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Technology and Health Care is intended to serve as a forum for the presentation of original articles and technical notes, observing rigorous scientific standards. Furthermore, upon invitation, reviews, tutorials, discussion papers and minisymposia are featured.
The following types of contributions and areas are considered:
1. Original articles:
Technology development in medicine: New concepts, procedures and devices associated with the use of technology in medical research and clinical practice are presented to a readership with a widespread background in engineering and/or medicine.
Significance of medical technology and informatics for healthcare: The appropriateness, efficacy and usefulness deriving from the application of engineering methods, devices and informatics in medicine and with respect to public health are discussed.
2. Technical notes:
Short communications on novel technical developments with relevance for clinical medicine.
3. Reviews and tutorials (upon invitation only):
Tutorial and educational articles for persons with a primarily medical background on principles of engineering with particular significance for biomedical applications and vice versa are presented.
4. Minisymposia (upon invitation only):
Under the leadership of a Special Editor, controversial issues relating to healthcare are highlighted and discussed by various authors.
Abstract: The macroscopical structure of the ventricular myocardium has been an unsolved problem since the XVIth century, when Anatomy started as an authentic science. Since then the spatial organization of the myocardial fibres has represented, as Pettigrew says, “an arrangement so unusual and perplexing, that it has long been considered as forming a kind of Gordian knot in Anatomy. Of the complexity of the arrangement I need not speak further than to say that Vesalius, Albinus, Haller and De Blainville, all confessed their inability to unravel it”. What is shown in the present paper is the result of an anatomical…work, developed over 43 years, by means of which it has been shown that the ventricular myocardial mass consists of a band, curled in a helical way, which extends from the pulmonary artery to the aorta. This is illustrated by a silicone rubber model cast from an actual unrolled myocardial band.
Abstract: An important determinant of cardiac output derives from the structure of the ventricular wall given by the arrangement of the cardiac muscle fibres. A key feature of this arrangement is both a global and local anisotropy. First, a preparation method necessary for analyzing the main aspects of spatial fibre architecture is outlined. Global anisotropy can be described by a gross band-like structure wrapping both left and right ventricles while local anisotropy results form the arrangement of the individual muscle fibres within the band. In pathologic cases this basic structure may be disturbed leading to cardiac failure. Second, a Finite Element…model, formulated on the basis of Magnetic Resonance measurements has been devised which is intended to reflect the global as well as the local anisotropy of the ventricles in order to further the understanding of cardiac performance.
Abstract: This paper develops several working hypotheses regarding the coupling between myocardial fiber architecture and left ventricular function. First, the coupling between spiral myocardial fibers and left ventricular torsional deformation and ejection fraction is examined. A proposal is then made to account for the observed change in orientation of myocardial fibers from a right hand helix in the subendocardium, through circumferential fibers in the midwall, to a left hand helix in the subepicardium in terms of a requirement for generating physiological values of both ejection fraction and pressure as well as equilibration of transmural fiber work. Finally, a pumping hypothesis is…developed linking the contraction of each transmural layer of fibers to one another via collagen struts and weaves, with the resulting force transmitted to the epicardium and thence, by means of hydraulic forces associated with the constant volume property of the LV wall, to the endocardium to reduce the volume of the left ventricular chamber.
Abstract: Opinions are divided as to whether the rope-like secondary structure, which Torrent-Guasp dissected out of the myocardial body by the blunt unwinding technique (BUT) reveals some kind of functional compartmentation of the heart muscle. The myocardial fibres are aligned parallel to the fibre disruption (cleavage) plane, along which the band has been prepared but they are not necessarily aligned parallel to the long axis of the band. Inconsistencies in the myocardial rope model arise from the obligatory zones of transmural inflection, which are obvious in the base and the apex of both ventricles. They are, however, merely discernible in…the midzone of the left ventricular cone. The investigator experienced in BUT knows that the cleavage plane is not unique. We doubt the assumption that the rope structure is the predominant stress transmission pathway, because the fibre strand peel-off technique (SPOT) delivers irregular fibre disruption planes which are definitely different from those which Torrent-Guasp prepares. The rope-like fibre arrangement could be just a redundant structure, a remnant of past developmental steps without, however, any functional implication to the human heart. On the other hand, peeling-off fibre strands from the ventricular wall produces deeply perforating, i.e., oblique transmurally grooved surfaces. Putative functions of force transmission in an oblique transmural direction are (1) ventricular dilation as a function of the variable inclination angle with respect to the epicardial surface, (2) monitoring of ventricular wall stress and ventricular size and (3) segmental stiffening which could serve other dependent segments as a punctum fixum.
Abstract: Myocardial contractile pathways which are not aligned strictly parallel to the heart’s epicardial surface, give rise to forces which also act in the ventricular dilating direction. We developed a method which allows us to assess any fibre orientation in the three-dimensional myocardial weave. Decollagenized hearts were prepared by peeling-off fibre strands, following their main fibre orientation down to near the endocardium. In the subepicardium the strands followed a course more or less parallel to the epicardium, whereas from the mid-wall on they tended to dive progressively deeper into the wall. The preparation displays more or less rugged surfaces rather…than smooth layers. The grooves and crests on the exposed surfaces were sequentially digitized by two methods: (1) Using a magnet tablet (3 Draw Digitizer System, Polhemus, Cochester VTO 5446, USA) on a dilated pig heart we manually followed the crests using a stylus, handling each groove and crest as an individual contractile pathway. (2) A constricted cow heart was digitized using a contact-free optical system (opto TOP, Dr. Breuckmann, Meersburg, Germany), which is based on the principle of imaging triangulation. Using specially developed software the inclination angles of selected crests and grooves with respect to the epicardial surface were calculated. The two digitizing methods yield comparable results. We found a depth- and side-specific weave component inclined to the epi-endocardial direction. This oblique netting component was more pronounced in the inner 1/3 of the wall than in the subepicardium. The inclination angle probably increases with increasing wall thickness during the ejection period. Manual digitizing is an easy and fast method which delivers consistent results comparable with those obtained by the cumbersome high resolution optical method. The rationales for the assessment of transmural fibre inclination are (1) the putative existence of dilating forces inherent in the myocardial weave and (2) the possible overproportional increase in the oblique transmural weave component during myocardial hypertrophy, which would entail a reduction in efficiency of ventricular performance in terms of haemodynamic work.
Abstract: The computation of the inclination angle of myocardial contractile pathways, based on the data from (1) optically and (2) manually digitized hearts is described. The measured raw data comprised: (1) A list epi of points on an ‘epicardial’ surface S . (2) For each selected contractile pathway f , a list of points along the contractile pathway. For any point p on a contractile pathway f , the angle of inclination α p = α p ( p , f , S )…is defined to be the angle (in degrees) between the tangent t p = t p ( f ) to the contractile pathway f at the point p and the tangent plane T v p to the surface S at the surface point v p = v ( p , S ) which is nearest to p . Thus α p is a generalization of the imbrication angle of Streeter. The angle of inclination was computed using two separate numerical methods: (1) A discrete method, applying finite differences to the raw data, to compute the tangents t p and the tangent planes T v p , after which the results were smoothed. (2) A smoothing method in which the data was first smoothed to obtain an approximation S epi to the epicardial surface and spline approximations to the contractual pathways f . We describe the results for two typical hearts: a manually digitized dilated pig heart and an optically digitized constricted cow heart. For each heart we first present the depths and angles of inclination of typical contractual pathways and then summarize the results in the form of histograms. The results are discussed in detail in the accompanying paper of Lunkenheimer, Redmann et al. [P.P. Lunkenheimer, K. Redmann, K.-H. Dietl, C. Cryer, K.-D. Richter, W.F. Whimster and P. Niederer, The heart’s fibre alignment assessed by comparing two digitizing systems. Methodological investigation into the inclination angle towards wall thickness, Technology and Health Care 5 (1997), 65–77], where the digitization methods are also described.
Abstract: The extracellular collagen matrix of the myocardium plays an important role in maintaining muscle fiber and cardiac alignment and ventricular shape and size. It also influences tissue and ventricle stiffness. This network consists of an organized hierarchy of collagen that is intimately associated with individual and groups of myocyte and muscle fibers, as well as the coronary vasculature. In renovascular and genetic hypertension, the hypertrophic response of the myocardium includes an increase in collagen concentration, thickening of existing fibrillar collagen, and addition of newly synthesized collagen to all of the matrix components. The consequences of this remodeling are a stiffer…myocardium and left ventricular diastolic dysfunction. With removal of less than half of the normal amount of collagen the opposite occurs. That is, the ventricle dilates and there is an increase in ventricular compliance. Thus an abnormal accumulation of collagen is a major distinguishing factor between physiologic and pathologic hypertrophy while an abrupt decrease in collagen concentration results in a ventricular remodeling similar to that of a heart in failure.
Abstract: The main local stress transmission pathways in the left ventricular base, midportion and apex in up to seven layers have been assessed in normal dog and porcine hearts, in hypertrophied dog hearts, and in three pig hearts having undergone a temporary left ventricular outflow stricture. The rotational sensitivity of needle force probes was used to determine the focal surface-parallel direction of the myocardial tension vector. In all places investigated the orientation of the force transmission pathways differs slightly from the morphologically determined fibre alignment. Vector rotation upon an axis normal to the epicardial surface is definitely tempered as compared to…fibre rotation. Alterations in the force transmission pathways assessed in hypertrophied dog hearts by micro-ergometry qualitatively confirm structural remodelling in so far as an irregularity in the transmural rotation of the main stress vector was found. The measured disparities between the alignment of the myocardial fibre weave and the direction of stress transmission both in the normal and the diseased heart is widely individual, and hence, scattering of the data is marked. However, it must also be called into consideration that the measured orientation of force vectors is that at the moment of highest developed force, only. Further investigations will elucidate if discrepancies between that force vector and morphology are less pronounced when the vector is averaged over the entire heart cycle.
Abstract: Microergometry is a method which we have developed as a tool to measure local mesh-tension within the myocardial weave at any measuring site of both ventricles and the septum on the beating heart in situ. In a mapping procedure on pig and dog hearts, both in control conditions and in the hypertrophied state after aortic banding, local mesh-tension was measured in several areas and in up to eight depths proceeding from the epicardium to the endocardium: Probe-to-fibre coupling is definitely more stable in the canine myocardium than in the porcine heart muscle, probably due to a more effective connective tissue…fettering of the canine myocardial weave. The observed longitudinal gradient, with the highest tension in the base, of control dog hearts was levelled out in the hypertrophied hearts. Furthermore, in control dog hearts mesh-tension in the subepi- and subendocardial layers was higher than in the midlayers. This pronounced midlayer-hypotension was smoothed in the hypertrophied hearts. Further studies will be dedicated to the question of whether the impact of ventricular size and shape on intersegmental stress transmission is determined by the Frank–Starling mechanism alone or whether protracted remodelling processes on the level of the local fibre weave cause slow coupling alterations.
Abstract: Myocardial contractile properties form the cornerstone of the heart’s ability to pump blood. Efforts have been made to characterize these properties via classic elasticity theory concepts, which can lead to spurious results, as demonstrated by experiments measuring intramyocardial pressure. Two ways out of these difficulties are identified. One is to start at the cellular level, the other at the chamber level. The latter allows separation of ventricle (source) and arterial (load) effects on measured pressure and flow, distinct from previous definitions of ventricular contractility which tended to lump the two.
Abstract: To characterize the complex force field generated in the ventricular myocardium, intramyocardial pressure (IMP) measurement is used as an indirect means of assessing the distribution of regional wall stress. To resolve the long term confusion associated with this measurement, IMP is divided into its two dominant components: intramyocardial fluid pressure (IFP) and intramyocardial fiber stress (IFS). The intramyocardial response to regional and global contractile function is examined in terms of changes in the magnitude and transmural gradient of IMP recording. The experimental results support the theoretical concept proposed where the hydraulic properties of the myocardium proved to have an influence…on cardiac function. To gain a deeper understanding of myocardial function, cellular and subcellular components must be considered.
Abstract: In the past the study of mechanical and electrical properties of the heart has been disjointed with minimal overlap and unification. The fact remains that these features are tightly coupled and central to the functioning heart. The maintenance of adequate cardiac output relies upon the highly integrated autoregulatory mechanisms and modulation of cardiac myocyte function. Regional ventricular mechanics and energetics are dependent upon muscle fiber stress–strain rate, the passive properties of myocardial collagen matrix, adequate vascular perfusion, transcapillary transport and electrical activation pattern. Intramural hydraulic “loading” is regulated by coronary arterial and venous dynamics. All of these components are under…the constant influence of intrinsic cardiac and extracardiac autonomic neurons, as well as circulating hormones. A brief overview of the putative regulation of these various components is presented in this paper.
Abstract: As the myocardial capillaries drain tassel-like into the peripheral end of sinusoids, the venous system of the myocardium begins in the sinusoids and plays an important role in the regulation of myocardial circulation. The sinusoids dilate in response to inadequacy of the arterial vascularization and their expansion has been found to be inversely proportional to the blood flow in the coronary arteries. The sinusoids become more dilated and prominent with coronary dilators and reinforcement of myocardial vascularization by cardiopexy techniques, causes the sinusoids to become dilated.