Cardiac function is characterised by haemodynamic parameters in the clinical scenario. Due to recent development in imaging techniques, the clinicians focus on the quantitative assessment of left ventricular size, shape and motion patterns mostly analysed by echocardiography and cardiac magnetic resonance. Because of the physiologically known antagonistic structure and function of the heart muscle, the effective performance of the heart remains hidden behind haemodynamic parameters. In fact, a smaller component of oblique transmural netting of cardiac muscle fibres simultaneously engenders contracting and dilating force vectors, while the predominant mass of the tangentially aligned fibres only acts in one direction. In case of hypertrophy, an increased influence of the dilating transmural fibre component might counteract systolic wall thickening, thereby counteract cardiac output. A further important aspect is the response to inotropic stimulation that is different for the tangentially aligned fibre component in comparison to the transmural component. Both aspects highlight the importance to integrate the analysis of intramural fibre architecture into the clinical cardiac diagnostics.

The mammalian myocardium making up the ventricles exhibits, on a microscopic scale, a lamellar structure.Lamellae consist of end-to-end connected myocyes in the form of long strains that are densly crosslinked by bridging myocytic offsprings and strongly bound by the endomysium.In contrast, between lamellae only weak myocytic crosslinking and sparse connective tissue is found.The latter property enables reorientation of lamellar segments during systole.Due to the overall crosslinking, however, the myocardium represents a continuum, albeit with significant local variation.While most lamellar segments are oriented and contract during systole in a mostly surface-paralell direction, enabling the ejection of blood, there is a notable presence of transversely oriented lamellar segments.Such segments develop a partly antagonistic function (with respect to the one of the surface parallel segments), in that they counteract systolic wall thickening, the major mechanism for the ejection of blood.This so far underestimated intrinsic antagonic organisation is substantiated by anatomic analyses; furthermore, significant consequences with respect to cardiodynamics and diseases of the heart are found.

Recent morphological studies provide evidence that the ventricular walls are arranged as a 3D meshwork of aggregated cardiomyocyte chains, exhibiting marked local structural variations. In contrary to previous findings, up to two-fifths of the chains are found to have a partially transmural alignment, thus deviating from the prevailing tangential orientation. Upon contraction, they produce, in addition to a tangential force, a radial force component that counteracts ventricular constriction and aids widening of the ventricular cavity. In experimental studies, we have provided evidence for the existence of such forces, which are auxotonic in nature. This is in contrast to the tangentially aligned myocytes that produce constrictive forces, which are unloading in nature. The ventricular myocardium is, therefore, able to function in an antagonistic fashion, with the prevailing constrictive forces acting simultaneously with a dilatory force component. The ratio of constrictive to dilating force varies locally according to the specific mural architecture. Such antagonism acts according to local demands to preserve the ventricular shape, store the elastic energy that drives the fast late systolic dilation and apportion mural motion to facilitate the spiralling nature of intracavitary flow. Intracavitary pressure and flow dynamics are thus governed concurrently by ventricular constrictive and dilative force components. Antagonistic activity, however, increases deleteriously in states of cardiac disease, such as hypertrophy and fibrosis. ß-blockade at low dosage acts selectively to temper the auxotonic forces.

How the cardiomyocytes are aggregated within the heart walls remains contentious. We still do not fully understand how the end-to-end longitudinal myocytic chains are arranged, nor the true extent and shape of the lamellar units they aggregate to form. In this article, we show that an understanding of the complex arrangement of cardiac musculature requires knowledge of three-dimensional myocyte orientation (helical and intrusion angle), and appreciation of myocyte packing within the connective tissue matrix. We show how visualization and segmentation of high-resolution three-dimensional image data can accurately identify the morphology and orientation of the myocytic chains, and the lamellar units. Some maintain that the ventricles can be unwrapped in the form of a "helical ventricular myocardial band," that is, as a compartmentalized band with selective regional innervation and deformation, and a defined origin and insertion like most skeletal muscles. In contrast to the simpler interpretation of the helical ventricular myocardial band, we provide insight as to how the complex myocytic chains, the heterogeneous lamellar units, and connective tissue matrix form an interconnected meshwork, which facilitates the complex internal deformations of the ventricular wall. We highlight the dangers of disregarding the intruding cardiomyocytes. Preparation of the band destroys intruding myocytic chains, and thus disregards the functional implications of the antagonistic auxotonic forces they produce. We conclude that the ventricular myocardium is not analogous to skeletal muscle, but is a complex three-dimensional meshwork, with a heterogeneous branching lamellar architecture.

Science and design are two completely separated areas of expertise with their own specialists. Science analyses the existing world to create new knowledge, design uses existing knowledge to create a new world. This tunnel-vision mentality and narrow-minded approach is dangerous for problem solving, where a broad view on potential solutions is required to realise a high-quality answer on the defined problem. We state that design benefits from scientific methods, resulting in a more effective design process and in better products, while science benefits from a design approach, resulting in more efficient and effective results. Our philosophy is illustrated using examples from the field of biomedical engineering. Both methods can benefit tremendously from each other. By applying scientific methods, superior choices will be made in the design process. With design, more accurate, effective and efficient science will be performed.

ABSTRACTRecent studies point toward the existence of a significant population of cardiomyocytes that intrude transmurally, in addition to those aligned tangentially. Our aim was to investigate the extent of transmural angulation in the porcine left ventricle using diffusion tensor magnetic resonance imaging (DTMRI). Hearts from eight 15 kg pigs were arrested in diastole. The ventricles were filled with polymer to maintain the end‐diastolic dimensions. All hearts were examined using DTMRI to assess the distribution of transmural angulation of the cardiomyocytes at 12 predetermined locations covering the entirety of the left ventricle. We found significant differences between the regions, as well as within the transmural subcomponents. In eight out of the 12 predetermined mural segments, the highest mean transmural angle was located sub‐endocardially. The greatest mean transmural angles were found in the anterior basal region, specifically 14.9 ± 6.0‐degree angle, with the greatest absolute value being 34.3‐degree angle. This is the first study to show the significant heterogeneities in the distribution of helical and transmural angles within the entirety of the left ventricular walls, not only for different depths within the ventricular walls, but also between different ventricular regions. The results show unequivocally that not all the contractile elements are aligned exclusively in tangential fashion within the left ventricle. The main function of the transmurally intruding component is most likely to equalize and normalize shortening of the cardiomyocytes at all depths within the myocardium, but our findings also support the notion of antagonistic forces existing within the myocardial walls. Anat Rec, 296:1724–1734, 2013. © 2013 Wiley Periodicals, Inc.

Die Wechselwirkung zwischen Kräften, Verteilung und Absorption des Kammerwassers im subkonjunktivalen Gewebe wird anhand eines kürzlich publizierten theoretischen Modells untersucht, das die Produktion von Flüssigkeit im Auge und deren Eliminierung durch das Trabekelwerk, das uveosklerale Gewebe und einen Shunt beschreibt. Zielgröße dabei ist der intraokulare Druck. Die Mechanismen von neu geschaffenen Abflusswegen werden mithilfe der Theorie der porösen Medien dargestellt, die sich auf ein Sickerkissen beziehen, das unter dem subkonjunktivalen Gewebe liegt. Die rechnerische Analyse basiert auf der Geometrie und den Parametern, die das Zu- und Abflusssystem charakterisieren. Diese sind durch die Produktion von Kammerwasser, den chirurgisch angelegten Abflusskanal, sodann durch die Resorption in den episkleralen Gefäßen und durch die hydraulischen Eigenschaften des subkonjunktivalen Gewebes und des Sickerkissens sowie durch dessen Geometrie gegeben. Anhand parametrischer Untersuchungen können klinische Befunde physikalisch begründet werden.

The architectural arrangement of cardiomyocytes aggregated together within the ventricular walls remains controversial. Two models currently attract clinical attention, with neither model standing rigorous anatomical scrutiny. The first is based on the notion that ventricular mass can be unraveled consistently to produce a unique myocardial band. The second model was initially based on the notion that cardiomyocytes were bundled together in uniform fashion, with fibrous shelves interposed in transmural fashion. This concept was subsequently modified to accept the fact that the fibrous matrix supporting the cardiomyocytes within the ventricular walls does not form transmural sheets. Current observations demonstrate that not all cardiomyocytes are aggregated together in tangential fashion. A significant netting component is aligned in obliquely intruding and transversal fashion. The interaction between the tangential and transversal chains of cardiomyocytes with the fibrous matrix produces antagonistic forces, with both unloading and auxotonic forces necessary to explain normal and abnormal cardiodynamics. This article is part of a JCTR special issue on Cardiac Anatomy.

In order to visualise the mammalian myocardial structure in its entirety, we distended excised porcine left ventricles by inflating the coronary arteries with compressed air, using rising pressures between 100 and 300 kPa. The ventricular walls became elongated, and left ventricular cavity widened with rising pressure albeit with insignificant changes in their mural thickness. High resolution computed tomographic analysis subsequent to pneumographic distension revealed a hierarchical structure. First, a feathered arrangement of the cardiomyocytes aggregated together mainly within the equatorial area of the ventricle, giving an overall appearance of systematically arranged spatially netted lamellar structures with pronounced local inhomogeneity. Second, histological examination in orthogonal planes, analysing samples dividing the ventricular walls into 18 segments, showed the lamellae themselves to be made up of aggregated chains of myocytes, the alignment of these chains producing the well-recognised change in so-called helical angle when traced through the thickness of the walls. Transmural length sections removed from the same positions in the ventricular walls showed inter-lamellar connections aligned in the direction from the ventricular base to the apex which were definitely longer than those we observed in transmural cross-sections. Electron-microscopy exposed the two compartments of interstitial connective tissue, suggesting the endomysium to bind long chains of myocytes to lamellar aggregates, while the loose perimysium strengthens the structure of the lubricating medium which eases the gliding of the lamellar aggregates relative to one another.

To help elucidate the interplay of physical forces, in particular pressure and flow, controlling the distribution and absorption of aqueous humor in subconjunctival tissue, a recently published computational model was considered where the fluid production in the eye, its removal via the trabecular/uveoscleral pathways and a surgical pathway are taken into account. The target quantity is the intraocular pressure. The surgical outflow pathway is linked to a fluid bleb that is positioned below the subconjunctival tissue and is modeled as a porous medium. The computational study was conducted on the basis of the geometry and relevant parameters characterizing fluid production, the surgically formed fluid pathway as well as absorption by the subconjunctival vessels, the hydraulic and geometrical characteristics of the bleb and the outflow facility. Clinical observations can be physically interpreted on the basis of parametric studies.

Objectives: Virtual reality models of human organs are needed in surgery simulators which are developed for educational and training purposes. A simulation can only be useful, however, if the mechanical performance of the system in terms of force-feedback for the user as well as the visual representation is realistic. We therefore aim at developing a mechanical computer model of the organ in question which yields realistic force-deformation behavior under virtual instrument-tissue interactions and which, in particular, runs in real time.Study design: The modeling of the human uterus is described as it is to be implemented in a simulator for minimally invasive gynecological procedures. To this end, anatomical information which was obtained from specially designed computed tomography and magnetic resonance imaging procedures as well as constitutive tissue properties recorded from mechanical testing were used. In order to achieve real-time performance, the combination of mechanically realistic numerical uterus models of various levels of complexity with a statistical deformation approach is suggested. In view of mechanical accuracy of such models, anatomical characteristics including the fiber architecture along with the mechanical deformation properties are outlined. In addition, an approach to make this numerical representation potentially usable in an interactive simulation is discussed.Results and conclusions: The numerical Simulation of hydrometra is shown in this communication. The results were validated experimentally. In order to meet the real-time requirements and to accommodate the large biological variability associated with the uterus, a statistical modeling approach is demonstrated to be useful. (c) 2009 Elsevier Ireland Ltd. All rights reserved.

To investigate the relation between intrauterine pressures and volumes for virtual-reality-based surgical training in hysteroscopy.

The low strain-rate behavior of the human myometrium under compression was determined. To this end, uniaxial, unconstrained compression experiments were conducted on a total of 25 samples from three excised human uteri at strain rates between 0.001 s(-1) and 0.008 s(-1). A three-dimensional finite element model of each sample was created and used together with an optimization algorithm to find material parameters in an inverse estimation process. Friction and shape irregularities of samples were incorporated in the models. The uterine specimens in compression were modeled as viscoelastic, non-linear, nearly incompressible and isotropic continua. Simulations of uniaxial, frictionless compressions of an idealized cuboid were used to compare the resulting material parameters among each other. The intra- and inter-subject variability in stiffness of specimens was found to be large and to cover such a wide range that the effect of anisotropy which is of minor influence under compressive deformations in the first place could be neglected. Material parameters for a viscoelastic model based on a decoupled, reduced quadratic strain-energy function were presented for the uterine samples representing a median stiffness.

"There is always an easy solution to every human problem—neat, plausible and wrong."—Henry Louis Mencken. New York Evening Mail; November 16, 1917; later published in Prejudices: Second Series (1920), and A Mencken Chrestomathy (1949)

Near-infrared spectroscopy (NIRS), applied to a human head, is a noninvasive method in neurointensive care to monitor cerebral hemodynamics and oxygenation. The method is particularly powerful when it is applied in combination with indocyanine green (ICG) as a tracer substance. In order to assess contributions to the measured optical density (OD) which are due to extracerebral circulation and disturb the clinically significant intracerebral signals, we simulated the light propagation in an anatomically representative model of the adult head derived from MRI measurements with the aid of Monte Carlo methods. Since the measured OD signal depends largely on the relative blood content in various transilluminated tissues, we weighted the calculated densities of the photon distribution under baseline conditions within the tissues with the changes and aberrations of the relative blood volumes which we expect to prevail under physiological conditions. Furthermore, the influence of the IGC dye as a tracer substance was assessed. We conclude that up to about different 70% of the measured OD signal may have its origin in the tissues of interest under optimal conditions, which is mainly due to the extrapolated high relative blood content of brain tissue along with the influence of ICG.

The myocytes comprising the ventricular mass are arranged so as to function in antagonistic fashion, the walls having the capacity to generate both constrictive and dilatory forces. This dualistic activity is organized on the basis of a site-specific morphologic pattern, permitting marked regional specificity for mural motion and providing a target for regional therapy. Diseased regions can be removed surgically without danger of jeopardizing the remaining healthy mural segments. The sensitivity of the intruding population of myocytes to positive and negative inotropic medication is markedly more pronounced than that of the prevailing tangentially aligned myocytes. This asymmetrical action of inotropes in the setting of global ventricular imbalance promotes the potential to restore constrictive as opposed to dilatory actions.