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PubMed1989

The effect of swimming activity on bone architecture in growing rats.

The effect of non-habitual physical activity on bone architecture in the rat humeral shaft was examined. Two groups of rats were trained to swim for 1 h a day, for 20 weeks, at two training levels. The control group consisted of sedentary rats. Parameters of cross-sectional bone morphology (cross-section areas, principal area moments of inertia and their ratio) were used to evaluate the response of bone architecture to mechanical loading. The strength of bone was assessed by measuring the ultimate compressive force and stress. The cortical cross-section area and principal moments of inertia were found to be significantly higher in the swimming groups than in the controls. Examination of the ratio between the major and minor moments of inertia revealed a pronounced change in the shape of the bone cross-section which became more rounded following swimming training. The ultimate compressive force was significantly higher in the swimming rats while the changes in ultimate stress were not significant. Our results indicate a gain of bone strength due to increased periosteal apposition and modified bone tissue distribution. The marked changes in bone morphology are attributed to the different nature of the forces and moments exerted on the humerus during swimming compared to those prevailing during normal locomotion.

Adaptation, Physiological↗
PubMed1992

Quantitative method for comparison of skeletal muscle architectural properties.

A numerical method is presented which calculates the architectural difference index between two muscles. This index is based upon the parameters, identified using statistical discriminant analysis, which best characterize the various muscles. This index can be used to reduce multiple architectural properties into a single value and may be useful in selecting donor muscles which are required to perform a substitute function for another muscle which has been lost or injured.

Animals↗
PubMed1993

Bone and bones, architecture and stress, fossils and osteoporosis.

The combined use of architectural and stress technologies in osteological studies is starting to provide the basic biomechanical underpinnings to both evolutionary and applied medical investigations of bone. The architectural investigations, though tested using invasive methods, are aimed at non-invasive ways of obtaining information from radiographs of bones, fossils and people. They include optical (Fourier) data analysis (ODA) and computational Fourier transformations (FFT). The stress studies, though initially involving older techniques such as photoelastic stress analysis, now employ finite element analysis (FEA) and, most recently, fast Lagrangian analysis of continua (FLAC). Taken together, these methods are capable of providing more detailed knowledge of bone form and function that is important (a) in revealing functional adaptation in evolutionary studies of fossils and (b) for making early diagnosis and understanding pathological fractures in the late stages of osteoporosis.

Animals↗
PubMed1995

The influence of inhomogeneity in architecture on the modelled force-length relationship of muscles.

In this study a model has been developed to assess the length-force relationship of skeletal muscle, accounting for inhomogeneity in the muscular architecture. The muscle was modelled as a number of parallelepipeds parallel to but geometrically different from each other. For each of the parallelepipeds the force at a given length was calculated. The force-length relationship of the whole muscle was obtained by summing the forces of each of the parallelepipeds. Four kinds of inhomogeneities were simulated using this model: (i) variation of the aponeuroses lengths over the parallel parallelepipeds; (ii) variation of the muscle fibre lengths; (iii) variation of the pennation angles; (iv) variation of the fibre lengths keeping the pennation angle constant. By varying geometry parameters a total of 1000 inhomogeneous muscles was created. The force-length relationships were also calculated neglecting the inhomogeneities, by taking the extreme, or the median of the inhomogeneous parameter value, as descriptive for a homogeneous model. It was found that an inhomogeneity of the aponeuroses length has only minimal influence on the calculated force-length relationship. In the cases of the three other inhomogeneities simulated considerable differences were found. Especially when in the model neglecting inhomogeneities one of the extreme architectural variables was used, unacceptable large differences with the model considering the inhomogeneities occurred. The model was also applied to the equine M. flexor carpi radialis. Considerable differences in the calculated force-length relationship were found after incorporating inhomogeneity. These appeared to depend largely on the pennation angles, either being kept constant, or changing with varying fibre lengths over the parallel parallelepipeds.

Animals↗
PubMed1978

The trichurid egg-shell: evidence in support of the Bouligand hypothesis of helicoidal architecture.

Electron microscopy of thin sections and freeze etch replicas of the eggs of the nematodes Trichuris suis and T. muris is used to provide evidence in support of the Bouligand hypothesis of helicoidal architecture. The evidence presented is as follows: 1. The specific objections to the Bouligand model raised by Dennell (1974) and Dalingwater (1975b) are answered by reference to a pyramid of helicoidal tissue in which the corners are blunt. 2. Sections cut normal to the plane of the laminae do not show parabolic patterning. Parabolae appear if the section is tilted--their direction depending upon the direction of tilting. 3. Freeze etching allows the direct visualization of helicoidal architecture. Fibres are parallel within any one lamina but the fibre direction rotates by an angle of 9 degrees in successive laminae. Parabolic arcs are made up of short lengths of straight fibres--curved fibres were not observed. Planes of sectioning producing single and double spiral artifacts are described and the formation of these artifacts discussed. The sense of rotation of the helicoid is shown to be asymmetrical about any mid-plane through the egg.

Animals↗
PubMed1994

Fibrin in human plasma: gel architectures governed by rate and nature of fibrinogen activation.

The porosity, fiber dimension and architecture of fibrin gels formed in recalcified plasma on addition of thrombin are, within a certain range of thrombin concentrations, determined by the initial rate of fibrinogen activation. Furthermore, the initial network formed in this range creates the scaffold into which subsequently activated fibrinogen molecules are deposited. Change in thrombin concentration that occurs during gelation, as a result of indigenous thrombin generation in plasma, does not qualitatively alter this scaffold. The formation of the networks obeys a more complex rule when low amounts of thrombin are added or with recalcified plasma without added thrombin. These networks are tighter than would be expected from the initial rate of fibrinogen activation. In this case an extremely porous network is probably formed initially, followed by formation of a secondary, superimposed network of a less porous architectural quality. The latter structure appears to be governed by the rate of indigenous generation in plasma of thrombin-like enzymes in combination with the particular type of fibrinmonomers being produced. In addition our findings establish the rules for proper determination of gel structures in clinical plasma samples. The sequelae of a variety of clot structures that may be formed in vivo are discussed.

Blood Coagulation↗
PubMed1995

Reversal of intrinsic DNA bends in the IFN beta gene enhancer by transcription factors and the architectural protein HMG I(Y).

In this paper, we investigate DNA bending induced by proteins required for virus induction of the human interferon-beta (IFN beta) gene. We show that NF-kappa B-DNA complexes that are functionally distinct in the context of the IFN beta enhancer are also conformationally distinct and that two sites in the enhancer contain in-phase bends that are counteracted or reversed by the binding of NF-kappa B, ATF-2/c-Jun, and HMG I(Y). Strikingly, this modulation of intrinsic enhancer architecture results in an orientation that favors predicted protein-protein interactions in a functional nucleoprotein complex, the enhanceosome. Furthermore, the subtle modulation of DNA structure by HMG I(Y) in this process distinguishes it from other architectural factors.

Activating Transcription Factor 2↗
PubMed1990

Functional architecture of basal ganglia circuits: neural substrates of parallel processing.

Concepts of basal ganglia organization have changed markedly over the past decade, due to significant advances in our understanding of the anatomy, physiology and pharmacology of these structures. Independent evidence from each of these fields has reinforced a growing perception that the functional architecture of the basal ganglia is essentially parallel in nature, regardless of the perspective from which these structures are viewed. This represents a significant departure from earlier concepts of basal ganglia organization, which generally emphasized the serial aspects of their connectivity. Current evidence suggests that the basal ganglia are organized into several structurally and functionally distinct 'circuits' that link cortex, basal ganglia and thalamus, with each circuit focused on a different portion of the frontal lobe. In this review, Garrett Alexander and Michael Crutcher, using the basal ganglia 'motor' circuit as the principal example, discuss recent evidence indicating that a parallel functional architecture may also be characteristic of the organization within each individual circuit.

Animals↗
PubMed1985

Abnormal architecture of the ventricles in hearts with an overriding aortic valve and a perimembranous ventricular septal defect ("Eisenmenger VSD").

Among 111 hearts with so-called "isolated" ventricular septal defect, 18 specimens were found to have a subaortic perimembranous defect with an overriding aortic valve but without pulmonary stenosis. The ventricular architecture was characterized by several abnormalities. A constant finding was the wide right ventricular outflow tract. The outlet septum had its normal continuity with the septomarginal trabecula, but its parietal extension was located relatively far anteriorly. Part of the aortic valve thus inserted to the right ventricular component of the ventriculo-infundibular fold in the gap between the outlet septum and the tricuspid valve. Left ventricular abnormalities comprised mitral valve anomalies in all cases. There was an anteroseptal twist (leftward thickening of the anterior part of the ventricular septum) in 16 cases. A bicuspid aortic valve and/or malformed cusps were observed in 4 cases. Because of the linking phenomenon of aortic override, we also examined 10 hearts with tetralogy of Fallot and, in the latter, such abnormalities were not found. Our observations indicate that this seemingly simple type of defect is part of a complex malformation involving both septation and valve formation. Awareness of the existence of the architectural abnormalities might make them accessible for echocardiographic diagnosis. It was noteworthy that 11 of the 18 patients had chromosomal abnormalities, 9 of them presenting with trisomy-18.

Aortic Valve↗
PubMed1991

Calculation of normal tissue complication probability and dose-volume histogram reduction schemes for tissues with a critical element architecture.

We investigate a model of normal tissue complication probability for tissues that may be represented by a critical element architecture. We derive formulas for complication probability that apply to both a partial volume irradiation and to an arbitrary inhomogeneous dose distribution. The dose-volume isoeffect relationship which is a consequence of a critical element architecture is discussed and compared to the empirical power law relationship. A dose-volume histogram reduction scheme for a "pure" critical element model is derived. In addition, a point-based algorithm which does not require precomputation of a dose-volume histogram is derived. The existing published dose-volume histogram reduction algorithms are analyzed. We show that the existing algorithms, developed empirically without an explicit biophysical model, have a close relationship to the critical element model at low levels of complication probability. However, we also show that they have aspects which are not compatible with a critical element model and we propose a modification to one of them to circumvent its restriction to low complication probabilities.

Algorithms↗
PubMed1994

An architecture for EEG signal processing and interpretation during sleep (ESPIS).

The project's aim is to develop a dedicated workstation in order to process multiple channels of electrophysiological signals in real-time during sleep. In ESPIS we are aiming to define both an architecture and an environment for EEG signal interpretation in medicine based on computer science gold standards (Unix, XWindow, Motif). Signal processing and pattern recognition analysis are provided by parallel processing on a specific developed acquisition architecture (DSP) based on transputers. The main result is a high performance prototype demonstrating signal interpretation during sleep which has already been tested in a medical environment. The overall specifications allow this biomedical device to be extended to other types of medical signals.

Algorithms↗
PubMed1990

A knowledge-based architecture for protein sequence analysis and structure prediction.

Methods for analyzing the amino-acid sequence of a protein for the purposes of predicting its three-dimensional structure were systematically analyzed using knowledge engineering techniques. The resulting entities (data) and relations (processing methods and constraints) have been represented within a generalized dependency network consisting of 29 nodes and over 100 links. It is argued that such a representation meets the requirements of knowledge-based systems in molecular biology. This network is used as the architecture for a prototype knowledge-based system that simulates logically the processes used in protein structure prediction. Although developed specifically for applications in protein structure prediction, the network architecture provides a strategy for tackling the general problem of orchestrating and integrating the diverse sources of knowledge that are characteristic of many areas of science.

Amino Acid Sequence↗
PubMed1989

Structure and supramolecular architecture of membrane channel-forming peptides.

Peptides gathering together to induce channels in lipid bilayers may be classified in several categories according to the spatial structures involved. For example, gramicidin A forms intramolecular tubes, alamethicin, bundles of helical rods with intermolecular pores, porins (being proteins, properly speaking) are rich in beta-sheets that may form barrels, whereas cyclic peptides might stack together resulting in the formation of pores. The chemical structure of these compounds is now well characterized. The transmembrane electrical signals that they transmit are also typical of the particular supramolecular configurations (or architecture). Investigations in this field are thus relevant to structure-function relationship studies due to the availability of natural or synthetic analogues allowing the measurement of the influence of physico-chemical parameters upon the energy profiles of the pores. Consequently, questions such as the existence and probabilities of conductance substrates, their voltage-dependence and their ion or molecular selectivity can be tackled. Today, the loosest aspect of these studies lies in the actual molecular conformations and architecture in the membranes of the peptide aggregates, the knowledge of which remains imprecise, even 'at rest' in the best-studied cases. This review attempts to point out still unresolved questions and to propose some plausible approaches concerning, for example: 1) the configurations of the molecular aggregates responsible for ion transfer; 2) the mechanisms for channel-opening and closing (gating); 3) the eventual cooperative phenomena between channels, via the bilayer or interfacial components. Possible applications of these structures will be tentatively outlined.

Alamethicin↗
PubMed1990

Architecture of selected wrist flexor and extensor muscles.

The architectural features of 25 wrist flexor and extensor muscles were studied. Muscles included the flexor carpi ulnaris, the flexor carpi radialis, the extensor carpi ulnaris, the extensor capri radialis brevis, and the extensor carpi radialis longus. Muscle length, mass, fiber pennation angle, fiber length, and sarcomere length (by use of laser diffraction techniques) were determined. In addition, physiological cross-sectional area and fiber length/muscle length ratio were calculated. The muscles were found to be highly specialized, with architectural features of same muscles very similar. The fiber length/muscle length ratio, muscle length, and pennation angle represented the major differences between muscles. Thus using these parameters in discriminant analysis permitted correct identification of each of the 25 muscles. In terms of size and intrinsic design, these individual muscles were highly specialized for their function.

Forearm↗
PubMed1992

Architectural design of the human intrinsic hand muscles.

The architectural features of twenty different muscles (18 intrinsics and 2 thumb extrinsics, n = 180 total muscles) were studied. Muscle length, mass, fiber pennation angle, fiber length, and sarcomere length were determined. From these values, physiologic cross-sectional area and fiber length/muscle length ratio were calculated. Intrinsic muscle lengths were relatively similar to one another, which we interpreted as representing a space constraint within the hand. However, several specialized architectural designs were observed: lumbrical muscles had an extremely high fiber length/muscle length ratio, implying a design toward high excursion. The first dorsal interosseous and adductor pollicis had physiologic cross-sectional areas comparable to those of extrinsic muscles and much greater than those of the other intrinsic muscles. The interosseous muscles had relatively high physiologic cross-sectional areas with low fiber length/muscle length ratios, suggesting their adaptation for high force production and low excursion. Taken together, these observations illustrate the underlying structural basis for the functional capacities of the intrinsic muscles.

Hand↗
PubMed1993

Tetralogy of Fallot, truncus arteriosus, abnormal myocardial architecture and anomalies of the aortic arch system induced by bis-diamine in rat fetuses.

OBJECTIVES: The aim of this study was to analyze the relation between anomalies of the heart and aortic arch arteries in near-term rat fetuses exposed to the chemical bis-diamine. BACKGROUND: Bis-diamine is known to induce cardiovascular anomalies. METHODS: Bis-diamine was given orally to normal pregnant rats, and the 65 fetuses were examined under a dissecting microscope after formalin fixation. RESULTS: There were 26 rat fetuses (40%) with a ventricular septal defect in the perimembranous portion, of which 14 (22%) had tetralogy of Fallot, 4 (6%) had truncus arteriosus and 8 (12%) had a relatively small defect with no other major anomalies. In 44 fetuses (68%) the middle latitudinal muscle bundle of the ventricular septum was continuous with the right ventricular free wall. There were, isolated or in association, a double- or right aortic arch in 6 fetuses (9%), aberrant subclavian arteries in 9 (14%), right ductus arteriosus in 12 (18%) and agenetic ductus in 4 (6%). The cross-sectional area of the ductus, as corrected by that of the aortic isthmus, was abnormally small in 47 rats (72%). The rat fetuses with a septal defect or abnormal myocardial architecture, or both, usually had a small ductus; it was very small or absent in those fetuses with tetralogy of Fallot. Of the four fetuses with truncus arteriosus, two had a vestigial vasculature on the truncus root and three had a rudimentary infundibulum. CONCLUSIONS: The cardinal defect may be the anomalous and reduced development of the sixth arch arteries, which by imposing pressure overload on the fetal right ventricle, may have led to either or both the persistence of ventricular septal defect as a vent or the formation of myocardial architecture favorable for the generation of pressure in the right ventricle.

Abnormalities, Drug-Induced↗
PubMed1995

Epidermal architecture that depends on turnover time.

The concept of epidermal architecture that depends on epidermal turnover time is described. The epidermal architecture is determined, not by a simple proliferative condition, but rather by an epidermal turnover time (that depends both on cell number as well as on the proliferative condition). This is in relation to 'keratinization process' that requires a definite time to be completed. Using the concept, hyperproliferative 'psoriasiform' epidermis and hypoproliferative 'atrophic' epidermis are naturally described.

Atrophy↗
PubMed1990

A model of vertebral trabecular bone architecture and its mechanical properties.

An idealized, structural model of vertebral trabecular bone is presented. The architecture of the model (thick vertical columns and thinner horizontal struts) is based on studies of samples taken from the central part of vertebral bodies from normal individuals aged 30 to 90 years. With trabecular diameters and spacings typical for persons aged 40, 60, and 80 years respectively, the model accounts reasonably well for age-related changes in vertical and horizontal stiffness and trabecular bone volume, as seen in experimental data. By introducing a measure for the randomness of lattice joint positions in the modeled trabecular network, it is demonstrated that the apparent stiffness varies by a factor of between 5 and 10 from a perfect cubic lattice to a network of maximal irregularity, even though trabecular bone volume remains almost constant. A considerable change in mechanical behaviour is also seen, without changing the overall trabecular bone volume, when the bone material is slightly redistributed among vertical and horizontal trabeculae. It is concluded that measured bone mass should not be the sole indicator of trabecular bone biomechanical competence (stiffness and stress). It is crucial that measurements of bone density are considered in combination with a detailed description of the architecture.

Adult↗