Video-assisted technique for resection of a large mediastinal hemangioma

We present a video-assisted technique (VATS) for resection of a large tumor located in the posterior mediastinum in a 16-year-old patient. A large vascular mass in the upper and middle posterior mediastinum, encasing the great vessels and extending to the aorto-pulmonary window, was completely resected under video-assistance using a 5-cm large working incision. The tumor dissection was performed using special videoscopic instruments and electrocautery under respect of the great vessels and vascular pedicles. The VATS technique combined with specially designed endoscopical instruments is offering today the possibility of safe resection even in large mediastinal tumors, thus avoiding late functional complications and/or the morbidity associated with large thoracotomy incisions.

Graphical user interfaces for molecular dynamics-quo vadis?

In the past years an increasing number of graphical user interfaces for Molecular Dynamics (MD) were presented and concomitantly, more and more Molecular Dynamics studies were published. With the easier application of MD software packages the field runs the risk however, of being pervaded with unreliable results. Therefore, possible benefits and caveats have to be carefully balanced. Here we outline in which respects a broader access of MD via graphical user interfaces may help to increase the usability of Molecular Dynamics simulations while maintaining their quality.

Article Commentary: Graphical User Interfaces for Molecular Dynamics—Quo Vadis?

In the past years an increasing number of graphical user interfaces for Molecular Dynamics (MD) were presented and concomitantly, more and more Molecular Dynamics studies were published. With the easier application of MD software packages the field runs the risk however, of being pervaded with unreliable results. Therefore, possible benefits and caveats have to be carefully balanced. Here we outline in which respects a broader access of MD via graphical user interfaces may help to increase the usability of Molecular Dynamics simulations while maintaining their quality.

Adsorption of Protein GlnB of Herbaspirillum seropedicae on Si(111) Investigated by AFM and XPS

The protein GlnB-Hs (GlnB of Herbaspirillum seropedicae) in diazotroph micro-organisms signalizes levels of nitrogen, carbon, and energy for a series of proteins involved in the regulation of expression and control of the activity of nitrogenase complex that converts atmospheric nitrogen in ammonia, resulting in biological nitrogen fixation. Its structure has already been determined by X-ray diffraction, revealing a trimer of (36 kDa) with lateral cavities having hydrophilic boundaries. The interactions of GlnB-Hs with the well-known Si(111) surface were investigated for different incubation times, protein concentrations in initial solution, deposition conditions, and substrate initial state. The protein solution was deposited on Si(111) and dried under controlled conditions. An atomic force microscope operating in dynamic mode shows images of circular, linear, and more complex donut-shaped protein arrangement, and also filament types of organization, which vary from a few nanometers to micrometers. Apparently, the filament formation was favored because of protein surface polarity when in contact with the silicon surface, following some specific orientation. The spin-coating technique was successfully used to obtain more uniform surface covering.

Bronchopleural fistula in the surgery of non-small cell lung cancer: incidence, risk factors, and management

BACKGROUND

The incidence of a bronchopleural fistula (BPF) as a major complication after non-small cell lung carcinoma (NSCLC) surgery has decreased in recent years, due to new surgical refinements and a better understanding of the bronchial healing process. We reviewed our most recent experience with BPFs and tried to determine methods which may effectively reduce its occurrence.

METHODS

Data on 490 patients with lung resections for NSCLC over a period from 1990 to 1999 were retrospectively reviewed. Details regarding surgery and the subsequent treatment were carefully reviewed. Particular attention was paid to factors possibly affecting the occurrence of BPFs: the technique of the initial bronchial closure, previous radiation and/or chemotherapy, need for postoperative ventilation and presence of residual carcinomatous tissue at the bronchial suture line. Information about age, sex, clinical diagnosis, associated conditions, TNM stage, period between primary operation and rethoracotomy and postoperative outcome was also recorded.

RESULTS

The overall BPF incidence was 4.4% (22/490). There were 21 (95.5%) males and 1 (4.5%) female, mean age was 57.8 years. BPFs occurred after pneumonectomy in 12 (54.6%), after lobectomy in 9 (40.9%) patients and after sleeve resections in 1 (4.5%) patient. Mortality rate was 27.2% (6/22). Right-sided pneumonectomy and postoperative mechanical ventilation were identified as risk factors for BPFs (p<0.05). Initial chest re-exploration was performed in 20 (90.9%) patients. After debridement, the bronchial stump was reclosed by hand suture in 10 (45.4%) patients. All 10 (45.4%) patients with a post-lobectomy- and sleeve resection BPF necessitated completion surgery. The BPF was additionally covered with a vascularized flap in 20 (90.9%) patients. In 2 (9%) patients with small BPFs and poor overall condition the initial treatment was endoscopic. In both the fistula persisted and the stump had to be surgically resutured.

CONCLUSIONS

A BPF remains a major complication in the surgery of NSCLC because of its high mortality and morbidity rate. A BPF is more common after right-sided pneumonectomy and is frequently associated with postoperative mechanical ventilation. The management varies according to the initial type of surgery, the size of the BPF, the overall patient condition and that of the remaining lung. Endoscopic treatment is reserved only for small fistulas associated with poor general condition.

Outer radius-wall thickness ratio, a postmortem quantitative histology in human coronary arteries

Although the anatomy, histology and pathology of human coronary arteries have been studied extensively, little is known about the functional relationship between vessel radius and wall thickness. It is the purpose of this study to present detailed measurements and to describe this relationship covering the range from the feeding coronary artery to the arterioles. Human hearts of 10 adults less than 36 +/- 3 years old were investigated immediately postmortem. Ten cubic tissue blocks, measuring about 10 mm in length on each side, were dissected from the left ventricular wall. After fixation by immersion, 15-microm sections were prepared and outer and inner perimeters of 52 arterial segments were digitalized. Vessel radius and wall thickness were calculated and plotted to show their relationship over the whole range of vessel calibers. Outer vessel radii ranged from 100 to 3,000 microm and wall thickness from 80 to 800 microm. Plotting the outer vessel radius against the wall thickness, the data points were found to cluster around a straight line. A significant correlation between the two parameters was found (R2 = 0.79). This mathematical correlation and the good agreement of the presented results with data from other species indicate a common physiologic concept.

Functional characteristics of optimized arterial tree models perfusing volumes of different thickness and shape

The relationship between the 'shape of an organ' and the 'cost of blood transport' to perfuse its tissue was evaluated on the basis of optimized arterial model trees simulated to perfuse square-based 100-cm(3) volumes of different shape ('flat' versus 'thick' as defined by the ratio of thickness to side-length h/s < or =1). Specifically, the effects of 'shape' on tree structure, blood transport, and on hemodynamic characteristics were investigated. Branching models of arterial trees were generated by constrained constructive optimization (CCO), based on an identical set of model parameters. All model trees were geometrically and topologically optimized for intravascular volume. Tree structures achieved tremendous savings of blood (transport medium) in comparison to a system of separate tubes. Thickening the perfusion volume (increasing h/s) resulted in a significant decrease of mean transport length, deposition time, and intravascular total volume in the tree. 'Thick' perfusion volumes induced CCO trees to branch more symmetrically into a number of equivalent subtrees repetitiously splitting into smaller ones; 'flat' structures were dominated throughout by a few asymmetrically branching major vessels. In summary, we conclude from systematic variation of shape that thicker perfusion volumes (h/s >0.1) facilitate efficient delivery of blood in comparison to large amounts of 'dead volume' to be carried over long distances in very thin pieces of tissue.

Staged growth of optimized arterial model trees

There is a marked difference in the structure of the arterial tree between epi- and endocardial layers of the human heart. To model these structural variations, we developed an extension to the computational method of constrained constructive optimization (CCO). Within the framework of CCO, a model tree is represented as a dichotomously branching network of straight cylindrical tubes, with flow conditions governed by Poiseuille's law. The tree is grown by successively adding new terminal segments from randomly selected points within the perfusion volume while optimizing the geometric location and topological site of each new connection with respect to minimum intravascular volume. The proposed method of "staged growth" guides the generation of new terminal sites by means of an additional time-dependent boundary condition, thereby inducing a sequence of domains of vascular growth within the given perfusion volume. Model trees generated in this way are very similar to reality in their visual appearance and predict diameter ratios of parent and daughter segments, the distribution of symmetry, the transmural distribution of flow, the volume of large arteries, as well as the ratio of small arterial volume in subendocardial and subepicardial layers in good agreement with experimental data. From this study we conclude that the method of CCO combined with staged growth reproduces many characteristics of the different arterial branching patterns in the subendocardium and the subepicardium, which could not be obtained by applying the principle of minimum volume alone.

Shear stress distribution in arterial tree models, generated by constrained constructive optimization

Models of arterial trees are generated by the algorithm of Constrained Constructive Optimization (CCO). Straight cylindrical, binary branching tubes are arranged in an optimized fashion so as to convey blood to the terminal sites of the tree, which are distributed over a predefined area, representing the tissue to be perfused. All terminal segments supply equal flows at a unique terminal pressure, and the radii of parent and daughter segments are related via a bifurcation law. The connective structure and geometry of the model are optimized according to a target function such as total intravascular volume. The shear rate between blood and the vessel walls is computed in each segment and a new method is presented for rescaling a given CCO tree to a desired value of shear rate in the root segment. The effect of viscosity varying with shear rate is evaluated and a new method is presented for rescaling a CCO-tree segment by segment to consistent values of radii and variable viscosity. Shear stress is evaluated for its deviation from being proportional to shear rate and then subjected to various types of analyses. Usually both, shear stress and its variability, are found to be larger in the smaller than in the larger segments of the CCO-model trees. However, it is shown how the shear-stress distribution can be reshuffled between small and large segments when rescaling a CCO tree to obey a different bifurcation law, while its whole geometry remains unchanged and all boundary conditions remain fulfilled. The selection of optimization target is found to drastically affect shear-stress variability within bifurcations, which reaches a distinct minimum if the model is optimized according to intravascular volume. Finally, a rank-analysis of shear stress within each bifurcation shows that only two out of six possible rank patterns actually occur: the parent segment always experiences medium shear stress while minimum shear stress resides mostly in the larger, less frequently in the smaller daughter.

A three-dimensional model for arterial tree representation, generated by constrained constructive optimization

The computational method of constrained constructive optimization (CCO) has been generalized in two important respects: (1) arterial model trees are now grown within a convex, three-dimensional piece of tissue and (2) terminal flow variability has been incorporated into the model to account for the heterogeneity of blood flow observed in real vascular beds. Although no direct information from topographic anatomy enters the model, computer-generated CCO trees closely resemble corrosion casts of real arterial trees, both on a visual basis and with regard to morphometric parameters. Terminal flow variability was found to induce transitions in the connective structure early in the trees' development. The present generalization of CCO offers--for the first time--the possibility to generate optimized arterial model trees in three dimensions, representing a realistic geometrical substrate for hemodynamic simulation studies. With the implementation of terminal flow variability the model is ready to simulate processes such as the adaptation of arterial diameters to changes in blood flow rate or the formation of different patterns of angiogenesis induced by changing needs of blood supply.

Morphometry of human coronary arterial trees

BACKGROUND

Some groups, including ours, have been generating arterial tree models using constrained constructive optimization (CCO). Arterial trees have been grown to arbitrary resolution without input of anatomical data. We performed this study to learn about the shortcomings that might have resulted from neglecting the anatomical data in CCO models.

METHODS

In a total of 450 segments obtained from 4 human cast hearts, the ratio ofbifurcating daughter segment radii (O < Sbif = r(2)/r(1) < 1) was examined, which corresponds to the split of the total flow of the mother segment. For any complete bifurcation, where the radii of the parent segments and the radii of daughters were known, the area expansion ratio was computed (Aexp = [r(1)2 + r(2)2]/r(parent)2).

RESULTS

The bifurcating ratio was found to be distributed in a nonnormal fashion, with a median of 0.76. The average area expansion ratio Aexp, characterizing the change of cross-sectional area of the vasculature from proximal to distal, was 0.93+/-0.26. The 'rate of branching' (d(i)/(d(0)) was defined by the segment diameter relative to the diameter of the root segment. Averaging the rate of branching over segments within each bifurcation level resulted in a decreasing function of bifurcation level.

CONCLUSIONS

This article provides new experimental data on branching geometry of coronary arteries (i.e., the trees evaluated in this study are purely delivering rather than conveying). Based on these facts, we suggest that the analytical bifurcation law in CCO might be replaced by the bifurcation rule obeyed on a stochastic basis only.

Use of non-pneumatic antishock garments for ruptured abdominal aortic aneurysm

Two cases of near-fatal aortic abdominal aneurysm (AAA) are described which were successfully stabilized by a new principle for exerting abdominal compression, the non-pneumatic medical antishock trousers (NP-MAST). Obviously, the compression obtained with the NP-MAST suffices for this dramatic emergency. Moreover, compared with pneumatic antishock garments (PASG), the NP-MAST has the advantage of being light, independent of flight height and unable to produce dangerously high pressures. Moreover, it contains no manometers, which could detract the doctor's attention from more important measures. The need for endotracheal intubation in advance to application of any kind of abdominal compression (PASG or NP-MAST) is stressed.

Variable platelet response to low-dose ASA and the risk of limb deterioration in patients submitted to peripheral arterial angioplasty

A group of 100 patients with intermittent claudication (70 male, 30 female), treated with I00 mg ASA per day, were followed over 18 months after elective percutaneous balloon angioplasty. Platelet function was monitored over a period of 12 months by corrected whole blood aggregometry (CWBA). Upon stimulation by arachidonic acid (AA), adenosine diphosphate (ADP) and collagen, CWBA-results were obtained by an electronic acquisition and evaluation system correcting for hematocrit and platelet count of the blood sample. All patients showed a completely inhibited platelet response to AA stimulation. Comparison of the CWBA-results with clinical parameters revealed that reocclusions at the site of angioplasty occurred exclusively in male patients for which CWBA failed to prove an inhibition of aggregation upon both agonists, ADP and collagen, and for these patients the risk of complication is at least 87% higher (p = 0.0093). Only 40% of male patients show the expected effect of ASA on in vitro platelet aggregation at any given point in time and CWBA is capable of predicting those male patients which are at an elevated risk of reocclusion following peripheral angioplasty.

Anatomical variability and functional ability of vascular trees modeled by constrained constructive optimization

The aim of this study was to investigate the extent that functional capability of vascular trees is related to anatomical variability. To these ends we used the method of Constrained Constructive Optimization (CCO) to generate optimized computer models of coronary arterial trees. All these model trees were optimized according to the same principle under equal boundary conditions of pressures and flows. However, by stochastically casting the locations of the terminal segments, different tree structures were generated, each of which conformed to the same boundary conditions. The structural variability of these models was interpreted as the correlate of the anatomical variability found in real arterial trees. The advantage that computer model trees are known in numerical detail was exploited to perform comprehensive and exact classifications of all segments into bifurcation levels, STRAHLER orders and composite vessels, and to compute the area expansion ratio. The unexpected result was that, despite striking visual differences in anatomical structure, the model trees were almost identical with regard to functional performance. We conclude that models optimized on the computer for a given perfusion task show little differences in their morphometric parameters even if they differ considerably regarding the course of the large vessels.

Five-year follow-up after heart valve replacement with the CarboMedics bileaflet prosthesis

BACKGROUND

The CarboMedics valve is a relatively new, low-profile, bileaflet, mechanical prosthesis. The results of a prospective follow-up study after valve replacement with this prosthesis in a university hospital are presented.

METHODS

We implanted 640 CarboMedics prostheses in 583 patients in the aortic (n = 359), mitral (n = 167), or aortic and mitral positions (double valve replacement; n = 57). Patient ages ranged from 11 to 81 years (mean age, 58 +/- 12.3 years).

RESULTS

Overall hospital mortality was 9.0%; however, when high-risk urgent cases were removed from the calculation, the operative mortality fell to 4.5%. Follow-up was 98% complete, comprising 2,027 patient-years for a mean follow-up of 44 months (range, 6 to 72 months). Actuarial freedom from complications (linearized rates in parentheses) was as follows: late mortality, 85% +/- 2.0% (2.3%/patient-year); thromboembolism, 92% +/- 1.1% (1.6%/patient-year); anticoagulation-related hemorrhage, 87% +/- 1.2% (2.8%/patient-year); prosthetic valve endocarditis, 98% +/- 0.5% (0.1%/patient-year); and overall valve-related morbidity and mortality, 76% +/- 2.1% (4.3%/ patient-year).

CONCLUSIONS

The CarboMedics valve shows a low rate of valve-related complications comparable with other new mechanical heart valve prostheses.

Limited bifurcation asymmetry in coronary arterial tree models generated by constrained constructive optimization

Models of coronary arterial trees are generated by the algorithm of constrained constructive optimization (CCO). In a given perfusion area a binary branching network of straight cylindrical tubes is generated by successively adding terminal segments to the growing structure. In each step the site of connection is chosen according to an optimization target function (total intravascular volume), and in any stage of development the tree fulfills physiologic boundary conditions (constraints involving pressures, flows and bifurcation rules). CCO generates structures which in many aspects resemble real coronary arterial trees, except for very asymmetric bifurcations, occurring when a large branch gives off a tiny terminal segment. In the present work we evaluate an additional constraint within CCO, namely imposing a limit on the asymmetry of bifurcations during the construction process. Model trees are grown with different limits imposed, and the effects on structure are studied both phenomenologically and via statistical descriptors. As the limit to asymmetry is tightened, blood is conveyed to the perfusion sites via detours rather than directly and the comparison with measured data shows that the structure to change from a conveying to a delivering type of function. Simultaneously total intravascular volume, surface and sum of segments' lengths increase. It is shown why and how local bifurcation asymmetry is able to determine the global structure of the optimized arterial tree model. Surprisingly, the pressure profile from inlet to terminals, being a functional characteristic, remains unaffected.

Cyclosporine may affect improvement of cognitive brain function after successful cardiac transplantation

BACKGROUND

The effects of cardiac transplantation on cognitive brain function are uncertain.

METHODS AND RESULTS

We measured cognitive brain function and quality of life in out-of-hospital cardiac transplant candidates (n = 55; ejection fraction, 19.9%; age, 54.8 years [means]). After transplantation, the patients were serially reevaluated at 4 months (n = 25) and at 12 months (n = 19). Brain function was measured objectively by cognitive P300 evoked potentials. Additionally, standard psychometric tests (Trail Making Test A, Mini-Mental State Examination, and Profile of Mood State test) were performed. Cognitive P300 evoked potentials were impaired in cardiac transplant candidates (359 ms, recorded at vertex) compared with 55 age- and sex-matched healthy subjects (345 ms, P < .01). Trail Making Test A was also abnormal (45 versus 31 seconds in 55 healthy subjects, P < .01). After transplantation, P300 measures were normalized at 4 months (345 ms, P < .05 versus before transplantation) but declined again at 12 months (352 ms, P = NS versus before transplantation). Stepwise multiple regression analysis revealed that cumulative cyclosporine dosage was the only predictor of individual cognitive brain function 4 months (753 mg/kg body wt, P < .05) and 12 months (2006 mg/kg body wt, P < .01) after transplantation, respectively.

CONCLUSIONS

Objective cognitive P300 auditory evoked potential measurements indicate that cognitive brain function is significantly impaired in patients suffering from stable end-stage heart failure. Successful cardiac transplantation is effective to fully normalize impaired brain function. Subsequent relative long-term decline of cognitive brain function after successful cardiac transplantation is strongly suggested to be related to cumulative cyclosporine neurotoxicity.

Structural quantification and bifurcation symmetry in arterial tree models generated by constrained constructive optimization

Arterial tree models are generated by Constrained Constructive Optimization according to minimum intravascular volume. These models, which have been shown to adequately reproduce pressure profiles and branching angles, are analysed topologically and geometrically in order to investigate how structure influences the functional capabilities. Therefore, the number of bifurcation levels and STRAHLER orders was evaluated for the complete trees as well as for subtrees of all possible sizes. Bifurcation symmetry, being a particular aspect of structure, was found to be higher in the smaller than in the larger subtrees. This confirms a more delivering type of function for the small subtrees, as expected from intuitive arguments. Conversely, lower symmetry in larger subtrees relates to their conveying type of function. Moreover, different shapes of the tissue to be perfused lead to different symmetry properties of optimized tree models.