Cerebral arterial vasospasm leads to delayed cerebral ischemia and constitutes the major delayed complication following aneurysmal subarachnoid hemorrhage. Cerebral vasospasm can be reduced by ...increased blood clearance from the subarachnoid space. Clinical pilot studies allow the hypothesis that the clearance of subarachnoid blood is facilitated by means of head shaking. A major obstacle for meaningful clinical studies is the lack of data on appropriate parameters of head shaking. Our in vitro study aims to provide these essential parameters.
A model of the basal cerebral cistern was derived from human magnetic resonance imaging data. Subarachnoid hemorrhage was simulated by addition of dyed experimental blood to transparent experimental cerebrospinal fluid (CSF) filling the model of the basal cerebral cistern. Effects of various head positions and head motion settings (shaking angle amplitudes and shaking frequencies) on blood clearance were investigated using the quantitative dye washout method. Blood washout can be divided into two phases: Blood/CSF mixing and clearance. The major effect of shaking consists in better mixing of blood and CSF thereby increasing clearance rate. Without shaking, blood/CSF mixing and blood clearance in the basal cerebral cistern are hampered by differences in density and viscosity of blood and CSF. Blood clearance increases with decreased shaking frequency and with increased shaking angle amplitude. Head shaking facilitates clearance by varying the direction of gravitational force.
From this in vitro study can be inferred that patient or head shaking with large shaking angles at low frequency is a promising therapeutic strategy to increase blood clearance from the subarachnoid space.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Blood pressure measurement on the cheek Schneider, Sarah; Affeld, Klaus; Kopic, Claudia ...
Current directions in biomedical engineering,
9/2016, Letnik:
2, Številka:
1
Journal Article
Recenzirano
Odprti dostop
In a large group of patients, it is impossible to measure blood pressure using an upper arm cuff. An alternative, non-invasive method of blood pressure measurement is required for patients with ...severe limb deformities or obesity, for amputees, and in the emergency medicine. The device proposed here measures blood pressure in the cheek using a small pressure pad and a pump to occlude the cheek artery – arteria facialis – and assesses blood flow with an infrared light source and a detector. The infrared light signal is analysed to assess the systolic and diastolic blood pressure of the patient. Manual evaluation of the light intensity signal showed a good agreement between cheek blood pressure measurement and a reference measurement using an upper arm cuff.
The aim of this work was the development of an isolated heart setup to delineate the interactions between intraventricular flow features, hemodynamic parameters and mechano-energetics after certain ...mitral valve therapies. Five porcine hearts were explanted and prepared for (i) edge-to-edge mitral valve repair, (ii) implantation of a rotatable biscupid mechanical valve prosthesis. Flow structures were visualized using echocardiography while hemodynamics was recorded in terms of pressures, flow rates and ventricular volume. Hemodynamic and cardiac mechano-energetics implied a marginal effect (<5%) of alternating leaflet orientation on ventricular pre-load and stroke work. After edge-to-edge repair, substantial variations in flow structures were observed. Beside promoting profound insights into fundamental physiologic mechanisms, the setup may be used for validation of computer aided therapy planning tools.
Anterior rhinomanometry is the current gold standard for the objective assessment of nasal breathing by determining the nasal resistance. However, computational fluid dynamics would allow spatially ...and temporally well- resolved investigation of additional flow parameters. In this study, measured values of nasal resistance are compared with measured values. An unclear discrepancy between the two methods was found, suggesting further investigation.
Background
The study of blood trauma, such as hemolysis in blood‐carrying devices, is crucial due to the high incidence of adverse events like alteration of blood function, bleeding, and multi‐organ ...failure. The extent of flow‐induced hemolysis, predominantly influenced by stress duration and intensity, is described by established model parameters based on the power law approach. In recent years, various parameters were determined using different Couette shearing devices and donor species. However, they have not been validated due to limited experimental data.
Methods
This study provides hemolysis measurements in a Couette shearing device and evaluates the suitability of different power law parameters. The revised Couette shearing device generates well‐defined dynamic stress loads that are repeatedly applied to blood samples at a defined temperature. Human blood samples with an adjusted hematocrit of 30%, were tested with varying repetitions (20 to 80 times). The half‐sinusoidal stress loads had amplitudes of 73 to 140 Pa and exposure times of 24 msec per repetition. The parameters of five common power law hemolysis approaches were then compared with the experimental data.
Results
The prediction with the power law model parameters C = 3.458 × 10−6, α = 0.2777 and β = 2.0639 showed a good agreement with the experimental results.
Conclusion
The effect of multiple short‐time stresses on hemolysis was investigated to validate the power law hemolysis model with the Couette shearing device of this study.
This study provides hemolysis measurements in a Couette shearing device and evaluates the suitability of different power law parameters. The fitted experimental results of this study (colored plane) and calculated index of hemolysis (IH, colored data points) using the parameters of A Zhang et al. (2011) (ovine blood) and B Ding et al. (2015) (human blood) showed a good agreement.
Anatomic pathologies such as stenosed or regurgitating heart valves and artificial organs such as heart assist devices or heart valve prostheses are associated with non-physiological flow. This ...regime is associated with regions of spatially high-velocity gradients, high-velocity and/or pressure fluctuations as well as neighbouring regions with stagnant flow associated with high residence time. These hemodynamic conditions cause destruction and/or activation of blood components and their accumulation in regions with high residence time. The development of next-generation artificial organs, which allow long-term patient care by reducing adverse events and improve quality of life, requires the development of blood damage models serving as a cost function for device optimization. We summarized the studies underlining the key findings with subsequent elaboration of the requirements for blood damage models as well as a decision tree based on the classification of existing blood damage models. The four major classes are Lagrangian or Eulerian approaches with stress- or strain-based blood damage. Key challenges were identified and future steps towards the translation of blood damage models into the device development pipeline were formulated. The integration of blood damage caused by turbulence into models as well as in vitro and in vivo validation of models remain the major challenges for future developments. Both require the development of novel experimental setups to provide reliable and well-documented experimental data.
Clinical studies suggest that local wall shear stress (WSS) patterns modulate the site and the progression of atherosclerotic lesions. Computational fluid dynamics (CFD) methods based on in-vivo ...three-dimensional vessel reconstructions have recently been shown to provide prognostically relevant WSS data. This approach is, however, complex and time-consuming. Methodological simplifications are desirable in porting this approach from bench to bedside. The impact of such simplifications on the accuracy of geometry and wall shear stress calculations has to be investigated.
We investigated the influence of two methods of lumen reconstruction, assuming circular versus elliptical cross-sections and using different resolutions for the cross-section reconstructions along the vessel axis. Three right coronary arteries were used, of which one represented a normal coronary artery, one with "obstructive", and one with "dilated" coronary atherosclerosis. The vessel volume reconstruction was performed with three-dimensional (3D) data from a previously validated 3D angiographic reconstruction of vessel cross-sections and vessel axis.
The difference between the two vessel volumes calculated using the two evaluated methods is less than 1 %. The difference, of the calculated pressure loss, was between 2.5% and 8.5% for the evaluated methods. The distributions of the WSS histograms were nearly identical and strongly cross-correlated (0.91-0.95). The good agreement of the results was confirmed by a Chi-square test.
A simplified approach to the reconstruction of coronary vessel lumina, using circular cross-sections and a reduced axial resolution of about 0.8 mm along the vessel axis, yields sufficiently accurate calculations of WSS.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Objective :Total artificial hearts (TAH) serve as a temporary treatment for severe biventricular heart failure. The limited durability and complication rates of current devices hamper long-term ...cardiac replacement. The aim of this study was to assess the feasibility of a novel valveless pumping principle for a durable pulsatile TAH ( ShuttlePump ). Methods: The pump features a rotating and linearly shuttling piston within a cylindrical housing with two in- and outlets. With a single moving piston, the ShuttlePump delivers pulsatile flow to both systemic and pulmonary circulation. The pump and actuation system were designed iteratively based on analytical and in silico methods, utilizing finite element methods (FEM) and computational fluid dynamics (CFD). Pump characteristics were evaluated experimentally in a mock circulation loop mimicking the cardiovascular system, while hemocompatibility-related parameters were calculated numerically. Results: Pump characteristics cover the entire required operating range for a TAH, providing 2.5 - 9 L/min of flow rate against 50 - 160 mmHg arterial pressures at stroke frequencies of 1.5 - 5 Hz while balancing left and right atrial pressures. FEM analysis showed mean overall copper losses of 8.84 W, resulting in a local maximum blood temperature rise of < 2 K. The CFD results of the normalized index of hemolysis were 3.57 mg/100L, and 95% of the pump's blood volume was exchanged after 1.42 s. Conclusion and significance: This study indicates the feasibility of a novel pumping system for a TAH with numerical and experimental results substantiating further development of the ShuttlePump
Circulating endothelial cells (CECs) are a reliable biomarker for cardiovascular diseases (CVDs). A major unresolved challenge limiting the widespread use of CECs for the diagnosis and monitoring of ...CVDs is their unreliable detection. This problem is mainly attributed to the low sample volume (5–10 mL) of commonly used ex vivo CEC isolation methods. To overcome this limitation, the BMProbe for the in vivo isolation of CECs is proposed. It consists of a twisted medical flat wire with a polymer‐coated surface functionalized with anti‐CD105 antibodies. A combined experimental and numerical study is performed to investigate which flow conditions lead to an increased cell attachment to the probe's surface. Endothelial cells are solved in a dextran solution and circulated in a flow system containing the BMProbes. Microscopic images of the attached CECs are taken. In addition, the experiments are simulated using a computational fluid dynamics (CFD) flow solver to quantify the flow conditions at the probe's surface. The microscopic images are superimposed with the CFD data to investigate the influence of wall shear rate and wall normal rate on the attachment of CECs to the probe. Most of all attached cells (85.5%) are found in areas of negative wall normal rate.
To isolate circulating endothelial cells in vivo from patient's blood for prognosis and diagnosis of cardiovascular diseases, a probe consisting of a coated wire is proposed. A combined experimental and numerical study shows which near‐wall flow conditions lead to enhanced cell attachment to the surface of the probe.
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