Parallel two-phase flows are omnipresent in technological applications that require contact between two immiscible fluids for a finite amount of time. Precise control over the flow and separation of the fluids once they have been in contact are therefore the key challenges in these applications. Here, using experiments and numerical simulations, we show that the interface between two immiscible fluids flowing at the same flow rate in a symmetric channel can become unstable locally near the exit junction, where the two fluids are separated. This instability leads to the shedding of the droplets of one phase into the other, preventing a complete separation. We characterize this instability and show that the period of drop shedding is inversely proportional to the flow rate. We derive a stability criterion based on the balance between the Laplace pressure across the liquid-liquid interface and viscous pressure drop along each flow stream. The stability criterion and our experimental results are used to highlight the extreme sensitivity of this flow system to the parameters involved such as viscosity difference and exit geometry, which introduces gravitational effects and characteristics of the exit tubing.

The PATIENT manikin (Physical Anatomical Trainer Instrumented for Education and Non-subjective Testing) is designed with the conflicting needs of a highly modular system for ultimate scenario flexibility and cost containment, and a highly realistic system. PATIENT provides a unique combination of capital and disposable components, with each organ treated as a limited-reuse component. The organs contain unobtrusive instrumentation which informs the PATIENT control unit of the organ status. The control unit can adjust whole-body parameters to reflect the local physiology. PATIENT enables tailored simulations, from Point of Injury training of basic life support, through hospital training including surgical interventions.

Introduction: Simulator sickness causes vestibulo-autonomic responses that increase sympathetic activity and decrease parasympathetic activity. The purpose of the study was to quantify these responses through electrogastrography and cardiac interbeat intervals during flight simulation. Methods:There were 29 subjects that were randomly assigned to 2 parallel arms: 1) oculovestibular recoupling, where galvanic vestibular stimulation was synchronous with the visual field; and 2) control. Electrogastrography and interbeat interval data were collected during baseline, simulation, and post-simulation periods. A simulator sickness questionnaire was administered. Results: Statistically significant differences were observed in percentage of recording time with the dominant frequency of electrogastrography in normogastric and bradygastric domains between the oculovestibular recoupling and control groups. Normogastria was dominant during simulation in the oculovestibular recoupling group. In the control group, the percentage of recording time with the dominant frequency decreased by 22% in normogastria and increased by 20% in bradygastria. The percentage change of the dominant power instability coefficient from baseline to simulation was 26% in the oculovestibular recoupling group vs. 108% in the control group. The power of high-frequency components for interbeat intervals did not change significantly in the oculovestibular recoupling group and was decreased during simulation in the control group. Discussion: Electrogastrography and interbeat intervals are sensitive indices of autonomic changes in subjects undergoing flight simulation. These data demonstrate the potential of oculovestibular recoupling to stabilize gastric activity and cardiac autonomic changes altered during simulator and motion sickness.

BACKGROUND:We have introduced a method to guide radiofrequency catheter ablation (RCA) procedures that estimates the location of a catheter tip used to pace the ventricles and the target site for ablation using the single equivalent moving dipole (SEMD). OBJECTIVE:To investigate the accuracy of this method in resolving epicardial and endocardial electrical sources. METHODS:Two electrode arrays, each of nine pacing electrodes at known distances from each other, sutured on the left- and right-ventricular (LV and RV) epicardial surfaces of swine, were used to pace the heart at multiple rates, while body surface potentials from 64 sites were recorded and used to estimate the SEMD location. A similar approach was followed for pacing from catheters in the LV and RV. RESULTS:The overall (RV & LV) error in estimating the interelectrode distance of adjacent epicardial electrodes was 0.38 ± 0.45 cm. The overall endocardial (RV & LV) interelectrode distance error, was 0.44 ± 0.26 cm. Heart rate did not significantly affect the error of the estimated SEMD location (P > 0.05). The guiding process error became progressively smaller as the SEMD approached an epicardial target site and close to the target, the overall absolute error was ∼ 0.28 cm. The estimated epicardial SEMD locations preserved their topology in image space with respect to their corresponding physical location of the epicardial electrodes. CONCLUSION:The proposed algorithm suggests one can efficiently and accurately resolve epicardial electrical sources without the need of an imaging modality. In addition, the error in resolving these sources is sufficient to guide RCA procedures.

Radio-frequency catheter ablation (RCA) is an established treatment for ventricular tachycardia (VT). A key feature of the RCA procedure is the need for a mapping approach that facilitates the identification of the target ablation site. In this study, we investigate the effect of the location of the reference potential and spatial anatomical constraints on the accuracy of an algorithm to identify the target site for ablation therapy of VT. This algorithm involves processing body surface potentials using the single equivalent moving dipole (SEMD) model embedded in an infinite homogeneous volume conductor to model cardiac electrical activity. We employed a swine animal model and an electrode array of nine electrodes that was sutured on the epicardial surface of the right ventricle. We identified two potential reference electrode locations: at an electrode most far away from the heart (R1) and at the average of all 64 body surface electrode potentials (R2). Also, we developed three spatial "constraining" schemes of the algorithm used to obtain the SEMD location: one that does not impose any constraint on the inverse solution (S1), one that constrains the solution into a volume that corresponds to the heart (S2), and one that constrains the solution into a volume that corresponds to the body surface (S3). We have found that R2S1 is the most accurate approach (p < 0.05 versus R1S1 at earliest activation time-EAT) for localizing epicardial electrical sources of known locations in vivo. Although the homogeneous volume conductor introduces systematic error in the estimated compared to the true dipole location, we have observed that the overall error of the estimated interelectrode distance compared to the true one was 0.4 +/- 0.4 cm and 0.4 +/- 0.1 cm for the R1S1 and R2S1 combinations, respectively, at the EAT (p = N.S.) and 1.0 +/- 0.6 and 0.5 +/- 0.4 cm, respectively, at the pacing spike time (PST, p < 0.05). In conclusion, our algorithm to estimate the SEMD parameters from body surface potentials can potentially be a useful method to rapidly and accurately guide the catheter tip to the target site during a RCA procedure without the need for spatial anatomical information obtained by conventional imaging modalities.

We have developed a system that could potentially be used to identify the site of origin of ventricular tachycardia (VT) and to guide a catheter to that site to deliver radio-frequency ablation therapy. This system employs the Inverse Solution Guidance Algorithm based upon Single Equivalent Moving Dipole (SEMD) localization method. The system was evaluated in in vivo swine experiments. Arrays consisting of 9 or 16 bipolar epicardial electrodes and an additional mid-myocardial pacing lead were sutured to each ventricle. Focal tachycardia was simulated by applying pacing pulses to each epicardial electrode at multiple pacing rates during breath hold at the end-expiration phase. Surface potentials were recorded from 64 surface electrodes and then analyzed using the SEMD method to localize the position of the pacing electrodes. We found a close correlation between the locations of the pacing electrodes as measured in computational and real spaces. The reproducibility error of the SEMD estimation of electrode location was 0.21 ± 0.07 cm. The vectors between every pair of bipolar electrodes were computed in computational and real spaces. At 120 bpm, the lengths of the vectors in the computational and real space had a 95% correlation. Computational space vectors were used in catheter guidance simulations which showed that this method could reduce the distance between the real space locations of the emulated catheter tip and the emulated arrhythmia origin site by approximately 72% with each movement. We have demonstrated the feasibility of using our system to guide a catheter to the site of the emulated VT origin.

Galvanic stimulation has long been used as a nonmechanical means of activating the vestibular apparatus through direct action on the vestibular nerve endings. This stimulation has been reported to be safe, but no studies have examined the potential changes in the corresponding cochlear receptors. The aim of the present study was to evaluate the effect of galvanic vestibular stimulation (GVS) on distortion product otoacoustic emissions (DPOAEs). Fourteen subjects underwent DPOAEs during several conditions of GVS. The DPOAEs ranged from ∼ 1 kHz to ∼ 8 kHz at 65/55 dB for f1/f2 and with an f2/f1 ratio of 1.2. The subjects were evaluated at 10 stimulation conditions that ranged from -2.0 mA to +2.0 mA for each frequency. Statistical analysis showed no significant differences in DPOAE amplitudes for all conditions with and without GVS. Results also showed no significant differences between DPOAE amplitudes before and after GVS. Multivariate analysis found subject variability in DPOAE amplitude, which was not thought to be GVS related. Results indicated that GVS produced neither temporary nor permanent changes in DPOAEs.

INTRODUCTION Despite improvement in the computational capabilities of visual displays in flight simulators, intersensory visual-vestibular conflict remains the leading cause of simulator sickness (SS). By using galvanic vestibular stimulation (GVS), the vestibular system can be synchronized with a moving visual field in order to lessen the mismatch of sensory inputs thought to result in SS. METHODS A multisite electrode array was used to deliver combinations of GVS in 21 normal subjects. Optimal electrode combinations were identified and used to establish GVS dose-response predictions for the perception of roll, pitch, and yaw. Based on these data, an algorithm was then implemented in flight simulator hardware in order to synchronize visual and GVS-induced vestibular sensations (oculo-vestibular-recoupled or OVR simulation). Subjects were then randomly exposed to flight simulation either with or without OVR simulation. A self-report SS checklist was administered to all subjects after each session. An overall SS score was calculated for each category of symptoms for both groups. RESULTS The analysis of GVS stimulation data yielded six unique combinations of electrode positions inducing motion perceptions in the three rotational axes. This provided the algorithm used for OVR simulation. The overall SS scores for gastrointestinal, central, and peripheral categories were 17%, 22.4%, and 20% for the Control group and 6.3%, 20%, and 8% for the OVR group, respectively. CONCLUSIONS When virtual head signals produced by GVS are synchronized to the speed and direction of a moving visual field, manifestations of induced SS in a cockpit flight simulator are significantly reduced.

Objective1) Report a novel method for measuring vestibular sensations of movement induced by galvanic vestibular stimulation (GVS). 2) Introduce a new approach to quantify vestibular symptoms in patients with vertigo and related disorders.MethodWe created a software program using a Logitech wireless joystick to measure and display in three dimensions the manner in which subjects felt movement in response to GVS. Each subject underwent thirty 20‐second protocols utilizing ten different combinations of GVS scalp electrode pairs.ResultsThree dimensional avatar displays of subject responses to GVS indicated the direction and magnitude of pitch, roll, and yaw as well as the angular velocity of motion. As evident on the avatar display in response to a 2.5 mA GVS pulse, the majority of subjects reported sensation of movement, 19 out of 21 (90%) reporting pitch, 17 out of 21 (81%) reporting yaw, and 17 out of 21 (81%) reporting roll sensations.Conclusion1) These data demonstrate a software‐based 3 dimensional avatar display system to represent perceived vestibular sensation in response to GVS. 2) This technology may play a role in clinical practice by providing the ability to quantify vestibular symptoms in the assessment of patients with vertigo and related disorders.