USING THE RESERVOIR WAVE APPROACH TO STUDY THE HORIZON EFFECT

INTRODUCTION Differing theories and models have been explored in the field of arterial hemodynamics in an effort to better understand how the blood flows in the body. The existence of discrete reflection sites remains a source of disagreement. As a wave proceeds along an artery, any local change in impedance will result in partial reflection. Thus, because of the great complexity of the arterial system, it has been suggested that no distinct reflector sites should exist. On the other hand, there is recent experimental evidence using the reservoir-wave approach (RWA) that implies discrete positive and negative reflection sites. The pattern of wave propagation and reflection is plausible, as are the modifications produced by pharmacologic interventions [1]. The classical, frequency-domain, “impedance analysis” approach uses Fourier analysis to break down pressure and flow waveforms into summations of sinusoids, resulting in an impedance spectrum [2]. The RWA is a novel alternative, positing that measured pressures and flows are the instantaneous sums of “excess” (wave-related) and reservoir (volume-related) components [2]. The “Horizon Effect” (HE) [3] implies that a reflector site can never be reached no matter how far into the periphery one measures (Figure 1). As such, it supports the idea that there are no distinct reflector sites. Measuring peripheral pressure and flow and using the RWA, the purpose of this study was to evaluate the HE and the question of fixed reflector sites. METHODS Eight anesthetized pigs were catheterized and pressure and flow were measured simultaneously at 4 locations: the aortic root and the brachial, carotid and renal arteries. Pharmacologic interventions were used to manipulate propagation and reflection patterns. MatLab (The MathWorks Inc., Natick, MA) was used to calculate the reservoir pressure, the local wave speed and to carry out wave intensity analysis (WIA) to obtain the forwards and backwards components of pressure. RESULTS Analysis has been completed on 4 of the 8 animals studied. Each showed minimal backward wave activity at the aortic root and in the carotid artery. However, in the brachial and renal arteries, no backward waves could be detected. DISCUSSION AND CONCLUSIONS Backward waves were scarcely detected in the periphery using either the RWA or classical analysis. This may suggest that the pig model was inappropriate to study the HE. Porcine anatomy does not allow measurement at remote peripheral sites and reflection sites cannot be studied if no reflections are to be found. Further analysis of the data is needed before more definitive conclusions can be made

LONG TERM IN VIVO KINEMATICS OF THE OVINE STIFLE JOINT FOLLOWING ANTERIOR CRUCIATE LIGAMENT TRANSECTION

INTRODUCTION Osteoarthritis (OA) is a degenerative joint disease involving the breakdown of articular cartilage, which is common after injury or with aging1. Following knee injury, sheep develop OA at a slightly accelerated rate compared to humans but with some similar patterns2. In an ovine knee injury model3,4, altered gait mechanics and degradation of the cartilage has been observed 20 weeks post anterior cruciate ligament (ACL) transection (Tx) surgery; however, potential alterations in gait at 40 weeks post ACL Tx surgery remain to be determined. Therefore, the objective of this study was to investigate the in vivo kinematics of the ovine stifle joint over time (20 weeks and 40 weeks) following ACL Tx. METHODS Force Plate Testing. Three skeletally mature 3 to 4-year-old female Suffolk-cross sheep (average weight 77.1kg) were led across an embedded force platform (Kistler Instrumente, Winterthur, Switzerland) until 20 hind limb hoof strikes were recorded at 1200 Hz. Peak hind limb vertical ground reaction force was determined prior to surgical plate implantation, and then serially prior to each kinematic data collection. Surgical Procedure. All sheep had a bone plate implanted onto each of the proximomedial aspect of the tibia and the distolateral aspect of the femur of their right hind limb, four weeks prior to kinematic testing. Kinematic Collection and Bone Digitization. On the day of kinematic testing, a stainless steel post was attached to each plate and an instrumented spatial linkage (ISL) mounted between them. The ISL consisted of six rotational encoders providing a measurement of position and orientation in six degrees of freedom (6-DOF) to its motion throughout gait. The in vivo kinematics of the stifle joint were measured while the sheep walked on a treadmill at 2 mph (0.89 m/s). Each sheep then underwent arthroscopic ACL Tx surgery on their right hind limb. The in vivo gait kinematics were measured again over time at 20 and 40 weeks post ACL Tx. Following kinematic testing at 40 weeks, the animals were euthanized. A coordinate measuring machine was used to measure anatomic landmarks on the bone with respect to the ISL in order to create an anatomically relevant coordinate system. Analysis. Data are presented as mean ± SD. RESULTS Figure 1: The 6-DOF in vivo gait kinematics of the ovine stifle joint, intact (black), 22 weeks post ACL Tx (red), and 40 weeks post ACL Tx (blue). DISCUSSION AND CONCLUSIONS These data indicate that the in vivo kinematics of the ovine stifle joint do change over time following ACL Tx. The kinematic changes appear to be more drastic after 22 weeks, and do not entirely return back to pre-injury mechanics in all rotations and translations after 40 weeks. As shown in Figure 1, the medial-lateral as well as posterior-anterior translation of the joint is progressively altered post ACL Tx over time. Rotationally, the internal-external kinematic curve at 22 weeks is dissimilar to the intact motion, however by 40 weeks a recovery towards the intact measurement is seen as the animal compensates for the injury. In the future, principal component analysis will be utilized to compare these gait changes. In conclusion, the transection of the ACL causes long-term changes in the in vivo kinematics of the joint. Alterations of the kinematics may result in degradation of cartilage due to abnormal loading of the joint and overall damage in the joint due to compensation of the instability post ACL Tx, which is a painful and destructive condition

Strength and deformation of confined and unconfined grouted concrete masonry

Although concrete masonry is a composite material, its gross properties are used in structural design. It is well known that under uniaxial compression, grouted concrete masonry fails under stress levels lower than that of the hollow masonry blockwork. To improve the compressive strength of masonry, the authors examined the effectiveness of inserting rolled fine wire mesh or welded wire mesh into the voids of the hollow concrete masonry prior to grouting. This inexpensive method of confining the grout increased the compressive strength of the masonry up to 38%. Simple and refined equations have been fitted to the stress-strain data of the masonry with the refined form of the equation being found more appropriate. The stress-strain curves appear to predict the peak and postpeak characteristics of the unconfined and confined prisms accurately. The appropriateness of the refined equation is demonstrated by predicting the moment curvature relations of short masonry piers tested under axial and lateral loading

The Effect of the Amount, Distribution and End Anchorage Conditions of Bond Beam Reinforcement on the Behaviour of Concrete Masonry Shear Walls

The behaviour of square shape partially grouted concrete masonry shear walls with fixed end boundary conditions subjected to constant average axial stress and cyclic lateral loading was investigated. Two replicas were tested of each combination of horizontal reinforcement ratio (0.12%, 0.06% and 0.03%) and four end anchorage conditions (straight, 90, 180 and shear studs). The behaviour of the walls was compared in terms of strength, ductility, stiffness and dissipated energy. While the effect of horizontal bar size was greater than that of end anchorage, neither improved end anchorage nor the smaller bar size increased yielding at critical locations on the rebars. The highest course of the wall should be reinforced and grouted as it improves performance of the walls. In addition, the amount of horizontal reinforcement did not significantly affect the strength of the shear walls, therefore changes to the shear design equations in the Canadian Standard are recommended.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Shear in plain, bed joint reinforced, and post-tensioned masonry

Masonry is cost competitive on a life cycle basis with other forms of construction, and should therefore be considered as a structural material more frequently by both architects and engineers. Post-tensioned geometric sections of masonry are structurally efficient wall systems. Post-tensioning with carbon fibre reinforced polymer (CFRP) is an attractive solution to potential corrosion problems with unbonded tendons. Tests on CFRP post-tensioned diaphragm walls have revealed that shear strength in prestressed masonry is an area deserving more study and improvement. The tests also showed that the bonding pattern of the masonry at the web-flange junction can have a substantial effect on the resulting strength of that connection. A test series to evaluate the effects of prestress force and bed reinforcement on shear strength has been carried out and a summary of the results is presented here. Tests to determine the effect of bonding pattern on the strength of the web-flange connection have also been conducted

Homo sapiens May Incorporate Daily Acute Cycles of “Conditioning–Deconditioning” to Maintain Musculoskeletal Integrity: Need to Integrate with Biological Clocks and Circadian Rhythm Mediators

Human evolution required adaptation to the boundary conditions of Earth, including 1 g gravity. The bipedal mobility of Homo sapiens in that gravitational field causes ground reaction force (GRF) loading of their lower extremities, influencing the integrity of the tissues of those extremities. However, humans usually experience such loading during the day and then a period of relative unloading at night. Many studies have indicated that loading of tissues and cells of the musculoskeletal (MSK) system can inhibit their responses to biological mediators such as cytokines and growth factors. Such findings raise the possibility that humans use such cycles of acute conditioning and deconditioning of the cells and tissues of the MSK system to elaborate critical mediators and responsiveness in parallel with these cycles, particularly involving GRF loading. However, humans also experience circadian rhythms with the levels of a number of mediators influenced by day/night cycles, as well as various levels of biological clocks. Thus, if responsiveness to MSK-generated mediators also occurs during the unloaded part of the daily cycle, that response must be integrated with circadian variations as well. Furthermore, it is also possible that responsiveness to circadian rhythm mediators may be regulated by MSK tissue loading. This review will examine evidence for the above scenario and postulate how interactions could be both regulated and studied, and how extension of the acute cycles biased towards deconditioning could lead to loss of tissue integrity

Numerical investigation of creep effects on FRP-strengthened RC beams

Numerical analysis using a finite-element model was performed to simulate and investigate the long-term behavior of two RC beams with similar steel reinforcement, cast from the same batch of concrete. One beam was a plain RC beam and the other beam was strengthened using carbon fiber-reinforced polymer (FRP) strips. The deflections of both beams have been monitored for 5 years after loading. The finite-element model included both creep of concrete and viscoelasticity of the epoxy adhesive at the concrete-carbon FRP (CFRP) interface. The results of the finite-element analysis are compared to experimental observations of the two beams. The finite-element analysis was found to be able to simulate the long-term behavior of the CFRP-strengthened beam and help us understand the complex changes in the stress state that occur over time