Justin Whitty

Microarterial anastomoses: A parameterised computational study examining the effect of suture position on intravascular blood flow

This study investigates the extent to which individual aspects of suture placement influence local haemodynamics within microarterial anastomoses. An attempt to physically quantify flow characteristics of blood past microvascular sutures is made using computational fluid dynamics (CFD) software. Particular focus has been placed on increased shear strain rate (SSR), a known precipitant of intravascular platelet activation and thrombosis. Measurements were taken from micrographs of sutured anastomoses in chicken femoral vessels, with each assessed for bite width, suture angle and suture spacing. Computational geometries were then created to represent the anastomosis. Each suture characteristic was parameterised to allow independent or simultaneous adjustment. Flow rates were obtained from anonymised Doppler ultrasound scans of analogous vessels during preoperative assessment for autologous breast reconstruction. Vessel simulations were performed in 2.5mm ducts with blood as the working fluid. Vessel walls were non-compliant and a continuous Newtonian flow was applied, in accordance with current literature. Suture bite angle and spacing had significant effects on local haemodynamics, causing notably higher local SSRs, when simulated at extremes of surgical practice. A combined simulation, encompassing subtle changes of each suture parameter simultaneously i.e. representing optimum technique, created a more favourable SSR profile. As such, haemodynamic changes associated with optimum suture placement are unlikely to influence thrombus formation significantly. These findings support adherence to the basic principles of good microsurgical practice.

Analysis of the passive yaw mechanism of small horizontal-axis wind turbines

This paper analyzes passive yaw mechanisms for small, fixed-pitch, variable-speed wind turbines. There are several mechanisms which can provide passive yaw-control. This paper compares different passive yaw-control mechanisms by considering both their technical viabilities and costs. It is demonstrated that small wind turbines with a tilting tail hinge and an offset pivot axis are simpler and more economical than other passive yaw-control small wind turbines. Finally, the paper summarizes the working principles of the passive-yaw mechanisms for both wind direction tracking and over-speed protection under high winds, and presents the mathematical calculation of the back-position-torque, aerodynamic moment which indicates the torque balance throughout the working wind speed range.

A Review on the Application of Nanofluids in Coiled Tube Heat Exchangers

Due to their compact design, ease of manufacture and high efficiency in heat and mass transfer, helically coiled tubes are widely used in a number of industries and processes such as in the food, nuclear, aerospace and power generation industries and in heat recovery, refrigeration, space heating and air-conditioning processes. Due to the formation of a secondary flow, which inherently enhances the mixing of the fluid, helically coiled tubes are known to yield enhanced heat transfer characteristics when compared to straight tube heat exchangers. The secondary flow is perpendicular to the axial fluid direction and reduces the thickness of the thermal boundary layer. Goering et al. [1] estimated the secondary flow to account for circa 16–20% of the mean fluid flow velocity.

Is a fractured mandible an emergency

We retrospectively audited the records of 708 patients who presented with the diagnosis of fractured mandible between January 2009 and July 2013 at the Queen Elizabeth Hospital, Birmingham. We assessed the different factors that may have altered their outcomes, and found that delay before definitive fixation caused no harm in either the short or the long term.

Microvascular Anastomoses: Suture and Non-suture Methods

A plethora of methods have been proposed for coapting microvessels, with the mainstay being hand-suturing under an operating microscope. A broad range of hand-sutured techniques have been described and these are still evolving today. Alongside this, non-suture methods of microvascular anastomosis have gained popularity over recent years with numerous intra- and extravascular approaches being proposed. This section addresses the development of microsurgical suture technique for microvascular anastomosis, and continues to present the array of non-suture methods currently proposed as alternatives to standard suturing.

Does Extraction or Retention of the Wisdom Tooth at the Time of Surgery for Open Reduction and Internal Fixation of the Mandible Alter the Patient Outcome

Whether to extract or retain wisdom teeth present in a fracture line is a controversial topic. This study reviewed the records of all patients who had mandibular wisdom teeth at the time of the injury, and had an open reduction and internal fixation procedure between January 2009 and January 2012. The cohort of patients who concomitantly had their wisdom tooth extracted at the time of fixation had a greater complication rate (24.3%) compared with patients who did not (14.9%). This suggests that if third molars in the line of a fracture have caries, are fractured, show signs of pericoronitis, are periodontally involved, or are interfering with the occlusion are extracted at the time of fixation, this will increase the incidence of complications.

On the Deflexion of Anisotropic Structural Composite Aerodynamic Components

This paper presents closed form solutions to the classical beam elasticity differential equation in order to effectively model the displacement of standard aerodynamic geometries used throughout a number of industries. The models assume that the components are constructed from in-plane generally anisotropic (though shown to be quasi-isotropic) composite materials. Exact solutions for the displacement and strains for elliptical and FX66-S-196 and NACA 63-621 aerofoil approximations thin wall composite material shell structures, with and without a stiffening rib (shear-web), are presented for the first time. Each of the models developed is rigorously validated via numerical (Runge-Kutta) solutions of an identical differential equation used to derive the analytical models presented. The resulting calculated displacement and material strain fields are shown to be in excellent agreement with simulations using the ANSYS and CATIA commercial finite element (FE) codes as well as experimental data evident in the literature. One major implication of the theoretical treatment is that these solutions can now be used in design codes to limit the required displacement and strains in similar components used in the aerospace and most notably renewable energy sectors.

Computational Actuator Disc Models for Wind and Tidal Applications

This paper details a computational fluid dynamic (CFD) study of a constantly loaded actuator disc model featuring different boundary conditions; these boundary conditions were defined to represent a channel and a duct flow. The simulations were carried out using the commercially available CFD software ANSYS-CFX. The data produced were compared to the one-dimensional (1D) momentum equation as well as previous numerical and experimental studies featuring porous discs in a channel flow. The actuator disc was modelled as a momentum loss using a resistance coefficient related to the thrust coefficient (). The model showed good agreement with the 1D momentum theory in terms of the velocity and pressure profiles. Less agreement was demonstrated when compared to previous numerical and empirical data in terms of velocity and turbulence characteristics in the far field. These models predicted a far larger velocity deficit and a turbulence peak further downstream. This study therefore demonstrates the usefulness of the duct boundary condition (for computational ease) for representing open channel flow when simulating far field effects as well as the importance of turbulence definition at the inlet.

Microvascular Coaptation Methods: Device Manufacture and Computational Simulation

The practice of joining blood vessels has been ongoing since the late nineteenth century, although it was initially restricted to animal studies and experimental techniques. At this time, fine silk thread and curved needles had been introduced [1], which was a significant advancement on previous suture materials such as leather, tendon, and catgut [2], although these were used for wound closure rather than vascular repair. It was not until the mid-twentieth century, circa World War II, that vascular anastomoses were performed whilst repairing or reconstructing traumatic injuries [3]. The natural progression from repairing vascular injuries was to perform these procedures in smaller and smaller vessels. Of course, this necessitated use of an operating microscope and development and manufacture of finer suture materials, needles, and more delicate instruments.

Influence of microvascular sutures on shear strain rate in realistic pulsatile flow

Arterial thrombus formation is directly related to the mechanical shear experienced by platelets within flow. High shear strain rates (SSRs) and large shear gradients cause platelet activation, aggregation and production of thrombus. This study, for the first time, investigates the influence of pulsatile flow on local haemodynamics within sutured microarterial anastomoses. We measured physiological arterial waveform velocities experimentally using Doppler ultrasound velocimetry, and a representative example was applied to a realistic sutured microarterial geometry. Computational geometries were created using measurements taken from sutured chicken femoral arteries. Arterial SSRs were predicted using computational fluid dynamics (CFD) software, to indicate the potential for platelet activation, deposition and thrombus formation. Predictions of steady and sinusoidal inputs were compared to analyse whether the addition of physiological pulse characteristics affects local intravascular flow characteristics. Simulations were designed to evaluate flow in pristine and hand-sutured microarterial anastomoses, each with a steady-state and sinusoidal pulse component. The presence of sutures increased SSRmax in the anastomotic region by factors of 2.1 and 2.3 in steady-state and pulsatile flows respectively, when compared to a pristine vessel. SSR values seen in these simulations are analogous to the presence of moderate arterial stenosis. Steady-state simulations, driven by a constant inflow velocity equal to the peak systolic velocity (PSV) of the measured pulsatile flow, underestimated SSRs by ∼ 9% in pristine, and ∼ 19% in sutured vessels compared with a realistic pulse. Sinusoidal flows, with equivalent frequency and amplitude to a measured arterial waveform, represent a slight improvement on steady-state simulations, but still SSRs are underestimated by 1-2%. We recommend using a measured arterial waveform, of the form presented here, for simulating pulsatile flows in vessels of this nature. Under realistic pulsatile flow, shear gradients across microvascular sutures are high, of the order ∼ 7.9 × 106 m-1 s-1, which may also be associated with activation of platelets and formation of aggregates.