Imperfect Positioning Research Articles

Placement of the feline V-gel Advanced supraglottic airway device and tracheal selectivity during controlled mechanical ventilation: a clinical and tomodensitometric evaluation.

The aims of the study was to assess the placement of the V-gel Advanced (V-gel-A) and to evaluate tracheal selectivity during controlled mechanical ventilation, using CT. In this prospective clinical study, 20 healthy cats undergoing general anaesthesia for an elective procedure underwent four successive CT scans from the nose to the mid-abdomen: at baseline (no device); after the placement of the V-gel-A, after a controlled mechanical ventilation (CMV) period of 5 mins; and after the placement of an endotracheal tube (ETT). Using both a purpose designed position score and a gas score estimating the quantity of gas in different digestive regions, the position of the V-gel-A and presence of gas in the digestive tract at each step were evaluated. Number of attempts and times required to place the V-gel-A and ETT were recorded and compared. The V-gel-A was found to be correctly placed, with position scores of 3/5 in six cats, 4/5 in 13 cats and 5/5 in one cat. Imperfect positioning was due to minor axial rotation or incomplete occlusion of the oesophagus by the tip of the device. The gas scores significantly increased after placement of the V-gel-A compared with baseline and after CMV was initiated. Correct positioning of the device was mostly achieved at the first attempt; no significant difference was found in the time required to place V-gel-A vs ETT, nor in the number of attempts (P >0.05). The V-gel-A was clinically easy to place and use in both spontaneous and controlled ventilation. The device properly fitted the larynx and was never observed to occlude the airway. However, incomplete occlusion of the oesophagus was frequently observed and may lead to a lack of complete tracheal selectivity.

Development of a dry mock-up system for verifying pyroprocess automation

This paper presents the design and operation of an autonomous robot for pyroprocess automation, which requires unique approaches beyond those used in industrial applications to achieve the desired performance. Maintaining an extremely dry atmosphere is crucial to handle various materials, including chloride, and an autonomous system ensures this dry environment. The drying room dehumidifier was carefully selected and designed to generate dry air, and different types of dry air conditioning performance were evaluated, including assessing worker accessibility inside the mock-up to determine the system's feasibility. Containers used for process materials were modified to fit the gripper system of the gantry robot for automation. The loading and unloading of process materials in each equipment were automatically performed to connect the process equipment with the robotic system. The gantry robot primarily operated through macro motion to approach waypoints containing process materials, eliminating the need for precise approach motion. The robot's tapered jaw design allowed it to grasp the target object even with imperfect positioning. Robot motions were programmed using a robot simulator for initial positioning and motion planning, and real accuracy was tested in a mock-up facility using the OPC platform.

Repeatability of the European Standardized Method for Measuring Sound Reflection and Sound Insulation of Noise Barriers

The EN 1793-5 and EN 1793-6 standards have been in use for many years as a method for measuring the intrinsic characteristics of noise barriers installed along highways and railways. They require a sound source and a grid of microphones, to be placed near the barrier and in free field conditions, according to predetermined distances. In principle, small errors in positioning the sound source and microphone grid may affect the results obtained. An international round-robin test was carried out in 2012 to evaluate the repeatability and reproducibility of the method, but until now no studies have been carried out to evaluate and compare the repeatability of laboratory versus in-place measurements performed with the same equipment and its variance when an imperfect positioning of sound source and microphones is taken into account. In the present work, multiple series of sound reflection index and sound insulation index measurements performed on noise barriers of the same kind installed in the laboratory or along a highway are presented. The measurements were repeated in different ways: (1) in the laboratory, leaving the source and microphones unmoved to assess the repeatability of the results and of the measurement system under controlled conditions; (2) in the laboratory, repositioning for each measurement the source and microphone grid to assess the robustness of the method under real conditions but in a controlled environment; (3) in situ, along a highway open to traffic, repositioning for each measurement the source and microphone grid to assess the repeatability of the method under real conditions in a critical environment. In both reflection index and sound insulation index measurements, the standard deviation on single-number ratings in all cases examined is well below the value presented in EN 1793-5 and EN 1793-6, which was obtained from statistical analysis of the international round-robin test performed a dozen years ago, suggesting that expert operators with state-of-the art equipment can achieve much better results now.

An audit on the accuracy of freehand acetabular cup positioning in total hip arthroplasty with the direct lateral approach at a tertiary institution over seven years

BACKGROUND: The direct lateral approach for total hip replacement has been traditionally reserved and described for neck of femur fractures. Advantages of this approach include technically easy access to the acetabulum and femur and low incidence of hip dislocation. Imperfect positioning of the acetabular component leads to increased risk for dislocations, accelerated wear, reduced range of motion and increased revision rate. Freehand technique has been the gold standard for many decades, but newer technologies like computer navigation and robotic-assisted surgery have shown to improve the accuracy of cup placement. This study reports on the accuracy of freehand cup positioning via the direct lateral approach with mention of the dislocation rate METHODS: We retrospectively reviewed 253 patients who had total hip replacements done via the direct lateral approach. The patients' files were evaluated for patient parameters, demographic details, aetiology of hip pathology, confirmation of approach used, comorbidities and history of previous relevant surgery. The postoperative radiographs were analysed for acetabular component position inclination and anteversion. Dislocation rates were calculated as a secondary objective RESULTS: The radiographic analysis was performed using the Liaw method based on trigonometry of the eclipse generated. This showed a mean cup inclination of 42.3° (95% CI: 41.3-43.3°) and anteversion of 12.7° (95% CI: 12.0-13.7°). A total of 57% of the acetabular cups were within the safe zones described by Lewinnek. Of them, 78% were in the 30-50° range for inclination and 73% in the 5-25° range for anteversion. There were ten dislocations within one year from the index procedure: a dislocation rate of 4.0% (95% CI: 2.8-8.5% CONCLUSION: The freehand technique using the direct lateral approach for acetabular cup placement produces a poor overall accuracy of only 57%. Although our study only commented on ten dislocations, the rate (4%) is significantly worse compared to the 0.43% reported in literature for the direct lateral approach. The radiographic results for inclination and anteversion are comparable to other freehand techniques, regardless of the approach used, but significantly worse than results achieved with navigation and robotics Level of evidence: Level 4

Research on the system characteristics of radial offset based on double LCCL

Wireless power transmission is one of the most active research direction which has a broad application prospect and huge development potential. A wireless charging system based on wireless power transmission consists of a transmitting coil at the charging station and a receiving coil in the electric vehicle. We calculate the mutual inductance between the transmitting coil and the receiving coil and analyze the trend of mutual inductance with the offset distance. Finally, we point out wireless charging system is very sensitive to an imperfect positioning of the vehicle. We think electric vehicles imperfect positioning is on a detuning state. So put forward a method that the operating frequency of the inverter is automatically adjusted to track the resonant frequency. Using the theory of reflection impedance, it is shown that the true reason for the decreases of transmission efficiency is that imaginary part impedance. It caused by the system offset. So the transmission efficiency of the system can reach a maximum when the imaginary part impedance is the smallest. Different migration of coil is verified by experiment; using MATLAB software for computer-aided analysis, we built an experimental platform of the 3.5 kW wireless charging. The experimental results verify the correctness of this view that the inverter tracks the output frequency by itself, which provides the theoretical basis for the further research in this field.

Scanning Electrochemical Microscopy of Single Spherical Nanoparticles: Theory and Particle Size Evaluation.

Experiments at individual metal nanoparticles (NPs) can provide important information about their electrochemical and catalytic properties. The scanning electrochemical microscope (SECM) equipped with a nanometer-sized tip was recently used to image single 10 or 20 nm gold particles and quantitatively investigate electrochemical reactions occurring at their surfaces. In this Article, the theory is developed for SECM current vs distance curves obtained with a disk-shaped tip approaching a comparably sized, surface-bound conductive or insulating spherical NP. The possibility of evaluating the size of a surface-bound particle by fitting the experimental current-distance curve to the theory is shown for NPs and tips of different radii. The effects of the NP being partially buried into an insulating layer and the imperfect positioning of the tip with respect to the NP center are considered. The collection efficiency is calculated for redox species generated at the nanoparticle surface and collected at the tip.

Automatic frequency tuning wireless charging system for enhancement of efficiency

An automatic frequency-tuned wireless charging system is proposed and successfully demonstrated to enhance the power transfer efficiency for different vertical spacings between the charging coils in the presence of proximal metallic objects. The frequency characteristics of wireless power transfer efficiency have been investigated through simulation and experimental measurements. It has been observed that the resonance-based wireless charging system is very sensitive to the imperfect positioning of charging coils and nearby metallic objects. At the operating frequency, the power transfer efficiency of the charging system reduces drastically. However, by allowing the transmitting frequency to adapt to the position of the coils and metallic objects through the automatic frequency-tuned system, the deteriorated power transfer efficiency is further improved.

Anterior cruciate ligament reconstruction with the ligament augmentation and reconstruction system: a systematic review

The Ligament Augmentation and Reconstruction System (LARS) is a third generation of synthetic ligament, designed to overcome the issues of graft failure and synovitis which led previous generations of synthetic ligaments to fall out of favour. The theoretical benefits of LARS are appealing but this has not led to widespread uptake of the system in preference to autograft. The aim of this systematic review is to assess whether the evidence exists to support the use of LARS with respect to outcomes and complications. A systematic search process was undertaken from January 1990 to June 2012 to identify primary evidence relating to the use of LARS in anterior cruciate ligament (ACL) single ligament reconstruction. Nine studies were found meeting the search criteria including a single randomised controlled trial, two comparative series and six further observational case series. Overall the methodological quality of the studies was poor with follow-up to a maximum of fiveyears. Reported outcome scores were good for LARS and comparable to autograft techniques. Complication rates were low and comparable to those published for autograft techniques within the wider literature. Two reported incidences of synovitis were identified in case reports. The current literature supports the use of LARS in the short to medium term. However, high-quality studies with long-term follow-up are required to determine whether the use of LARS is preferable to autograft for ACL reconstruction over the longer term. Synovitis appears to be a rare complication closely related to imperfect graft positioning.

Feasibility of computer-assisted surgery for trapeziometacarpal prosthesis: a preliminary experimental study

The main complication of trapeziometacarpal replacement is trapezial cup loosening due to an imperfect positioning of the trapezial component. This problem is quite similar to those related to other arthroplasties. Hip surgery was progressed toward computer-assisted surgery (CAS) for the improvement of acetabular cup positioning. In this study, we propose an analysis of the feasibility of CAS in trapeziometacarpal replacement. We implanted the hand of a cadaver with a trapeziometacarpal prosthesis (Elektra, by SBI). The surgical procedure and the analysis of motion with CAS were carried out in 6 steps: incision, bone morphing preparation and initialisation, trapezial and metacarpal recordings, first kinematic analysis, prosthesis insertion, and second kinematic analysis. The evaluation of the results was carried out as the comparison of the 2 curves sequences before and after prosthesis insertion. We did not notice any dislocation of the prosthesis. The comparison of 2 curves showed differences regarding motion. For instance, as for abduction-adduction movements, before prosthesis insertion, an opposed-phase automatic rotation was clearly observed whereas after prosthesis insertion, no rotation was observed. CAS makes it possible to analyze the trapeziometacarpal joint motion in terms of biomechanics rather than in terms of anatomy. Such progress should result in measurement standardization that in turn should improve the positioning of prostheses and perhaps the lengthening of their life expectancy by decreasing the rates of prosthesis loosening.

Total Hip Resurfacing as an Alternative to Total Hip Arthroplasty: Indications and Precautions

The concept of hip resurfacing arthroplasty is not new. Early designs by pioneers including Wagner, Freeman and Charnley failed mainly due to material, design and manufacturing flaws. Modern metal on metal hip resurfacing has become increasingly popular over the last decade however. Good early and intermediate results have been reported in young, active patients using this prosthesis. Theoretical benefits compared to conventional total hip arthroplasty (THA) include bone stock preservation, particularly on the femoral side, improved stability due to the large diameter bearing, improved range of motion and proprioception and technically less difficult revision to a total hip arthroplasty if necessary. This prosthesis must be used with strict indications however as the technique is more demanding than conventional THA and imperfect positioning of either the acetabular or femoral component are associated with complications. Unique complications thought to be due to hypersensitivity reactions have also been reported. This article outlines the evolution of hip resurfacing arthroplasty and discusses new designs, surgical techniques and potential complications, all of which the surgeon needs to be familiar with.

Design and Performance Assessment of High-Capacity MIMO Architectures in the Presence of a Line-of-Sight Component

In this paper, the capacity of multiple-input multiple- output (MIMO) communication systems is investigated in the presence of a line-of-sight (LoS) component. Under this scenario, the channel-response matrix is usually rank deficient due to the high correlation between the LoS responses. Previous studies have shown that this problem can be overcome by the use of specifically designed antenna arrays. The antenna elements are positioned to preserve orthogonality and, hence, maximize the LoS-channel rank. To help in the design of such architectures, we derive a 3-D criterion for maximizing the LoS MIMO capacity as a function of the distance, the orientation, and the spacing of the arrays. The sensitivity of these systems to imperfect positioning and orientation is examined using a geometric MIMO model. The spectral efficiency is also investigated in the presence of scattered signals in the environment using a stochastic channel model and a Monte Carlo simulator. To demonstrate the validity of our predictions, we present the results of two MIMO measurement campaigns in an anechoic and an indoor environment where the measured capacities are compared with the capacities obtained from our models. All experimental results validate our predictions and, hence, confirm the potential for superior MIMO performance (when the developed criterion is applied) in strong LoS channels.

Massive subcutaneous emphysema following bronchoscopy-guided percutaneous dilatational tracheostomy.

Although percutaneous dilatational tracheostomy (PDT) has become a safe procedure for airway management in critically ill patients, this operation can be associated with serious life-threatening complications. Massive subcutaneous emphysema is an unusual and sometimes lethal complication which may extend the length of stay in the intensive care unit (ICU). We report 2 cases, including 1 fatality, of massive subcutaneous emphysema without tracheal wall laceration that occurred in the ICU after elective bronchoscopy-guided Ciaglia Blue Rhino (Cook Critical Care, Bloomington, IL, USA) PDT. Our analysis of these cases suggested that PDT-related barotraumas and imperfect positioning of the fenestrated tracheostomy tube could be the possible mechanisms for the observed complications. In case 1, we reduced the ventilator pressure and prescribed bronchodilator to decrease the airway pressure and keep the airway patent. In case 2, the suggested approach was to check if the fenestration of tracheostomy tube was extraluminal or change to non-fenestrating cannulas. For diminishing the impact of PDT on respiratory mechanics, especially in patients with underlying lung diseases, we recommend introducing the bronchoscope only when needed, instead of keeping the bronchoscope in the airway throughout the PDT procedure and using forceps to create a larger stoma if the dilation procedure is not smooth.

A wall imperfection channel model for signal level prediction and its impact on smart antenna systems for indoor infrastructure WLAN

This paper presents a novel approach for the estimation of the local average signal level in an indoor environment based on a wall imperfection model. A ray-tracing tool based on the method of images with angular information, is first used to estimate the distribution of field strength (or coverage) in an arbitrary environment. The concept of spatial sampling is highlighted. The wall imperfection model is then introduced to study the sensitivity of the received signal level at an arbitrary location to imperfect wall positioning and electromagnetic material properties. An alternative approach to estimate the local mean signal level at a particular point is presented based on the wall imperfection model to reduce the computation time. The impact of the wall imperfection model on the patterns of a smart antenna system serving multiple users in an infrastructure WLAN is studied.

Emphysema and Pneumothorax After Percutaneous Tracheostomy: Case Reports and an Anatomic Study

Part 1: To describe cases of emphysema (subcutaneous and/or mediastinal) and pneumothorax after percutaneous dilational tracheostomy (PDT) in a series of 326 patients, and to review the existing literature describing the incidence and possible mechanisms. Part 2: To analyze the potential mechanisms for the development of emphysema and pneumothorax in human cadaver models. A retrospective analysis of PDTs, in combination with an anatomic study in human cadavers. Part 1: All ICU patients who underwent PDT between 1997 and 2002 were enrolled in the study. We analyzed the cases of emphysema and pneumothorax. Similar cases were retrieved from the literature and underwent a systematic review. Part 2: The relevant anatomic structures were studied. We simulated the clinical situation after PDT in a human pathologic study in order to induce subcutaneous emphysema and pneumothorax. Part 1: Five cases of subcutaneous emphysema (1.5%) and two cases of pneumothorax (0.6%) are described. In the literature search, we found 41 cases of emphysema (1.4%) and 25 cases of pneumothorax (0.8%) in a total of 3,012 patients. Part 2: Subcutaneous emphysema could easily be induced in a human cadaver model by inflating air in the pretracheal tissues and after posterior tracheal wall laceration. Air leakage was also possible through a fenestrated cannula via the space between the inner nonfenestrated cannula and outer cannula and then through the fenestration. We conclude that one mechanism for the development of emphysema is an imperfect positioning of the fenestrated cannula, whereby the fenestration is extraluminal. For this reason, fenestrated cannulas should not be used immediately after placement of a PDT. Posterior tracheal wall laceration is another mechanism responsible for emphysema after PDT. After perforation of the posterior tracheal wall, the pleural space can be reached easily. This may result in a pneumothorax.

Detection and correction of endotracheal-tube position in premature neonates.

Due to the short airways in premature children, an accurate position of the endotracheal tube (ETT) is crucial for adequate mechanical ventilation. Verification of ETT-position is done in chest radiographs. However, ETT-position varies substantially with head movement. When the head is flexed, the tube might appear too deeply inserted, and inadvertent extubation may occur in cases of retraction of ETT after radiography. Extension of the cervical spine will suggest an inappropriately high ETT-position, so that intended corrections can lead to main-stem intubation. Radiographic visible skeletal structures could serve as reference points to allow the detection of head declination and imperfect positioning of ETT. Ratios of anatomical landmarks were used to estimate head position. In this study, 111 radiographs of 24 preterm neonates with a gestational age of 24-29 weeks and weights of 500-1,000 g were analyzed. A mathematical algorithm for the detection and correction of ETT-positions, based on common chest radiographs, was developed. In 108 cases (97.3%), ETT-distance from the midtracheal level was less than 2 mm after use of the proposed correction.Thus, the suggested correction equation for head position enables verification of the actual ETT-position without requiring a defined placement of the head during radiography. Moreover, it can be helpful for estimating the depth of ETT-insertion in conditions when radiography is not available.

A reciprocating antiplane shear load with harmonic vibration on the surface of an elastic half space

The steady state response of an elastic half space to a reciprocating antiplane shear load is considered. Its magnitude varies harmonically with a frequency different from that of the reciprocating motion. This reciprocating motion is considered as a model of the imperfect positioning of the loading. By applying an integral transform, the solution is obtained in the form of single integral and then an approximate form of the solution is derived. Although the well-known harmonic vibration solution is valid only when the reciprocating motion is slow, this approximate solution is valid for a wide range of both motions, reciprocating and vibrating. It is shown that the response is much affected by the imperfect positioning (reciprocating motion) when the frequency of vibration is small. Results of some numerical computations are presented.

EFFECTS OF CROSS-AXIS SENSITIVITY AND MISALIGNMENT ON THE RESPONSE OF MECHANICAL-OPTICAL ACCELEROGRAPHS

Recorded strong-motion accelerograms may be affected by cross-axis sensitivity and the misalignment of their transducer sensitivity axes. The cross-axis sensitivity arises from the fact that the transducer mass when deflected from its ideal equilibrium position may experience additional deflection caused by the inertial forces perpendicular to the transducer's principal sensitivity axis. The misalignment effects result from imperfect positioning of transducers into the instrument housing so that the nominal sensitivity directions are not mutually perpendicular and/or do not coincide with the orthogonal reference frame attached to the instrument housing. If the misalignment effects cannot be accounted for, the recorded accelerations can be distorted by an amount, which for large input accelerations, may exceed the digitization noise level by as much as one order of magnitude. In this paper a method is presented for a complete dynamic correction procedure which can eliminate any cross-axis and misalignment effects and yield exact accelerations for a reference coordinate system conveniently attached to the instrument housing. To carry out these correction procedures it is necessary to know the precise orientations of all transducers relative to the selected reference frame. A simple sequence of static tilt tests is proposed which provides adequate information for computation of all misalignment angles and estimation of transducer sensitivity constants.

STABILITY AND UNION IN SUBCAPITAL FRACTURES OF THE FEMUR

1. Practical experience has shown that subcapital fractures of the femur unite freely if reduction is stable and fixation is secure. 2. Stable reduction is obtained when the muscular and gravitational forces tending to redisplace the fracture are opposed by equal and opposite counterforces, and inherent stability is believed to depend upon the integrity of the flared cortical buttress at the postero-inferior junction of the femoral neck and head. 3. In the stable subcapital fracture a state of equilibrium is reached when the forward and upward thrust of the fixation appliance in the femoral head is opposed by the counterthrust of the closely applied and cleanly broken fragments at the postero-inferior aspect of the fracture. When the postero-inferior cortical buttress is comminuted, inherent stability is lost, lateral rotation deformity recurs and the fixation device is avulsed from the cancellous bone of the head. 4. Stability may be restored by reduction in the "valgus" position, by various forms of osteotomy, by refashioning the fracture fragments or by a postero-inferiorly positioned bone graft. Theoretically, stability may also be obtained by a double lever system of fixation in which an obliquely placed fixation device or bone graft is combined with a horizontally disposed wire, pin, nail or screw crossing it anteriorly. Multilever fixation by three or more threaded wires or pins inserted at different angles and lying in contact at their point of crossing may likewise provide stability. 5. Fixation by two crossed screws has been chosen for clinical trial in 100 displaced subcapital fractures. Imperfect positioning of the screws in seven patients has been followed by early breakdown of reduction and non-union, but satisfactory positioning has been associated with radiological union in fifty patients who have been observed for twelve months or more. 6. Ultimate breakdown in some of these fractures is certain to follow avascular necrosis, and this complication has already been seen in a few patients treated by cross screw fixation more than two years ago. It is also expected that non-union will occur in some of those patients still under observation for less than a year. Even so, these preliminary findings indicate a percentage of union far greater than that obtained by previous methods of treatment, and, although statistically inadequate, they are presented in support of the belief that it should no longer be considered impossible to achieve the same percentage of union in subcapital fractures of the femur as we are accustomed to expect in the treatment of fractures elsewhere. It is not implied, however, that this ideal will be reached merely by the adoption of some form of double or multilever fixation, and much will continue to depend upon the quality of the radiographic services, the precision of reduction and the perfection of operative technique. 7. Every advance in our understanding of what is meant by "perfection of operative technique" lends increasing support to the ultimate truth of Watson-Jones's (1941) dictum: "A perfect result may be expected from a technically perfect operation; an imperfect result is due to imperfect technique." But the simple and foolproof method of fixation which will end the search for technical perfection in the treatment of the displaced subcapital fracture has yet to be evolved, and many questions remain to be answered about this injury. Nevertheless, it is clear that the surgeon should now be prepared to attribute early mechanical failure in the treatment of femoral neck fractures to his own shortcomings, and the temptation to blame capital ischaemia for every disaster should be resisted.