Stability Analysis of Arteries Under Torsion

Vascular tortuosity may impede blood flow, occlude the lumen, and ultimately lead to ischemia or even infarction. Mechanical loads like blood pressure, axial force, and also torsion are key factors participating in this complex mechanobiological process. The available studies on arterial torsion instability followed computational or experimental approaches, yet single available theoretical study had modeled the artery as isotropic linear elastic. This paper aim is to validate a theoretical model of arterial torsion instability against experimental data. The artery is modeled as a single-layered, nonlinear, hyperelastic, anisotropic solid, with parameters calibrated from experiment. Linear bifurcation analysis is then performed to predict experimentally measured stability margins. Uncertainties in geometrical parameters and in measured mechanical response were considered. Also, the type of rate (incremental) boundary conditions (RBCs) impact on the results was examined (e.g., dead load, fluid pressure). The predicted critical torque and twist angle followed the experimentally measured trends. The closest prediction errors in the critical torque and twist rate were 22% and 67%, respectively. Using the different RBCs incurred differences of up to 50% difference within the model predictions. The present results suggest that the model may require further improvements. However, it offers an approach that can be used to predict allowable twist levels in surgical procedures (like anastomosis and grafting) and in the design of stents for arteries subjected to high torsion levels (like the femoropopliteal arteries). It may also be instructive in understanding biomechanical processes like arterial tortuosity, kinking, and coiling.

Helicity Enhanced Torsion Sensor Based on Liquid Filled Twisted Photonic Crystal Fibers

A highly sensitive torsion sensor can be constructed by combining a twisted photonic crystal fiber with a liquid-filled waveguide in its air-hole cladding. The torsion sensitivity of this type of sensor is determined directly by the phase-matching conditions between the fiber core mode and the liquid waveguide mode, which can be improved by tuning the helicity (denoted by the initial twist rate, α0) of the twisted photonic crystal fiber. The enhancement mechanism of α0 on the sensitivity of the proposed torsion sensor is investigated theoretically, followed by experimental verifications, and a torsion sensitivity as high as 446 nm∙mm∙rad−1 can be obtained by tailoring these parameters. Experimental results show that the torsion sensitivity increases with α0 decreasing from 3.142 to 3.925 rad/mm, which are in consistence with that of the numerical predictions. The demonstrated torsion sensor is expected to contribute to the development of highly sensitive torsion-related photonic crystal fiber devices.

P332 is 3D analysis of longitudinal strain useful to predict cardiac events in patients undergoing mitral valve repair?

Background The presence of abnormal 3D left ventricular (LV) strain values in patients diagnosed with mitral valve prolapse (MVP) and significant mitral regurgitation (MR) has been described previously. Recently, some studies showed an addictive prognostic role of Global Longitudinal Strain (GLS) in patients with severe aortic regurgitation. Few data are available about the prognostic role of LV strain in patients diagnosed with severe MR secondary to Myxomatous or fibroelastic deficiency (FED) MVP, undergoing MV repair. Purpose The aim of the study was to determinate whether LV GLS, strain rate, twist rate and left atrial strain (LAS) may identify a subgroup of patients with MVP and severe MR at higher risk of clinical events after surgical repair in both Myxomatous and FED disease. Methods We retrospectively studied 100 patients diagnosed with MVP and severe MR due to Myxomatous or FED disease, eligible for MV surgery between 2012 and 2015. Only patients with normal LV function who underwent a 3D transthoracic echocardiographic examination were included. 3D LV GLS, strain rate, twist rate and LAS were measured using 3D analysis software. Clinical data were recorded during a median follow-up of 48 months. Clinical events included cardiac death, arrhythmia and cardiac hospitalization for heart failure or arrhythmic events. Results 65 patients were diagnosed with Myxomatous and 35 with FED disease. A total of 13 events were recorded during the follow-up, including 1 death, 2 hospitalizations for heart failure and 10 minor arrhythmic events, mostly isolated premature ventricular complex. The number of events was not statistically different between the two groups. In both groups no significant correlation was found between clinical events and each of the echocardiographic parameters measured. Conclusion In patients with MVP and severe MR but normal LV function, undergoing MV repair, LV strain analysis was not able to predict long term cardiac events., regardless of the etiology.

Polarimetric Sensitivity to Torsion in Spun Highly Birefringent Fibers

We report on experimental studies of polarimetric sensitivity to torsion in spun highly birefringent fibers. Two classes of spun fibers were examined, namely spun side-hole fibers and birefringent microstructured fibers with different birefringence dispersion, spin pitches, and spin directions. The polarimetric sensitivity to torsion was determined by monitoring a displacement of the spectral interference fringes arising in the output signal because of interference of polarization modes and induced by an additional fiber twist. Both the experimental results and the analytical predictions showed that the sensitivity to torsion normalized to the fringe width in the spun highly birefringent fibers increased asymptotically with the twist rate to the value of 1/ π rad−1. We have also studied the polarimetric response to temperature in the spun side-hole fibers. We have found that, in contrast to the torsional sensitivity, the temperature sensitivity decays asymptotically to zero with increasing fiber twist rate. Therefore, the spun fibers with short spin pitches are especially well suited for torsion measurements because the torsional sensitivity and the range of linear response are both enhanced in such fibers, while at the same time, the cross-sensitivity to temperature is reduced.

Numerical Simulation Study on the Law of Attenuation of Hydrate Particles in a Gas Transmission Pipeline

Based on the swirl flow of gas hydrate pipeline safety flow technology, the numerical simulation method is used to study the attenuation law of hydrate particles, which is of great significance for expanding the boundary of safe flow. The results show that the size of the initial swirl number is mainly related to the twist rate and has nothing to do with the Reynolds number; the smaller the twist rate, the greater the Reynolds number, the greater the number of swirling flow in the same position in the pipeline. The concentration has almost no effect on the change of the swirl number; for the non-dimensional swirl number, and the numerical simulation is roughly the same as the results of the paper, the attenuation coefficient beta and ln (Re) has a linear relationship. The no twist tape is six to eight times larger than the volume fraction of the twisted belt, and the smaller the twist tape twist, the smaller the particle deposition is, the higher the initial concentration of the particles in the pipe, and the larger the volume fraction of the hydrate particles deposited by the tube wall.

Twist-induced guidance in coreless photonic crystal fiber: A helical channel for light

A century ago, Einstein proposed that gravitational forces were the result of the curvature of space-time and predicted that light rays would deflect when passing a massive celestial object. We report that twisting the periodically structured “space” within a coreless photonic crystal fiber creates a helical channel where guided modes can form despite the absence of any discernible core structure. Using a Hamiltonian optics analysis, we show that the light rays follow closed spiral or oscillatory paths within the helical channel, in close analogy with the geodesics of motion in a two-dimensional gravitational field. The mode diameter shrinks, and its refractive index rises, as the twist rate increases. The birefringence, orbital angular momentum, and dispersion of these unusual modes are explored.