Strength Metrics Research Articles

Grip strength is associated with markers of central hemodynamics

Objectives. Reduced muscular strength (measured by grip strength) has been associated with an increased risk of cardiovascular complications. Further research is needed to identify how muscular strength is associated with various markers of cardiovascular function to provide at least some mechanistic explanation for observed interrelations. We, therefore, addressed the question of whether handgrip (HG) strength is associated with descriptors of peripheral and central hemodynamics in the population of healthy individuals. Design. Two hundred thirty-one healthy volunteers (90 men and 141 women, mean age 54 years) were studied. Patients were asked to perform the maximum handgrip trial in the standing position with the dominant arm, using hydraulic hand dynamometer. Applanation tonometry was used to execute the non-invasive assessment of the pressure waveform. Results. HG strength was associated with various markers of hemodynamics and clinical characteristics, e.g. correlated significantly and positively with BMI [body mass index, r = 0.21, p = .001], PPA [pulse pressure amplification, r = 0.43, p < .0001], Tr [time to return of pressure wave, r = 0.43, p < .0001] and significantly and negatively with AP [augmentation pressure, r = −0.45, p < .0001]. Multiple linear regression showed that sex, handgrip and mean blood pressure were independently associated with AP (R2 = 0.38), PPA (R2 = 0.21) and Tr (R2 = 0.29). Conclusions. Our study demonstrated the association between handgrip strength and central hemodynamic metrics. These interactions may add a mechanistic explanation for the role of muscle strength as a risk marker for incident cardiovascular complications.

Multi-regional input-output and linkage analysis for water-PM2.5 nexus

Water shortage and air pollution are two major threatens to the rapid processes of urbanization and industrialization, whereas the current single-minded environmental management might ignore the hidden correlations between resources and emissions, and potentially lead to unintended effects. In order to bridge this gap, this study attempts to investigate the nexus between water and particulate matter 2.5 (PM2.5), termed water-PM2.5 nexus, via Environmentally-Extended Multi-Regional Input-Output model, combining with Integrated Nexus Strength metric and linkage analysis. The basic water-PM2.5 coupling flows are quantified by Environmentally-Extended Multi-Regional Input-Output model, and the Integrated Nexus Strength metric is proposed to examine all economic sectors to reveal dominant water-PM2.5 nexus nodes. Then the major water-PM2.5 nexus sectors are evaluated through linkage analysis to characterize their consuming or supplying behaviors in water-PM2.5 nexus. Finally, net embodied water and PM2.5 flows among these water-PM2.5 nexus nodes are quantified to reveal crucial industrial chains. Using Beijing-Tianjin-Hebei area of China as a case study, results show that energy supply sectors, metal-related sectors, agricultural sectors, and services sectors are major water-PM2.5 nexus nodes. Sectors of “Electricity and Heating Power Production and Supply” are dominant suppliers of embodied PM2.5 emissions and water flows, while sectors of “Metal Production” and “Residential Service” are the major consumers. More than 70% of the net embodied PM2.5 flows and around 20% of net embodied water flows lie in the industrial chains correlated with the sectors of “Smelting and Pressing of Metals ” and “Electricity and Heating Power Production and Supply” in Hebei province. This study provides a framework for the investigation of water-PM2.5 nexus considering the economic and environmental correlations between sectors in the socio-economic systems, and enables the collaborative management of water utilization and PM2.5 emission as well as facilitates the enaction of multi-tasking environmental policies.

Improvements in Isokinetic Quadriceps and Hamstring Strength Testing After Focused Therapy in Patients With Flexion Instability

BackgroundThere is a paucity of literature to guide non-operative treatment for patients with problems after total knee arthroplasty (TKA). We sought to quantify how quadriceps and hamstring strength could improve with focused physical therapy (PT) and whether improving leg strength may prevent revision surgery for patients with flexion instability (FI) after TKA. MethodsThis retrospective study included patients diagnosed with FI by one of the 4 fellowship-trained arthroplasty surgeons at a single academic institution. Patients with FI were referred for strength measurements and a focused PT program. In total, 166 patients completed isokinetic testing to quantify their relative quadriceps and hamstring power, torque, and work measures compared to their contralateral leg. Fifty-five (33.5%) patients subsequently completed post-PT isokinetic testing. Statistical analysis was conducted to evaluate strength deficits in the knee with FI. ResultsPatients with FI were found to be 20.5%-38.4% weaker in all strength domains compared to the contralateral leg (P < .001). Patients who completed PT and pre-isokinetic and post-isokinetic testing demonstrated statistically significant gains in all extension metrics by a net range of 24.7%-34.2% (P = .011-.029) and their flexion strength metrics improved by 32.5%-40.2% (P = .002-.005). About 81.9% of patients in this subgroup did not undergo revision TKA. Those subjects who went on to revision did not statistically improve in any strength domain (P = .063-.121). ConclusionPatients with FI after TKA have significantly weaker quadriceps and hamstrings in the operative compared to contralateral leg. Patients who did not undergo revision knee arthroplasty and completed a formal PT program improved quadriceps and hamstring strength by 30%. Level of evidenceIV (Case series).

Early-Stage Diabetic Neuropathy Reduces Foot Strength and Intrinsic but Not Extrinsic Foot Muscle Size.

Background Tracking progression of diabetic peripheral polyneuropathy (DPN) is usually focused on sensory nerves and subjective testing methods. Recent studies have suggested that distal muscle atrophy may precede sensation loss. Methods to objectively measure distal muscle size and strength are needed to help understand how neuropathy affects muscle function. Purpose To evaluate individual intrinsic and extrinsic foot muscle sizes and functional foot strength in participants with DPN. Methods Thirty individuals participated in this cross-sectional study (15 DPN and 15 matched controls). Sizes of 10 separate muscles of the lower leg and foot were measured using ultrasound imaging. Functional foot strength was also quantified using custom great toe and lateral toe flexion tests along with a doming test. Muscle size and strength metrics were compared between groups using ANOVAs and paired t-tests (α = 0.05). Correlations between strength and relevant muscle sizes were also evaluated. Results The sizes of all four intrinsic foot muscles were smaller in individuals with DPN (p ≤ 0.03), while only one (toe extensor) of the six extrinsic muscles was smaller (p ≤ 0.03), while only one (toe extensor) of the six extrinsic muscles was smaller (p ≤ 0.03), while only one (toe extensor) of the six extrinsic muscles was smaller (p ≤ 0.03), while only one (toe extensor) of the six extrinsic muscles was smaller (r ≤ 0.80) with several corresponding intrinsic muscle sizes. The doming strength test did not show any difference between groups and was moderately correlated with one muscle size (r ≤ 0.80) with several corresponding intrinsic muscle sizes. The doming strength test did not show any difference between groups and was moderately correlated with one muscle size (Conclusion Diabetic peripheral polyneuropathy affects intrinsic muscles before extrinsics. Ultrasound imaging of individual muscles and functional toe flexion tests can be used clinically to monitor DPN progression and foot function. Participants need to be trained in the doming test before a relationship can be established between this test and DPN foot function. Future studies should include muscle quality measurements to better understand characteristics of affected muscles.

Effectiveness of an Unexpected Disturbance Program in the Early Stage of Rehabilitation in Athletes With Unilateral Knee Ligament Injury.

Sensorimotor, proprioceptive, and neuromuscular programs are critical for the successful rehabilitation of injured athletes, and these decrease reinjury rates. To investigate the effects of an unexpected disturbance program (UDP) on balance and unilateral strength metrics in athletes with unilateral knee ligament injury. A 3-week parallel-group experimental design consisting of 9 rehabilitation sessions. National Sports Institute. Twenty-one national-level athletes (age 21.4 [4.4]y, body mass 63.9 [10.8]kg, height 169.0 [10.2]cm) who had sustained a unilateral knee ligament injury. An UDP program designed to evoke rapid sensorimotor responses was compared with traditional training and a nonexercise control group. Unilateral total, anteroposterior, and mediolateral sway with eyes open and closed and unilateral isometric strength. Traditional exercises tended to outperform the UDP when unilateral balance testing was performed with eyes open; however, balance improvement following UDP tended to be greater in the eyes-closed condition. Significant strength gains in both the injured and uninjured legs were only observed following the UDP. This increase in unilateral isometric strength was 23.4 and 35.1 kg greater than the strength improvements seen in the traditional rehabilitation and control groups (P < .05). UDP could improve neural aspects of rehabilitation to improve rehabilitation outcomes by improving strength, sensorimotor function, and proprioception. Given the complementary adaptations, an UDP could provide an effective adjunct to traditional rehabilitation protocols and improve return-to-play outcomes.

Association between eccentric knee flexor strength and hamstring injury risk in 185 elite Gaelic football players.

Hamstring strains are the most common time-loss injury in elite Gaelic football affecting over 20% of players per season. Thus, there is a need to identify factors contributing to the onset of hamstring injuries in order to inform injury risk management strategies. The current study investigated whether eccentric knee flexor strength and between-limb imbalances were associated with increased risk of sustaining a time-loss hamstring injury in elite Gaelic football players. A total of 185 elite male players (26.9±2.7years, 86.4±6.2kg, 183.4±5.6) were prospectively followed for 12weeks from the day of testing. Injury data were provided by the team medical staff. Twenty-eight players (16%) sustained a time-loss hamstring injury following testing. Players that did not sustain a hamstring injury had greater average between-limb asymmetries (uninjured=9.1%, 95% CI 7.8-10.1; injured=5.1%, 95% CI 3.7-6.7; P=.001). Eccentric knee flexor strength profiles were not associated with increased or decreased risk of sustaining a hamstring injury and did not alter the post-test probability of sustaining a hamstring injury across the investigation period. These findings do not support the use of eccentric knee flexor strength metrics in managing hamstring injury risk in elite male Gaelic football players.

MRI-based assessment of proximal femur strength compared to mechanical testing.

Half of the women who sustain a hip fracture would not qualify for osteoporosis treatment based on current DXA-estimated bone mineral density criteria. Therefore, a better approach is needed to determine if an individual is at risk of hip fracture from a fall. The objective of this study was to determine the association between radiation-free MRI-derived bone strength and strain simulations compared to results from direct mechanical testing of cadaveric femora. Imaging was conducted on a 3-Tesla MRI scanner using two sequences: one balanced steady-state free precession sequence with 300μm isotropic voxel size and one spoiled gradient echo with anisotropic voxel size of 234×234×1500μm. Femora were dissected free of soft-tissue and 4350-ohm strain-gauges were securely applied to surfaces at the femoral shaft, inferior neck, greater trochanter, and superior neck. Cadavers were mechanically tested with a hydraulic universal test frame to simulate loading in a sideways fall orientation. Sideways fall forces were simulated on MRI-based finite element meshes and bone stiffness, failure force, and force for plastic deformation were computed. Simulated bone strength metrics from the 300μm isotropic sequence showed strong agreement with experimentally obtained values of bone strength, with stiffness (r=0.88, p=0.0002), plastic deformation point (r=0.89, p<0.0001), and failure force (r=0.92, p<0.0001). The anisotropic sequence showed similar trends for stiffness, plastic deformation point, and failure force (r=0.68, 0.70, 0.84; p=0.02, 0.01, 0.0006, respectively). Surface strain-gauge measurements showed moderate to strong agreement with simulated magnitude strain values at the greater trochanter, superior neck, and inferior neck (r=-0.97, -0.86, 0.80; p≤0.0001, 0.003, 0.03, respectively). The findings from this study support the use of MRI-based FE analysis of the hip to reliably predict the mechanical competence of the human femur in clinical settings.

Evaluation of corporate success using synergistic CPA and CPR corporate citizenship

Corporate Political Activities (CPA) and Corporate Public Relations (CPR) are both non-market communication strategies that effect market positioning, brand strength and the business success of a company. In this study, the use of CPA and CPR by several companies are analyzed based on their economic and brand strength metrics, which confirms the hypothesis that use of these strategies has a positive impact on their market position and brand stability. Using the Multi-Value Comparative Quality Analysis (mvCQA), the research strives to measure the synergistic influence of CPA and CPR on a company's performance. Building on the existing literature for the uses and implementation of mvCQA, this research reinforces the role mvCQA plays in delivering quality and comparative findings of correlation between CPR and CPA toward market strength. This study confirms that the synergy between CPR and CPA improves corporate strategic development. It is inferred that CPR and CPA maintain non-linear correlation with industry and market niches, specific cultural and business environments, as well as overall corporate strategy goals.

Hybritus: a password strength checker by ensemble learning from the query feedbacks of websites

Password authentication is vulnerable to dictionary attacks. Password strength measurement helps users to choose hard-to-guess passwords and enhance the security of systems based on password authentication. Although there are many password strength metrics and tools, none of them produces an objective measurement with inconsistent policies and different dictionaries. In this work, we analyzed the password policies and checkers of top 100 popular websites that are selected from Alexa rankings. The checkers are inconsistent and thus they may label the same password as different strength labels, because each checker is sensitive to its configuration, e.g., the algorithm used and the training data. Attackers are empowered to exploit the above vulnerabilities to crack the protected systems more easily. As such, single metrics or local training data are not enough to build a robust and secure password checker. Based on these observations, we proposed Hybritus that integrates different websites’ strategies and views into a global and robust model of the attackers with multiple layer perceptron (MLP) neural networks. Our data set is comprised of more than 3.3 million passwords taken from the leaked, transformed and randomly generated dictionaries. The data set were sent to 10 website checkers to get the feedbacks on the strength of passwords labeled as strong, medium and weak. Then we used the features of passwords generated by term frequency-inverse document frequency to train and test Hybritus. The experimental results show that the accuracy of passwords strength checking can be as high as 97.7% and over 94% even if it was trained with only ten thousand passwords. User study shows that Hybritus is usable as well as secure.

Differences in geometric strength at the contralateral hip between men with hip fracture and non-fractured comparators.

Older men sustain excess bone mineral density (BMD) declines after hip fracture; however, BMD provides no information on mechanical structure and strength. The aim was to assess whether changes in hip bone geometry in older men after hip fracture differ than that expected with aging. Two cohorts were used: Baltimore Hip Studies 7th cohort (BHS-7) and Baltimore Men's Osteoporosis Study (MOST). The sample (N=170) included older Caucasian men with hip fracture that were propensity score matched (1:1) to community-dwelling non-fractured comparators. Hip Structural Analysis (HSA) calculated aerial BMD and metrics of bone structural strength: cross-sectional bone area (CSA), cortical outer diameter (OD), section modulus (SM), and centroid position (CP). Mixed-effect models estimated changes in HSA parameters and adjusted robust regression models evaluated between-cohort differences in annual percent change at the narrow neck (NN), intertrochanteric (IT), and femoral shaft (FS). Hip fracture was associated with statistically greater declines in NN CSA (β=-2.818; 95% CI: -3.300%, -2.336%), SM (β=-1.896%; 95% CI: -2.711%, -1.080%) and CP (β = -0.884%; 95% CI: -0.889%, -0.880%) and significantly larger increases in NN OD (β=0.187%; 95% CI: 0.185%, 0.190%). Differences in IT HSA parameters were like the NN but larger in magnitude, while there were favorable changes in FS geometry where fragility fractures are rare. Findings indicate there are declines in bone structure and strength at the NN and IT regions of the proximal femur in older men during hip fracture recovery that far exceed what occurs during normal aging.

Holding on Tight: Relationship Between Grip Strength and Marksmanship Stability

Evaluating marksmanship performance is crucial for Warfighters and competitive shooters alike. Traditionally, only accuracy or hit/miss has been used as the quantitative metric to report performance. In this study, grip strength from U.S. Army Soldiers is compared to marksmanship stability metrics recorded after a field training mission. The data analysis revealed that there is a relationship between grip strength and stability, especially in the less stable standing position. The horizontal and vertical stability measures, as well as trigger control offer new insights into weapon control during target acquisition and trigger pull. These metrics, combined with accuracy and precision, offer a more robust evaluation of a shooter’s performance. Correlating these metrics to grip strength shows a relationship between a shooter’s strength and performance, and can lead to targeted training for better performance. Future studies should continue to use stability metrics when defining performance, as well as investigate additional strength metrics.

Enhanced default mode connectivity predicts metacognitive accuracy in traumatic brain injury.

To examine the role that intrinsic functional networks, specifically the default mode network, have on metacognitive accuracy for individuals with moderate to severe traumatic brain injury (TBI). A sample of 44 individuals (TBI, n = 21; healthy controls [HCs], n = 23) were included in the study. All participants underwent an MRI scan and completed neuropsychological testing. Metacognitive accuracy was defined as participants' ability to correctly judge their item-by-item performance on an abstract reasoning task. Metacognitive values were calculated using the signal detection theory approach of area under the receiver operating characteristic curve. Large-scale subnetworks were created using Power's 264 Functional Atlas. The graph theory metric of network strength was calculated for six subsystem networks to measure functional connectivity. There were significant interactions between head injury status (TBI or HC) and internetwork connectivity between the anterior default mode network (DMN) and salience network on metacognitive accuracy (R2 = 0.13, p = .047) and between the posterior DMN and salience network on metacognitive accuracy (R2 = 0.15, p = .038). There was an interpretable interaction between head injury status and internetwork connectivity between the attention network and salience network on metacognitive accuracy (R2 = 0.13, p = .067). In all interactions, higher connectivity predicted better metacognitive accuracy in the TBI group, but this relationship was reversed for the HC group. Enhanced connectivity to both anterior and posterior regions within the DMN facilitates metacognitive accuracy postinjury. These findings are integrated into a larger literature examining network plasticity in TBI. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Optimizing 802.15.4 Outdoor IoT Sensor Networks for Aerial Data Collection

Rural IoT sensor networks, prevalent in environmental monitoring and precision agriculture, commonly operate over some variant of the IEEE 802.15.4 standard. Data collection from these networks is often challenging, as they may be deployed in remote regions where existing backhaul infrastructure is expensive or absent. With the commercial and industrial success of Unmanned Aircraft Systems (UAS), there is understandable interest in using UASs for delay tolerant data collection from 802.15.4 IoT sensor networks. In this study, we investigate how to optimize 802.15.4 networks for aerial data collection, which, unlike other wireless standards, has not received rigorous evaluation for three-dimensional aerial communication. We analyze experimental measurements from an outdoor aerial testbed, examining how factors, such as antenna orientation, altitude, antenna placement, and obstruction, affect signal strength and packet reception rate. In our analysis, we model and predict the quality of service for aerial data collection, based on these network configuration variables, and contrast that with the Received Signal Strength Indication (RSSI)—a commonly used signal strength metric. We find that network configuration plays a significant role in network quality, which RSSI, a mediator variable, struggles to account for in the presence of high packet loss. We conclude with a discussion of strategies for optimizing sensor network configuration for aerial data collection, in light of our results.

Implantable hyaluronic acid-deferoxamine conjugate prevents nonunions through stimulation of neovascularization

Approximately 6.3 million fractures occur in the U.S. annually, with 5–10% resulting in debilitating nonunions. A major limitation to achieving successful bony union is impaired neovascularization. To augment fracture healing, we designed an implantable drug delivery technology containing the angiogenic stimulant, deferoxamine (DFO). DFO activates new blood vessel formation through iron chelation and upregulation of the HIF-1α pathway. However, due to its short half-life and rapid clearance, maintaining DFO at the callus site during peak fracture angiogenesis has remained challenging. To overcome these limitations, we composed an implantable formulation of DFO conjugated to hyaluronic acid (HA). This compound immobilizes DFO within the fracture callus throughout the angiogenic window, making it a high-capacity iron sponge that amplifies blood vessel formation and prevents nonunions. We investigated implanted HA-DFO’s capacity to facilitate fracture healing in the irradiated rat mandible, a model whereby nonunions routinely develop secondary to obliteration of vascularity. HA-DFO implantation significantly improved radiomorphometrics and metrics of biomechanical strength. In addition, HA-DFO treated mandibles exhibited a remarkable 91% bone union rate, representing a 3.5-fold improvement over non-treated/irradiated controls (20% bone union rate). Collectively, our work proposes a unique methodology for the targeted delivery of DFO to fracture sites in order to facilitate neovascularization. If these findings are successfully translated into clinical practice, millions of patients will benefit from the prevention of nonunions.

Unrivaled: why America will remain the world's sole superpower

The rise of China and the unravelling of American power provide the subject of voluminous studies on the evolution of the global interstate system in the twenty-first century. Many see the question as not whether China can surpass the US but rather when. Others have even speculated on how the world will look ‘when China rules it’ (Martin Jacques, When China rules the world, Penguin, 2012). Michael Beckley's Unrivaled: why America will remain the world's sole superpower offers an audacious counter-argument. Beckley does not buy the usual metrics of national power; that is, GDP or the more elaborate Composite Indicator of National Capability (CINC). He argues that those ‘gross indexes’ distort the true capacity of states to innovate, fight advanced technological wars or compete across the board for global norms and standards. Beckley believes that a more appropriate indicator of national power is the multiple of GDP by GDP per capita—an index introduced by legendary historian Paul Bairoch (p. 17). Building on years of groundbreaking research on the key metrics of national strength, Beckley asserts that nations with a higher ‘GDP efficiency index’ (calculated based on human capital, productive capital, natural capital and, most crucially, political institutions) have prevailed over nations with larger gross indexes. Great Britain and France easily defeated the Qing empire. Meiji Japan obliterated the Chinese military. The Soviet Union, which surpassed the US by CINC estimations, eventually lost the Cold War (p. 29). With China's GDP efficiency index being only about 11 per cent of America's, Beijing will have a hard time challenging Washington.

VALIDITY OF HAND-HELD DYNAMOMETRY IN MEASURING QUADRICEPS STRENGTH AND RATE OF TORQUE DEVELOPMENT

A hand-held dynamometer (HHD) offers a reliable and valid method to quantify quadriceps strength in a clinical environment. While measures of peak strength provide functional insights, most daily activities are performed quickly and do not require maximum strength. Rate of torque development (RTD) measures better reflect both the demands of daily activity and athletic movements. The capacity to obtain RTD measures in clinical settings is possible with an HHD, but the validity of RTD measures has not been quantified. To determine the validity of an HHD to measure quadriceps isometric strength metrics compared to isometric strength measures obtained on an isokinetic dynamometer. It was hypothesized that the HHD would be a valid measure of peak torque and RTD at all time intervals when compared to the isokinetic dynamometer. Descriptive laboratory study. Twenty healthy participants (12 male, 8 female) (age = 23.7 ± 2.9 years, height = 174.6 ± 10.1 cm, mass = 76.4 ± 15.9 kg, and Tegner = 6.7 ± 1.2) performed maximum isometric quadriceps contractions on an isokinetic dynamometer and with an HHD. Outcome measures included quadriceps peak torque and RTD at three intervals (0-100, 0-250 ms, and average). Pearson product-moment correlation coefficients and Spearman's rank correlation coefficient were used to determine relationships between devices. Bland-Altman Plots with Limits of Agreement (LOA) calculations were used to quantify systematic bias between measurement techniques. There was a significant correlation between the isokinetic dynamometer and the HHD for peak torque (p<.001, r = .894) and all RTD measurements (p<.002, r = .807; ρ = .502-.604). Bland-Altman plot LOA indicated the HHD overestimated peak torque values (19.4 ± 53.2 Nm) and underestimated all RTD measurements (-55.2 ± 190.7 Nm/s to -265.2 ± 402.6 Nm/s). These results show it is possible to obtain valid measures of quadriceps peak torque and late RTD using an HHD. Measures of early RTD and RTDAvg obtained with an HHD were more variable and should be viewed with caution. Diagnostic, Level 3.

Non-invasive Measurement of Dynamic Myocardial Stiffness Using Acoustic Radiation Force Impulse Imaging

Myocardial stiffness exhibits cyclic variations over the course of the cardiac cycle. These trends are closely tied to the electromechanical and hemodynamic changes in the heart. Characterization of dynamic myocardialstiffness can provide insights into the functional state of the myocardium, as well as allow for differentiation between the underlying physiologic mechanisms that lead to congestive heart failure. Previous work has revealed the potential of acoustic radiation force impulse (ARFI) imaging to capture temporal trends in myocardial stiffness in experimental preparations such as the Langendorff heart, as well as on animals in open-chest and intracardiac settings. This study was aimed at investigating the potential of ARFI to measure dynamic myocardial stiffness in human subjects, in a non-invasive manner through transthoracic imaging windows. ARFI imaging was performed on 12 healthy volunteers to track stiffness changes within the interventricular septum in parasternal long-axis and short-axis views. Myocardial stiffness dynamics over the cardiac cycle was quantified using five indices: stiffness ratio, rates of relaxation and contraction and time constants of relaxation and contraction. The yield of ARFI acquisitions was evaluated based on metrics of signal strength and tracking fidelity such as displacement signal-to-noise ratio, signal-to-clutter level, temporal coherence of speckle and spatial similarity within the region of excitation. These were quantified using the mean ARF-induced displacements over the cardiac cycle, the contrast between the myocardium and the cardiac chambers, the minimum correlation coefficients of radiofrequency signals and the correlation between displacement traces across simultaneously acquired azimuthal beams, respectively. Forty-one percent of ARFI acquisitions were determined to be “successful” using a mean ARF-induced displacement threshold of 1.5 μm. “Successful” acquisitions were found to have higher (i) signal-to-clutter levels, (ii) temporal coherence and (iii) spatial similarity compared with “unsuccessful” acquisitions. Median values of these three metrics, between the two groups, were measured to be 13.42dB versus 5.42dB, 0.988 versus 0.976 and 0.984 versus 0.849, respectively. Signal-to-clutter level, temporal coherence and spatial similarity were also found to correlate with each other. Across the cohort of healthy volunteers, the stiffness ratio measured was 2.74 ± 0.86; the rate of relaxation, 7.82 ± 4.69/s; and the rate of contraction, –7.31±3.79 /s. The time constant of relaxation was 35.90 ± 20.04ms, and that of contraction was 37.24 ± 19.85ms. ARFI-derived indices of myocardial stiffness were found to be similar in both views. These results indicate the feasibility of using ARFI to measure dynamic myocardial stiffness trends in a non-invasive manner and also highlightthe technical challenges of implementing this method in the transthoracic imaging environment.

Representation of Western Disturbances in CMIP5 Models

AbstractWestern disturbances (WDs) are synoptic extratropical disturbances embedded in the subtropical westerly jet stream. They are an integral part of the South Asian winter climate, both for the agriculture-supporting precipitation they bring to the region and for the associated isolated extreme events that can induce devastating flash flooding. Here, WD behavior and impacts are characterized in 23 CMIP5 historical simulations and compared with reanalysis and observations. It is found that WD frequency has a strong relationship with model resolution: higher-resolution models produce significantly more WDs and a disproportionately high fraction of extreme events. Exploring metrics of jet strength and shape, we find that the most probable cause of this relationship is that the jet is wider in models with coarser resolution, and therefore the northern edge in which WDs are spun up sits too far north of India. The frequency of WDs in both winter and summer is found to be overestimated by most models, and thus the winter frequency of WDs estimated from the multimodel mean (30 per winter) is above the reanalysis mean (26 per winter). In this case, the error cannot be adequately explained by local jet position and strength. Instead, we show that it is linked with a positive bias in upstream midtropospheric baroclinicity. Despite a positive winter precipitation bias in CMIP5 models over most of India and Pakistan and a dry bias in the western Himalayas, the fraction of winter precipitation for which WDs are responsible is accurately represented. Using partial correlation, it is shown that the overestimation in WD frequency is the largest contributor to this bias, with a secondary, spatially heterogeneous contribution coming from the overestimation of WD intensity.

Nonvascularized Bone Graft Reconstruction of the Irradiated Murine Mandible: An Analogue of Clinical Head and Neck Cancer Treatment.

Nonvascularized bone grafts (NBGs) represent a practical method of mandibular reconstruction that is precluded in head and neck cancer patients by the destructive effects of radiotherapy. Advances in tissue-engineering may restore NBGs as a viable surgical technique, but expeditious translation demands a small-animal model that approximates clinical practice. This study establishes a murine model of irradiated mandibular reconstruction using a segmental iliac crest NBG for the investigation of imperative bone healing strategies. Twenty-seven male isogenic Lewis rats were divided into 2 groups; control bone graft and irradiated bone graft (XBG). Additional Lewis rats served as graft donors. The XBG group was administered a fractionated dose of 35Gy. All rats underwent reconstruction of a segmental, critical-sized defect of the left hemi-mandible with a 5 mm NBG from the iliac crest, secured by a custom radiolucent plate. Following a 60-day recovery period, hemi-mandibles were evaluated for bony union, bone mineralization, and biomechanical strength (P < 0.05). Bony union rates were significantly reduced in the XBG group (42%) compared with controls (80%). Mandibles in the XBG group further demonstrated substantial radiation injury through significant reductions in all metrics of bone mineralization and biomechanical strength. These observations are consistent with the clinical sequelae of radiotherapy that limit NBGs to nonirradiated patients. This investigation provides a clinically relevant, quantitative model in which innovations in tissue engineering may be evaluated in the setting of radiotherapy to ultimately provide the advantages of NBGs to head and neck cancer patients and reconstructive surgeons.

Structural changes in the shallow and transition branch of the Brewer–Dobson circulation induced by El Niño

Abstract. The stratospheric Brewer–Dobson circulation (BDC) determines the transport and atmospheric lifetime of key radiatively active trace gases and further impacts surface climate through downward coupling. Here, we quantify the variability in the lower stratospheric BDC induced by the El Niño–Southern Oscillation (ENSO), using satellite trace gas measurements and simulations with the Lagrangian chemistry transport model, CLaMS, driven by ERA-Interim and JRA-55 reanalyses. We show that despite discrepancies in the deseasonalized ozone (O3) mixing ratios between CLaMS simulations and satellite observations, the patterns of changes in the lower stratospheric O3 anomalies induced by ENSO agree remarkably well over the 2005–2016 period. Particularly during the most recent El Niño in 2015–2016, both satellite observations and CLaMS simulations show the largest negative tropical O3 anomaly in the record. Regression analysis of different metrics of the BDC strength, including mean age of air, vertical velocity, residual circulation, and age spectrum, shows clear evidence of structural changes in the BDC in the lower stratosphere induced by El Niño, consistent with observed O3 anomalies. These structural changes during El Niño include a weakening of the transition branch of the BDC between about 370 and 420 K (∼100–70 hPa) and equatorward of about 60∘ and a strengthening of the shallow branch at the same latitudes and between about 420 and 500 K (∼70–30 hPa). The slowdown of the transition branch is due to an upward shift in the dissipation height of the large-scale and gravity waves, while the strengthening of the shallow branch results mainly from enhanced gravity wave breaking in the tropics–subtropics combined with enhanced planetary wave breaking at high latitudes. The strengthening of the shallow branch induces negative tropical O3 anomalies due to enhanced tropical upwelling, while the weakening of the transition branch combined with enhanced downwelling due to the strengthening shallow branch leads to positive O3 anomalies in the extratropical upper troposphere–lower stratosphere (UTLS). Our results suggest that a shift in the ENSO basic state toward more frequent El Niño-like conditions in a warmer future climate will substantially alter UTLS trace gas distributions due to these changes in the vertical structure of the stratospheric circulation.