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Background: A new cooling method is proposed for preventing electrode-tissue overheating during cardiac catheter ablation using a vibrating catheter. Previous work has shown that vibration that results from increased flow velocity around the catheter can have a cooling effect on the electrode.Objective: Contact force has been shown to be an important factor that affects cooling and lesion formation, because contact force determines the ratio of power delivery between blood and tissue. In this study, the effect of contact force on electrode cooling and tissue heating was investigated during the operation of an electrode cooled by vibration.Methods: Using PVA-H or myocardium ablation tissue models under conditions of no flow, electrode and tissue temperatures and lesion sizes were measured at various vibrational frequencies and contact force conditions.Results: The experiments showed that the catheter vibration still decreases the electrode temperature over a contact force range of 2-30 gf. The lesion size was increased with increasing contact force at each vibrational frequency.Conclusions: Increasing contact force can increase lesion size with cooling by vibration remaining effective. [ABSTRACT FROM AUTHOR]

Cardiovascular diseases are closely related to blood flow. Ultrasonic-Measurement-Integrated (UMI) simulation, in which results of ultrasonic measurement are fed back to the flow simulation, was proposed in a previous study in order to reproduce the real blood flow accurately and efficiently. The usability of the UMI simulation was confirmed by numerical experiment, but the effectiveness of this simulation was strongly affected by the accuracy of the ultrasonic measurement. In this paper, we examined the accuracy of a commercial ultrasonic measurement device by an experiment with a PVA-H straight tube phantom. By analyzing the measured color Doppler images for a developed laminar flow inside the phantom, we obtained the relationship between the color Doppler value and the Doppler velocity (C-V relationship). It was revealed that the original C-V relationship provided in the device as a color bar was not suitable for quantitative evaluation of Doppler velocity to be used in UMI simulation. Compared with the original C-V relationship, the present C-V relationship results are in far better agreement with the analytic solution. Investigation of the normalized error confirmed that the result obtained with the present C-V relationship was reliable in cases of relatively high Reynolds number in the flow domain except near the wall. The two signal conditioning factors of the device had little influence on the Doppler velocity. Finally, we investigated the effect of temporal and spatial averaging of ultrasonic measurement data to clarify the relation between the number of averagings and the level of agreement with the analytic solution.

A new electrode cooling system using a vibrating catheter is described for conditions of low blood flow when saline irrigation cannot be used. Vibrations of the catheter are hypothesized to disturb blood flow around the electrode, leading to increased convective cooling of the electrode. The aim of this study is to confirm the cooling effect of vibration and investigate the associated mechanisms. As methods, an in vitro system with polyvinyl alcohol-hydrogel (PVA-H) as ablated tissue and saline flow in an open channel was used to measure changes in electrode and tissue temperatures under vibration of 0–63 Hz and flow velocity of 0–0.1 m/s. Flow around the catheter was observed using particle image velocimetry (PIV). Results show that under conditions of no flow, electrode temperatures decreased with increasing vibration frequency, and in the absence of vibrations, electrode temperatures decreased with increasing flow velocity. In the presence of vibrations, electrode temperatures decreased under conditions of low flow velocity, but not under those of high flow velocity. PIV analyses showed disturbed flow around the vibrating catheter, and flow velocity around the catheter increased with higher-frequency vibrations. In conclusion, catheter vibration facilitated electrode cooling by increasing flow around the catheter, and cooling was proportional to vibration frequency. [ABSTRACT FROM AUTHOR]

Objective: In this paper, we investigated the parameters with effective traceability to assess the mechanical properties of interventional devices.Methods: In our evaluation system, a box-shaped poly (vinyl alcohol) hydrogel (PVA-H) and silicone were prepared with realistic geometry, and the measurement and evaluation of traceability were carried out on devices using load hand force. The phantom models had a total of five curve pathways to reach the aneurysm sac.Results: Traceability depends on the performance of the interventional devices in order to pass through the curved part of the model simulation track. The traceability of the guide wire was found to be much better than that of the balloon and stent loading catheter, as it reached the aneurysm sac in both phantom models.Conclusions: Observation using the video record is another advantage of our system, because the high transparency of the materials with silicone and PVA-H can allow visualization of the inside of an artery. [ABSTRACT FROM AUTHOR]

In this paper, we investigated several parameters with effect on the compressive force to assess the mechanical properties of interventional device. We find several parameters are highly influential and others are not. In our evaluation system, we prepared a box-shaped PVA-H and silicone with realistic geometry and carried out the measurement and evaluation of the pushability by using load cell machine. The parameters of velocity, position of device in the system do not affect the compressive force, whereas the length of catheter from the tip to fixed point is one of the most influential parameters for the force. Several behaviors such as passing through the curve or slip and stop can be observed and defined using this system. The balance of the bending force and the pushing force may make the tip with behavior of slip and stop or passing thorough the curve. The investigation of the evaluation system confirmed that high reproducibility with short error bar is indicated. The observation with movie record is also an advantage of our system because the high transparency of materials with silicone and PVA-H can check the inside of artery. [ABSTRACT FROM AUTHOR]

BACKGROUND: Plaques in blood vessels exhibit a wide range of stiffness depending on disease conditions: stiffness is an important factor in plaque behavior. The geometrical change in plaque based on its behavior can affect blood flow patterns. Thus, it is important to study both blood flow and deformation of plaques and blood vessels.OBJECTIVE: This study aims to identify the differences in flow conditions between in vitro models to discuss experimental materials for arterial wall and flow observation.METHODS: In order to observe the blood flow pattern and plaque deformation simultaneously, a PVA-H stenosis model was used. In addition, a silicone model was also used as a rigid-like model for comparison with the PVA-H model. PIV was employed to measure the flow velocity distribution and determine the flow levels in the models.RESULTS: PVA-H model exhibits expansion with an increase in upstream pressure and silicone model maintains the diameter. The expansion depends on their mechanical properties and influences flow conditions such as velocity changes and RAP in the parent artery. The balance between the expansion and change in flow conditions determines the final geometries of PVA-H model and flow pattern. CONCLUSIONS: The results suggest that the stiffness measurement for blood vessels and plaques such as ultrasound measurements would be important for accurate treatments. [ABSTRACT FROM AUTHOR]

In this paper, we investigated several parameters with effect on the compressive force to assess the mechanical properties of interventional device. We find several parameters are highly influential and others are not. In our evaluation system, we prepared a box-shaped PVA-H and silicone with realistic geometry and carried out the measurement and evaluation of the pushability by using load cell machine. The parameters of velocity, position of device in the system do not affect the compressive force, whereas the length of catheter from the tip to fixed point is one of the most influential parameters for the force. Several behaviors such as passing through the curve or slip and stop can be observed and defined using this system. The balance of the bending force and the pushing force may make the tip with behavior of slip and stop or passing thorough the curve. The investigation of the evaluation system confirmed that high reproducibility with short error bar is indicated. The observation with movie record is also an advantage of our system because the high transparency of materials with silicone and PVA-H can check the inside of artery. [ABSTRACT FROM AUTHOR]

As a potential artificial cartilage material, the friction and wear properties of nano-hydroxy apatite (HA) particles filled poly (vinyl alcohol) hydrogel (PVA-H) composites sliding against stainless steel disk under water lubrication condition were studied by using a four ball tester. The worn surfaces were investigated by using a scanning electron microscope (SEM) to determine the wear mechanisms. Experimental results show that filling HA to PVA-H will slightly increase the friction coefficient of composites with the increasing of HA content under water lubrication condition. Meanwhile, HA particles can greatly reduce the wear mass loss of the PVA-H composites and enhance the load carrying capacity, the wear loss of the 1 wt% HA reinforced PVA-H composites can be decreased by 30 percent under 2.0 MPa to 50 percent under 0.5 MPa contact pressure. We also found that 2 wt% HA content of composites increase the wear mass loss under the same condition. SEM examination shows that the worn surface of low HA containing (1 wt%) composites are much smoother than that of pure PVA-H or high HA containing (2 wt%) composites under 1.5 MPa contact pressure. It is also found that there are big hole and big reunited HA particles in the surface of 2 wt% HA containing composites, which leads to deterioration of the surface of samples under higher loads in water lubrication. These results may be useful in the tribological design of artificial articular cartilage material. [ABSTRACT FROM AUTHOR]