Dissecting muscle synergies in the task space.

The muscle synergy is a guiding concept in motor control research that relies on the general notion of muscles 'working together' towards task performance. However, although the synergy concept has provided valuable insights into motor coordination, muscle interactions have not been fully characterised with respect to task performance. Here, we address this research gap by proposing a novel perspective to the muscle synergy that assigns specific functional roles to muscle couplings by characterising their task-relevance. Our novel perspective provides nuance to the muscle synergy concept, demonstrating how muscular interactions can 'work together' in different ways: (1) irrespective of the task at hand but also (2) redundantly or (3) complementarily towards common task-goals. To establish this perspective, we leverage information- and network-theory and dimensionality reduction methods to include discrete and continuous task parameters directly during muscle synergy extraction. Specifically, we introduce co-information as a measure of the task-relevance of muscle interactions and use it to categorise such interactions as task-irrelevant (present across tasks), redundant (shared task information), or synergistic (different task information). To demonstrate these types of interactions in real data, we firstly apply the framework in a simple way, revealing its added functional and physiological relevance with respect to current approaches. We then apply the framework to large-scale datasets and extract generalizable and scale-invariant representations consisting of subnetworks of synchronised muscle couplings and distinct temporal patterns. The representations effectively capture the functional interplay between task end-goals and biomechanical affordances and the concurrent processing of functionally similar and complementary task information. The proposed framework unifies the capabilities of current approaches in capturing distinct motor features while providing novel insights and research opportunities through a nuanced perspective to the muscle synergy.

Development and Validation of HAS (Hajibandeh Index, ASA Status, Sarcopenia) - A Novel Model for Predicting Mortality After Emergency Laparotomy.

OBJECTIVES: To develop and validate a predictive model to predict the risk of postoperative mortality after emergency laparotomy taking into account the following variables: age, age ≥ 80, ASA status, clinical frailty score, sarcopenia, Hajibandeh Index (HI), bowel resection, and intraperitoneal contamination. SUMMARY BACKGROUND DATA: The discriminative powers of the currently available predictive tools range between adequate and strong; none has demonstrated excellent discrimination yet. METHODS: The TRIPOD and STROCSS statement standards were followed to protocol and conduct a retrospective cohort study of adult patients who underwent emergency laparotomy due to non-traumatic acute abdominal pathology between 2017 and 2022. Multivariable binary logistic regression analysis was used to develop and validate the model via two protocols (Protocol A and B). The model performance was evaluated in terms of discrimination (ROC curve analysis), calibration (calibration diagram and Hosmer-Lemeshow test), and classification (classification table). RESULTS: One thousand forty-three patients were included (statistical power = 94%). Multivariable analysis kept HI (Protocol-A: P =0.0004; Protocol-B: P =0.0017), ASA status (Protocol-A: P =0.0068; Protocol-B: P =0.0007), and sarcopenia (Protocol-A: P <0.0001; Protocol-B: P <0.0001) as final predictors of 30-day postoperative mortality in both protocols; hence the model was called HAS (HI, ASA status, sarcopenia). The HAS demonstrated excellent discrimination (AUC: 0.96, P <0.0001), excellent calibration ( P <0.0001), and excellent classification (95%) via both protocols. CONCLUSIONS: The HAS is the first model demonstrating excellent discrimination, calibration, and classification in predicting the risk of 30-day mortality following emergency laparotomy. The HAS model seems promising and is worth attention for external validation using the calculator provided. HAS mortality risk calculator https://app.airrange.io/#/element/xr3b_E6yLor9R2c8KXViSAeOSK .

Hospital-based violence prevention programmes in South Wales Emergency Departments: A process evaluation protocol.

BACKGROUND: Addressing violence related harm is a global public health priority. While violence is primarily managed in the criminal justice system, healthcare supports and manages those injured by violence. Emergency Departments (EDs), the primary destination for those seriously injured, have emerged as a candidate location for violence prevention initiatives. There is limited evaluation of ED-based violence prevention, and a lack of guidance for the implementation and delivery of them. Nurse-led Violence Prevention Teams (VPTs) have been developed and implemented in two EDs in Wales, UK. This protocol describes methods used in the process evaluation of these VPTs. AIM: To understand how VPTs function, how they were implemented, and mechanisms of impact, as well as the exploration of wider contextual factors influencing their function. METHODS: Adopting a critical realist approach and informed by the Medical Research Council (MRC) guidance for process evaluations, the process evaluation will employ qualitative methods to collect and analyse data: a scoping review of evidence of effectiveness that considers the causal mechanisms underpinning violence; a documentary analysis to determine operational considerations concerning the development, implementation and delivery of the VPTs; a descriptive analysis of routine ED data to characterise the prevalence of violence-related attendances in each ED; interviews with professional stakeholders (N = 60) from the violence prevention ecologies in which the VPTs are embedded. DISCUSSION: This protocol outlines a process evaluation of a novel, nurse led violence prevention intervention. Findings will be used to inform policy makers' decision making on whether and how VPTs should be used in practice in other EDs across the UK, and the extent that a single operational model should be adjusted to address the local characteristic of violence. To the authors knowledge, this is the first process evaluation of a UK-based, nurse led Emergency Department Violence Prevention Team. TRIAL REGISTRATION: Protocol registration ISRCTN: 15286575. Registered 13th March, 2023.

Follow up after surgery for colorectal liver metastases: A systematic review.

INTRODUCTION: Recurrence post hepatectomy for colorectal liver metastases (CRLM) occurs in 70 % of patients within two years. No established guidance on the method or intensity of follow-up currently exists. The aim of this systematic review was to summarise literature and determine whether it is possible to identify an optimal follow up regime. To this date there are no randomised prospective studies investigating this. METHODS: A systematic review was performed according to PRISMA guidelines. Outcomes included general demographics, method, frequency and duration of follow up, survival and recurrence data. Quality assessment of the papers was performed. RESULTS: Twenty-five articles published between 1994 and 2022 were included, including 9945 patients. CT was the most common imaging modality (n = 14) and CEA most common blood test (n = 11). Intensity of follow up was higher in the first two years post resection and only two papers continued follow up post 5 years resection. There was wide variation in outcome measures - Overall survival (OS) was most commonly reported. Nine papers reported OS ranging between 39 and 78.1 %. CONCLUSIONS: There is wide variation in follow up methods and outcome reporting. There is no strong evidence to support intensive follow up, and the benefits of long term follow up are also unknown due to the lack of patient centred data. High quality, prospective studies should be the focus of future research as further retrospective data is unlikely to resolve uncertainties around optimal follow up.

Need for standardization in the use of structures in the intensity-modulated radiation therapy planning of head and neck cancers, a GORTEC study.

BACKGROUND: Most radiotherapy structures contoured on CT scans during IMRT planning are defined by the ICRU, forming part of standard practice. Associated dose-volume constraints serve as parameters for dose computation algorithms to produce optimized dose maps. On the ground, however, physicists/dosimetrists routinely delineate auxiliary "non-standard" radiotherapy structures (nsRS). MATERIALS/METHODS: From 287 patients' data, five categories of nsRS were identified. Inter-center, inter-patient variability, and temporal trends in nsRS use were investigated. Relation of nsRS with topological complexity, plan quality, calculated quality assurance (QA) and expert QA, was investigated using machine learning classification. RESULTS: nsRS accounted for 19.2% of all structures. Average number of nsRS per patient was 8.92 ± 6.70. Variation coefficient across centers was > 70% for nsRS frequency. There was no effect of patient volume per center on averaged nsRS number between low, intermediate, and high-volume centers. No temporal trends in nsRS use were detected at the high-volume centers, except for an increase in 'forced-dose' nsRS (p = 3.08 × (10)^(-5)) at one center. Machine learning prediction accuracy including nsRS features were 0.70 ± 0.06 for topological complexity, 0.58 ± 0.05 for calculated QA and 0.72 ± 0.05 for expert QA. CONCLUSION: Use of nsRS is frequent but heterogeneous and should be standardized further in line with ICRU initiatives in IMRT planning. Use of nsRS should be documented with respect to the need for nsRS from dose computation algorithms of treatment planning systems and IMRT machines in terms of modulation capacity and plan robustness.

A pilot project investigating the use of ONCOpatient®-An electronic patient-reported outcomes app for oncology patients.

Purpose: To investigate the feasibility of implementing a remote patient monitoring system using an electronic patient-reported outcomes (ePROs) platform in a tertiary cancer center in the Republic of Ireland. Methods: Patients receiving oral chemotherapy and oncology clinicians were invited to participate in the study. Patients were asked to submit weekly symptom questionnaires through an ePRO mobile phone application (app)-ONCOpatient®. Clinical staff were invited to use the ONCOpatient® clinician interface. After 8 weeks all participants submitted evaluation questionnaires. Results: Thirteen patients and five staff were enrolled in the study. The majority of patients were female (85%) with a median age of 48 years (range 22-73). Most (92%) were enrolled over telephone requiring on average 16 minutes. Compliance with the weekly assessments was 91%. Alerts were triggered by 40% of patients who then required phone calls to aid with symptom management. At the end of study, 87% of patients reported they would use the app frequently, 75% reported that the platform met their expectations, and 25% that it exceeded their expectations. Similarly, 100% of staff reported they would use the app frequently, 60% reported that it met their expectations, and 40% that it exceeded their expectations. Conclusions: Our pilot study showed that it is feasible to implement ePRO platforms in the Irish clinical setting. Small sample bias was recognized as a limitation, and we plan to confirm our findings on a larger cohort of patients. In the next phase we will integrate wearables including remote blood pressure monitoring.

The risk of recurrent pancreatitis after first episode of acute pancreatitis in relation to etiology and severity of disease: A systematic review, meta-analysis and meta-regression analysis.

BACKGROUND AND AIM: The study aims to determine and quantify the stratified risk of recurrent pancreatitis (RP) after the first episode of acute pancreatitis in relation to etiology and severity of disease. METHODS: A systematic review and meta-analysis in compliance with PRISMA statement standards was conducted. A search of electronic information sources was conducted to identify all studies investigating the risk of RP after the first episode of acute pancreatitis. Proportion meta-analysis models using random effects were constructed to calculate the weighted summary risks of RP. Meta-regression was performed to evaluate the effect of different variables on the pooled outcomes. RESULTS: Analysis of 57,815 patients from 42 studies showed that the risk of RP after first episode was 19.8% (95% confidence interval [CI] 17.5-22.1%). The risk of RP was 11.9% (10.2-13.5%) after gallstone pancreatitis, 28.7% (23.5-33.9%) after alcohol-induced pancreatitis, 30.3% (15.5-45.0%) after hyperlipidemia-induced pancreatitis, 38.1% (28.9-47.3%) after autoimmune pancreatitis, 15.1% (11.6-18.6%) after idiopathic pancreatitis, 22.0% (16.9-27.1%) after mild pancreatitis, 23.9% (12.9-34.8%) after moderate pancreatitis, 21.6% (14.6-28.7%) after severe pancreatitis, and 6.6% (4.1-9.2%) after cholecystectomy following gallstone pancreatitis. Meta-regression confirmed that the results were not affected by the year of study (P = 0.541), sample size (P = 0.064), length of follow-up (P = 0.348), and age of patients (P = 0.138) in the included studies. CONCLUSIONS: The risk of RP after the first episode of acute pancreatitis seems to be affected by the etiology of pancreatitis but not the severity of disease. The risks seem to be higher in patients with autoimmune pancreatitis, hyperlipidemia-induced pancreatitis, and alcohol-induced pancreatitis and lower in patients with gallstone pancreatitis and idiopathic pancreatitis.

Treatment Decisions for Resectable Non-Small-Cell Lung Cancer: Balancing Less With More?

For patients with non-small-cell lung cancer (NSCLC), the outcomes for patients with resectable disease are historically poor compared with other solid organ malignancies. In recent years, there have been significant advances in multidisciplinary care, which have resulted in improved outcomes. Innovations in surgical oncology include the use of limited resection and minimally invasive techniques. Recent data in radiation oncology have suggested refinements in pre- and postoperative radiation therapy, resulting in optimization of techniques in the curative setting. Finally, the success of immune checkpoint inhibitors and targeted therapies in the advanced setting has paved the way for inclusion in the adjuvant and neoadjuvant settings, resulting in recent regulatory approvals for four regimens (CheckMate-816, IMpower010, PEARLS, ADAURA). In this review, we will provide an overview of the seminal studies informing advancements in optimal surgical resection, radiation treatment, and systemic therapy for resectable NSCLC. We will summarize the key data on survival outcomes, biomarker analyses, and future directions for perioperative studies.

The risk of hepatic pseudoaneurysm after liver trauma in relation to the severity of liver injury: a meta-analysis and meta-regression analysis.

AIM: To determine the risk of hepatic pseudoaneurysm after liver trauma in relation to the severity of liver injury. METHODS: We performed a systematic review and meta-analysis in compliance with PRISMA statement standards (Registration Number: CRD42022328834). A search of electronic information sources was conducted to identify all studies reporting the risk of hepatic pseudoaneurysm after liver trauma. The JBI assessment tool was used to assess the risk of bias of the included studies. Random-effects models were applied to calculate pooled outcome data. RESULTS: A total of 2030 patients from six studies were included. Based on the American Association for the Surgery of Trauma classification system, 21% had grade I injury; 33% grade II injury; 28% grade III injury; 12% grade IV injury and 5% grade V injury. The pooled risk of hepatic pseudoaneurysm was 1.8% (95% CI 1.1-2.5%). The risk was 0.4% (0-1.2%) in patients with grade I injury, 0.7% (0-1.7%) in patients with grade II injury; 1.5% (0.4-2.7%) in patients with grade III injury; 4.6% (1.4-7.7%) in patients with grade IV injury and 10.6% (1.8-22.9%) in patients with grade V injury. The average time between liver injury and detection of hepatic pseudoaneurysm was 6 days (95% CI 1-10) CONCLUSIONS: The risk of hepatic pseudoaneurysm after liver trauma increases as the severity of liver injury increases. Hepatic pseudoaneurysms are rare after grade I or grade II injuries, and increasingly common after grades III, IV and V injuries. We recommend routine surveillance imaging in patients with grade III to V injuries.

Uptake of BRCA1/BRCA2 predictive genetic testing in an Irish population is low: a missed opportunity.

INTRODUCTION: Predictive testing for BRCA1 or BRCA2 allows at-risk individuals to engage with appropriate screening and treatment services if a pathogenic mutation is identified. Previous studies have shown uptake of predictive testing to most commonly range between 20% and 40% (Table 2). This represents a missed cancer prevention opportunity. Possible explanations for this low uptake include lack of disclosure of at-risk status to relatives, lack of awareness of cancer genetics services, or patient preference. The goal of the current study was to investigate the uptake of BRCA1 or BRCA2 predictive testing in an Irish population. METHODS: We performed a multicentre, retrospective analysis of 63 pedigrees from two Irish tertiary referral hospitals over a five-year period (2012-2017). Family pedigrees were reviewed to identify at-risk family members eligible for predictive BRCA1 or BRCA2 mutation testing as per international guidelines, and testing rates were determined. RESULTS: A total of 1048 eligible individuals were identified, 318 (30.4%) proceeded to BRCA1 or BRCA2 germline testing including [215 (37.5%) females and 99 males (21.5%)]. Women were significantly more likely to test than men (T = 3.7, p < .0002). Uptake of testing was significant higher amongst first-degree relatives 45% (150/323) compared to 20% (50/258) amongst second degree relatives, and 10 % (33/317) amongst more distant relatives (F = 25.32, p < 0.00001). CONCLUSIONS: Uptake of BRCA1 OR BRCA2 mutation testing in Ireland is suboptimal, particularly amongst Irish males and distant relatives. Further research is needed to identify strategies which may improve uptake within current legal and ethical frameworks.

Direct Observation of Charge, Energy, and Hydrogen Transfer between the Backbone and Nucleobases in Isolated DNA Oligonucleotides.

Understanding how charge and energy, as well as protons and hydrogen atoms, are transferred in molecular systems as a result of an electronic excitation is fundamental for understanding the interaction between ionizing radiation and biological matter on the molecular level. To localize the excitation at the atomic scale, it was chosen to target phosphorus atoms in the backbone of gas-phase oligonucleotide anions and cations, by means of resonant photoabsorption at the L- and K-edges. The ionic photoproducts of the excitation process were studied by a combination of mass spectrometry and X-ray spectroscopy. The combination of absorption site selectivity and photoproduct sensitivity allowed the identification of X-ray spectral signatures of specific processes. Moreover, charge and/or energy as well as H transfer from the backbone to nucleobases has been directly observed. Although the probability of one versus two H transfer following valence ionization depends on the nucleobase, ionization of sugar or phosphate groups at the carbon K-edge or the phosphorus L-edge mainly leads to single H transfer to protonated adenine. Moreover, our results indicate a surprising proton-transfer process to specifically form protonated guanine after excitation or ionization of P 2p electrons.

Cost and public reimbursement of cancer medicines in the UK and the Republic of Ireland.

INTRODUCTION/AIMS: There are disparities in the availability of systemic anticancer therapies (SACTs) globally. We set out to investigate the cost and reimbursement of SACTs in the United Kingdom (UK) and the Republic of Ireland (ROI) in conjunction with efficacy and licensing authority decisions in the United States (US) and the European Union (EU). METHODS: We sought data pertaining to licensing in the EU, reimbursement in ROI/UK and cost/efficacy of SACTs licensed by the Food and Drug Administration (FDA) between January 2015 and May 2021. Independent samples t tests, chi-square test and Pearson's correlation were used for statistical analysis. RESULTS: We identified that the majority of FDA-approved regimens are licensed by the European Medicines Agency (EMA) (n = 91, 67.9%). However, only a minority of these are currently reimbursed in the UK (n = 60, 45%) or the ROI (n = 28, 21%) as of the 1st of May 2021. In addition, only a minority of regimens have demonstrated a statistically significant OS benefit (n = 54, 40%). There was no association between cost of regimens and either the presence (t = 0.846, p = 0.40) or duration of OS benefit (t = - 0.84, p = 0.64). CONCLUSIONS: Our study highlights that many licensed systemic anticancer treatments are not currently reimbursed in ROI/UK. The high cost of these medicines is independent of the presence of an OS benefit. Collaboration between regulatory agencies, governments and industry partners is needed to ensure health expenditure is directed towards the most effective treatments.

Cohort study of long-term survival and recurrence patterns following operative management of colorectal liver metastasis - is follow-up beyond 5 years warranted?

AIMS: To evaluate the patterns of overall survival (OS) and recurrence following surgical resection of colorectal liver metastases (CRLM). METHODS: In compliance with STROCSS guideline, a single-centre retrospective cohort study was conducted. All consecutive patients undergoing resection of CRLM between 2003 and 2019 were considered eligible for inclusion. The outcome measures included OS, recurrence-free survival (RFS), recurrence rate, time to recurrence (TTR) and longest TTR. Statistical analyses included simple descriptive statistics and Kaplan-Meier survival statistics. RESULTS: We included 486 liver resections in 472 patients. The estimated median OS and RFS were 5.1 years and 3.1 years, respectively. The probability of 1-year, 3-year, 5-year and 10-year OS was 93%, 69%, 50% and 34%, respectively. The probability of 1-year, 3-year, 5-year and 10-year RFS was 81%, 50%, 34% and 33%, respectively. Recurrence occurred in 56% (271/486) of patients, and the median TTR was 1.6 years (IQR: 0.8-2.7) with longest TTR of 4.8 years. Although there were no recurrences in the 66 patients that entered the 6th year, the 95% CI for true rate of recurrence in the population given these data is 0-5.4%. CONCLUSIONS: Our results suggest that recurrences that occur after operative management of CRLM are almost certain to occur within the first 5 years even for patients surviving longer than 5 years. This does not disprove the requirement for follow up beyond 5 years. However, based on this data, we have altered our follow up from 10 to 6 years. The need for the 6th year of follow up will be reassessed in light of further observations.

A network information theoretic framework to characterise muscle synergies in space and time.

Objective. Current approaches to muscle synergy extraction rely on linear dimensionality reduction algorithms that make specific assumptions on the underlying signals. However, to capture nonlinear time varying, large-scale but also muscle-specific interactions, a more generalised approach is required.Approach. Here we developed a novel framework for muscle synergy extraction that relaxes model assumptions by using a combination of information and network theory and dimensionality reduction. We first quantify informational dynamics between muscles, time-samples or muscle-time pairings using a novel mutual information formulation. We then model these pairwise interactions as multiplex networks and identify modules representing the network architecture. We employ this modularity criterion as the input parameter for dimensionality reduction, which verifiably extracts the identified modules, and also to characterise salient structures within each module.Main results. This novel framework captures spatial, temporal and spatiotemporal interactions across two benchmark datasets of reaching movements, producing distinct spatial groupings and both tonic and phasic temporal patterns. Readily interpretable muscle synergies spanning multiple spatial and temporal scales were identified, demonstrating significant task dependence, ability to capture trial-to-trial fluctuations and concordance across participants. Furthermore, our framework identifies submodular structures that represent the distributed networks of co-occurring signal interactions across scales.Significance. The capabilities of this framework are illustrated through the concomitant continuity with previous research and novelty of the insights gained. Several previous limitations are circumvented including the extraction of functionally meaningful and multiplexed pairwise muscle couplings under relaxed model assumptions. The extracted synergies provide a holistic view of the movement while important details of task performance are readily interpretable. The identified muscle groupings transcend biomechanical constraints and the temporal patterns reveal characteristics of fundamental motor control mechanisms. We conclude that this framework opens new opportunities for muscle synergy research and can constitute a bridge between existing models and recent network-theoretic endeavours.

Patient-reported experiences of consultation with an advanced nurse practitioner: Factor structure and reliability analysis of the patient enablement and satisfaction survey.

AIM: The aim was to analyse the psychometric properties of a patient-reported-experience measure, the Patient Enablement and Satisfaction Survey (PESS), when used to evaluate the care provided by Advanced Nurse Practitioners (ANPs) in terms of factor structure and internal consistency. The PESS is a 20-item, patient-completed data collection tool that was originally developed to measure patient experience and enablement following consultation with nurses in general practice. DESIGN: Cross-sectional survey; validity and reliability analysis. METHODS: The sample in this study consisted of 178 patients who consulted with 26 ANPs working in four different specialities. Data were collected between June and December 2019. An exploratory factor analysis of the PESS was conducted to determine convergent validity which was supported by parallel analysis and the traditional Kaiser criterion. The internal consistency of individual PESS items was determined via Cronbach's alpha, McDonald's omega, the Average Variance Extracted tests and item-subscale/total score correlations. RESULTS: A three-factor structure (PESS-ANP) was found through exploratory factor analysis and this was supported by parallel analysis, the traditional Kaiser criterion and the percentage of variance explained criterion. A high degree of internal consistency was reported across all factors. One question was omitted from the analysis ('Overall Satisfaction') following the identification of problematic cross-loadings. The three factor solution was identified as: patient satisfaction, quality of care provision and patient enablement. CONCLUSION: The findings of this study propose a three-factor model that is sufficiently reliable for analysing the experience and enablement of patients following consultation with an ANP. IMPACT: Increasingly, patient-reported experience measures are being used to evaluate patients' experience of receiving care from a healthcare professional. The PESS was identified to be reliable in evaluating the experience of patients who receive care from an ANP while a three-factor structure was proposed that can capture specific attributes of this care.

Pregnancy-associated breast cancer: evaluating maternal and foetal outcomes. A national study.

PURPOSE: Pregnancy-associated breast cancer (PABC) is defined as breast cancer diagnosed during the gestational period (gp-PABC) or in the first postpartum year (pp-PABC). Despite its infrequent occurrence, the incidence of PABC appears to be rising due to the increasing propensity for women to delay childbirth. We have established the first retrospective registry study of PABC in Ireland to examine specific clinicopathological characteristics, treatments, and maternal and foetal outcomes. METHODS: This was a national, multi-site, retrospective observational study, including PABC patients treated in 12 oncology institutions from August 2001 to January 2020. Data extracted included information on patient demographics, tumour biology, staging, treatments, and maternal/foetal outcomes. Survival data for an age-matched breast cancer population over a similar time period was obtained from the National Cancer Registry of Ireland (NCRI). Standard biostatistical methods were used for analyses. RESULTS: We identified 155 patients-71 (46%) were gp-PABC and 84 (54%) were pp-PABC. The median age was 36 years. Forty-four patients (28%) presented with Stage III disease and 25 (16%) had metastatic disease at diagnosis. High rates of triple-negative (25%) and HER2+ (30%) breast cancer were observed. We observed an inferior 5-year overall survival (OS) rate in our PABC cohort compared to an age-matched breast cancer population in both Stage I-III (77.6% vs 90.9%) and Stage IV disease (18% vs 38.3%). There was a low rate (3%) of foetal complications. CONCLUSION: PABC patients may have poorer survival outcomes. Further prospective data are needed to optimise management of these patients.

Investigation into early stage fatigue-damage accumulation in glutaraldehyde-fixed bovine pericardium using a novel equibiaxial bulge inflation system.

A primary cause of bioprosthetic heart valve failure is premature degeneration of the pericardial leaflets, owing specifically to mechanical fatigue. There remains a paucity of experimental data and understanding of the fatigue-damage behaviour of this collagenous tissue under complex loading regimes. To meet this knowledge gap, a novel pressure inflation system was designed and built, to cyclically load circular samples of glutaraldehyde fixed bovine pericardium, under equibiaxial bulge conditions. A study up to 60 million cycles revealed new insights into the fatigue behaviour of pericardial tissue, where a statistically significantly higher level of permanent set was found in samples with high collagen fibre dispersion, in comparison to those with highly aligned fibres. Whilst permanent set is known to occur in the non-collagenous matrix of pericardium, this study demonstrates that at physiological loads, which elicit a matrix dominant mechanical response, permanent set and thus tissue-level damage, is still mediated by the underlying collagen fibres.