Changes In Longitudinal Strain Research Articles

Relation of Insulin Resistance to Longitudinal Changes in Left Ventricular Structure and Function in a General Population.

BackgroundPopulation data on the longitudinal changes of left ventricular (LV) structure and function in relation to insulin resistance are sparse. Therefore, we assessed in a general population whether hyperinsulinemia predicts longitudinal changes in LV and arterial characteristics.Methods and ResultsIn 627 participants (mean age 50.7 years, 51.4% women), we assessed echocardiographic indexes of LV structure and function and carotid‐femoral pulse wave velocity by applanation tonometry at baseline and after 4.7 years. We regressed longitudinal changes in these indexes on baseline insulin and its change during follow‐up, and reported standardized effect sizes as a percentage of the SD of LV changes associated with a doubling of insulin. After adjustment, higher baseline insulin predicted a greater temporal increase in LV mass index (effect size: +15.1%) and E/e′ ratio (+22.1%), and a greater decrease in e′ peak and longitudinal strain (−11.2% to −17.1%). A greater increase in insulin during follow‐up related to a greater increase in LV mass index (+10.7%) and decline in ejection fraction and longitudinal strain (−11.4% to −15.7%). Participants who became or remained insulin resistant during follow‐up experienced worse changes in longitudinal strain, E/e′, and LV mass index as compared with participants who did not develop or had improved insulin resistance over time (P≤0.033). Moreover, multivariable‐adjusted increase in pulse wave velocity was higher in participants with diabetes mellitus than in participants without diabetes mellitus (+1.46 m/s versus +0.71 m/s; P=0.039).ConclusionsHyperinsulinemia at baseline and during follow‐up predicted worsening of LV function and remodeling over time. Our findings underline the importance of management of insulin resistance.

The effect of an aerobic exercise bout 24h prior to each doxorubicin treatment for breast cancer on markers of cardiotoxicity and treatment symptoms: a RCT.

In rodents, a single exercise bout performed 24h prior to a single doxorubicin treatment provides cardio-protection. This study investigated whether performing this intervention prior to every doxorubicin treatment for breast cancer reduced subclinical cardiotoxicity and treatment symptoms. Twenty-four women with early stage breast cancer were randomly assigned to perform a 30-min, vigorous-intensity treadmill bout 24h prior to each of four doxorubicin-containing chemotherapy treatments or to usual care. Established echocardiographic and circulating biomarkers of subclinical cardiotoxicity, as well as blood pressure and body weight were measured before the first and 7-14days after the last treatment. The Rotterdam symptom checklist was used to assess patient-reported symptoms. The exercise and usual care groups did not differ in the doxorubicin-related change in longitudinal strain, twist, or cardiac troponin. However, the four total exercise bouts prevented changes in hemodynamics (increased cardiac output, resting heart rate, decreased systemic vascular resistance, p<0.01) and reduced body weight gain, prevalence of depressed mood, sore muscles, and low back pain after the last treatment (p<0.05) relative to the usual care group. No adverse events occurred. An exercise bout performed 24h prior to every doxorubicin treatment did not have an effect on markers of subclinical cardiotoxicity, but had a positive systemic effect on hemodynamics, musculoskeletal symptoms, mood, and body weight in women with breast cancer. A single exercise bout prior to chemotherapy treatments may be a simple clinical modality to reduce symptoms and weight gain among women with breast cancer.

Protective effects of acute exercise prior to doxorubicin on cardiac function of breast cancer patients: A proof-of-concept RCT

BackgroundPreclinical studies have reported that a single treadmill session performed 24h prior to doxorubicin provides cardio-protection. We aimed to characterize the acute change in cardiac function following an initial doxorubicin treatment in humans and determine whether an exercise session performed 24h prior to treatment changes this response. MethodsBreast cancer patients were randomized to either 30min of vigorous-intensity exercise 24h prior to the first doxorubicin treatment (n=13), or no vigorous exercise for 72h prior to treatment (control, n=11). Echocardiographically-derived left ventricular volumes, longitudinal strain, twist, E/A ratio, and circulating NT-proBNP, a marker of later cardiotoxicity, were measured before and 24–48h after the treatment. ResultsFollowing treatment in the control group, NT-proBNP, end-diastolic and stroke volumes, cardiac output, E/A ratio, strain, diastolic strain rate, twist, and untwist velocity significantly increased (all p≤0.01). Whereas systemic vascular resistance (p<0.01) decreased, and ejection fraction (p=0.02) and systolic strain rate (p<0.01) increased in the exercise group only. Relative to control, the exercise group had a significantly lower NT-proBNP (p<0.01) and a 46% risk reduction of exceeding the cut-point used to exclude acute heart failure. ConclusionThe first doxorubicin treatment is associated with acutely increased NT-proBNP, echocardiographic parameters of myocardial relaxation, left ventricular volume overload, and changes in longitudinal strain and twist opposite in direction to documented longer-term changes. An exercise session performed 24h prior to treatment attenuated NT-proBNP release and increased systolic function. Future investigations should verify these findings in a larger cohort and across multiple courses of doxorubicin.

Digitally controlled chirped pulse laser for sub-terahertz-range fiber structure interrogation.

This Letter reports a sweep velocity-locked laser pulse generator controlled using a digital phase-locked loop (DPLL) circuit. This design is used for the interrogation of sub-terahertz-range fiber structures for sensing applications that require real-time data collection with millimeter-level spatial resolution. A distributed feedback laser was employed to generate chirped laser pulses via injection current modulation. A DPLL circuit was developed to lock the optical frequency sweep velocity. A high-quality linearly chirped laser pulse with a frequency excursion of 117.69GHz at an optical communication band was demonstrated. The system was further adopted to interrogate a continuously distributed sub-terahertz-range fiber structure (sub-THz-fs) for sensing applications. A strain test was conducted in which the sub-THz-fs showed a linear response to longitudinal strain change with predicted sensitivity. Additionally, temperature testing was conducted in which a heat source was used to generate a temperature distribution along the fiber structure to demonstrate its distributed sensing capability. A Gaussian temperature profile was measured using the described system and tracked in real time, as the heat source was moved.

Variability of longitudinal strain in left ventricular segments supplied by non-stenosed coronary artery: insights from speckle tracking analysis of dobutamine stress echocardiograms in patients with high coronary risk profile.

IntroductionAlthough global deformation parameters have been increasingly used for myocardial function analysis, there are sparse data concerning segmental deformation of the left ventricle (LV). Moreover, some studies suggest heterogeneity of strain among LV segments, which may be especially significant during stress echocardiography. We assessed quantitatively regional LV function in the setting of dobutamine stress echocardiography (DSE), to examine differences of longitudinal strain between basal, mid and apical LV segments and to compare variability of regional deformation between rest and the peak stage of DSE.Material and methodsAmong 250 patients examined by DSE applied for diagnosis of ischemia, a subset of 111 patients without significant coronary stenoses in angiography was selected (68 females, mean age: 60 ±10 years). Systolic longitudinal strain (SLS) in individual LV segments at baseline and the peak stage of DSE was analyzed with speckle tracking echocardiography.ResultsInhomogeneity of SLS among the LV segments (p < 0.001) was observed at baseline and the peak stage. Dispersion indices were higher at the peak stage of DSE than at baseline (p < 0.001), and the lowest heterogeneity was observed among mid segments. The analysis of changes in SLS during DSE showed SLS reduction in basal and mid-ventricular segments and an increase in apical segments.ConclusionsSignificant heterogeneity of strain and the opposite direction of the longitudinal strain changes during DSE between apical and basal LV segments were observed. This variability among non-ischemic LV segments ought to be considered in quantification of LV function during DSE.

Noninvasive Measures of Ventricular-Arterial Coupling and Circumferential Strain Predict Cancer Therapeutics–Related Cardiac Dysfunction

ObjectivesThis study sought to determine the relationships between echocardiography-derived measures of myocardial mechanics and cancer therapeutics–related cardiac dysfunction (CTRCD). BackgroundDoxorubicin and trastuzumab are highly effective breast cancer therapies, but have a substantial risk of CTRCD. There is a critical need for the early detection of patients at increased risk of toxicity. MethodsWe performed a prospective, longitudinal cohort study of breast cancer participants undergoing doxorubicin and/or trastuzumab therapy. Echocardiography was performed prior to therapy initiation (baseline) and at standardized follow-up intervals during and after completion of therapy. Ejection fraction (EF), strain, strain rate, and ventricular-arterial coupling (effective arterial elastance [Ea]/end-systolic elastance [Eessb]) were quantitated. CTRCD was defined as a ≥10% reduction in EF from baseline to <50%. Multivariable logistic regression models were used to determine the associations between baseline levels and changes from baseline in echocardiographic measures and CTRCD. Receiver-operating characteristic curves were used to evaluate the predictive ability of these measures. ResultsIn total, 135 participants contributed 517 echocardiograms to the analysis. Over a median follow-up time of 1.9 years (interquartile range: 0.9 to 2.4 years), 21 participants (15%) developed CTRCD. In adjusted models, baseline levels and changes in Ea/Eessb, circumferential strain, and circumferential strain rate were associated with 21% to 38% increased odds of CTRCD (p < 0.001). Changes in longitudinal strain (p = 0.037), radial strain (p = 0.015), and radial strain rate (p = 0.006) were also associated with CTRCD. Ea/Eessb (area under the curve: 0.703; 95% confidence interval: 0.583 to 0.807) and circumferential strain (area under the curve: 0.655; 95% confidence interval: 0.517 to 0.767) demonstrated the greatest predictive utility. Sensitivity analyses using an alternative CTRCD definition did not impact our results. ConclusionsOver an extended follow-up time, ventricular-arterial coupling and circumferential strain were strongly predictive of CTRCD. Our findings suggest a noninvasive strategy to identify high-risk patients prior to, during, and after cardiotoxic cancer therapy.

Abstract 19564: Short Term Improvement in Subtle Cardiac Dysfunction in Severely Obese Patients After Bariatric Surgery is Not Associated With Changes in Nt-pro-bnp: A Speckle Tracking Study

Background and objective: The impact of bariatric surgery on sub-clinical alteration of cardiac function assessed using speckle-tracking strain and its relationship with metabolic changes is unknown. We assessed in obese patients with normal left ventricle (LV) systolic function who underwent the biliopancreatic diversion with duodenal switch (BPD-DS); 1) prevalence of subclinical cardiac dysfunction and dyssynchrony in comparison with gender-matched subjects and, 2) the impact of bariatric surgery on myocardial function and its association with changes in NT-proBNP levels and insulin sensitivity. Methods: Prospective, observational study of the effect of BPD-DS after six months on strain, strain rate (SR) and displacement curves using a repeated measures mixed linear regression model analysis. Changes in systolic (LV end-systolic dimension, longitudinal strain) and diastolic (E/A, ESr) parameters were correlated with changes in body mass index (BMI), HOMA and NT-proBNP. Results: Thirty-eight severely obese patients (BMI 48.4±7.4 Kg/m 2 ) had decreased longitudinal strain (-17.0±2.5%) in comparison with 20 patients without obesity (-19.7±1.5%) (p&lt;0.001), which was comparable to controls after surgery (19.3±1.8%) at a mean BMI of 35.7±6 mg/m 2 . Eighteen patients (47%) had a global longitudinal strain considered clinically abnormal. Following surgery, 94% of these patients improved their LV mechanics, with normalization of their global longitudinal strain (p&lt;0.001). Changes in longitudinal strain were not related with changes in NT-proBNP or improvement in insulin sensitivity. Conclusions: There is significant subclinical cardiac dysfunction in patients with severe obesity with normal systolic function. Improvement in longitudinal strain after surgery was not explained by improved insulin sensitivity or changes in NT-proBNP.

Abstract 17179: Combined Doxycycline and Tauroursodeoxycholic Acid Slows Progression of Transthyretin Cardiac Amyloidosis

Introduction: Transthyretin (TTR) cardiac amyloidosis (CA) is a progressive infiltrative cardiomyopathy with no specific therapy. In animals, doxycycline disrupts existing amyloid fibrils and may prevent fibrillogenesis. Tauroursodeoxycholic acid (TUDCA), a bile acid, prevents extracellular TTR monomer deposits, and the 2 drugs work synergistically in a mouse model of amyloidosis to decrease tissue amyloid. We sought to determine whether a combination of TUDCA and doxycycline could slow the progression of amyloid-associated LV dysfunction in patients with TTR cardiac amyloidosis. Methods: 17 patients with biopsy-proven TTR cardiac amyloidosis, mean age 71.3 yr (all men: 16 wild-type and 1 mutant TTR), received doxycycline 100 bid and TUDCA 250 mg tid for 12 months. The primary endpoint was change in longitudinal strain (LS) at 12 months, when compared to a group of 14 patients studied serially without therapy (mean age 72.4 yr, all men). All patients had echocardiograms performed on a GE Vivid machine, and analyzed by the same investigator. LS was measured from the apical 4-chamber view. Results: Doxycycline/TUDCA was well-tolerated. Mean baseline LS was no different between treatment group and untreated patients, and both groups showed deterioration of LS at 12 months. However, deterioration of LS was less in the treated group than controls (table). NTproBNP, a marker of disease was measured in the treatment group only, and rose slightly from a mean of 3108 pg/ml to 3669 pg/ml,(p&lt;0.05) consistent with the change in LS. Conclusion: 1. TTR cardiac amyloidosis is characterized by a consistent decrease in LV strain over a 1 year period, associated with a rise in NTproBNP. 2. Although doxycycline/TUDCA combination does not entirely halt progression of LV dysfunction, it appears to significantly slow the progression of disease and offers a well-tolerated therapy for disease modification.

The ultimate axial bearing capacity of alkali-activated concrete-filled steel tubes

This paper aims to study the mechanical properties of composite structure, which is alkali-activated concrete-filled steel tube. A commercial alkali-activated binder provided by an industrial partner was used as the in-filled concrete of alkali-activated concrete-filled steel tube. The ultimate axial-bearing capacity was determined at a static loading rate of 10 kN per stage with each stage maintaining for 2 minutes. The longitudinal strain changes at vertical direction and circumstantial strain changes at the mid-section of steel tubes during the loading process were measured by related strain gauges. The results show that four stages can be classified based on the load–deformation relationship, whereas the elastic stage can account for around 70–80% of ultimate bearing capacity. On the other hand, compared with ordinary cement concrete-filled steel tube, improved mechanical properties were observed for alkali-activated concrete-filled steel tube.

Changes in Myocardial Contractility and Electromechanical Interval During the First Month of Life in Healthy Neonates.

This study aims at documenting the changes in ventricular tissue velocities, longitudinal strain and electromechanical coupling during the first month of life. During the neonatal period, when the ventricular myocardium is not yet fully maturated, the heart is subjected to significant hemodynamic changes. We studied the ventricular performance of 16 healthy neonates at three time points over the first month of life: on days 2 (IQR [2;2]), 13 [12;14] and 27 [25;29]. We found that systolic and diastolic tissue velocities increased significantly in both left and right ventricle (by 1.2-1.7 times, p < 0.001). Congruently, we found that peak systolic longitudinal strain of the right and left ventricles increased significantly. However, no significant changes in longitudinal strain rate were observed. Finally, QS-intervals shortened during the neonatal period: being measured at 12 points throughout the left ventricle, time to peak systolic velocity decreased on average to 89 % in the second and to 80 % in the fourth week of life (22.3 ± 0.2 vs. 19.8 ± 0.3 vs. 17.8 ± 0.5 ms, r = -0.564, p < 0.001). When comparing opposing walls of the left ventricle, no dyssynchrony in left ventricular contraction was found. In addition to increasing systolic and diastolic tissue velocities during the first month of life, the time to peak systolic contraction shortens in the neonatal heart, which may reflect an increasing efficiency of the excitation-contraction coupling in the maturing myocardium. While there appears to be no dyssynchrony in ventricular contraction, these findings may extend our appreciation of the immature neonatal heart and certain disease states.

Three-dimensional morphology and strain of the human Achilles free tendon immediately following eccentric heel drop exercise.

Our understanding of the immediate effects of exercise on Achilles free tendon transverse morphology is limited to single site measurements acquired at rest using 2D ultrasound. The purpose of this study was to provide a detailed 3D description of changes in Achilles free tendon morphology immediately following a single clinical bout of exercise. Freehand 3D ultrasound was used to measure Achilles free tendon length, and regional cross-sectional area (CSA), medio-lateral (ML) diameter and antero-posterior (AP) diameter in healthy young adults (N=14) at rest and during isometric muscle contraction, immediately before and after 3×15 eccentric heel drops. Post-exercise reductions in transverse strain were limited to CSA and AP diameter in the mid-proximal region of the Achilles free tendon during muscle contraction. The change in CSA strain during muscle contraction was significantly correlated to the change in longitudinal strain (r=-0.72) and the change in AP diameter strain (r=0.64). Overall findings suggest the Achilles free tendon experiences a complex change in 3D morphology following eccentric heel drop exercise that manifests under contractile but not rest conditions, is most pronounced in the mid-proximal tendon and is primarily driven by changes in AP diameter strain and not ML diameter strain.

Renal artery denervation affects the circulating microRNA profile in patients with resistant arterial hypertension

Background: Small non-coding RNAs (microRNAs, miR) control mRNA signaling at the level of post-transcriptional regulation. Several miR are regulated in arterial hypertension and myocardial hypertrophy, as demonstrated in animal models and recently also in patient studies. Renal denervation (RDN) reduces blood pressure, left ventricular mass and improves diastolic dysfunction in patients with resistant hypertension. The effect of RDN on circulating miR expression is unknown. Methods and results: RDN reduced systolic and diastolic blood pressure from 168.4±4.5 to 144.0±5.5 mmHg and 88.0±3.1 to 76.8±2.4 mmHg (p<0.001), respectively. Total RNA was isolated from peripheral blood plasma of 20 patients before and 6 months after RDN. RNA was subjected to miR profiling using Agilent 8x60k Homo sapiens microRNA v16 microarrays. Following quantile normalization of the data and determination of differential expression (corrected for multiple testing) we found 34 differentially expressed miRs at a false discovery rate < 5%. 26 miRs were found to be expressed at a higher level following RD, while 3 miRs were expressed at a lower level. Pathway analysis (KEGG, Kyoto Encyclopedia of Genes and Genomes) on the target genes of the downregulated miR suggested MAP kinase and insulin signaling pathways to be affected. Next, we analyzed a quantitative correlation between unique miR and several clinical parameters using regression analysis. MicroRNA expression was related to the ratio (post/pre RD) of left ventricular mass indexed to body surface area (LV mass index, LVMI) and function, as measured by echocardiography. We found the ratio 43 miRs to be positively and the ratio of 17 miRs to be inversely correlated to the ratio of LVMI change. The change of 18 miRs was negatively correlated to change in longitudinal strain determined by speckle tracking echocardiography. The change in 8 miRs was positively correlated to the change in left atrial volume index. Real-time RT-PCR was used to verify selected targets both in the original 20 patients undergoing array analysis and in an independent validation group consisting of further 20 patients. Conclusion: Renal denervation in patients with resistant hypertension substantially influences plasma microRNA expression profile. Changes in specific miR s showed a quantitative correlation with changes in blood pressure and left-ventricular mass. These data identify potential marker miRs and provide insights into miR signaling in hypertension.

Dispersion of regional longitudinal strain and strain rate in nonischemic left ventricular segments: insights from speckle tracking Dobutamine Stress Echocardiography (DSE)

Background: The measurement of deformation parameters - Strain (S) and Strain Rate (SR) - allows the quantitative analysis of myocardial function. There is still a paucity of data concerning regional deformation during Dobutamine Stress Echocardiography (DSE) and little is known about potential differences of basal, midventricular and apical segments of the Left Ventricle (LV). Aim: Our aim was to assess regional values of longitudinal S and SR in 18 segments of LV during baseline and peak stage of DSE and change of these parameters between baseline and peak using Speckle Tracking Echocardiographic quantification (STE) and Automated Function Imaging (AFI). Methods: 238 patients were examined by DSE with acquisition of high temporal resolution data. The whole group had the coronary anatomy status established by angiography or computed tomography. A subset of 111 patients without significant coronary lesions was selected for this analysis: 68 female, mean age 60±10 years. Results: The significant dispersion of strain values among the LV segments (measured both by AFI and STE and confirmed by ANOVA, p<0.0001) was observed during baseline and peak stage of DSE. The comparison of changes in strain between peak and baseline stage showed reduction in strain amplitude of basal and mid-ventricular segments and increased amplitude of strain in apical segments of the LV. Contrarily, absolute values of SR increased during DSE in all segments. Dispersion of the change in strain and designation of segments are presented in Figure. ![Figure][1] Conclusions: We observed opposite direction of the longitudinal strain changes during DSE between apical and basal 2/3 part of myocardium. This significant dispersion among nonischemic LV segments must be considered in LV function quantification during stress echo. [1]: pending:yes

Speckle echocardiographic left atrial strain and stiffness index as predictors of maintenance of sinus rhythm after cardioversion for atrial fibrillation: a prospective study

BackgroundEchocardiographic left atrial (LA) strain parameters have been associated with atrial fibrillation (AF) in prior studies. Our goal was to determine if strain measures [peak systolic longitudinal strain (LAS) and stiffness index (LASt)] changed after cardioversion (CV); and their relation to AF recurrence.Methods and results46 participants with persistent AF and 41 age-matched participants with no AF were recruited. LAS and LASt were measured before and immediately after CV using 2D speckle tracking imaging (2DSI). Maintenance of sinus rhythm was assessed over a 6-month follow up. Mean LAS was lower, and mean LASt higher, in participants with AF before CV as compared to control group (11.9 ± 1.0 vs 35.7 ± 1.7, p<0.01 and 1.31 ± 0.17 vs 0.23 ± 0.01, p<0.01, respectively). There was an increase in the mean LAS immediately after CV (11.9 ± 1.0 vs 15.9 ± 1.3, p<0.01), whereas mean LASt did not change significantly after CV (p=0.62). Although neither LAS nor LASt were independently associated with AF recurrence during the follow-up period, change in LAS after cardioversion (post-CV LAS – pre-CV LAS) was significantly higher among individuals who remained in sinus rhythm when compared to individuals with recurrent AF (3.6 ± 1.1 vs 0.4 ± 0.8, p=0.02).ConclusionsLAS and LASt differed between participants with and without AF, irrespective of the rhythm at the time of echocardiographic assessment. Baseline LAS and LASt were not associated with AF recurrence. However, change in LAS after CV may be a useful predictor of recurrent arrhythmia.

Comparative investigation of mechanical characteristics of stable and unstable carotid atherosclerotic plaques

The prognosis of patients with carotid atherosclerosis is determined by the factor of unstable atherosclerotic plaque. Change of longitudinal strain in junction place of healthy artery wall to plaque determined by local artery elasticity and leads to instability. Aim of the study: Comparative investigation of mechanical characteristics of the stable and unstable plaques in a carotid artery. Methods: In the main group (MGr) were studied 16 plaques with stenosis 7090%, and control group (CGr) 33 plaques with stenosis 25-45%. Carotid ultrasound examinations (PHILIPS iU22) were performed for estimated structure and stenosis of plaques. The ”healthy” wall stiffness (free from plaques -bhw) and plaques zone stiffness (in adventitia -badv and in plaques surface -bpl) were estimated using echo-tracking method by ALOKAa7 in B/M mode ultrasound imaging. Results: In the MGr majority of plaques had structure with hypoechogenic area (>50%) and calcification, third plaques had rough or ulcerated surface. In CGr dominated heterogeneous plaques with smooth surface. In both groups bhw was significantly lower, than badv (MGr: 8,95 3,14 vs 22,73 10,43, CGr: 9,43 2,64 vs 14,45 6,7, p<0,001), badv was significantly higher than bpl (MGr: 22,73 10,43 vs 7,7 5,04; CGr: 14,45 6,7 vs 11,69 6,84, p<0,001). Relative changes of plaques zone stiffness (100bpl 100/badv) was significantly higher in the MGr (51,28 24,17% vs 26,93 21,45%, pZ0,036). Conclusions: Our results confirm presence the significant gradient of stiffness in junction place of healthy artery wall to plaque. In group with unstable plaques this gradient was significantly higher, that allows considering the possibility of the unstable plaques criteria developing by echotracking method.

Right Ventricular Systolic Pressures in Patients with Normal Left Ventricular Systolic Function—A Study of 51,429 Australian Echocardiograms

Objective: To evaluate the longitudinal function of left side (Ls) and right side ventricular septum (Rs) during treatment of patients with pulmonary hypertension (PAH). Background: Leftwards shift and flattening of the interventricular septum are recognised consequences of RV pressure overload. Rs and Ls respond differently to various conditions, however little is known about longitudinal strain changes in patients with PAH. Method: Twenty controls and 21 chronic PAH patients were studied.A 3.5MHz transducer (GE,Vivid 7)was used for imaging (frame rate 50–80). Rs and Ls segmental peak systolic longitudinal strains were obtained in the apical four chamber view at baseline and at sixmonthly intervals over 24 months follow up during treatment with either Bosentan or Sildenafil. Results: In control subjects, Rs and Ls longitudinal Figure 1.

Structural health monitoring of marine composite structural joints using embedded fiber Bragg grating strain sensors

This paper presents a method for the health monitoring of composite joints based on strain measurements using distributed embedded fiber Bragg grating (FBG) sensors. Secondary bonded woven E-glass/vinyl ester composite doubler plate joints were subjected to fatigue tension loading to induce stable crack propagation. A finite element (FE) model was developed to correlate experimental strain measurements prior to cyclic loading with the numerical predictions and to determine the sensitivity of the sensors to changes in longitudinal strain due to crack growth. Initial quasi-static tension tests demonstrated satisfactory correlation between the strains from the FBG sensors and FE predictions. The changes in longitudinal strain distribution during the fatigue tests were correlated with crack growth. A progressive shift in the strain distribution in the vicinity of the crack was observed. The experimental results demonstrated that a strain-based methodology can be utilized to detect crack propagation in this type of composite joints.

Ferroelectric properties of monoclinicPb(Mg1/3Nb2/3)O3−PbTiO3crystals

A monoclinic phase was recently discovered near the morphotropic phase boundary in several high-performance piezoelectric perovskite solid solutions, but its properties have not been reported. In this paper the dielectric, piezo- and ferroelectric properties of the monoclinic Pm phase in the (1-x)Pb(Mg1/3Nb2/3)O3 -xPbTiO3 perovskite system are studied. In a (001)-oriented crystal of composition x=0.33, ferroelectric hysteresis loops with remanent polarization of 23 uC/cm^2 are displayed. In poled monoclinic crystals, under unipolar drive up to 10 kV/cm, the domain walls remain unchanged, the polarization and longitudinal strain change almost linearly, but the piezoelectric response (d33=9x10^(-10) C/N) is much weaker than in the rhombohedral phase of close composition. The relative dielectric permittivity of the Pm phase is also smaller (with a small-signal value of ~ 2500), but the piezoelectric constant (g33 = 3 x10^(-2) m^2/C) and the electromechanical coupling factor (kt = 0.60) are practically the same as in the rhombohedral phase. The properties of the various phases in the range of the morphotropic phase boundary are related to the different rotation paths of the polarization vector induced by the external drive.

Strain analysis of a Northern Apennine shear zone using deformed marble breccias

The Alpi Apuane region of the Northern Apennines appears to have been deformed within a large-scale, low-angle shear zone with an overthrust sense of movement. The presence of mineral stretching lineations, folds progressively rotated into the X strain direction, and schistosities which intersect the nappe boundaries at small angles suggest that a component of shear strain occurred during the deformation. The strain ratios and orientations on two-dimensional sections have been determined from deformed marble breccias, reduction spots, and oncalites. Data from three or more non-perpendicular, non-principal sections have been combined to determine the finite strain ellipsoids at 33 sites within the shear zone. The finite strains have been separated into components of simple shear (γ), longitudinal strain (λ), and volume change (Δ). Algebraic expressions have been derived and graphs constructed which enable components of γ, γ and Δ, and γ and λ to be determined directly from a knowledge of strain ratio ( R) within the shear zone and the angle (θ) between the principal strain direction and the shear zone boundary. The Alpi Apuane data indicate that neither simple shear alone, nor simple shear with volume change can satisfactorily explain the observed strains. Consideration of simple shear plus longitudinal strain leads to a general relationship in which the value of shear increases, and the values of longitudinal strain change along a SW-NE profile across the zone. Integration of the resulting shear strain-distance curves gives a minimum displacement of 4 km within the shear zone. Combination of the finite strains with the total time of deformation known from K/Ar studies leads to average strain rates from 1.4 to 9.6 × 10 −15 sec −1. A characteristic flat-ramp-flat geometry initially formed the boundaries of what was later to develop into the overthrust shear zone, and deformation of the underlying crystalline basement is believed to have occurred by ductile shearing. Estimates of 21% crustal shortening for the region suggest that the crustal thickness prior to deformation was approximately 20 km in this part of the Northern Apennines.

Transient longitudinal strain changes during welding

Experimental measurements are presented to demonstrate the longitudinal strain changes that occur when structural sections are welded. The measurements show that the final deformation in the upset zone can be as much as 35 percent more than the transient deformation on heating. The assumption in the Okerblom analysis that these two deformations are equal is discussed in view of the results.1 In addition, measured final deformations are compared to those predicted from this same analysis for a wide range of edge-welded rectangular bar sections.