High-fat diet impact on intestinal cholesterol conversion by the microbiota and serum cholesterol levels

Cholesterol-to-coprostanol conversion by the intestinal microbiota has been suggested to reduce intestinal and serum cholesterol availability, but the relationship between intestinal cholesterol conversion and the gut microbiota, dietary habits, and serum lipids has not been characterized in detail. We measured conserved proportions of cholesterol high and low-converter types in individuals with and without obesity from two distinct, independent low-carbohydrate high-fat (LCHF) dietary intervention studies. Across both cohorts, cholesterol conversion increased in previous low-converters after LCHF diet and was positively correlated with the fecal relative abundance of Eubacterium coprostanoligenes. Lean cholesterol high-converters had increased serum triacylglycerides and decreased HDL-C levels before LCHF diet and responded to the intervention with increased LDL-C, independently of fat, cholesterol, and saturated fatty acid intake. Our findings identify the cholesterol high-converter type as a microbiome marker, which in metabolically healthy lean individuals is associated with increased LDL-C in response to LCHF.publishedVersio

Real-Time GPU-Based Digital Image Correlation Sensor for Marker-Free Strain-Controlled Fatigue Testing

Digital image correlation (DIC) is a highly accurate image-based deformation measurement method achieving a repeatability in the range of σ= 10−5 relative to the field-of-view. The method is well accepted in material testing for non-contact strain measurement. However, the correlation makes it computationally slow on conventional, CPU-based computers. Recently, there have been DIC implementations based on graphics processing units (GPU) for strain-field evaluations with numerous templates per image at rather low image rates, but there are no real-time implementations for fast strain measurements with sampling rates above 1 kHz. In this article, a GPU-based 2D-DIC system is described achieving a strain sampling rate of 1.2 kHz with a latency of less than 2 milliseconds. In addition, the system uses the incidental, characteristic microstructure of the specimen surface for marker-free correlation, without need for any surface preparation—even on polished hourglass specimen. The system generates an elongation signal for standard PID-controllers of testing machines so that it directly replaces mechanical extensometers. Strain-controlled LCF measurements of steel, aluminum, and nickel-based superalloys at temperatures of up to 1000 °C are reported and the performance is compared to other path-dependent and path-independent DIC systems. According to our knowledge, this is one of the first GPU-based image processing systems for real-time closed-loop applications

GPU-based digital image correlation system for real-time strain-controlled fatigue and strain field measurement

This article reports a novel GPU-based 2D digital image correlation system (2D-DIC) overcoming two major limitations of this technique: It measures marker-free, i.e. without sample preparation, and the sampling rate meets the recommendations of ASTM E606. The GPU implementation enables zero-normalized cross correlation (ZNCC) calculation rates of up to 25 kHz for 256 × 256 pixel ROIs. This high-speed image processing system is combined with a high-resolution telecentric lens observing a 10 mm field-of-view, coaxial LED illumination, and a camera acquiring 2040 × 256 pixel images with 1.2 kHz. The optics resolve the microstructure of the surface even of polished cylindrical steel specimen. The displacement uncertainty is below 0.5 μm and the reproducibility in zero-strain tests approximately 10-5 (1 σ) of the field-of-view. For strain-controlled testing, a minimum of two displacement subsets per image are evaluated for average strain with a sampling rate of 1.2 kHz. Similar to mechanical extensometers, an analogue 0-10V displacement signal serves as a feedback for standard PID controllers. The average latency is below 2 ms allowing for cycle frequencies up to 10 Hz. For strain-field measurement, the number of ROIs limits the frame rate, e.g., the correlation rate of 25 kHz is sufficient to evaluate 10 images per second with 2500 ROIs each. This frame rate is still sufficient to compare the maximum and minimum strain fields within a cycle in real-time, e.g. for crack detection. The result is a marker-free and non-contact DIC sensor suitable for both strain-controlled fatigue testing and real-time full-field strain evaluation

Central venous catheter-associated bloodstream infection and colonisation of insertion site and catheter tip : What are the rates and risk factors in haematology patients?

Skin colonisation is an important source for central venous catheter (CVC) colonisation and infection. This study intended to identify risk factors for skin colonisation prior to CVC placement (baseline colonisation) and within 10 days after CVC insertion (subsequent colonisation), for CVC-tip colonisation and for bloodstream infection (BSI). Within a randomised clinical trial, data of 219 patients with haematological malignancies and inserted CVC (with a total of 5,501 CVC-days and 4,275 days at risk) in two university hospitals were analysed. Quantitative skin cultures were obtained from the insertion site before CVC placement and at regular intervals afterwards. CVC-tip cultures were taken on CVC removal and data collection was performed. Statistical analysis included linear and logistic regression models. Age was an independent risk factor for colonisation prior to CVC placement (baseline colonisation). Independent risk factors for subsequent colonisation were baseline colonisation and male gender. High level of subsequent skin colonisation at the insertion site was a predictor of CVC-tip colonisation, and a predictor of BSI. High level of skin colonisation predicts catheter tip colonisation and possibly subsequent infection. Sustained reduction of bacterial growth at the CVC insertion site is therefore indispensable. Male patients are at particular risk for skin colonisation and may be a target population for additional insertion-site care before and during catheterisation

Marker-free GPU-based digital image correlation system for high-temperature strain-controlled fatigue measurements: Presentation held at Annual International DIC Society Conference 2017, November 6-9, 2017, Barcelona, Spain

In contrast to tactile extensometers 2D digital image correlation (2D-DIC) works contactless and thus without slip. It measures not only the average strain between two points, it also allows for full-field analysis, e.g. the analysis of material failure cause. While these advantages also apply to the standard DIC systems available today, such systems so far have a significant disadvantage – their slow measuring speed with maximum sampling rates below 100 Hz. Strain-controlled fatigue measurements with such sensors are possible but limited by their low speed. According to ASTM E 606, at least 400 images per fatigue cycle are necessary to resolve strain amplitude better than 1 %. Hence the fatigue cycle frequency is limited to 0.25 Hz for such DIC systems resulting in a measurement time of more than 11 h for a typical strain-controlled low cycle fatigue experiment with 10.000 cycles. So far, mechanical extensometers have sampling frequencies in the kHz range and thus accelerate those experiments to less than 1 h. To overcome this limitation of slow optical measurement, the 2D-DIC evaluation was implemented on a NVIDIA GeForce GTX 1080 graphics processing unit (GPU) allowing for up to 25.000 FFT evaluations per second (both, forward and backward) of 256 x 256 pixel ROIs. For subpixel displacement calculation, 2D polynomials of second order are fitted to the 3 x 3 pixel area surrounding the correlation maximum. The standard deviation of the “Low Contrast Subpixel Contrast Images” was below 0.01 pixels (1 sigma) for a 30 x 30 pixel kernel size. This high-speed GPU evaluation was paired with a high-resolution telecentric lens with 10 mm FOV minimizing the out-of-plane error, coaxial LED illumination allowing for an exposure time of 300 µs, and a fast CameraLink camera acquiring 2040 x 256 pixel images with 1.3 kHz. This is sufficient to resolve the microstructure even on polished cylindrical samples. A blue LED was used to separate the blackbody radiation from the illumination light by a short pass filter. The result is a high-speed DIC system with a strain measurement rate of 1.2 kHz, 6 ms delay time and a total error in the range of 2*10(-5) (1 sigma). The strain signals were even less noisy than those measured mechanically and they were sufficient to resolve the turning points of a 10 Hz triangular force controlled measurement. So the DIC sensor is well suited for strain-controlled measurements combing the advantages of both, marker-free optical and fast tactile mechanical extensometers