Circumferential Hoop Stresses Research Articles

Irradiation creep measurement and microstructural analysis of chromium nitride–coated zirconium alloy using pressurized tubes

Environmental barrier coatings for Zr-based materials are currently under development to reduce oxidation and embrittlement in light-water reactors. Chromium nitride is one such candidate for this application, particularly as accident-tolerant fuel cladding. However, quantifying the impact of coatings on the irradiation-induced creep of zircaloy (Zry) is critical as this mechanism often exceeds thermal creep rates under light-water reactor operating conditions and can be a limiting design characteristic. Additionally, examining irradiation effects in the microstructure at the coating interface is key to understanding the compatibility of the material system. To accelerate the experimental measurement of irradiation creep and microstructure evolution in CrN-Zry, compact, pressurized creep tubes were fabricated and irradiated in the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory. Miniature, thin-walled rodlets fabricated from annealed Zr-Sn barstock were coated with CrN using physical vapor deposition (PVD) to nominal thicknesses of 4 and 8 μm. Coated and uncoated rodlet specimens were internally pressurized and welded, generating nominal circumferential hoop stresses of 0, 90, or 180 MPa under 300∘C irradiation conditions. Twelve specimens were measured diametrically prior to irradiation using a low-cost, automated, contactless laser profilometer developed for this work. Specimens were irradiated in sealed capsules for one 25-day HFIR cycle, accumulating approximately 1.8×1021n/cm2 fast fluence (En>1.0MeV). The irradiated samples were retrieved and remeasured using the same profilometry system in a shielded hot cell facility. Irradiation creep between specimens was compared using standard statistical tests and showed that both thicknesses of CrN coating had a negligible effect on the irradiation creep strain of the Zry material. Microstructure characterization of pre- and post-irradiated CrN-Zry specimens showed minimal changes due to irradiation but did show a substantial O-rich region at the Zry-CrN interface.

Meniscal Circumferential Fiber Augmentation: A Biomechanical Arthroscopic Meniscal Repair Technique

Radial tears of the human knee meniscus result in the loss of circumferential hoop stress and are highly correlated with knee degeneration. Although a variety of surgical techniques are available to repair radial meniscal tears, including inside-out, outside-in, and all-inside techniques, conventional repair techniques focus only on stabilizing the damaged portion. This Technical Note describes a biomechanical meniscus repair technique of meniscal circumferential fiber augmentation, concomitant with conventional repair, to promote meniscal healing from a biomechanical perspective.

Medial Meniscal Allograft Transplantation: The Bone Plug Technique

Background: The medial and lateral menisci act as shock absorbers for the knee joint by converting and redistributing axial load into circumferential hoop stresses. Disruptions of these hoop stresses occur in the setting of meniscal deficiency and lead to long-term degenerative changes. Therefore, maintaining the distinctive composition and organization of the menisci is essential. In selective cases of meniscal deficiency, meniscus allograft transplantation can be a valuable treatment option. Indications: Meniscus transplantation should be considered in patients with symptomatic meniscal deficiency, without the presence of advanced degenerative pathologies, who have failed all conservative treatments. Technique description: We can divide the surgery into 4 steps: (1) graft preparation, (2) arthroscopic joint preparation, (3) allograft attachment preparation, and (4) graft fixation. Results: Meniscus allograft transplantation yields good to excellent results in up to 85% of cases. Improvement of pain and knee function occurs in approximately 70% of the patients at 10 years. The associated complications are mainly joint stiffness, early osteoarthritis, and incomplete healing accompanied by graft failure. Graft failure is the most feared complication, yet shows good results over the midterm. Conclusion: The bone plug technique we have shown here is a hybrid approach combining soft tissue and bone fixation techniques. It provides synergistic advantages with good osseous integration and is minimally invasive through arthroscopy without true arthrotomy. In our experience, this approach elegantly eases the complexity of this demanding surgery while yielding excellent results for patients. Patient Consent Disclosure Statement: The author(s) attests that consent has been obtained from any patient(s) appearing in this publication. If the individual may be identifiable, the author(s) has included a statement of release or other written form of approval from the patient(s) with this submission for publication.

High-Speed Spin Testing of Bi-2212 Superconducting Wires for High-Field NMR Magnet Qualification: Final Progress Report

This paper summarizes an NIH-funded research project designed to study the strength of high temperature superconductors under high circumferential hoop stress, in order to qualify these materials for high-field (> 1 GHz-class) NMR magnets. The unique approach presented here is to spin test coils at high rotational speeds, approaching 50,000 rpm, in order to induce mechanical hoop stresses which are equivalent to the magnetic Lorentz stresses experienced by a high-field solenoid insert coil. Bi-2212 wires and coils were tested in sub-cooled nitrogen to determine if any mechanical damage was imparted by each spin test. These preliminary experimental results demonstrate that, with further development, this test could prove to be a simple method for qualifying superconducting wires for high-field insert magnets.

In preprints: buckling under pressure during gastrulation.

In preprints: buckling under pressure during gastrulation.

Acute Stent-Induced Endothelial Denudation: Biomechanical Predictors of Vascular Injury.

Recent concern for local drug delivery and withdrawal of the first Food and Drug Administration-approved bioresorbable scaffold emphasizes the need to optimize the relationships between stent design and drug release with imposed arterial injury and observed pharmacodynamics. In this study, we examine the hypothesis that vascular injury is predictable from stent design and that the expanding force of stent deployment results in increased circumferential stress in the arterial tissue, which may explain acute injury poststent deployment. Using both numerical simulations and ex vivo experiments on three different stent designs (slotted tube, corrugated ring, and delta wing), arterial injury due to device deployment was examined. Furthermore, using numerical simulations, the consequence of changing stent strut radial thickness on arterial wall shear stress and arterial circumferential stress distributions was examined. Regions with predicted arterial circumferential stress exceeding a threshold of 49.5 kPa compared favorably with observed ex vivo endothelial denudation for the three considered stent designs. In addition, increasing strut thickness was predicted to result in more areas of denudation and larger areas exposed to low wall shear stress. We conclude that the acute arterial injury, observed immediately following stent expansion, is caused by high circumferential hoop stresses in the interstrut region, and denuded area profiles are dependent on unit cell geometric features. Such findings when coupled with where drugs move might explain the drug–device interactions.

Accurate placement of a tibial tunnel significantly improves meniscal healing and clinical outcomes at 1year after medial meniscus posterior root repair.

A medial meniscus posterior root tear results in the loss of meniscal circumferential hoop stress and causes a pathological posteromedial extrusion of the medial meniscus. Although creating a tibial tunnel in the anatomic place improves postoperative medial meniscus posterior extrusion, no studies have evaluated the relationship between tibial tunnel position and clinical outcomes. This study aimed to evaluate how tibial tunnel positioning of medial meniscus posterior root pullout repair affects meniscal healing status and clinical outcomes. Sixty-two patients with 64 medial meniscus posterior root tears (mean age 62.8 ± 7.9years) who had undergone pullout repairs and second-look arthroscopies were included. All 62 patients were Lachman test negative. Three-dimensional computed tomography images of the tibial surface were evaluated using a rectangular measurement grid to assess the tibial tunnel centre and medial meniscus posterior root attachment centre. Spearman's rank correlation analysis was undertaken to determine displacement distance from the medial meniscus posterior root attachment centre to the tibial tunnel centre and a meniscal healing score, as well as clinical outcomes at 1year post-repair. Tibial tunnel centres were located more anteriorly and medially than the medial meniscus posterior root attachment centre (mean distance 5.0 ± 2.2mm). The mean meniscal healing score was 6.7 ± 1.8 of 10 possible points. The 1-year postoperative clinical scores showed significant improvement compared with preoperative scores for all the items. There was a significant negative correlation in the absolute distance between the medial meniscus posterior root attachment centre and the tibial tunnel centre with the meniscal healing score (ρ = - 0.39, p = 0.002). Furthermore, there were significant positive correlations between the distance between the medial meniscus posterior root attachment centre and the tibial tunnel centre in the mediolateral direction and patient-based clinical outcomes (ρ = 0.25-0.43, p < 0.05). Accurate placement of a tibial tunnel, especially in the mediolateral direction, significantly improved meniscal healing and clinical outcomes at 1year following medial meniscus posterior root repair. Surgeons should create a medial meniscus posterior root tibial tunnel at the anatomic attachment with particular attention to the mediolateral position. Level IV.

Abstract P006: Purinergic Receptor Activation Protects Glomerular Microvasculature From Increased Mechanical Stress In Angiotensin Ii-induced Hypertension: A Modeling Study

Angiotensin II (Ang II)-induced hypertension increases afferent and efferent arteriole resistances via the actions of Ang II on the AT1 receptor. In addition to the increased interstitial levels of Ang II, the increased arterial pressure increases interstitial ATP concentrations which act on the purinergic receptors P2X1 and P2X7, to constrict the AA, preventing increases in plasma flow and single nephron GFR (SNGFR). Blockade of the P2 receptors also mitigates the effects of Ang II, thus increasing blood flow and SNGFR, but the resulting increases in mechanical stresses (shear stress and circumferential hoop stress) on the glomerular microvasculature have not been quantified. A mathematical microvascular hemodynamic glomerular model was developed to simulate blood flow and plasma filtration at each of 320 capillary segments in an anatomically-accurate rat glomerular capillary network topology. Afferent and efferent arteriole resistances and network hydraulic conductivity were adjusted to match glomerular hemodynamic data for control, Ang II-induced hypertension and P2X1-blocked conditions (Franco, Martha, et al. Amer. J. Physiology-Renal 313.1 (2017): F9-F19). Ang II infusion increased both afferent and efferent resistances, reducing blood flow while slightly raising glomerular pressure. Blockade of the purinergic receptors reduced both afferent and efferent resistances, maintaining glomerular pressure at hypertensive levels but increasing blood flow significantly, increasing shear stress from 24.9 dynes/cm 2 in hypertensive conditions to 71.3 dynes/cm 2 after purinergic blockade. Because glomerular pressure was maintained, hoop stress barely changed from 69.5 kPa in hypertensive conditions to 70.9 kPa after purinergic blockade. Purinergic blockade also increased hydraulic conductivity and filtering surface area, increasing SNGFR. In hypertension, purinergic stimulation does not prevent the transmission of increased arterial pressure to the glomerular capillaries to reduce capillary hoop stress. However, activation of the purinergic system protects the glomerular microvasculature from increases in shear stress caused by a marked increase in blood flow that would occur in the absence of purinergic stimulation.

Progress in High-Speed Spin Testing of Superconducting Wire and Tapes for High-Field NMR Magnet Qualification

This paper summarizes the status of a 3-year, NIH-funded research project to study the strength of high temperature superconductors under high circumferential hoop stress, in order to qualify these materials for high-field (> 1 GHz-class NMR magnets. The unique approach presented here is to spin test coils at high rotational speeds, approaching 100,000 rpm, in order to induce the necessary hoop stress. Thermal strain compatibility between the Bi-2212 wire and Inconel wire has been qualified, including thermal cycling. Assembly and testing of the first low-speed (< 30,000 rpm) rotor is now in process, and the design of second, higher speed (> 60,000 rpm) rotor, is also underway.

Development of a hoop-strength test for model sphero-cylindrical dental ceramic crowns: FEA and fractography

Here we describe the development of a mechanical test that simulates a circumferential “hoop-stress” at the margins of model dental ceramic crowns. A simplified sphero-cylindrical geometry was modelled in two thicknesses and machined out of two glass-ceramic materials. The specimens were loaded by a conical metallic piston to induce circumferential hoop-stresses at the margins until fracture. Broken specimens were fractographically analyzed to determine the location of the fracture origin and to measure the dimensions of the critical defect, allowing the calculation of the stress at failure from fracture mechanics relations. For thick specimens, machining defects at the outer margins barely played a role in fracture initiation. For thin specimens, outer defects started to dominate the failure mode. CAD/CAM machining showed to predispose thinner margins to early fracture. Crowns should be designed with increased thickness in order to minimize the effect of marginal damage in the circumferential stress field inducing fracture.

Abstract 146: Glomerular Capillary Hypertrophy is Insufficient to Mitigate Mechanical Stresses in 5/6 Nephrectomy: A Modeling Study

The 5/6-nephrectomy (5/6 Nx) model of renal mass reduction shows an increased glomerular pressure (ΔP) and afferent plasma flow (Q a ) in the remaining glomeruli. These hemodynamic consequences are assumed to increase glomerular capillary wall circumferential hoop stress (HS) and shear stress (SS), respectively. Due to a lack of anatomically-accurate mathematical models of the glomerulus, the actual magnitudes of SS and HS in the entire network of glomerular capillaries remain uncertain in 5/6-Nx. These forces are of significance due to the sensitivity of endothelial cells to SS and podocytes to HS. We developed a mathematical model of blood flow through an anatomically-accurate rat glomerular capillary network to estimate the magnitudes of SS and HS on the glomerular capillary walls in 5/6-Nx. Filtration rates, wall HS and wall SS were calculated for each capillary segment of the network based on parameters obtained from a micropuncture study using normal rats and rats with 5/6-Nx (Kasiske, Bertram L., et al. Circ. Res. 62.2: 367-374. (1988)). In this study, 5/6-Nx increased Q a and ΔP by 174.8% and 19.0%, respectively. To simulate glomerular capillary hypertrophy in 5/6-Nx, the capillary diameters were all increased by 16.1%. Using these data, the Young-Laplace equation was used to calculate HS in each capillary, and SS was calculated assuming Poiseuille flow with blood viscosity scaled based on vessel diameter and hematocrit. Taking into account an increase in diameter of the glomerular capillaries, the model predicted mean SS values of 48.1 dynes/cm 2 in control and 79.4 dynes/cm 2 in 5/6-Nx. The increase in diameter of the glomerular capillaries was not sufficient to prevent the increase in SS, a finding in contrast to the previous experimental analysis which suggested normalization of SS. The increase in glomerular capillary diameter increased mean HS from 144.1 kPa to 199.2 kPa. This study demonstrates that this increase in diameter was not sufficient to mitigate the increased SS in 5/6-Nx and contributes to a significantly increased HS. These increased mechanical stresses on the glomerular capillaries may play a causative role in the progression of glomerular injury in 5/6-Nx thus leading to chronic kidney failure.

Scaling Laws for Vascular Buckling, Axial and Circumferential: Applications to Pulse Wave Velocity

Background: Scaling laws for cylindrical column buckling are reviewed, applicable to the cardio-vascular system arteries or veins of various thicknesses to diameter ratios. Methods: Critical buckling load scales as (hr/L^2) for axial loads, (h/r)^3 for compressive circumferential loads, and ( h/r)^0.5 for pulse wave velocity. Results: Arteries and veins are most susceptible to buckling failure in collapsible tube mode when circumferential hoop stress exceeds external pressure. Conclusions: Applications include alternating positive (+) and negative (-) wall stresses to investigate the onset of plastic yielding, fatigue, creep, and pulse wave velocity, all relevant to aneurisms, venous thrombosis, hypertension, and arterial sclerosis.

A case of bilateral posterior medial meniscus root tear: Partial menisectomy versus pull-out suture repair

The meniscal roots are sites where the knee meniscus attaches to the central tibial plateau, adjacent to the tibial insertions of the cruciate ligaments. Medial meniscus root tears (MMRTs) are commonly associated with other intra-articular pathology and have a debilitating effect on knee kinematics due to loss of circumferential hoop stresses. Many surgical options for repair have been described in the literature including partial or total menisectomy, pullout sutures and suture anchors. We present a unique case of a 27 year old female who sustained a bilateral posterior horn MMRT. One knee was repaired using the pullout suture technique and the other knee underwent partial menisectomy. We found no significant difference in Lysholm scores in the short or medium term between the two methods. To our knowledge, this is the first reported case of a bilateral medial meniscus root tear.

Meniscal Root Tears

Meniscal root tears, less common than meniscal body tears and frequently unrecognized, are a subset of meniscal injuries that often result in significant knee joint disorders. The meniscus root attachment aids meniscal function by securing the meniscus in place and allowing for optimal shock-absorbing function in the knee. With root tears, meniscal extrusion often occurs, and the transmission of circumferential hoop stresses is impaired. This alters knee biomechanics and kinematics and significantly increases tibiofemoral contact pressure. In recent years, meniscal root tears, which by definition include direct avulsions off the tibial plateau or radial tears adjacent to the root itself, have attracted attention because of concerns that significant meniscal extrusion dramatically inhibits normal meniscal function, leading to a condition biomechanically similar to a total meniscectomy. Recent literature has highlighted the importance of early diagnosis and treatment; fortunately, these processes have been vastly improved by advances in magnetic resonance imaging and arthroscopy. This article presents a review of the clinically relevant anatomic, biomechanical, and functional descriptions of the meniscus root attachments, as well as current strategies for accurate diagnosis and treatment of common injuries to these meniscus root attachments.

Role of the anterior intermeniscal ligament in tibiofemoral contact mechanics during axial joint loading

The anterior intermeniscal ligament (AIML) is an anatomically distinct structure that connects the anterior horns of the medial and lateral menisci. We hypothesized that both menisci work together as a unit in converting axial joint loading into circumferential hoop stresses, due to intermeniscal attachments. Therefore, loss of the AIML could lead to increased tibiofemoral contact stress and predispose to arthritic change. In this cadaveric study, we compared tibiofemoral contact pressures on axial loading, before and after sectioning of the AIML. Five fresh frozen human cadaveric knees were mounted on a linear x–y motion table and loaded in extension under axial compression of 1800N (about 2.5 times body weight for a 70kg individual), using a materials testing machine. Tibiofemoral contact pressures before and after sectioning of the AIML were measured using resistive pressure sensors. Contrary to our hypothesis, sectioning of the AIML produced no statistically significant increase in mean contact pressure, peak contact pressure or change in contact area, in either the medial or lateral compartment of the knees. This implies that the menisci work independently in converting axial loads into circumferential hoop stresses, and is probably due to their individual root attachments to the tibia. Based on this study, inadvertent sectioning of the AIML during knee surgery, e.g., arthroscopy, anterograde tibia nailing, anterior cruciate ligament reconstruction, meniscus transplantation and unicondylar knee replacement, is functionally insignificant.

Geomechanics Optimizes Field-Development Strategy of Deep Gas Reservoir

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 108891, "Using Geomechanics To Optimize Field-Development Strategy of Deep Gas Reservoir in Saudi Arabia," by Mahbub S. Ahmed, SPE, Saudi Aramco; Thomas Finkbeiner, SPE, GeoMechanics International; and Adnan A. Kannan, SPE, Saudi Aramco, prepared for the 2007 SPE Asia Pacific Oil &amp; Gas Conference and Exhibition, Jakarta, 30 October-1 November. The paper has not been peer reviewed. Saudi Aramco has embarked on drilling long horizontal and maximum-reservoir-contact wells in deep gas reservoirs. The regional stress is important in predicting wellbore stability and production performance. A detailed geomechanics study was made, and its results were incorporated into the decision tree. The objectives were to find the optimum azimuth to place horizontal wells that would minimize the risk of hole breakouts, optimize drilling-mud weights, and ensure sustainable production under depletion mode. Introduction The subject field is a north/south-trending anticline. The target reservoir is the Permian Unayzah formation, which was discovered in 2000. The reservoir has three geological units: Unayzah-A, siltstone, and Unayzah-B. Because of stratigraphic considerations and constraints on wellhead placement on the surface, field development with highly deviated horizontal drilling is required to reach the target reservoirs. Reservoir management decided to extend the horizontal wells as far as possible to maximize reservoir contact and, hence, production from the Unayzah formation. Because of the highly deviated/horizontal nature of the planned development wells, it was decided to gain a better understanding of whether geomechanical processes might be of concern to wellbore stability. If so, could well integrity be maximized by use of correct mud weights and well directions that would ensure stable conditions during drilling and production? Determining Stress Orientation Approximately 2,500 ft of electrical wellbore-image data covering the Unayzah-A, -B, and parts of Unayzah-C reservoirs from the first four vertical wells drilled in this field were analyzed. The image data were calibrated, verified, and dynamically normalized to provide optimal image quality. Overall image-data quality in all four wells was fair to good. This analysis identified and characterized stress-induced wellbore failure, such as stress-induced borehole breakouts and drilling-induced tensile fractures. Wellbore breakouts are enlargements of the wellbore wall with 180° spacing caused by localized shear failure, where the circumferential hoop stress is most compressive and exceeds the ultimate compressive strength (UCS) of the rock. In vertical wells, breakouts always form in the direction of the least principal horizontal stress. In deviated wells, the position of breakouts in a well is a function of the wellbore trajectory and the stresses acting on the wellbore. Therefore, when wellbore failures can be detected, their occurrence and characteristics (i.e., azimuth and width) can be used to determine in-situ stress magnitudes, effective rock strength, and stress orientations. In general, an abundance of stress-induced wellbore breakouts and some drilling-induced tensile fractures were detected. These fractures occurred intermittently throughout all three Unayzah formations. Cumulative length of these breakouts ranged from 86 to 142 ft in each well.

Atomistic Studies of Crack Branching at Bimaterial Interfaces: Preliminary Results

ABSTRACTIn this paper, we summarize recent progress in applying atomistic studies of cracking along interfaces of dissimilar materials under quasi-static crack growth conditions. We consider two linear-elastic material strips in which atoms interact with harmonic potentials, with a different spring constant in each layer leading to a soft and a stiff strip. The two strips are bound together with a tunable potential, which allows to independently control the interface and bulk fracture surface energy. An initial crack serves as initiation point for the failure. This provides a model system to investigate how elastic properties and interface strength interplay and determine the crack growth direction, leading to either interfacial cracking or branching into the film material. We observe a clear transition to interface failure when the interface fracture energy is less than 80% of the bulk fracture energy. We further find that branching in the film material is controlled by the elastic properties of the film material, suggesting interfacial cracking for extremely soft films and branching for stiffer films. Analysis of the virial stress field around the crack suggests that the circumferential hoop stress controls the branching behavior.

Stress analysis of hemispherical ceramic hip prosthesis bearings

We present design criteria and test data for ceramic hemispherical ‘resurfacing’ prosthesis bearings that are attached by placement on the conical trunnion of the prosthesis stem. These large diameter bearings will be subjected to higher torques than conventional 28 mm bearings. Prototypes were fabricated and tested. The pattern of failure and subsequent analysis suggests that fracture initiated on the surface of the bore and that this was preceded by the development of large circumferential hoop stresses. Widening the bore will improve stability under torque loads but this may be at the expense of bearing strength. A finite element analysis has shown that the optimum taper bore to bearing diameter ratio is 0.43 and that designs with large taper bore to bearing diameter ratios (over 0.6) should be avoided due to the development of excessively high hoop stresses on the inner bore surface. High meridional tensile stresses can appear where the internal roof surface joins the conical bore surface as the load is removed. A smooth radius between the conical bore and the roof will help to overcome this. Further improvements include a thinner roof that is smoothly arched internally. Thus, the design of the component can be optimised, making it less susceptible to fracture without compromising the stability of the ceramic head on its trunnion.

An anatomical study of meniscal allograft sizing.

Meniscus-to-femoral condyle congruity is essential for the development of circumferential hoop stresses and thus function of the meniscus. When meniscal allograft transplantation is performed using bony anchorage of the insertional ligaments, accurate graft-to-host size matching is therefore essential. The standard method currently employed for size matching of meniscal allografts is to rely on plain radiographs of the host's knee, from which expected meniscal dimensions are measured. This study aimed to examine the correlation between tibial plateau dimensions and meniscal dimensions. We studied 44 donor tibial plateaus with medial and lateral meniscal allografts attached intact. Meniscal and tibial plateau dimensions were measured. Linear regression analysis was used to calculate expected meniscal dimensions from each specimen's plateau dimensions. Using specific medial and lateral tibial plateau width and length measurements, meniscal dimensions could be predicted with a mean error of only 5.0+/-6.4%. When predicting meniscal dimensions from only total bony plateau width, the mean error observed was 6.2+/-8.0%. The difference between the two methods was not statistically significant. The results suggest that meniscal dimensions can be predicted accurately from tibial plateau measurements, with only small mean errors. However, potential size mismatches should be carefully borne in mind by surgeons using meniscal allografts.

Cholesterol in Vascular and Valvular Calcification

In the early 1990s, the late Jeff Hoeg had the foresight to ask whether vascular calcification relates to the duration and severity of exposure to cholesterol. In a group of homozygous hyperlipidemic patients for whom detailed records of cholesterol levels were available over a long period of time, he and his colleagues found that coronary calcification scores by ultrafast computed tomographic scanning correlated significantly with the cholesterol year product.1 Studies that lack long-term cholesterol history may miss a correlation between lipids and calcification, because current treatments so dramatically change cholesterol levels as to make them unrepresentative of long-term exposure. See p 1927 In the present issue of Circulation , Pohle et al2 successfully overcame these difficulties by studying the rate of change in calcification as a function of change in lipid levels, excluding patients in whom treatment was altered during the study period. These investigators found that both coronary calcification and aortic valve calcification progress more rapidly in subjects with levels of LDL >130 mg/dL. This finding dovetails with those of Callister et al,3 who discovered that patients who successfully lowered their cholesterol levels with lipid-lowering agents significantly reduced the progression of coronary calcification. In a large population of young subjects, the risk factor that correlated most significantly with coronary calcification was LDL cholesterol.4 This relation was stronger than the correlation with age, smoking, fasting insulin, blood pressure, or male sex.4 In another study of asymptomatic outpatients, LDL cholesterol was the only risk factor correlating with progression of coronary calcification by electron-beam computed tomography over an 18-month period.5 The correlation of LDL cholesterol exposure to valvular and vascular calcification raises the possibility of a mechanistic role, which is also supported by in vitro studies. Two groups …