Coronary plaque composition influences biomechanical stress and predicts plaque rupture in a morpho-mechanic OCT analysis

Plaque rupture occurs if stress within coronary lesions exceeds the protection exerted by the fibrous cap overlying the necrotic lipid core. However, very little is known about the biomechanical stress exerting this disrupting force. Employing optical coherence tomography (OCT), we generated plaque models and performed finite-element analysis to simulate stress distributions within the vessel wall in 10 ruptured and 10 non-ruptured lesions. In ruptured lesions, maximal stress within fibrous cap (peak cap stress [PCS]: 174 ± 67 vs. 52 ± 42 kPa, p<0.001) and vessel wall (maximal plaque stress [MPS]: 399 ± 233 vs. 90 ± 95 kPa, p=0.001) were significantly higher compared to non-ruptured plaques. Ruptures arose in the immediate proximity of maximal stress concentrations (angular distances: 21.8 ± 30.3° for PCS vs. 20.7 ± 23.7° for MPS); stress concentrations excellently predicted plaque rupture (area under the curve: 0.940 for PCS, 0.950 for MPS). This prediction of plaque rupture was superior to established vulnerability features such as fibrous cap thickness or macrophage infiltration. In conclusion, OCT-based finite-element analysis effectively assesses plaque biomechanics, which in turn predicts plaque rupture in patients. This highlights the importance of morpho-mechanic analysis assessing the disrupting effects of plaque stress.

Retrograde extrapolation of VO2max from recovery values recorded breath by breath (Extrapolación retrógrada del VO2max a partir de valores de recuperación recogidos respiración a respiración)

The aim of this study was to assess the validity of VO2max prediction using retrograde extrapolation in a breath-by-breath (BxB) gas measurement system. A retrospective study was performed, analysing 31 incremental and maximal stress tests carried out in our laboratory, corresponding to male subjects who practised different sporting activities (age: 29.9 ± 14.45 years; height: 174.4 ± 6.5 cm; weight: 71.4 ± 7.2 kg). A linear regression of the first minute of recovery was used to obtain extrapolated VO2max data and, subsequently, a correction equation was applied that provided predicted VO2max values. Given the variability of data in BxB measurement systems, extrapolated values can be expected to vary significantly from those actually measured, but differences disappeared in the predicted values, which were almost identical to those measured. This method enables stress tests to be performed without having to record gas measurements until the end. It could be useful for the validation of specific field tests, measuring VO2 trackside after the test, during recovery. Resumen. El objetivo de este estudio fue evaluar la validez de la predicción del VO2máx mediante la extrapolación retrógrada en un sistema de medición de gases respiración a respiración (BxB). Se realizó un estudio retrospectivo, analizando 31 pruebas de esfuerzo incrementales y máximas realizadas en nuestro laboratorio, correspondientes a sujetos masculinos que practicaban diferentes actividades deportivas (edad: 29,9 ± 14,45 años; talla: 174,4 ± 6,5 cm; peso: 71,4 ± 7,2 kg). Se utilizó una regresión lineal del primer minuto de recuperación para obtener datos de VO2max extrapolados y, posteriormente, se aplicó una ecuación de corrección que proporcionó valores de VO2max predichos. Dada la variabilidad de los datos en los sistemas de medición BxB, se puede esperar que los valores extrapolados varíen significativamente de los realmente medidos, pero las diferencias desaparecieron en los valores predichos, que eran casi idénticos a los medidos. Este método permite realizar pruebas de esfuerzo sin tener que registrar mediciones de gas hasta el final. Podría ser útil para la validación de pruebas de campo específicas, midiendo el VO2 a pie de campo después de la prueba, durante la recuperación.

Predicting Exertion from Metabolic, Physiological and Cognitive Variables in Older Adults

Objective. To determine the association between perceived exertion (RPE) and physiological variables and to determine the predictive factors of RPE during submaximal and maximal exertion in older adults. Method. Older adults from Kansas (n = 100) and Costa Rica (n = 79) performed a submaximal and maximal stress test. RPE, education level and a total score of cognitive function (CFTS) were collected. Correlation and multiple regression analyses were computed using RPE as the criterion variable and oxygen consumption (VO2), respiratory exchange ratio (RER), CFTS and education level as predictors. Results. There was a significant correlation between VEP and RER (r = 0.22, p = 0.029) at maximal exertion. The RPE predictors for women were VO2, RER, and CFTS at different stages of the test. For men, VEP was predicted by RER, education level, and VO2 at different stages. Conclusion. Metabolic and physiological variables predicted RPE in older adults. Age, cognition, and heart rate were unrelated to RPE at maximal exertion, and RER predicted RPE scores during submaximal and maximal exertion.

Comparison in Four Different Implant Systems of Mechanical Resistance to Maximal Stress in Prosthetic Screws—An In Vitro Study

Micromovements of the implant–abutment connection influence peri-implant bone preservation. This study evaluates and quantifies the maximal torque after a cycle of implant prosthetic screws tightening using original components. A total of 40 samples were tested: Megagen®—Daegu, South Korea; Dentium®—Gangnam-Gu, Seoul, Korea; BIOMET 3i®—West Palm Beach, FL, USA and BTI®—Álava, Spain. Screws from each manufacturer were subjected to maximal stress force until they fractured. The fracture points were recorded and compared among all samples. To compare the mean values of fracture torques, the reference values associated with each brand and the sample results were used in t-tests. ANOVA (analysis of variance) was used to compare the maximal resistance limit between brands, complemented with Tukey’s multiple-comparison test. The maximal considered level of significance was 5%. The average fracture force for the brands was 40.07 Ncm for Megagen®, 53.39 Ncm for Dentium®, 39.74 Ncm for Biomet 3i®, and 68.84 Ncm for BTI®. BTI® screws showed the most resistance to fracture. According to the protocol that was applied, the implant–abutment connection demonstrated good resistance and a precise fit between these interfaces; therefore, in some cases, the presented values showed a lack of quality control and low fracture resistance.

P0747STRESS ERGOMETRY PERFORMANCE AND ABDOMINAL AORTIC CALCIFICATION PREDICT PATIENT OUTCOMES IN CKD STAGE 4-5

Background and Aims Patients with chronic kidney disease (CKD) stage 4-5 have an increased risk of cardiovascular morbidity and mortality. Method We recruited 174 consecutive patients with CKD stage 4-5 between 2013 and 2017 into a prospective follow-up study assessing arterial disease, quality of life, mortality and their predictors. Together with baseline medical data, standard maximal bicycle ergometry stress testing, abdominal aortic calcification score (AAC) and echocardiography was collected. Patients were followed up for mean 42 months. Results Mean age at recruitment was 61 years, 54 (31%) were women and estimated glomerular filtration rate (eGFR) was 12.9 ml/min. Altogether, 36 (21%) patients died during follow-up with a mean time to death of 835 days. At baseline, all but one patient were hypertensive, 75 patients had diabetes and 21 patients had coronary artery disease. Mean AAC was 6.27±5.68 and work load of the last 4 minutes of maximal stress (WMAX) was 83.7±36.5W, respectively. In the multivariate proportional hazard models pro-BNP [1.98 (95% CI 1.36 – 2.90), p=0.0004], WMAX [HR 0.45 (95% CI 0.27 – 0.77), p=0.0033], AAC [HR 2.51 (95% CI 1.37 – 4.61), p=0.0030], E/e’ –ratio [HR 1.66 (95% CI 1.08 – 2.56), p=0.0221] and albumin [HR 0.59 (95% CI 0.39 – 0.90), p=0.0134] were significant predictors for mortality when adjusted with age, sex, diabetes and previous coronary artery disease. Patients who perished, especially those who died in less than 2 years, within follow-up had significantly higher AAC and lower WMAX compared to those surviving to the end of the study (Figure 1). Conclusion Maximal stress ergometry test work load and AAC are associated with patient survival in severe CKD.

Enhanced Performance of Fabry–Perot Tunable Filter by Groove Geometry Design of Double Folded Cantilever

Different grooves (v-shaped groove, trapezoidal groove and rectangular groove) are introduced into the traditional double-folded cantilever of Fabry–Perot Tunable Filter (FPTF) for the optical sensor. Using finite element simulation, the influence of groove geometry on the voltage–displacement relationship, stress distribution and reflector flatness of the FPTF are studied. The results show that the reflector supported by double folded cantilever with rectangular groove has a maximal displacement of 0.88 μm under 8 V driving voltage, which is 95% higher than double folded cantilever without groove. At 0.5 μm, the best flatness (warping angle of reflector) is only 0.0032° for reflector supported by double folded cantilever with rectangular groove, where the generated maximal stress in the double folded cantilever is 8.49 MPa. Compared with other double folded cantilevers with v-shaped groove, trapezoidal groove and without groove, the unique properties of double folded cantilever with rectangular groove are attributed to lower elastic modulus. The double folded cantilever with rectangular groove enlarges displacement results in wide range of bandpass wavelength of FPTF, and a best flatness to enhance the monochrome of bandpass wavelength.

Influence of injection parameters on the dynamics of Hydraulic Fracturing monitored by Acoustic Emission

&lt;p&gt;Understanding the processes of Hydraulic Fracturing (HF) initiation and propagation in different types of rocks is important for the design and optimization of HF during the exploitation of underground resources. The main goals were to study the dynamics of the process of hydraulic fracture growth and possible optimization of HF technology for both homogeneous and heterogeneous rocks. Laboratory experiments on HF with different injection parameters were carried out on natural limestone, dolomite and shale specimens. The dynamics of HF process was monitored by Acoustic Emission (AE) technique, on the analogy of induced microseismicity monitoring of HF in the field conditions. The shape of created HF and the size of leak-off zone were analyzed by X-Ray CT scanning technique after the testing.&lt;/p&gt;&lt;p&gt;Experiments on dolomite were conducted using fluids with different viscosities (1000-10000 cP) injected into the rock with a rate of 0.5 ml/min. In case of low viscosity, we observed low AE activity. After the test, the sample was cut in several pieces transverse to the expected fracture plane. We have found that HF has initiated, but did not reach the sample boundaries and leak-off was significant. The ten times increase of fluid viscosity resulted in significantly increased AE activity, smaller size of leak-off zone and higher breakdown pressure (21.8 against 18.7 MPa). The post-test 3D shape of HF surface obtained by X-Ray CT closely correlates with 3D shape of localized AE events, confirming that the fracture propagated in the direction of maximal stress, as expected. It means that viscosity of fracturing fluid had a significant effect on fracturing breakdown pressure and fracture behavior.&lt;/p&gt;&lt;p&gt;The influence of different rock types on hydraulic fracturing was studied with dolomite, limestone and shale samples. In case of dolomite and shale, sufficient number of Acoustic Emission events were recorded, which allowed tracing the direction and dynamics of fracture propagation. However, for the limestone, a very small number of AE events were localized with the same parameters of injected fluid. Comparison of dolomite and shale HFs shows that the crack in the shale had a more complex shape, deviating from the maximal stress direction, which was explained by rock heterogeneity, by the presence of natural cracks and inclined planes of weakness. It led us to conclusion that the rock fabric plays an important role in the behavior of hydraulic fracture in heterogeneous rock.&lt;/p&gt;

Transverse shear stress within surface layer and its effects

When the transverse shear stress within a surface layer is taken into account, what happens in the deformation of micro- or nanoscale solids? The relevant problems are investigated by analyzing the deformation of a micro- or nanosized solid ellipsoid. The results show that both the stress and the deformation of a micro- or nanosized ellipsoid increase after the transverse shear stress within the surface layer is introduced, and that the maximal stress always occurs at both ends of the long axis of the ellipsoid. Unlike the prediction given by the Gurtin–Murdoch model, the calculation coming from the model of this paper predicts that the micro- or nanosized ellipsoid subjected to hydrostatic pressure contracts radially in the middle section and expands radially on both sides of the middle section. This difference provides an experimental standard to verify two models.

The Dynamic and Correlation of Skin Temperature and Cardiorespiratory Fitness in Male Endurance Runners

During endurance exercise, skin temperature (Tsk) plays a fundamental role in thermoregulatory processes. Environmental temperature is the biggest determinant of the Tsk. During exercise, the response of the skin temperature might be influenced by aerobic fitness (VO2peak). The aim of this study was to analyze and compare the dynamic of Tsk in high (HF) and moderately (MF) fit endurance runners during a progressive maximal stress test. Seventy-nine male endurance runners were classified into HF (n = 35; VO2peak = 56.62 ± 4.31 mL/kg/min) and MF (n = 44; VO2peak = 47.86 ± 5.29 mL/kg/min) groups. Tsk and cardiovascular data were continuously monitored during an incremental exercise, followed by a recovery period of five minutes. Results revealed that the MF group exhibited lower VO2peak, Speedpeak, ventilation (VE), muscle mass %, and higher BMI and fat mass % than the HF group (all p < 0.001). HF had significantly higher Tsk at baseline, and at 60% and 70% of peak workload (all p < 0.05). Tskpeak correlated with age, fat mass %, muscle mass %, VO2peak, Speedpeak, HR and VE (all p < 0.05). These findings indicate that VO2peak was positively associated with increased Tsk during incremental exercise in male endurance runners.