Circumferential Fibers Research Articles

A biomechanical model of agonist-initiated contraction in the asthmatic airway.

This paper presents a modelling framework in which the local stress environment of airway smooth muscle (ASM) cells may be predicted and cellular responses to local stress may be investigated. We consider an elastic axisymmetric model of a layer of connective tissue and circumferential ASM fibres embedded in parenchymal tissue and model the active contractile force generated by ASM via a stress acting along the fibres. A constitutive law is proposed that accounts for active and passive material properties as well as the proportion of muscle to connective tissue. The model predicts significantly different contractile responses depending on the proportion of muscle to connective tissue in the remodelled airway. We find that radial and hoop-stress distributions in remodelled muscle layers are highly heterogenous with distinct regions of compression and tension. Such patterns of stress are likely to have important implications, from a mechano-transduction perspective, on contractility, short-term cytoskeletal adaptation and long-term airway remodelling in asthma.

Architecture of the left ventricle: insights for optimal surgical ventricular restoration

The normal left ventricular shape has been defined as prolate ellipsoid. This shape is an adaptation to evolution. A knowledge of its unique macro and micro architecture forms the cornerstone in the understanding of its complex function. The left ventricle has a unique architecture with three different myofiber orientations, the longitudinal, circumferential and oblique fibers. The oblique orientation of fibers is essential for effective clockwise and anticlockwise torsional movements during systole and diastole, for optimal ventricular ejection and filling. The orientation and fiber angle decide the shape of the ventricle. An ellipsoid shape is vital for optimal function. Pathological disease states such as ischemic heart disease, valvular heart disease and cardiomyopathies cause a loss of obliquity of the myofibers. The myofibers become more horizontal resulting in ventricular dilatation and increased sphericity. The change from ellipsoid to globular shape with disease heralds the onset of left ventricular dysfunction and initiates the cascade of heart failure. Several strategies have been successful in reverting ventricular dilatation and sphericity to a more ellipsoid geometry. Pharmacological therapies like beta blockade and angiotensin converting enzyme inhibition have proven beneficial in early stages of heart failure with pathological remodeling. However, these agents in isolation are limited in reversing pathological remodeling in advanced heart failure. In some cases of advanced heart failure due to postinfarction left ventricular aneurysms, ventricular volume reduction with restoration surgeries have a role in restoring ventricular geometry with beneficial clinical outcomes. Surgical ventricular restoration has progressively evolved from the 1950s. Initially, aneurysmal resection and linear repair was done. This was gradually replaced by endoventricular patch plasty, which had better results. The resulting left ventricle was smaller in size but still continued to have a spherical configuration. Exclusion of the infarct area with a smaller longitudinal patch results in realignment of the non-diseased ventricular fibers with a resulting ellipsoid shape. This ellipsoid shape ensures clinical benefits. The geometry of the endoventricular patch thus holds the key to optimal ventricular shape in these patients. The technique to optimally restore a diseased ventricle to normal continues to evolve. This requires insights into the normal architecture and function, and the pathophysiologic effects of disease.

Collagen orientation in periosteum and perichondrium is aligned with preferential directions of tissue growth

A feedback mechanism between different tissues in a growing bone is thought to determine the bone's morphogenesis. Cartilage growth strains the surrounding tissues, eliciting alterations of its matrix, which in turn, creates anisotropic stresses, guiding directionality of cartilage growth. The purpose of this study was to evaluate this hypothesis by determining whether collagen fiber directions in the perichondrium and periosteum align with the preferential directions of long bone growth. Tibiotarsi from chicken embryos across developmental stages were scanned using optical projection tomography (OPT) to assess preferential directions of growth at characteristic sites in perichondrium and periosteum. Quantified morphometric data were compared with two-photon laser-scanning microscopy images of the three-dimensional collagen network in these fibrous tissues. The diaphyseal periosteum contained longitudinally oriented collagen fibers that aligned with the preferential growth direction. Longitudinal growth at both metaphyses was twice the circumferential growth. This concurred with well-developed circumferential fibers, which covered and were partly interwoven with a dominant network of longitudinally oriented fibers in the outer layer of the perichondrium/periosteum at the metaphysis. Toward both articulations, the collagen network of the epiphyseal surface was randomly oriented, and growth was approximately biaxial. These findings support the hypothesis that the anisotropic architecture of the collagen network, detected in periosteum and perichondrium, concurs with the assessed growth directions.

Tympanic Membrane Collagen Fibers: A Key to High‐Frequency Sound Conduction

To investigate the significance of tympanic membrane collagen fiber layers in high frequency sound transmission. Human cadaver temporal bone study. Laser Doppler vibrometry was used to measure stapes footplate movement in response to acoustic stimulation. The tympanic membrane was altered by creating a series of slits and applying paper patches to isolate the effects of specifically oriented collagen fibers. Three groups of membrane alterations were evaluated: 1) circumferentially oriented slits involving each quadrant to primarily disrupt radial fibers, made sequentially within superior-anterior, inferior-anterior, inferior-posterior, and superior-posterior quadrants; 2) the same slits made in the reverse order; and 3) radially oriented slits from the umbo to the annulus to primarily disrupt circumferential fibers. For each group, measurements of the middle-ear cavity pressure, ear canal pressure, and stapes velocity were made each time the tympanic membrane was altered. Regardless of the order in which the circumferentially oriented slits were made, there was a consistent decrease in stapes velocity above 4 kHz for the third and fourth cuts compared to the control. The mean decrease in the range of 4 to 12.5 kHz was 11 dB for the third patched slit and 14 dB for the fourth patched slit (P < .01). Radially oriented slits appear to produce smaller effects. Radial collagen fibers in the tympanic membrane play an important role in the conduction of sound above 4 kHz.

The extent of laceration of circumferential fibers with suture repair of the knee meniscus

Cannulas used with suture based meniscal repair techniques can potentially injure the load transmitting fibers of the meniscus. The subject of this study was to quantify this effect in a porcine in vitro model. From fresh frozen medial porcine menisci tissue specimens were harvested following the course of the peripheral circumferential fibers bundles. In the first part of the study the tissue samples were perforated with the cannulas of either a Fast Fix or a Rapidloc device or with an 18-gauge needle. The specimens were then visually inspected for fiber damage using low power microscopy and the mean size of the laceration was measured. Finally, the extent of the tissue laceration was indirectly determined using non-contact strain measurements of the samples before and after puncture. When advanced with the cutting edge perpendicular to the fibers, the cannulas consistently cut the fibers while those were rather separated with the opposite orientation. It could be shown that specimens with a mean width of 8.1 mm lost 25% of the load transmitting cross section when being perforated two times with a Fast Fix device (P < 0.001). This effect is negated when the cannula was oriented in line with the fibers. Cannulas used for suture based meniscal repair can cause a substantial laceration of the meniscal tissue. The effect strongly depends on the orientation of the cutting edge of the cannula relative to the course of the fibers and can thus potentially be avoided by an appropriate handling and design.

Focal Arrhythmia Confined Within the Coronary Sinus and Maintaining Atrial Fibrillation

The coronary sinus (CS) is a complex structure comprising a mesh of circumferential muscular fibers with oblique connections to both atria. We describe further evidence for the clinical importance of CS arrhythmogenicity in maintaining atrial fibrillation (AF) in humans. Since January 2004, following a sequential approach, the CS and the inferior left atrium were ablated in 144 patients with symptomatic drug refractory AF. Patients were included for analysis when this step resulted in the electrical dissociation of the CS from both atria with restoration of sinus rhythm, but with continued arrhythmic activity in the CS. The electrophysiologic mechanism of the confined arrhythmia was considered as focal activity (automaticity or triggered activity) by the presence of electrograms spanning less than 75% of the cycle length in the CS. After restoration of sinus rhythm, four male patients (3% of the patients, three persistent and one permanent AF) were identified in whom arrhythmia continued within the CS. Repetitive activity confined to the disconnected CS was inconsistent in occurrence, as well as in duration (1 sec to 15 min) and cycle length (from 158 to 380 ms). For all four patients, electrogram mapping of the entire CS was compatible with a focal mechanism. In two patients, bursts alternating with slow dissociated activity suggested automaticity. In one patient, local activity consistently coupled to the previous sinus beat favored triggered activity. This study provides evidence that the CS may be a potential source of focal rapid activity maintaining AF.

Free Vibration of Composite Annular Plates Embedded with SMA Fibers in the Circumferential Direction

Based on Brinson’s one-dimensional thermo-constitutive law of SMA and classical plate theory, linear non-axisymmetric vibration of uniform heated composite annular plate embedded with circumferential SMA fibers is investigated. Natural frequencies of the annular plates with immovably clamped boundary condition, depending on the temperature rise are obtained by using shooting method. The characteristic curves of first four natural frequencies of non-axisymmetric vibration versus temperature rise are plotted. Influences of the volume fraction and the initial strain of SMA on the natural frequencies of plate are analyzed. The numerical results show that, the activation of SMA can enhance the natural frequency both in the inverse martensite transformation temperature range and the thermal buckling temperature.

Influence of fibre orientation and stacking sequence on petalling of glass/polyester composite cylindrical shells under axial compression

The energy absorbing capability of FRP composite cylindrical tubes used as energy absorbers, by destroying itself progressively, depends on the way in which the tube material is crushed i.e., trend of petalling. This paper investigates the influence of fibre orientation and stacking sequence on the petal formation and specific energy absorption (SEA) of four and six-ply, 0°/90° glass/polyester composite cylindrical shells under axial compression. Number of petals formed and the trend of petalling are changed with proportion of axial (0°) and circumferential (90°) fibre content and stacking sequence in the tubes. In the tubes undergo petalling, presence of axial fibres close to inner surface and the proper proportion of circumferential fibres close to outer surface of the tube wall lead to higher energy dissipation. The axial fibres placed nearer to outer surface leads to more number of petal formation, leading to a stable crushing mechanism. The contribution of mode I strain energy release rate ( G Ic) to the energy dissipation in the form of circumferential delamination is also studied with double cantilever beam (DCB) tests. Analytical model which considers petalling is developed, and used to predict the mean crush load and SEA of cylindrical composite shells under axial compression. Results from the analytical model agree well with experimental results and are presented.

Modified cruciate suture technique for arthroscopic meniscal repair: a technical note

Arthroscopic meniscal repair is the procedure of choice whenever a reparable tear is diagnosed. The cruciate suture for arthroscopic meniscal repair is a type of the outside-in technique. It has advantages like: (1) its ultimate tension load (UTL) is 1.6 times higher than the UTL of the vertical suture (gold standard), (2) it holds the circumferential collagen fibers of the meniscus in a three-dimensional plane compared to the vertical and horizontal sutures which hold the circumferential fibers of the meniscus in a two-dimensional plane, (3) simple instrumentation, (4) could withstand not only distraction forces on the repaired meniscal tear but also, shear forces because of the oblique orientation of the cruciate suture limbs. It has disadvantages like: being difficult to perform and time-consuming. A modified technique is presented in this study which has the following advantages; (1) less time-consuming, (2) performed through a smaller skin incision, (3) a sliding knot is used to tie the cruciate suture.

Diffusion Tensor Magnetic Resonance Imaging Mapping the Fiber Architecture Remodeling in Human Myocardium After Infarction

Diffusion tensor magnetic resonance imaging (DT-MRI) provides a means for nondestructive characterization of myocardial architecture. We used DT-MRI to investigate changes in direction-dependent water diffusivity to reflect alterations in tissue integrity (trace apparent diffusion coefficients [ADCs] and fractional anisotropy [FA]), as well as indicators of remodeling of fiber helix angles, in patients after myocardial infarction. Thirty-seven patients (35 men, 2 women; median age, 59) after acute myocardial infarction (median interval from onset, 26 days) were enrolled. DT-MRI was performed at the midventricular level to measure trace ADC, FA, and helix angles of myofibers. Helix angles were grouped into left-handed helical fibers, circumferential fibers, and right-handed helical fibers. Measurements were correlated with viability and regional wall motion assessed by contrast-delay-enhancement and cine MRI, respectively. The infarct zone showed significantly increased trace ADC and decreased FA than the remote zone. The percentage of left-handed helical fibers increased from the remote zone (mean +/- SD, 13.3 +/- 5.8%) to the adjacent zone (19.2 +/- 9.7%) and infarct zone (25.8 +/- 18.4%) (MANOVA, P = 0.004). The percentage of right-handed helical fibers decreased from the remote zone (35.0 +/- 9.0%) to the adjacent zone (25.5 +/- 11.5%) and infarct zone (15.9 +/- 9.2%) (P < 0.001). Multiple linear regression showed that the percentage of left-handed helical fibers of the infarct zone was the strongest correlate of infarct size and predictor of ejection fraction. In vivo DT-MRI of postinfarct myocardium revealed a significant increase in trace ADC and a decrease in FA, indicating altered tissue integrity. The redistribution of fiber architecture correlated with infarct size and left ventricular function. This technique may help us understand structural correlates of functional remodeling after infarction.

Determination of strain energy function for arterial elastin: Experiments using histology and mechanical tests

The long-range reversible deformation of vertebrate arteries is primarily mediated by elastin networks that endure several million deformation cycles without appreciable fatigue. To determine how elastin contributes to the composite arterial properties, we studied the three-dimensional microstructure and biomechanics of isolated elastin. We initially estimated the sensitivity of these studies by comparing two elastin isolation protocols, autoclaving and alkali-extraction, and measured their effect on isolated elastin using uniaxial tests and histology. These studies show that autoclaved tissues have (1) a trend for higher modulus ( 900.79 ± 678.02 kPa ) than alkali-extracted samples ( 417.74 ± 162.23 kPa ) albeit with higher collagen–proteoglycan impurities, and (2) greater optical density ( 78.6 ± 9.1 % ) than alkali-extracted groups ( 46.2 ± 5.9 % ) , suggesting that autoclaving is superior to alkali-extraction for biomechanical tests on elastin. Using these data we show that an isotopic Mooney–Rivlin model cannot adequately represent arterial elastin. The neo-Hookean model, with coefficient 162.57 ( ± 115.44 ) kPa for autoclaved and 76.94 ( ± 27.76 ) kPa for alkali-extracted samples, fits the uniaxial data better. Autoclaved elastins also show linear stress–strain response and equal stiffness in circumferential and axial directions suggesting equal number of layers in these directions and that elastin may help distribute tensile stresses during vessel inflation. Histology of autoclaved and control porcine arteries reveals axial elastin fibers in intimal and adventitial layers but circumferential medial fibers. We propose an orthotropic material symmetry for arterial elastin with two orthogonally oriented and symmetrically placed mechanically equivalent fibers. An exact form of the constitutive equation will be obtained in a future study.

Subclinical Left Ventricular Dysfunction in Migraine Attacks

The aim of the present study was to evaluate cardiac performance of patients with migraine attacks during the overload produced by phenylephrine infusion. Background.-It is known that circulatory changes occur during migraine. However, the relationship between this finding and transient cardiac dysfunction is still unknown. By means of two-dimensional direct M-mode echocardiography, we measured fractional shortening, ejection fraction, and mean velocity of circumferential fibers shortening in 18 patients with migraine and in 10 normal subjects as a control group. These measures were performed in two different periods: during attack-free intervals and during attacks. Pain intensity of typical migraine attack was evaluated on a 0 to 10 scale. Cardiac size and function were normal at rest in both groups. However, during migraine attacks, phenylephrine infusion provoked significant decrease in fractional shortening, EF, and mean velocity of circumferential fibers shortening, followed by concomitant increase of headache severity. On the other hand, during the attack-free interval and in the control group phenylephrine infusion did not show significant changes in cardiac function parameters. Our data suggest that left ventricular dysfunction during the phenylephrine test could participate in the complex pathophysiological mechanism of migraine attacks.

Pseudoblock and pseudoconduction across the cavotricuspid isthmus

Ablation of typical atrial flutter is dependent on creating a line of block in the inferior vena cava-tricuspid annulus isthmus (CTI), a critical part of the macroreentrant circuit. 1 Saoudi N. Atallah G. Kirkorian G. Touboul P. Catheter ablation of the atrial myocardium in human type I atrial flutter. Circulation. 1990; 81: 762-771 Crossref PubMed Google Scholar , 2 Cosio F.G. Lopez G.M. Goicolea A. Arribas F. Barrosa J.L. Radiofrequency ablation of the inferior vena cava-tricuspid valve isthmus in common atrial flutter. Am J Cardiol. 1993; 71: 705-709 Abstract Full Text PDF PubMed Scopus (511) Google Scholar Success of the linear lesion is confirmed by the presence of bidirectional block during pacing maneuvers from the low lateral right atrium and proximal coronary sinus (CS). 3 Poty H. Saoudi N. Nair M. Radiofrequency catheter ablation of atrial flutter: Further insights into the various types of isthmus block. Application to ablation during sinus rhythm. Circulation. 1996; 94: 3204-3213 Crossref PubMed Scopus (282) Google Scholar , 4 Cauchemez B. Haissaguerre M. Fischer B. Electrophysiological effects of catheter ablation of inferior vena cava-tricuspid annulus isthmus in common atrial flutter. Circulation. 1996; 93: 284-294 Crossref PubMed Scopus (307) Google Scholar The ability to accurately assess CTI block during CS pacing is dependent on at least two critical assumptions: (1) when pacing from the CS, the impulse does not propagate across the crista terminalis, and (2) clockwise activation of the CTI during CS pacing occurs via circumferential muscle fibers surrounding the CS rather than by superior transseptal propagation across Bachmann’s bundle.

Proteoglycan 4 (PRG4) synthesis and immunolocalization in bovine meniscus

Proteoglycan 4 (PRG4) is synthesized and secreted into the synovial fluid by articular chondrocytes and synovial cells, lining the cavity of joints. A thin layer of PRG4 is also present at the articular surface, where it appears to be involved in boundary lubrication. This study investigated if PRG4 is also synthesized and secreted by the cells within meniscus, and if PRG4 is also present in, and at the surface of, meniscus. PRG4 was visualized in sections of bovine calf menisci by immunohistochemistry. PRG4 was detected in two regions: (1) at the femoral and tibial surfaces of the meniscus, and within cells below these surfaces; and (2) within and near cells along the radial tie fibers and circumferential fibers. From meniscus tissue harvested from these surfaces, PRG4 was extracted with 4 M GuHCl and quantified by ELISA. There was 0.20 ± 0.01 and 0.25 ± 0.04 μg PRG4/cm 2 area of lateral and medial meniscus surface, respectively. ELISA analysis of spent medium from other samples of meniscus surface tissue incubated in medium supplemented with serum and ascorbate showed that 8.1 ± 1.1 μg PRG4/cm 2 area of meniscus surface was secreted over six days. These results demonstrate that PRG4 is synthesized and secreted by certain cell populations in the meniscus, and that PRG4 is present in the meniscus at surfaces and also internal fibers where it may contribute to boundary lubrication.

Conduit arterial stiffness is associated with impaired left ventricular subendocardial function

Longitudinal function of the left ventricle is governed by the subendocardial myocardial fibres, whereas radial function is due mainly to contraction of circumferential fibres, localised in the subepicardial layer of the myocardium.1 In patients with diabetes or hypertension the subendocardial fibres are more likely to be affected by microvascular ischaemia. This can be caused by structural changes in the coronary vasculature that reduce myocardial perfusion such as arterial wall thickening, decreased capillary density, and periarteriolar fibrosis, and by haemodynamic changes such as increased wall stress, and the microcirculatory effects of endothelial dysfunction.2 Since tissue Doppler echocardiography can now assess longitudinal and radial myocardial velocities separately, we tested the further hypothesis that subendocardial dysfunction is related to conduit arterial stiffness. ### Study group We studied 83 subjects (mean (SD) age 54 (12) years, 59 men), including 27 normal individuals and 56 patients with varying degrees of left ventricular (LV) dysfunction caused by diabetes (35), hypertension (17), and ischaemic dilated cardiomyopathy (4). We excluded patients not in sinus rhythm, or with ventricular aneurysm or severe regional wall motion abnormalities, mitral or aortic stenosis, or more than mild valvar regurgitation. Twenty nine patients were taking an angiotensin converting enzyme (ACE) inhibitor, 23 a diuretic, 8 a β blocker, 27 a statin, and 7 a calcium antagonist. The protocol was approved by the local research ethics committee, and …

Is the circumferential tensile modulus within a human medial meniscus affected by the test sample location and cross-sectional area?

Quantifying the material properties of the human menisci is paramount to understanding their biomechanical functions within the knee. One important intrinsic material property governing the biomechanical functions of the meniscus is the circumferential tensile modulus. The purpose of this study was to determine if the circumferential tensile modulus of the human medial meniscus depends on the location and thickness of the sample tested. The following three hypotheses were tested: (a) the circumferential location (anterior, central, and posterior) does not significantly affect the tensile modulus, (b) the radial location (inner to outer) significantly affects the tensile modulus, and (c) the thickness (cross-sectional area) significantly affects the tensile modulus. Test samples, whose length was oriented in parallel with the circumferential collagen fibers, were collected from different circumferential and radial locations throughout 30 human medial menisci. Samples of three different thicknesses (0.5, 1.5, and 3.0 mm) were taken from three equal groups of 10 menisci (i.e., one thickness per group). The circumferential tensile modulus was measured under quasi-static loading. Statistical analysis showed no significant effect of the circumferential or radial location of the sample on the circumferential tensile modulus. This indicates that an overall circumferential tensile modulus may be calculated for the human medial meniscus by averaging the values determined at the various locations. However, the thickness of the test sample had a significant effect on the measured circumferential tensile modulus; the modulus varied inversely with the thickness. Thus, moduli determined from test samples that are too small in cross-sectional area overestimate the effective modulus of the tissue on the whole, and the cross-sectional area of the sample must be considered when determining a representative circumferential tensile modulus for the medial meniscus in a human knee.

Left Ventricular Midwall Mechanics in Healthy Children and Adolescents

The assessment of left ventricular function in pediatric age generally has been made by measuring the extent and velocity of fiber shortening at the endocardium and relating these parameters to systolic wall stress. It has been suggested from animal and human studies that this “endocardial method” can result in an overestimation of myocardial function when healthy hearts and those with hypertrophy are compared. Thus an assessment of left ventricular pump function and contractility that takes into account the epicardial migration of the midwall circumferential fibers during systole (midwall analysis) is warranted. Although the normal range for midwall indexes of left ventricular mechanics has been established in adult subjects, up to now it has not been studied in pediatric subjects. To establish normal values for left ventricular midwall mechanics, 70 healthy children ranging in age from 3 days to 18 years were evaluated with 2-dimensional and M-mode echocardiography. Midwall fractional shortening (FSmw), rate-corrected mean velocity of circumferential fiber shortening (VCFcmw), and the relation between these indexes and left ventricular end-systolic wall stress (ESS) were calculated separately for the children younger than 2 (group 1, 20 subjects) and older than 2 (group 2, 50 subjects) years of age. Group 1 had significantly higher FSmw and VCFcmw compared with group 2. An inverse linear relation between FSmw and ESS and between VCFcmw and ESS was found in both age groups. The y-intercept was higher in group 1, and the slope of the mean regression line was steeper than in group 2 for both the relationships, suggesting an age-dependent midwall left ventricular pump function and contractility. These normative data can be used to assess the left ventricular midwall mechanics in pediatric patients with pressure or volume overload. (J Am Soc Echocardiogr 1999;13:932-40.)

Pulsed Tissue Doppler Imaging of Left Ventricular Systolic and Diastolic Wall Motion Velocities to Evaluate Differences Between Long and Short Axes in Healthy Subjects

Our objective was to evaluate in healthy subjects the left ventricular (LV) wall motion velocities along the long and short axes by means of pulsed tissue Doppler imaging (TDI) to clarify the differences in the LV systolic and diastolic function between both axes. Wall motion velocities were recorded at the mid-wall portion of the middle site of the LV posterior wall in the parasternal long-axis view, and at the subendocardial portion of the middle site of the LV posterior wall in the apical long-axis view by pulsed TDI in 35 healthy subjects (mean age 26 ± 10 years, mean heart rate 72 ± 7 bpm). In all subjects, the LV pressure curve, its first derivative (dP/dt), the LV wall motion velocity, the phonocardiogram, and the electrocardiogram were simultaneously recorded. The systolic wave of the LV posterior wall motion velocity exhibited 2 peaks: the first and second systolic waves (Sw l and Sw 2 , respectively). The diastolic wave also exhibited 2 peaks, the early diastolic and atrial systolic waves. The Sw l along the long axis was greater than either the Sw 1 and Sw 2 along the short axis or the Sw 2 along the long axis. The peak Sw 1 along the long axis coincided with the peak dP/dt and was slightly earlier than the peak Sw l along the short axis. The onset of Sw 1 along the long axis coincided with the onset of the first heart sound. The Sw 2 along the short axis was greater than that along the long axis. The early diastolic wave along the short axis was greater than that along the long axis, whereas the atrial systolic wave along the long axis was greater than that along the short axis. Thus, in healthy subjects, shortening of the longitudinal fibers predominated over that of the circumferential fibers during early systole, whereas shortening of the circumferential fibers predominated over the longitudinal fibers during the ejection phase. During diastole, the circumferential fibers predominated in the LV wall expansion at early diastole, whereas the longitudinal fibers predominated at atrial systole. In conclusion, pulsed TDI provided information that is useful in understanding the characteristics of LV wall motion along the long and short axes. (J Am Soc Echocardiogr 1999;12:308-13.)

Demonstration of a Dynamic Polymer Composite Connector

This paper introduces the dynamic polymer composite (DPC) connector concept for creating structural joints of tubular composite members. DPC connectors are fiber-reinforced tubular elements featuring pretensioned circumferential fibers and a thermoplastic matrix. Application of heat softens the thermoplastic, allowing the circumferential fibers to clamp the connector onto the tubes to be joined. A laboratory demonstration of the DPC connector concept is described. General design relationships are presented to relate the basic performance measures to material properties and prestress levels. The need to maximize certain properties of the prestressing fiber and the thermoplastic matrix is discussed.

Myocardial fiber architecture and left ventricular function

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.