Treatment of Arrhythmias by Radiofrequency Ablation

Radiofrequency ablation may be described as a thermal strategy to destroy tissue by increasing its temperature and causing irreversible cellular injury. Radiofrequency ablation is a relatively new modality which has found use in a wide range of medical applications and gained acceptance. RF ablation has been used to destroy tumors in the liver, prostate, breasts, lungs, kidneys, bones, and eyes. One of the early clinical applications was its use in treating supraventricular arrhythmias by selectively destroying cardiac tissue. Radiofrequency ablation has become established as the primary modality of transcatheter therapy for the treatment of symptomatic arrhythmias. Radiofrequency catheter ablation of cardiac arrhythmias was investigated using a finite-element based solution of the bioheat transfer equation. Spatial and temporal temperature profiles in the cardiac tissue were visualized.

Preparation and Characterization of Drug-Loaded Thermosensitive Hydrogels

Hydrogels are the promising classes of polymeric drug delivery systems with the controlled release rates. Among them, injectable thermosensitive hydrogels with transition temperature around the body temperature have been wildly considered. Chitosan is one of the most abundant natural polymers, and its biocompatibility and biodegradability makes it a favorable thermosensitive hydrogel that has been attracted much attention in biomedical field worldwide. In this work, a thermosensitive and injectable hydrogel was prepared using chitosan and β-glycerophosphate (β-GP) incorporated with an antibacterial drug (gentamycin). This drug loaded hydrogel is liquid at room temperature, and becomes more solidified gel when heated to the body temperature. Adding β-GP into chitosan and drug molecules and heating the overall solution makes the whole homogenous liquid into gel through a 3D network formation. The gelation time was found to be a function of temperature and concentration of β-GP. This thermosensitive chitosan based hydrogel system was characterized using FTIR and visual observation to determine the chemical structure and morphology. The results confirmed that chitosan/(β-GP) hydrogels could be a promising controlled-release drug delivery system for many deadly diseases.

DDPM-DEM Simulations of Particulate Flows in Human Tracheobronchial Airways

Dense particle-suspension flows in which particle-particle interactions are a dominant feature encompass a diverse range of industrial and geophysical contexts, e.g., slurry pipeline, fluidized beds, debris flows, sediment transport, etc. The one-way dispersed phase model (DPM), i.e., the conventional one-way coupling Euler-Lagrange method is not suitable for dense fluid-particle flows [1]. The reason is that such commercial CFD-software does not consider the contact between the fluid, particles and wall surfaces with respect to particle inertia and material properties. Hence, two-way coupling of the Dense Dispersed Phase Model (DDPM) combined with the Discrete Element Method (DEM) has been introduced into the commercial CFD software via in-house codes. As a result, more comprehensive and robust computational models based on the DDPM-DEM method have been developed, which can accurately predict the dynamics of dense particle suspensions. Focusing on the interaction forces between particles and the combination of discrete and continuum phases, inhaled aerosol transport and deposition in the idealized tracheobronchial airways [2] was simulated and analyzed, generating more physical insight. In addition, it allows for comparisons between different numerical methods, i.e., the classical one-way Euler-Lagrange method, two-way Euler-Lagrange method, EL-ER method [3], and the present DDPM-DEM method, considering micron- and nano-particle transport and deposition in human lungs.

A Numerical Investigation of the Fluid Flow in a Chandler Loop for Thrombus Studies

The Chandler loop is an artificial circulatory platform for in vitro hemodynamic experiments. In most experiments, the working fluid is subjected to a stress field via rotation of the Chandler loop, which, in turn, induces biochemical responses of the suspended cells. For very low rotation rates, the stress field can be approximated using laminar flow in a straight tube as a model. However, as the rotation rate increases, while still maintaining laminar flow, the effect of the tube curvature causes the stress field to deviate considerably from the straight tube approximation. In this manuscript, we investigate the flow and associated strain rate field of an incompressible Newtonian fluid in a Chandler loop as a function of the governing non-dimensional fluid dynamic parameters. We find that the Dean number, which is proportional to the rotation rate, is the dominant parameter in determining the fluid strain rate. We propose an empirical formula for predicting the average fluid strain rate magnitude in the working fluid that is valid over a wide parameter space to be used in lieu of the common, yet restrictive, straight tube-based prediction.

Analysis of Thrombus Formation Process by Flow Induced High Shear Rate Using Optical Observation Method

This paper describes visualization of thrombus formation process on orifice flows by laser sheet beam and normal illumination. The aim is to investigate the effects of shear stress or shear rate on the thrombus formation or thrombus formation rate. It was found that the white thrombus formation rate is proportional to square root of shear rate, and the white thrombus is dominant when the shear rate is more than 450 (1/s).

Benchmarking the Accuracy of Inertial Measurement Units for Estimating Joint Reactions

Newly developed miniature wireless inertial measurement units (IMUs) hold great promise for measuring and analyzing multibody system dynamics. This relatively inexpensive technology enables non-invasive motion tracking in broad applications, including human motion analysis. The second part of this two-part paper advances the use of an array of IMUs to estimate the joint reactions (forces and moments) in multibody systems via inverse dynamic modeling. In particular, this paper reports a benchmark experiment on a double-pendulum that reveals the accuracy of IMU-informed estimates of joint reactions. The estimated reactions are compared to those measured by high precision miniature (6 dof) load cells. Results from ten trials demonstrate that IMU-informed estimates of the three dimensional reaction forces remain within 5.0% RMS of the load cell measurements and with correlation coefficients greater than 0.95 on average. Similarly, the IMU-informed estimates of the three dimensional reaction moments remain within 5.9% RMS of the load cell measurements and with correlation coefficients greater than 0.88 on average. The sensitivity of these estimates to mass center location is discussed. Looking ahead, this benchmarking study supports the promising and broad use of this technology for estimating joint reactions in human motion applications.

Control Mechanisms in Oscillatory Motor Behavior

Studies on unimpaired humans have demonstrated that the central nervous system employs internal representations of limb dynamics and intended movement trajectories for planning muscle activation during pointing and reaching tasks. However, when performing rhythmic movements, it has been hypothesized that a control scheme employing an autonomous oscillator — a simple feedback circuit lacking exogenous input — can maintain stable control. Here we investigate whether such simple control architectures that can realize rhythmic movement that we observe in experimental data. We asked subjects to perform rhythmic movements of the forearm while a robotic interface simulated inertial loading. Our protocol included unexpected increases in loading (catch trials) as a probe to reveal any systematic changes in frequency and amplitude. Our primary findings were that increased inertial loading resulted in reduced frequency of oscillations, and in some cases multiple frequencies. These results exhibit some agreement with an autonomous oscillator model, though other features are more consistent with feedforward planning of force. This investigation provides a theoretical and experimental framework to reveal basic computational elements for how the human motor system achieves skilled rhythmic movement.

Acoustics and Computational Models for Diagnosing Arterial Blockages

Arterial blockages can occur in small or large arteries for a variety of reasons, such as obesity, stress, smoking and high cholesterol. This paper presents a feasibility study on a novel method to detect the behaviour of the blood pressure wave propagation for arteries in both healthy and diseased conditions in order to develop a relatively inexpensive method for early detection of arterial disease. The trend of this behaviour is correlated to the early development of the arterial blockage at various locations. Invasive sets of data (gathered from experiments performed on animals) are implemented into a 3D Computational Fluid Dynamic (CFD) model to determine how the arterial wall compliance changes when any abnormalities occur to the blood flow profile. At the same time, a 1D acoustical model is developed to transfer the information gathered (wave propagation for blood pressure, flow and arterial wall displacement) from the CFD model. Wave forms were collected at a location which was invasively accessible (the femoral artery). The computational and acoustical models are validated against the clinical trials and show good agreement. Any changes to the arterial wall displacement could be detected by systolic and diastolic blood pressure values at the femoral artery.

Modeling Control Adaptations During Recovery From Anterior Cruciate Ligament Reconstruction

In this paper, we aim to model a functional task affected by injury, along with the corresponding neuromuscular compensation strategy, in order to understand differences in task performance during recovery from the injury. This study is motivated by differing rates of functional task improvements during recovery from anterior cruciate ligament repair. In particular, clinical studies have shown faster recovery times for single-limb forward hopping versus single-limb crossover hopping (hopping back and forth laterally while moving forward). Modeling this hopping task will help us understand whether the main factor of the differing functional results is from the physical restrictions of the injury, the compensation strategies used to overcome these restrictions, or a combination of both. Our hypothesis is that the discrepancies in clinical functional results will be reproduced by employing a feedforward compensation strategy, where the compensation is learned and adjusted over time.

Modeling Prion Transport in a Tunneling Nanotube

We develop a model for simulating prion transport in a tunneling nanotube (TNT). We simulate the situation when two cells, one of which is infected, are connected by a TNT. We consider two mechanisms of prion transport: lateral diffusion in the TNT membrane and active actin-dependent transport inside endocytic vesicles. Endocytic vesicles are propelled by myosin Va molecular motors. Since the transit time of prions through a TNT is short (several minutes), the two population model developed here assumes that there is no interchange between the two prion populations, and that partitioning between the prion populations is decided by prion loading at the TNT entrance. The split between the two prion populations at the TNT entrance is decided by the degree of loading, which indicates the portion of prions that enter a TNT in endocytic vesicles. An analytical solution describing prion concentrations and fluxes is obtained.