Ventricular unloading causes prolongation of the QT interval and induces ventricular arrhythmias in rat hearts.

Introduction: Ventricular unloading during prolonged bed rest, mechanical circulatory support or microgravity has repeatedly been linked to potentially life-threatening arrhythmias. It is unresolved, whether this arrhythmic phenotype is caused by the reduction in cardiac workload or rather by underlying diseases or external stimuli. We hypothesized that the reduction in cardiac workload alone is sufficient to impair ventricular repolarization and to induce arrhythmias in hearts. Methods: Rat hearts were unloaded using the heterotopic heart transplantation. The ECG of unloaded and of control hearts were telemetrically recorded over 56 days resulting in >5 × 106 cardiac cycles in each heart. Long-term electrical remodeling was analyzed using a novel semi-automatic arrhythmia detection algorithm. Results: 56 days of unloading reduced left ventricular weight by approximately 50%. While unloading did not affect average HRs, it markedly prolonged the QT interval by approximately 66% and induced a median tenfold increase in the incidence of ventricular arrhythmias in comparison to control hearts. Conclusion: The current study provides direct evidence that the previously reported hypertrophic phenotype of repolarization during cardiac unloading translates into an impaired ventricular repolarization and ventricular arrhythmias in vivo. This supports the concept that the reduction in cardiac workload is a causal driver of the development of arrhythmias during ventricular unloading.

Synergistic interplay between radiation and microgravity in spaceflight-related immunological health risks.

Spaceflight poses a myriad of environmental stressors to astronauts´ physiology including microgravity and radiation. The individual impacts of microgravity and radiation on the immune system have been extensively investigated, though a comprehensive review on their combined effects on immune system outcomes is missing. Therefore, this review aims at understanding the synergistic, additive, and antagonistic interactions between microgravity and radiation and their impact on immune function as observed during spaceflight-analog studies such as rodent hindlimb unloading and cell culture rotating wall vessel models. These mimic some, but not all, of the physiological changes observed in astronauts during spaceflight and provide valuable information that should be considered when planning future missions. We provide guidelines for the design of further spaceflight-analog studies, incorporating influential factors such as age and sex for rodent models and standardizing the longitudinal evaluation of specific immunological alterations for both rodent and cellular models of spaceflight exposure.

Mitigating skeletal muscle wasting in unloading and augmenting subsequent recovery.

Skeletal muscle wasting is the hallmark pathophysiological adaptation to unloading or disuse that demonstrates the dependency on frequent mechanical stimulation (e.g. muscle activation and subsequent loading) for homeostasis of normally load-bearing muscles. In the absence of mitigation strategies, no mammalian organism is resistant to muscle atrophy driven by unloading. Given the profound impact of unloading-induced muscle wasting on physical capacity, metabolic health and immune function; mitigation strategies during unloading and/or augmentation approaches during recovery have broad healthcare implications in settings of bed-bound hospitalization, cast immobilization and spaceflight. This topical review aims to: (1) provide a succinct, state-of-the-field summary of seminal and recent findings regarding the mechanisms of unloading-induced skeletal muscle wasting; (2) discuss unsuccessful vs. promising mitigation and recovery augmentation strategies; and (3) identify knowledge gaps ripe for future research. We focus on the rapid muscle atrophy driven by relatively short-term mechanical unloading/disuse, which is in many ways mechanistically distinct from both hypermetabolic muscle wasting and denervation-induced muscle atrophy. By restricting this discussion to mechanical unloading during which all components of the nervous system remain intact (e.g. without denervation models), mechanical loading requiring motor and sensory neural circuits in muscle remain viable targets for both mitigation and recovery augmentation. We emphasize findings in humans with comparative discussions of studies in rodents which enable elaboration of key mechanisms. We also discuss what is currently known about the effects of age and sex as biological factors, and both are highlighted as knowledge gaps and novel future directions due to limited research.

Science of left ventricular unloading.

The concept of left ventricular unloading has its foundation in heart physiology. In fact, the left ventricular mechanics and energetics represent the cornerstone of this approach. The novel sophisticated therapies for acute heart failure, particularly mechanical circulatory supports, strongly impact on the mechanical functioning and energy consuption of the heart, ultimately affecting left ventricle loading. Notably, extracorporeal circulatory life support which is implemented for life-threatening conditions, may even overload the left heart, requiring additional unloading strategies. As a consequence, the understanding of ventricular overload, and the associated potential unloading strategies, founds its utility in several aspects of day-by-day clinical practice. Emerging clinical and pre-clinical research on left ventricular unloading and its benefits in heart failure and recovery has been conducted, providing meaningful insights for therapeutical interventions. Here, we review the current knowledge on left ventricular unloading, from physiology and molecular biology to its application in heart failure and recovery.

Effect of true triaxial principal stress unloading rate on strain energy density of sandstone.

Deep rock are often in a true triaxial stress state. Studying the impacts of varying unloading speeds on their strain energy (SE) density is highly significant for predicting rock stability. Through true triaxial unloading principal stress experiments and true triaxial stress equilibrium unloading experiments on sandstone, this paper proposes a method to compute the SE density in a true triaxial compressive unloading principal stress test. This method aims to analyze the SE variation in rocks under the action of true triaxial unloading principal stresses. Acoustic emission is used to verify the correctness of the SE density calculation method in this paper. This study found that: (1) Unloading in one principal stress direction causes the SE density to rise in the other principal stress directions. This rise in SE, depending on its reversibility, can be categorized into elastic and dissipated SE. (2)When unloading principal stresses, the released elastic SE density in the unloading direction is influence by the stress path and rate. (3) The higher the unloading speed will leads to greater increases in the input SE density, elastic SE density, and dissipative SE density in the other principal stress directions. (4) The dissipated SE generated under true triaxial compression by unloading the principal stress is positively correlated with the damage to the rock; with an increase in unloading rate, there is a corresponding increase in the formation of cracks after unloading. (5) Utilizing the stress balance unloading test, we propose a calculation method for SE density in true triaxial unloading principal stress tests.

The effect of robot-assisted versus standard training on motor function following subacute rehabilitation after ischemic stroke - protocol for a randomised controlled trial nested in a prospective cohort (RoboRehab).

BACKGROUND: Body weight unloaded treadmill training has shown limited efficacy in further improving functional capacity after subacute rehabilitation of ischemic stroke patients. Dynamic robot assisted bodyweight unloading is a novel technology that may provide superior training stimuli and continued functional improvements in individuals with residual impairments in the chronic phase after the ischemic insult. The aim of the present study is to investigate the effect of dynamic robot-assisted versus standard training, initiated 6 months post-stroke, on motor function, physical function, fatigue, and quality of life in stroke-affected individuals still suffering from moderate-to-severe disabilities after subacute rehabilitation. METHODS: Stroke-affected individuals with moderate to severe disabilities will be recruited into a prospective cohort with measurements at 3-, 6-, 12- and 18-months post-stroke. A randomised controlled trial (RCT) will be nested in the prospective cohort with measurements pre-intervention (Pre), post-intervention (Post) and at follow-up 6 months following post-intervention testing. The present RCT will be conducted as a multicentre parallel-group superiority of intervention study with assessor-blinding and a stratified block randomisation design. Following pre-intervention testing, participants in the RCT study will be randomised into robot-assisted training (intervention) or standard training (active control). Participants in both groups will train 1:1 with a physiotherapist two times a week for 6 months (groups are matched for time allocated to training). The primary outcome is the between-group difference in change score of Fugl-Meyer Lower Extremity Assessment from pre-post intervention on the intention-to-treat population. A per-protocol analysis will be conducted analysing the differences in change scores of the participants demonstrating acceptable adherence. A priori sample size calculation allowing the detection of the minimally clinically important between-group difference of 6 points in the primary outcome (standard deviation 6 point, α = 5% and ß = 80%) resulted in 34 study participants. Allowing for dropout the study will include 40 participants in total. DISCUSSION: For stroke-affected individuals still suffering from moderate to severe disabilities following subacute standard rehabilitation, training interventions based on dynamic robot-assisted body weight unloading may facilitate an appropriate intensity, volume and task-specificity in training leading to superior functional recovery compared to training without the use of body weight unloading. TRIAL REGISTRATION: ClinicalTrials.gov. NCT06273475. TRIAL STATUS: Recruiting. Trial identifier: NCT06273475. Registry name: ClinicalTrials.gov. Date of registration on ClinicalTrials.gov: 22/02/2024.

Extracellular C1qbp inhibits myogenesis by suppressing NFATc1.

Aging and lack of exercise are the most important etiological factors for muscle loss. We hypothesized that new factors that contribute to muscle loss could be identified from ones commonly altered in expression in aged and exercise-limited skeletal muscles. Mouse gastrocnemius muscles were subjected to mass spectrometry-based proteomic analysis. The muscle proteomes of hindlimb-unloaded and aged mice were compared to those of exercised and young mice, respectively. C1qbp expression was significantly upregulated in the muscles of both hindlimb-unloaded and aged mice. In vitro myogenic differentiation was not affected by altering intracellular C1qbp expression but was significantly suppressed upon recombinant C1qbp treatment. Additionally, recombinant C1qbp repressed the protein level but not the mRNA level of NFATc1. NFATc1 recruited the transcriptional coactivator p300, leading to the upregulation of acetylated histone H3 levels. Furthermore, NFATc1 silencing inhibited p300 recruitment, downregulated acetylated histone H3 levels, and consequently suppressed myogenic differentiation. The expression of C1qbp was inversely correlated with that of NFATc1 in the gastrocnemius muscles of exercised or hindlimb-unloaded, and young or aged mice. These findings demonstrate a novel role of extracellular C1qbp in suppressing myogenesis by inhibiting the NFATc1/p300 complex. Thus, C1qbp can serve as a novel therapeutic target for muscle loss.

Strain Measurement Technology and Precision Calibration Experiment Based on Flexible Sensing Fiber.

As the basic application of fiber optic sensing technology, strain measurement accuracy as a key index needs to be further calibrated and analyzed. In this paper, accuracy calibration experiments and the related analyses of two fiber-optic sensing technologies, the fiber-optic grating (FBG) and optical frequency domain reflectometry (OFDR), are carried out using a standard beam of equal strength and a mature resistive strain gauge (ESG). The fiber-optic single-point strain data for loading and unloading changes of the beams of equal strength show good continuity and linearity, with good cyclic stability, and the error in the strain test data is less than 2% after repeated loading. At the same time, using finite element theory to analyze the data and using the measured data error within 5%, a good strain test curve linearity is achieved and R2 is better than 0.998. After repeated loading and unloading tests, it is verified that the fiber grating and the distributed optical fiber in the strain test have good stability in repeatability accuracy. The calibration experiments and data analysis in this paper further illustrate the three sensing technologies in determining the strain test accuracy and the advantages and disadvantages of the indicators, and the development of the fiber optic sensing technology application provides basic technical support.

Automated control of Impella maintains optimal left ventricular unloading during periods of unstable hemodynamics and prevents myocardial damage in acute myocardial infarction.

BACKGROUND: Left ventricular (LV) unloading by Impella, an intravascular microaxial pump, has been shown to exert dramatic cardioprotective effects in acute clinical settings of cardiovascular diseases. Total Impella support (no native LV ejection) is far more efficient in reducing LV energetic demand than partial Impella support, but the manual control of pump speed to maintain stable LV unloading is difficult and impractical. We aimed to develop an Automatic IMpella Optimal Unloading System (AIMOUS), which controls Impella pump speed to maintain LV unloading degree using closed-feedback control. We validated the AIMOUS performance in an animal model. METHODS: In dogs, we identified the transfer function from pump speed to LV systolic pressure (LVSP) under total support conditions (n = 5). Using the transfer function, we designed the feedback controller of AIMOUS to keep LVSP at 40 mmHg and examined its performance by volume perturbations (n = 9). Lastly, AIMOUS was applied in the acute phase of ischemia-reperfusion in dogs. Four weeks after ischemia-reperfusion, we assessed LV function and infarct size (n = 10). RESULTS: AIMOUS maintained constant LVSP, thereby ensuring a stable LV unloading condition regardless of volume withdrawal or infusion (±8 ml/kg from baseline). AIMOUS in the acute phase of ischemia-reperfusion markedly improved LV function and reduced infarct size (No Impella support: 13.9 ± 1.3 vs. AIMOUS: 5.7 ± 1.9%, P < 0.05). CONCLUSIONS: AIMOUS is capable of maintaining optimal LV unloading during periods of unstable hemodynamics. Automated control of Impella pump speed in the acute phase of ischemia-reperfusion significantly reduced infarct size and prevented subsequent worsening of LV function.

Early unloading and clinical outcomes in patients with fulminant myocarditis undergoing VA-ECMO: results of a multicenter retrospective study.

INTRODUCTION AND OBJECTIVES: Although venoarterial extracorporeal membrane oxygenation (VA-ECMO) provides effective cardiocirculatory support in patients with fulminant myocarditis, the most effective timing of venting is uncertain. We aimed to investigate the benefit of early venting among patients who underwent VA-ECMO for fulminant myocarditis. METHODS: Among 841 patients with acute myocarditis from 7 hospitals in the Republic of Korea, 217 patients with fulminant myocarditis who underwent VA-ECMO were included in this analysis. The patients were categorized into 2 groups: an early unloading group that underwent venting within 24hours of ECMO insertion, and the no or delayed unloading group. The primary outcome was a composite of death, cardiac replacement, or cardiovascular rehospitalization. RESULTS: Among 217 patients, 56 underwent early venting, 54 underwent delayed venting, and 107 did not undergo venting. On spline curves in 110 patients who underwent venting, rapid deterioration was observed as the timing of venting was delayed. The incidence of the primary outcome was lower in the early venting group than in the no or delayed unloading group (37.5% vs 58.4%; HR, 0.491; 95%CI, 0.279-0.863; P=.014). Among patients not experiencing the primary outcome within 6 months, clinical outcomes were similar after 6 months (P=.375). CONCLUSIONS: Early left heart unloading within 24hours of ECMO insertion is associated with a lower risk of a composite of death, cardiac replacement therapy, and cardiovascular rehospitalization in patients with fulminant myocarditis undergoing VA-ECMO. Registered at ClinicalTrials.gov (NCT05933902).

Extracorporeal Life Support in Myocardial Infarction: New Highlights.

Background and Objectives: Cardiogenic shock (CS) is a potentially severe complication following acute myocardial infarction (AMI). The use of veno-arterial extracorporeal membrane oxygenation (VA-ECMO) in these patients has risen significantly over the past two decades, especially when conventional treatments fail. Our aim is to provide an overview of the role of VA-ECMO in CS complicating AMI, with the most recent literature highlights. Materials and Methods: We have reviewed the current VA-ECMO practices with a particular focus on CS complicating AMI. The largest studies reporting the most significant results, i.e., overall clinical outcomes and management of the weaning process, were identified in the PubMed database from 2019 to 2024. Results: The literature about the use of VA-ECMO in CS complicating AMI primarily has consisted of observational studies until 2019, generating the need for randomized controlled trials. The EURO-SHOCK trial showed a lower 30-day all-cause mortality rate in patients receiving VA-ECMO compared to those receiving standard therapy. The ECMO-CS trial compared immediate VA-ECMO implementation with early conservative therapy, with a similar mortality rate between the two groups. The ECLS-SHOCK trial, the largest randomized controlled trial in this field, found no significant difference in mortality at 30 days between the ECMO group and the control group. Recent studies suggest the potential benefits of combining left ventricular unloading devices with VA-ECMO, but they also highlight the increased complication rate, such as bleeding and vascular issues. The routine use of VA-ECMO in AMI complicated by CS cannot be universally supported due to limited evidence and associated risks. Ongoing trials like the Danger Shock, Anchor, and Recover IV trials aim to provide further insights into the management of AMI complicated by CS. Conclusions: Standardizing the timing and indications for initiating mechanical circulatory support (MCS) is crucial and should guide future trials. Multidisciplinary approaches tailored to individual patient needs are essential to minimize complications from unnecessary MCS device initiation.

Unloading Model of Elastic-Plastic Half-Space Contacted by an Elastic Spherical Indenter.

A new unloading contact model of an elastic-perfectly plastic half-space indented by an elastic spherical indenter is presented analytically. The recovered deformation of the elastic indenter and the indented half-space has been found to be dependent on the elastic modulus ratio after fully unloading. The recovered deformation of the indented half-space can be calculated based on the deformation of the purely elastic indenter. The unloading process is assumed to be entirely elastic, and then the relationship of contact force and indentation can be determined based on the solved recovered deformation and conforms to Hertzian-type. The model can accurately predict the residual indentation and residual curvature radius after fully unloading. Numerical simulations are performed to demonstrate the assumptions and the unloading model. The proposed unloading model can cover a wide range of indentations and material properties and is compared with existing unloading models. The cyclic behavior including loading and unloading can be predicted by combining the proposed unloading law with the existing contact loading model. The combined model can be employed for low-velocity impact and nanoindentation tests and the comparison results are in good agreement.

Investigations of Differential Hypoxemia During Venoarterial Membrane Oxygenation with and Without Impella Support.

PURPOSE: Venoarterial extracorporeal membrane oxygenation (VA ECMO) is used in patients with refractory cardiac or cardio-pulmonary failure. Native ventricular output interacts with VA ECMO flow and may hinder sufficient oxygenation to the heart and the brain. Further on, VA ECMO leads to afterload increase requiring ventricular unloading. The aim of the study was to investigate aortic blood flow and oxygenation for various ECMO settings and cannula positions with a numerical model. METHODS: Four different aortic cannula tip positions (ascending aorta, descending aorta, abdominal aorta, and iliac artery) were included in a model of a human aorta. Three degrees of cardiac dysfunction and VA ECMO support (50%, 75% and 90%) with a total blood flow of 6 l/min were investigated. Additionally, the Impella CP device was implemented under 50% support condition. Blood oxygen saturation at the aortic branches and the pressure acting on the aortic valve were calculated. RESULTS: A more proximal tip orientation is necessary to increase oxygen supply to the supra-aortic and coronary arteries for 50% and 75% support. During the 90% support scenario, proper oxygenation can be achieved independently of tip position. The use of Impella reduces afterload by 8-17 mmHg and vessel oxygenation is similar to 50% VA ECMO support. Pressure load on the aortic valve increases with more proximal tip position and is decreased during Impella use. CONCLUSIONS: We present a simulation model for the investigation of hemodynamics and blood oxygenation with various mechanical circulatory support systems. Our results underline the intricate and patient-specific relationship between extracorporeal support, cannula tip orientation and oxygenation capacity.

Arsenite Antiporter PvACR3 Driven by Its Native Promoter Increases Leaf Arsenic Accumulation in Tobacco.

Pteris vittata is the first-reported arsenic (As) hyperaccumulator, which has been applied to phytoremediation of As-contaminated soil. PvACR3, a key arsenite (AsIII) antiporter, plays an important role in As hyperaccumulation in P. vittata. However, its functions in plants are not fully understood. In this study, the PvACR3 gene was heterologously expressed in tobacco, driven by its native promoter (ProPvACR3). After growing at 5 µM AsIII or 10 µM AsV in hydroponics for 1-5 days, PvACR3-expression enhanced the As levels in leaves by 66.4-113 and 51.8-101%, without impacting the As contents in the roots or stems. When cultivated in As-contaminated soil, PvACR3-expressed transgenic plants accumulated 47.9-85.5% greater As in the leaves than wild-type plants. In addition, PvACR3-expression increased the As resistance in transgenic tobacco, showing that enhanced leaf As levels are not detrimental to its overall As tolerance. PvACR3 was mainly expressed in tobacco leaf veins and was likely to unload AsIII from the vein xylem vessels to the mesophyll cells, thus elevating the leaf As levels. This work demonstrates that heterologously expressing PvACR3 under its native promoter specifically enhances leaf As accumulation in tobacco, which helps to reveal the As-hyperaccumulation mechanism in P. vittata and to enhance the As accumulation in plant leaves for phytoremediation.

Potato spindle tuber viroid (PSTVd) loop 27 mutants promote cell-to-cell movement and phloem unloading of the wild type: Insights into RNA-based viroid interactions.

Variations in infection progression with concurrent or prior infections by different viruses, viroids, or their strains are evident, but detailed investigations into viroid variant interactions are lacking. We studied potato spindle tuber viroid intermediate strain (PSTVd-I) to explore variant interactions. Two mutants, U177A/A182U (AU, replication- and trafficking-competent) and U178G/U179G (GG, replication-competent but trafficking-defective) on loop 27 increased cell-to-cell movement of wild-type (WT) PSTVd without affecting replication. In mixed infection assays, both mutants accelerated WT phloem unloading, while only AU promoted it in separate leaf assays, suggesting that enhancement of WT infection is not due to systemic signals. The mutants likely enhance WT infection due to their loop-specific functions, as evidenced by the lack of impact on WT infection seen with the distantly located G347U (UU) mutant. This study provides the first comprehensive analysis of viroid variant interactions, highlighting the prolonged phloem unloading process as a significant barrier to systemic spread.

Wide Complex Tachycardia as a Rare Pointer of Intra-aortic Balloon Pump Migration Into the Left Ventricle: A Case Report and Literature Review.

Intra-aortic balloon pumps (IABPs) are used to assist with left ventricular (LV) unloading in patients with cardiogenic shock (CS). There are different mechanical devices that can be used in CS, of which the IABP represents the simplest, the easiest to insert and remove, and the most cost-effective. Compared to traditional femoral IABPs, axillary IABPs allow patients to remain ambulatory. This is especially beneficial in patients awaiting heart transplants. Our case presents a patient with CS, where axillary IABP was used to unload the LV. However, our patient developed ventricular arrhythmia secondary to IABP migration to the LV.

Impact of Left Ventricular Unloading on Outcome of Heart Transplant Bridging With Extracorporeal Membrane Oxygenation Support in New Allocation Policy.

BACKGROUND: The new heart allocation policy places veno-arterial extracorporeal membrane oxygenation (VA-ECMO)-supported heart transplant (HT) candidates at the highest priority status. Despite increasing evidence supporting left ventricular (LV) unloading during VA-ECMO, the effect of LV unloading on transplant outcomes following bridging to HT with VA-ECMO remains unknown. METHODS AND RESULTS: From October 18, 2018 to March 21, 2023, 624 patients on VA-ECMO at the time of HT were identified in the United Network for Organ Sharing database and were divided into 2 groups: VA-ECMO alone (N=384) versus VA-ECMO with LV unloading (N=240). Subanalysis was performed in the LV unloading group: Impella (N=106) versus intra-aortic balloon pump (N=134). Recipient age was younger in the VA-ECMO alone group (48 versus 53 years, P=0.018), as was donor age (VA-ECMO alone, 29 years versus LV unloading, 32 years, P=0.041). One-year survival was comparable between groups (VA-ECMO alone, 88.0±1.8% versus LV unloading, 90.4±2.1%; P=0.92). Multivariable Cox hazard model showed LV unloading was not associated with posttransplant mortality after HT (hazard ratio, 0.92; P=0.70). Different LV unloading methods had similar 1-year survival (intra-aortic balloon pump, 89.2±3.0% versus Impella, 92.4±2.8%; P=0.65). Posttransplant survival was comparable between different Impella versions (Impella 2.5, versus Impella CP, versus Impella 5.0, versus Impella 5.5). CONCLUSIONS: Under the current allocation policy, LV unloading did not impact waitlist outcome and posttransplant survival in patients bridged to HT with VA-ECMO, nor did mode of LV unloading. This highlights the importance of a tailored approach in HT candidates on VA-ECMO, where routine LV unloading may not be universally necessary.

Left Ventricular Unloading in Extracorporeal Membrane Oxygenation: A Clinical Perspective Derived from Basic Cardiovascular Physiology.

PURPOSE OF REVIEW: To present an abridged overview of the literature and pathophysiological background of adjunct interventional left ventricular unloading strategies during veno-arterial extracorporeal membrane oxygenation (V-A ECMO). From a clinical perspective, the mechanistic complexity of such combined mechanical circulatory support often requires in-depth physiological reasoning at the bedside, which remains a cornerstone of daily practice for optimal patient-specific V-A ECMO care. RECENT FINDINGS: Recent conventional clinical trials have not convincingly shown the superiority of V-A ECMO in acute myocardial infarction complicated by cardiogenic shock as compared with medical therapy alone. Though, it has repeatedly been reported that the addition of interventional left ventricular unloading to V-A ECMO may improve clinical outcome. Novel approaches such as registry-based adaptive platform trials and computational physiological modeling are now introduced to inform clinicians by aiming to better account for patient-specific variation and complexity inherent to V-A ECMO and have raised a widespread interest. To provide modern high-quality V-A ECMO care, it remains essential to understand the patient's pathophysiology and the intricate interaction of an individual patient with extracorporeal circulatory support devices. Innovative clinical trial design and computational modeling approaches carry great potential towards advanced clinical decision support in ECMO and related critical care.

Experimental Study on the Microfabrication and Mechanical Properties of Freeze-Thaw Fractured Sandstone under Cyclic Loading and Unloading Effects.

A series of freeze-thaw cycling tests, as well as cyclic loading and unloading tests, have been conducted on nodular sandstones to investigate the effect of fatigue loading and freeze-thaw cycling on the damage evolution of fractured sandstones based on damage mechanics theory, the microstructure and sandstone pore fractal theory. The results show that the number of freeze-thaw cycles, the cyclic loading level, the pore distribution and the complex program are important factors affecting the damage evolution of rocks. As the number of freeze-thaw cycles rises, the peak strength, modulus of elasticity, modulus of deformation and damping ratio of the sandstone all declined. Additionally, the modulus of elasticity and deformation increase nonlinearly as the cyclic load level rises. With the rate of increase decreasing, while the dissipation energy due to hysteresis increases gradually and at an increasing rate, and the damping ratio as a whole shows a gradual decrease, with a tendency to increase at a later stage. The NRM (Nuclear Magnetic Resonance) demonstrated that the total porosity and micro-pores of the sandstone increased linearly with the number of freeze-thaw cycles and that the micro-porosity was more sensitive to freeze-thaw, gradually shifting towards meso-pores and macro-pores; simultaneously, the SEM (Scanning Electron Microscope) indicated that the more freeze-thaw cycles there are, the more micro-fractures and holes grow and penetrate each other and the more loose the structure is, with an overall nest-like appearance. To explore the mechanical behavior and mechanism of cracked rock in high-altitude and alpine areas, a damage model under the coupling of freeze-thaw-fatigue loading was established based on the loading and unloading response ratio theory and strain equivalence principle.

Sugar delivery at the tomato root and root galls after Meloidogyne incognita infestation.

Root-knot nematodes (RKNs) infect host plants and obtain nutrients such as sugars for their own development. Therefore, inhibiting the nutrient supply to RKNs may be an effective method for alleviating root-knot nematode disease. At present, the pathway by which sucrose is unloaded from the phloem cells to giant cells (GCs) in root galls and which genes related to sugar metabolism and transport play key roles in this process are unclear. In this study, we found that sugars could be unloaded into GCs only from neighboring phloem cells through the apoplastic pathway. With the development of galls, the contents of sucrose, fructose and glucose in the galls and adjacent tissue increased gradually. SUT1, SUT2, SWEET7a, STP10, SUS3 and SPS1 may provide sugar sources for GCs, while STP1, STP2 and STP12 may transport more sugar to phloem parenchyma cells. At the early stage of Meloidogyne incognita infestation, the sucrose content in tomato roots and leaves increased, while the glucose and fructose contents decreased. SWEET7a, SPS1, INV-INH1, INV-INH2, SUS1 and SUS3 likely play key roles in root sugar delivery. These results elucidated the pathway of sugar unloading in tomato galls and provided an important theoretical reference for eliminating the sugar source of RKNs and preventing root-knot nematode disease.