Volume 57, Issue 2

Atrial arrhythmias are frequently treated using catheter ablation during electrophysiological (EP) studies. However, success rates are only moderate and could be improved with the help of personalized simulation models of the atria. In this work, we present a workflow to generate and validate personalized EP simulation models based on routine clinical computed tomography (CT) scans and intracardiac electrograms. From four patient data sets, we created anatomical models from angiographic CT data with an automatic segmentation algorithm. From clinical intracardiac catheter recordings, individual conduction velocities were calculated. In these subject-specific EP models, we simulated different pacing maneuvers and measurements with circular mapping catheters that were applied in the respective patients. This way, normal sinus rhythm and pacing from a coronary sinus catheter were simulated. Wave directions and conduction velocities were quantitatively analyzed in both clinical measurements and simulated data and were compared. On average, the overall difference of wave directions was 15° (8%), and the difference of conduction velocities was 16 cm/s (17%). The method is based on routine clinical measurements and is thus easy to integrate into clinical practice. In the long run, such personalized simulations could therefore assist treatment planning and increase success rates for atrial arrhythmias.

The discrimination of flow rates through bronchial arteries that are affected by pathological SPAS today still happens solely qualitatively. A reproducible quantification of flow rates, however, would enable the comprehension of phenomena like the intensified shunt perfusion seen in cases of chronic inflammations or the characterization of SPAS that may cause cardiovascular problems. A computational program is developed, that allows the modeling of individual bronchial arteries on the basis of the information provided by angiography. Angiographic images are available from the standard clinical assessment of SPAS. The flow through continuous and geometrically measurable vessel segments and SPAS is given by the law of Hagen-Poiseuille. The discharge through healthy branches is calculated by means of allometric scaling laws. The simulation results are verified by flow experiments in artificial vessel networks made of glass and PE tubing. The experimental set-up mimics realistic, pulsating pressure and flow conditions. When applied to the artificial vessel networks, the model described herein provides results for the volumetric flow rate that differ from values measured in laboratory experiments by <6%. The computer model is also applied to real angiographic images. Due to inaccuracies during the deduction of the geometry and due to necessary simplifications of the model, we expect significant deviations between calculated and real flow rates in bronchial systems. Nevertheless, the presented method enables the physician to objectively estimate the order of magnitude of volumetric flow through individual SPAS fairly independently from his experience and without the need of measurements additional to the mandatory angiography.

The aim of the present study was to evaluate and compare the in vitro and flow dynamics of the Magna (MB) and the Magna Ease aortic valve bioprosthesis (MEB) within the ascending aorta. A 2D-particle-image-velocimetry (2D-PIV) study was performed to compare the flow dynamics induced by each pericardial Carpentier-Edwards Magna and Magna Ease aortic valve prosthesis in the aortic flow field directly behind the valve. Both prostheses (diameter 23 mm) were placed inside an artificial aorta under pulsatile flow conditions (70 Hz and 70 ml stroke volume). The flow field was evaluated according to velocity, shear strength, and vorticity. Both prostheses showed a jet flow type profile with a maximum velocity of 0.97±0.09 m/s for MB and 0.83±1.8 m/s for MEB. Flow fields of both valves were similar in acceleration, peak flow deceleration and leakage phase. Maximum shear strength was 20,285±11,774 l/s 2 for MB and 17,006±8453 l/s 2 for MEB. Vorticity was nearly similar for counterclockwise and clockwise rotation in both prostheses, but slightly higher with MB (251±41 l/s and -250±39 l/s vs. 225±48 l/s and -232±48 l/s). The point-of-interest (POI)-analysis revealed a higher velocity for left-sided aortic wall compared to right-sided at MB (0.12±0.09 m/s vs. 0.18±0.10 m/s, p<0.001), but was consistent at MEB (0.09±0.05 m/s vs. 0.08±0.04 m/s, p=0.508), respectively. Velocity, shear strength and vorticity in an in vitro test set-up are lower with MEB compared to MB, thus resulting in improved flow dynamics with a similar flow field, which might have a positive influence on blood rheology and potential valve degeneration.

We describe an innovative computer-based method for the analysis of gas flow using a modified airway management technique to perform percutaneous dilatational tracheotomy (PDT) with a rigid tracheotomy endoscope (TED). A test lung was connected via an artificial trachea with the tracheotomy endoscope and ventilated using superimposed high-frequency jet ventilation. Red packed cells were instilled during the puncture phase of a simulated percutaneous tracheotomy in a trachea model and migration of the red packed cells during breathing was continuously measured. Simultaneously, the calculation of the gas-flow within the endoscope was numerically simulated. In the experimental study, no backflow of blood occurred during the use of superimposed high-frequency jet ventilation (SHFJV) from the trachea into the endoscope nor did any transportation of blood into the lower respiratory tract occur. In parallel, the numerical simulations of the openings of TED show almost positive volume flows. Under the conditions investigated there is no risk of blood aspiration during PDT using the TED and simultaneous ventilation with SHFJV. In addition, no risk of impairment of endoscopic visibility exists through a backflow of blood into the TED. The method of numerical simulation offers excellent insight into the fluid flow even under highly transient conditions like jet ventilation.

The mechanical complications of osteosyntheses after hip fractures are previously investigated by mostly static or dynamic uniaxial loading test systems. However, the physiologic loading of the hip joint during a normal gait is a multiplanar, dynamic movement. Therefore, we constructed a system to test osteosyntheses for hip fractures under physiologic multiplanar loading representative of normal gait. To evaluate the testing system, 12 femora pairs were tested under 25,000 cycles with two standard osteosyntheses (Proximal Femoral Nail Antirotation/Gamma3 Nail). For angular movement, the varus collapse to cut out (∝ CO ) (∝ CO =4.8°±2.1° for blade and ∝ CO =7.8°±3.8° for screw) was the dominant failure mode, and only slight rotational angle shifts (∝ Rot ) (∝ Rot =1.7°±0.4° for blade and ∝ Rot =2.4°±0.3° for screw) of the femoral head around the implant axis were observed. Angular displacements in varus direction and rotation were higher in specimens reinforced with screws. Hence, the cut out model and the migration directions showed a distinction between helical blade and hip screw. However, there were no significant differences between the different implants. The new setup is able to create clinical failures and allows to give evidence about the anchorage stability of different implant types under dynamic gait motion pattern.

The extent of porous coating of cementless total hip stems is held responsible for radiological periprosthetic changes, the rate of thigh pain, and even its long-term success. However, there is only sparse knowledge on how the biomechanical loading conditions of the femur are influenced by the extent of porous coating in the early phase after implantation of a cementless hip stem. Aiming to evaluate the effect of surface structuring on the strain pattern of the femur, we implanted three anatomic hip stems with different extents of porous coating (full, two-thirds proximal, and penguin type) in second-generation composite femora coated with a photoelastic layer. A cortical strain mapping was conducted before and after insertion of the implants under standardized loading conditions considering relevant muscle forces. The results of the statistical analysis of three different implantation sequences proved that composite femora are suitable for repeated measurements within the applied experimental setup. Cortical strain changes including stress-shielding effects medially (-60%) and laterally (-50%) were validated with a cadaver femur. The extent of porous coating had no significant influence on the surface strain pattern for an immediate postoperative situation. Zusammenfassung Die Ausdehnung des porös beschichteten Oberflächenanteils wird beim zementfreien Hüftstiel für die radiologisch sichtbaren periprothetischen Veränderungen, die Inzidenz von Oberschenkelschmerzen und sogar dessen Standzeit verantwortlich gemacht. Dennoch ist bisher nur wenig darüber bekannt, ob bereits in der frühen postoperativen Phase die biomechanische Lastsituation am Femur durch die Ausdehnung der Oberflächenstrukturierung beeinfl usst wird. Mit dem Ziel, den Effekt der porösen Strukturierung auf das corticale Dehnungsmuster des Femur zu evaluieren, implantierten wir drei anatomische Hüftstiele mit unterschiedlichem Ausmaß der porösen Strukturierung (voll, zwei Drittel proximal und „pinguinförmig“) in photoelastisch beschichtete Composite Femora der II. Generation. Vor und nach Einbringen der Implantate wurde eine corticale Dehnungsvermessung unter standardisierten Lastbedingungen und Berücksichtigung wichtiger Muskelkräfte durchgeführt. Die Ergebnisse der statistischen Auswertung dreier verschiedener Implantationsreihenfolgen bestätigten zunächst die grundsätzliche Eignung der Composite Femora für wiederholte Messungen mit dem vorliegenden Prüfaufbau. Stress-shielding Effekte einschließlich einer Reduktion der corticalen Dehnungen medial (-60% ) und lateral (-50% ) wurden anhand eines Humanfemur validiert. Die Ausdehnung der porösen Strukturierung der Implantatoberfläche hatte keinen signifikanten Einfl uss auf das Oberflächendehnungsmuster unter Annahme einer unmittelbar postoperativen Lastsituation.

For contactless monitoring of ventilation and heart activity, magnetic induction measurements are applicable. As the technique is harmless for the human body, it is well suited for long-term monitoring solutions, e.g., bedside monitoring, monitoring of home care patients, and the monitoring of persons in critical occupations. For such settings, a two-channel portable magnetic induction system has been developed, which is small and light enough to be fitted in a chair or bed. Because demodulation, control, and filtering are implemented on a front-end digital signal processor, a PC is not required (except for visualization/data storage during research and development). The system can be connected to a local area network (LAN) or wireless network (WiFi), allowing to connect several devices to a large monitoring system, e.g., for a residential home for the elderly or a hospital with low-risk patients not requiring standard ECG monitoring. To visualize data streams, a Qt-based (Qt-framework by Nokia, Espoo, Finland) monitoring application has been developed, which runs on Netbook computers, laptops, or standard PCs. To induce and measure the magnetic fields, external coils and amplifiers are required. This article describes the system and presents results for monitoring respiration and heart activity in a (divan) bed and for respiration monitoring in a chair. Planar configurations and orthogonal coil setups were examined during the measurement procedures. The measurement data were streamed over a LAN to a monitoring PC running Matlab (The MathWorks Inc, Natick, MA, USA).

This article describes two objective, instrumental approaches for the distinction of enamel lesion activity – the in vitro measurement of surface layer porosity and surface roughness – and on this basis, the in vivo measurement of vertical reflection intensity (VRI). They are based on the subjective visual and tactile criteria of a dull and rough or a shiny and smooth surface, accepted by the known diagnostic systems, Nyvad criteria, International Caries Detection and Assessment System II, and Universal Visual Scoring System. With a scanning white-light interference microscope, the active lesion surface had a high porosity (118 pores) and a high roughness (Ra 190 nm) constituting a field of view of 280×210 μm. The inactive lesion surface had almost no porosity (one pore) and a more than 10-fold lower roughness (Ra 10 nm) for the same area. These differences result in a different light reflection of the lesion surfaces, which can be measured as VRI with a chromatic confocal sensor with spacer (mean VRI: active lesions, 7%; inactive lesions, 25%; sound enamel, 35%). In addition to monitoring, this sensor allows an in vivo handheld evaluation in a single (visit) examination.

No abstract available.