accounts for fluid-structure interactions arising between endolymph, perilymph, and membranous labyrinth. The simulation results reveal a wave propagation phenomenon in the membranous canal, leading to two flow phenomena within the endolymph which are in close interaction. First, the periodic deformation of the membranous labyrinth causes oscillating endolymph flow which forces the cupula to oscillate in phase with the sound stimulus. Second, these primary oscillations of the endolymph induce a steady flow component by a phenomenon known as steady streaming. We find that this steady flow of the endolymph is typically in ampullofugal direction. This flow leads to a quasi-steady deflection of the cupula which increases until the driving forces of the steady streaming are balanced by the elastic reaction forces of the cupula, such that the cupula attains a constant deflection amplitude which lasts as long as the sound stimulus. Both response types have been observed in the literature. In a sensitivity study, we obtain an analytical fit which very well matches our simulation results in a relevant parameter range. Finally, we correlate the corresponding eye response (vestibulo-ocular reflex) with the fluid dynamics by a simplified model of lumped system constants. The results reveal a "sweet spot" for TP within the audible sound spectrum. We find that the underlying mechanisms which lead to TP originate primarily from Reynolds stresses in the fluid, which are weaker at lower sound frequencies. [ABSTRACT FROM AUTHOR]