Crimped fiber composites: mechanics of a finite-length crimped fiber embedded in a soft matrix.

Composites comprising crimped fibers of finite length embedded in a soft matrix have the potential to mimic the strain-hardening behavior of tissues containing fibrous collagen. Unlike continuous fiber composites, such chopped fiber composites would be flow-processable. Here, we study the fundamental mechanics of stress transfer between a single crimped fiber and the embedding matrix subjected to tensile strain. Finite element simulations show that fibers with large crimp amplitude and large relative modulus straighten significantly at small strain without bearing significant load. At large strain, they become taut and hence bear increasing load. Analogous to straight fiber composites, there is a region near the ends of each fiber which bears much lower stress than the midsection. We show that the stress-transfer mechanics can be captured by a shear lag model where the crimped fiber can be replaced with an equivalent straight fiber whose effective modulus is lower than that of the crimped fiber, but increases with applied strain. This allows estimating the modulus of a composite at low fiber fraction. The degree of strain hardening and the strain needed for strain hardening can be tuned by changing relative modulus of the fibers and the crimp geometry.

The Risk of Incarceration During Nonoperative Management of Incisional Hernias: A Population-based Analysis of 30,998 Patients.

OBJECTIVE: The aim of the study was to quantify the risk of incarceration of incisional hernias. BACKGROUND: Operative repair is the definitive treatment for incisional ventral hernias but is often deferred if the perceived risk of elective operation is elevated secondary to comorbid conditions. The risk of incarceration during nonoperative management (NOM) factors into shared decision making by patient and surgeon; however, the incidence of acute incarceration remains largely unknown. METHODS: A retrospective analysis of adult patients with an International Classification of Diseases, Ninth Revision or Tenth Revision diagnosis of incisional hernia was conducted from 2010 to 2017 in 15 hospitals of a single healthcare system. The primary outcome was incarceration necessitating emergent operation. The secondary outcome was 30-, 90-, and 365-day mortality. Univariate and multivariate analyses were used to determine independent predictors of incarceration. RESULTS: Among 30,998 patients with an incisional hernia (mean age 58.1 ±â€Š15.9 years; 52.7% female), 23,022 (78.1%) underwent NOM of whom 540 (2.3%) experienced incarceration, yielding a 1- and 5-year cumulative incidence of 1.24% and 2.59%, respectively. Independent variables associated with incarceration included: age older than 40 years, female sex, current smoker, body mass index 30 or greater, and a hernia-related inpatient admission. All-cause mortality rates at 30, 90, and 365 days were significantly higher in the incarceration group at 7.2%, 10%, and 14% versus 1.1%, 2.3%, and 5.3% in patients undergoing successful NOM, respectively. CONCLUSIONS: Incarceration is an uncommon complication of NOM but is associated with a significant risk of death. Tailored decision making for elective repair and considering the aforementioned risk factors for incarceration provides an initial step toward mitigating the excess morbidity and mortality of an incarceration event.

A retrievable, dual-chamber stent protects against warm ischemia of donor organs in a model of donation after circulatory death.

BACKGROUND: Ischemic injury during the agonal period of donation after circulatory death donors remains a significant barrier to increasing abdominal transplants. A major obstacle has been the inability to improve visceral perfusion, while at the same time respecting the ethics of the organ donor. A retrievable dual-chamber stentgraft could potentially isolate the organ perfusion from systemic hypotension and hypoxia, without increasing cardiac work or committing the donor. METHODS: Retrievable dumbbell-shaped stents were laser welded from nitinol wire and covered with polytetrafluoroethylene. Yorkshire pigs were assigned to either agonal control or dumbbell-shaped dual-chamber stentgraft. A central lumen maintained aortic flow, while an outer visceral chamber was perfused with oxygenated blood. A 1-hour agonal phase of hypoxia and hypotension was simulated. Stents were removed by simple sheath advancement. Cardiac monitoring, labs, and visceral flow were recorded followed by recovery of the animal to a goal of 48 hours. RESULTS: Cardiac stress did not increase during stent deployment. Visceral pO2 and flow were dramatically improved in stented animal relative to control animals. Five of 7 control animals were killed after renal failure complications, whereas all stent animals survived. Histology confirmed increased ischemic changes among control kidneys compared to stented animals. CONCLUSION: A dual-chamber stent improved outcomes after a simulated agonal phase. The stent did not increase cardiac work, thus respecting a key ethical consideration. The ability of a dual-chamber stent to prevent ischemia during organ recovery may become a powerful tool to address the critical donor organ shortage.

Machine learning for the prediction of pathologic pneumatosis intestinalis.

BACKGROUND: The radiographic finding of pneumatosis intestinalis can indicate a spectrum of underlying processes ranging from a benign finding to a life-threatening condition. Although radiographic pneumatosis intestinalis is relatively common, there is no validated clinical tool to guide surgical management. METHODS: Using a retrospective cohort of 300 pneumatosis intestinalis cases from a single institution, we developed 3 machine learning models for 2 clinical tasks: (1) the distinction of benign from pathologic pneumatosis intestinalis cases and (2) the determination of patients who would benefit from an operation. The 3 models are (1) an imaging model based on radiomic features extracted from computed tomography scans, (2) a clinical model based on clinical variables, and (3) a combination model using both the imaging and clinical variables. RESULTS: The combination model achieves an area under the curve of 0.91 (confidence interval: 0.87-0.94) for task I and an area under the curve of 0.84 (confidence interval: 0.79-0.88) for task II. The combination model significantly (P < .05) outperforms the imaging model and the clinical model for both tasks. The imaging model achieves an area under the curve of 0.72 (confidence interval: 0.57-0.87) for task I and 0.68 (confidence interval: 0.61-0.74) for task II. The clinical model achieves an area under the curve of 0.87 (confidence interval: 0.83-0.91) for task I and 0.76 (confidence interval: 0.70-0.81) for task II. CONCLUSION: This study suggests that combined radiographic and clinical features can identify pathologic pneumatosis intestinalis and aid in patient selection for surgery. This tool may better inform the surgical decision-making process for patients with pneumatosis intestinalis.

Development and validation of a five-factor score for prediction of pathologic pneumatosis.

BACKGROUND: The significance of pneumatosis intestinalis (PI) remains challenging. While certain clinical scenarios are predictive of transmural ischemia, risk models to assess the presence of pathologic PI are needed. The aim of this study was to determine what patient factors at the time of radiographic diagnosis of PI predict the risk for pathologic PI. METHODS: We conducted a retrospective cohort study examining patients with PI from 2010 to 2016 at a multicenter hospital network. Multivariate logistic regression was used to develop a predictive model for pathologic PI in a derivation cohort. Using regression-coefficient-based methods, the final multivariate model was converted into a five-factor-based score. Calibration and discrimination of the score were then assessed in a validation cohort. RESULTS: Of 305 patients analyzed, 102 (33.4%) had pathologic PI. We identified five factors associated with pathologic PI at the time of radiographic diagnosis: small bowel PI, age 70 years or older, heart rate 110 bpm or greater, lactate of 2 mmol/L or greater, and neutrophil-lymphocyte ratio 10 or greater. Using this model, patients in the validation cohort were assigned risk scores ranging from 0 to 11. Low-risk patients were categorized when scores are 0 to 4; intermediate, score of 5 to 6; high, score of 7 to 8; and very high risk, 9+. In the validation cohort, very high-risk patients (n = 17; 18.1%) had predicted rates of pathologic pneumatosis of 88.9% and an observed rate of 82.4%. In contrast, patients labeled as low risk (n = 37; 39.4%) had expected rates of pathologic pneumatosis of 1.3% and an observed rate of 0%. The model showed excellent discrimination (area under the curve, 0.90) and good calibration (Hosmer-Lemeshow goodness-of-fit, p = 0.37). CONCLUSION: Our score accurately stratifies patient risk of pathologic pneumatosis. This score has the potential to target high-risk individuals for expedient operation and spare low-risk individuals invasive interventions. LEVEL OF EVIDENCE: Prognostic Study, Level III.

An unexpected cause of pericardial effusion.

We present a case of pericardial effusion due to embolization of a fragment of an inferior vena cava (IVC) filter, with subsequent perforation of the right ventricle. This is a rare and unexpected cause of pericardial effusion. Fracture or embolization of IVC filters is a relatively uncommon complication, but these events may have serious clinical implications. Although IVC filters are often placed with the intent of removal, the device in many patients is never removed. The long-term implications of IVC filter placement must be kept in mind when making decisions about device placement and subsequent removal.