Assessment of drug delivery devices working at microflow rates.

Almost every medical department in hospitals around the world uses infusion devices to administer fluids, nutrition, and medications to patients to treat many different diseases and ailments. There have been several reports on adverse incidents caused by medication errors associated with infusion equipment. Such errors can result from malfunction or improper use, or even inaccuracy of the equipment, and can cause harm to patients' health. Depending on the intended use of the equipment, e.g. if it is used for anaesthesia of adults or for medical treatment of premature infants, the accuracy of the equipment may be more or less important. A well-defined metrological infrastructure can help to ensure that infusion devices function properly and are as accurate as needed for their use. However, establishing a metrological infrastructure requires adequate knowledge of the performance of infusion devices in use. This paper presents the results of various tests conducted with two types of devices.

Primary standards for measuring flow rates from 100 nl/min to 1 ml/min - gravimetric principle.

Microflow and nanoflow rate calibrations are important in several applications such as liquid chromatography, (scaled-down) process technology, and special health-care applications. However, traceability in the microflow and nanoflow range does not go below 16 µl/min in Europe. Furthermore, the European metrology organization EURAMET did not yet validate this traceability by means of an intercomparison between different National Metrology Institutes (NMIs). The NMIs METAS, Centre Technique des Industries Aérauliques et Thermiques, IPQ, Danish Technological Institute, and VSL have therefore developed and validated primary standards to cover the flow rate range from 0.1 µl/min to at least 1 ml/min. In this article, we describe the different designs and methods of the primary standards of the gravimetric principle and the results obtained at the intercomparison for the upper flow rate range for the various NMIs and Bronkhorst High-Tech, the manufacturer of the transfer standards used.

Computational fluid dynamics simulation of a-v fistulas: from MRI and ultrasound scans to numeric evaluation of hemodynamics.

PURPOSE: A-v anastomosis entails dramatic changes in hemodynamic conditions, which may lead to major alterations to the vessels involved; primarily dilatations and devastating stenoses. Wall shear stress is thought to play a key role in the remodeling of the vessels exposed to abnormal levels and oscillating wall shear stress. In this study we sought to develop a framework suitable for thorough in vivo analyses of wall shear stress and vessel morphology of a-v fistulas in patients. METHODS: Using ultrasound and magnetic resonance imaging (MRI) transverse image stacks from six patient a-v fistulas were obtained. From the image stacks three-dimensional geometries of the patient fistulas were created using dedicated segmentation software. Geometries of three a-v fistulas were imported into finite element software in order to perform fluid flow simulations of blood flows and frictional forces on the vessel walls in the a-v fistulas. Boundary conditions for the simulations were obtained using both a MRI phase contrast and an ultrasound Doppler technique. RESULTS: The segmentation of the six fistulas of very different age and morphology (two end-to-side and four side-to-side) showed the ability of the approach to create geometries of various fistula morphologies. Simulations of the three fistulas showed an instant picture of the present status of the exposure to different levels of wall shear stress and the morphological status in the vessel remodeling process. CONCLUSION: The study demonstrated the capability of the CFD framework to analyze patient a-v fistulas on a regular basis using both MRI and ultrasound-based approaches.