Wojciech Kowalczyk

Avoidance of Proximal Endoleak Using a Hybrid Stent Graft in Arch Replacement and Descending Aorta Stenting

BACKGROUND In complex thoracic aortic procedures, proximal repair and antegrade stent grafting of the descending aorta is an emerging technique to achieve one-stage treatment of the thoracic aorta. To overcome problems of proximal endoleak, a hybrid stent graft was designed and used. This study assessed technical feasibility and early results. METHODS From Jan 2005 to May 2008, 41 patients (age, 60 +/- 13 years) comprising 35 aortic dissections (AD) and 6 aortic aneurysms underwent arch replacement and antegrade stent grafting of the descending aorta using the hybrid stent graft. Endoleaks were evaluated by computed tomography (CT) scans. In AD cases, the false lumen (FL) was evaluated with CT volume measurements. RESULTS Combined arch replacement and antegrade stent grafting was technically successful. One proximal endoleak was observed, which was not related to the hybrid prosthesis (40 of 41, 98%). Three patients died (7%). No paraplegia occurred. Incidence of immediate FL thrombosis was 97% at the proximal and 80% at the distal stent graft level. During follow-up (17 +/- 11 months), complete thrombosis of the perigraft space was 91%. FL volume shrinkage was documented (p < 0.01). No perfusion of the perigraft space was observed in aneurysm cases. Intermediate survival was 33 of 38 (87%). CONCLUSIONS One-stage repair of complex thoracic aortic disease using a hybrid stent graft can be reliably performed with low hospital mortality. Proximal endoleak can be definitely avoided; in AD, exclusion and ongoing significant shrinkage of the FL can be achieved.

Advanced core decompression, a new treatment option of avascular necrosis of the femoral head--a first follow-up.

Aseptic necrosis of the femoral head (AVN) leads to destruction of the affected hip joint, predominantly in younger patients. Advanced core decompression (ACD) is a new technique that may allow better removal of the necrotic tissue by using a new percutaneous expandable reamer. A further modification is the refilling of the drill hole and the defect with an injectable, hard‐setting, composite calcium sulphate (CaSO4)–calcium phosphate (CaPO4) bone graft substitute. Compression tests were performed on seven pairs of femoral cadaver bones. One femur of each pair was treated with ACD, while the opposite side remained untreated. Clinically, the postoperative outcome of 27 hips in 23 patients was performed by physical examination 6 weeks after ACD and at average follow‐up of 9.69 months, and compared with the preoperative results. MRI was used to assess the removal of the necrotic tissue, any possible progression of AVN and evaluation of collapse. In the biomechanical analysis, the applied maximum compression force that caused the fracture did not significantly differ from the untreated opposite side. The overall results of postoperative physical examinations were significantly better than preoperatively. Five hips (18.5%) were converted to a total hip replacement. The follow‐up MRIs of the other patients showed no progression of the necrotic area. The first follow‐up results of ACD have been encouraging for the early stages of aseptic necrosis of the femoral head. In our opinion, an assured advantage is the high stability of the femoral neck after ACD, which allows quick rehabilitation. Copyright

Towards system theory based adaptive strategies for high pressure bioprocesses

High pressure has been shown to offer unique possibilities for designing novel bioprocesses and generating new structures. However, high pressure processes have to be considered also as instantaneous but not homogeneous. As a consequence of this, thermofluiddynamical processes influence molecular and cellular mechanisms and kinetics. Thus, the urgent requirement for creating an adaptive process management, missing in the literature, is obvious. In this paper, a first attempt towards the development of adaptive process strategies is presented. It is shown that adaptive strategies have to include considerations regarding the interactions of all the components of the high-pressure system, variances due to the biological origin of the substances, and, particularly, methods for managing different data and knowledge sources. Furthermore, suggestions for the suitable design of adaptive process management strategies are presented and discussed. By means of a few examples it is elucidated that hybrid methods can contribute significantly in achieving the adaptability required. This paper is conceived as a brief composition to a plenary lecture presented at the XLIV EHPRG Meeting 2006 in Prague.

A prospective randomized peri- and post-operative comparison of the minimally invasive anterolateral approach versus the lateral approach

There is still controversy as to whether minimally invasive total hip arthroplasty enhances the postoperative outcome. The aim of this study was to compare the outcome of patients who underwent total hip replacement through an anterolateral minimally invasive (MIS) or a conventional lateral approach (CON). We performed a randomized, prospective study of 75 patients with primary hip arthritis, who underwent hip replacement through the MIS (n=36) or CON (n=39) approach. The Western Ontario and McMaster Universities Osteoarthritis Index and Harris Hip score (HHS) were evaluated at frequent intervals during the early postoperative follow-up period and then after 3.5 years. Pain sensations were recorded. Serological and radiological analyses were performed. In the MIS group the patients had smaller skin incisions and there was a significantly lower rate of patients with a positive Trendelenburg sign after six weeks postoperatively. After six weeks the HHS was 6.85 points higher in the MIS group (P=0.045). But calculating the mean difference between the baseline and the six weeks HHS we evaluated no significant differences. Blood loss was greater and the duration of surgery was longer in the MIS group. The other parameters, especially after the twelfth week, did not differ significantly. Radiographs showed the inclination of the acetabular component to be significantly higher in the MIS group, but on average it was within the same permitted tolerance range as in the CON group. Both approaches are adequate for hip replacement. Given the data, there appears to be no significant long term advantage to the MIS approach, as described in this study.

Simulation of Fluid Flow in a Channel Induced by Three Types of Fin-Like Motion

One of many interesting research activities in biofluidmechanics is dedicated to investigations of locomotion in water. Some of propulsion mechanisms observed in the underwater world are used in the development process of underwater autonomic vehicles (AUV). In order to characterise several solutions according to their manoeuvrability, influence on the surrounding fluid and energetic efficiency, a detailed analysis of fin-like movement is indispensable.In the current paper an analysis of undulatory, oscillatory and combined fin-like movements by means of numerical simulation is carried out. The conservation equation of mass and the conservation equation of momentum are solved with the Finite Volume Method (FVM) by use of the software CFX–10.0. The undulatory and oscillatory fin movements are modelled with an equation that is implemented within an additional subroutine and joined with the main solver. Numericalsimulations are carried out in the computational domain, in which one fin is fixed in a flow-through water duct. Simulations are carried out in the range of the Re number up to 105. The results show significant influence of applied fin motion on the velocity distribution in the surrounding fluid.

Experimental and computational studies on the femoral fracture risk for advanced core decompression.

BACKGROUND Two questions are often addressed by orthopedists relating to core decompression procedure: 1) Is the core decompression procedure associated with a considerable lack of structural support of the bone? and 2) Is there an optimal region for the surgical entrance point for which the fracture risk would be lowest? As bioresorbable bone substitutes become more and more common and core decompression has been described in combination with them, the current study takes this into account. METHODS Finite element model of a femur treated by core decompression with bone substitute was simulated and analyzed. In-vitro compression testing of femora was used to confirm finite element results. FINDINGS The results showed that for core decompression with standard drilling in combination with artificial bone substitute refilling, daily activities (normal walking and walking downstairs) are not risky for femoral fracture. The femoral fracture risk increased successively when the entrance point is located further distal. The critical value of the deviation of the entrance point to a more distal part is about 20mm. INTERPRETATION The study findings demonstrate that optimal entrance point should locate on the proximal subtrochanteric region in order to reduce the subtrochanteric fracture risk. Furthermore the consistent results of finite element and in-vitro testing imply that the simulations are sufficient.

Comparison of flow dynamics of Perimount Magna and Magna Ease aortic valve prostheses

Abstract 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/s2 for MB and 17,006±8453 l/s2 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.

On convection phenomena during high pressure treatment of liquid media

In the current contribution, investigations of the high hydrostatic pressure process up to 400 MPa and temperatures up to 353 K are carried out by means of dimensional analysis. The thermofluiddynamical mechanisms are analysed for three different sizes of a high pressure chamber, two different pressure generation systems and two model-fluids that differ in viscosity. Forced convection during compression/decompression and free convection during constant pressure phase are considered separately. The results contain process parameter study based on dimensionless numbers derived from conservation equations of mass, momentum and energy. Either dimensionless process parameters or the fluid dynamical and thermodynamical time scales are presented as a function of pressure and temperature. Relations according to heat transfer and fluid flow mechanisms during high pressure treatment are discussed.

Simultaneous optimisation of earwig hindwings for flight and folding

ABSTRACT Earwig wings are highly foldable structures that lack internal muscles. The behaviour and shape changes of the wings during flight are yet unknown. We assume that they meet a great structural challenge to control the occurring deformations and prevent the wing from collapsing. At the folding structures especially, the wing could easily yield to the pressure. Detailed microscopy studies reveal adaptions in the structure and material which are not relevant for folding purposes. The wing is parted into two structurally different areas with, for example, a different trend or stiffness of the wing veins. The storage of stiff or more flexible material shows critical areas which undergo great changes or stress during flight. We verified this with high-speed video recordings. These reveal the extent of the occurring deformations and their locations, and support our assumptions. The video recordings reveal a dynamical change of a concave flexion line. In the static unfolded state, this flexion line blocks a folding line, so that the wing stays unfolded. However, during flight it extends and blocks a second critical folding line and prevents the wing from collapsing. With these results, more insight in passive wing control, especially within high foldable structures, is gained. Summary: Adjustments of the wing structure in earwig hindwings enable passive wing control during flapping flight. With an expansion of the claval flexion line, the highly foldable wing can withstand deformations during flapping flight and stay unfolded.

Visualization of pressure-shift freezing and thawing of concentrated aqueous sucrose solutions

A visualization of pressure-shift freezing of 0.7 w/w sucrose solutions was carried out at three temperatures 268, 253 and 235 K by release of pressure from 200 MPa to atmospheric value. Furthermore, pressure-shift freezing at 268 K and additionally pressure-shift thawing was carried out for a solution of 0.2 sucrose mass fraction. The solid phase observed at 268 K in the case of solution with 0.2 w/w sucrose fraction was ice I. The phase changes of 0.7 w/w sucrose solutions at 253 K and 235 K resulted in formation of spherical solids which are hypothesized to be eutectics, i.e. crystals with structure containing sucrose hydrates and water. The visual evaluation revealed differences in size and distribution of spherical crystals. The solids formed at 235 K were more numerous, more homogenously distributed and finally smaller than those observed at 253 K. It is explained by the higher supercooling of the solution in the former case, which provided higher driving force for nucleation and crystal growth.