A Numerical Model for Simulation of Blood Flow in Vascular Networks

An accurate study of blood flow is associated with an accurate vascular pattern and geometrical properties of the organ of interest. Due to the complexity of vascular networks and poor accessibility in vivo, it is challenging to reconstruct the entire vasculature of any organ experimentally. The objective of this study is to introduce an innovative approach for the reconstruction of a full vascular tree from available morphometric data. Our method consists of implementing morphometric data on those parts of the vascular tree that are smaller than the resolution of medical imaging methods. This technique reconstructs the entire arterial tree down to the capillaries. Vessels greater than 2 mm are obtained from direct volume and surface analysis using contrast enhanced computed tomography (CT). Vessels smaller than 2mm are reconstructed from available morphometric and distensibility data and rearranged by applying Murray's Laws. Implementation of morphometric data to reconstruct the branching pattern and applying Murray's Laws to every vessel bifurcation simultaneously, lead to an accurate vascular tree reconstruction. The reconstruction algorithm generates full arterial tree topography down to the first capillary bifurcation. Geometry of each order of the vascular tree is generated separately to minimize the construction and simulation time. The node-to-node connectivity along with the diameter and length of every vessel segment is established and order numbers, according to the diameter-defined Strahler system, are assigned. During the simulation, we used the averaged flow rate for each order to predict the pressure drop and once the pressure drop is predicted, the flow rate is corrected to match the computed pressure drop for each vessel. The final results for 3 cardiac cycles is presented and compared to the clinical data

A Numerical Model for Simulation of Blood Flow in Vascular Networks

An accurate study of blood flow is associated with an accurate vascular pattern and geometrical properties of the organ of interest. Due to the complexity of vascular networks and poor accessibility in vivo, it is challenging to reconstruct the entire vasculature of any organ experimentally. The objective of this study is to introduce an innovative approach for the reconstruction of a full vascular tree from available morphometric data. Our method consists of implementing morphometric data on those parts of the vascular tree that are smaller than the resolution of medical imaging methods. This technique reconstructs the entire arterial tree down to the capillaries. Vessels greater than 2 mm are obtained from direct volume and surface analysis using contrast enhanced computed tomography (CT). Vessels smaller than 2mm are reconstructed from available morphometric and distensibility data and rearranged by applying Murray's Laws. Implementation of morphometric data to reconstruct the branching pattern and applying Murray's Laws to every vessel bifurcation simultaneously, lead to an accurate vascular tree reconstruction. The reconstruction algorithm generates full arterial tree topography down to the first capillary bifurcation. Geometry of each order of the vascular tree is generated separately to minimize the construction and simulation time. The node-to-node connectivity along with the diameter and length of every vessel segment is established and order numbers, according to the diameter-defined Strahler system, are assigned. During the simulation, we used the averaged flow rate for each order to predict the pressure drop and once the pressure drop is predicted, the flow rate is corrected to match the computed pressure drop for each vessel. The final results for 3 cardiac cycles is presented and compared to the clinical data

A Numerical Model for Simulation of Blood Flow in Vascular Networks

An accurate study of blood flow is associated with an accurate vascular pattern and geometrical properties of the organ of interest. Due to the complexity of vascular networks and poor accessibility in vivo, it is challenging to reconstruct the entire vasculature of any organ experimentally. The objective of this study is to introduce an innovative approach for the reconstruction of a full vascular tree from available morphometric data. Our method consists of implementing morphometric data on those parts of the vascular tree that are smaller than the resolution of medical imaging methods. This technique reconstructs the entire arterial tree down to the capillaries. Vessels greater than 2 mm are obtained from direct volume and surface analysis using contrast enhanced computed tomography (CT). Vessels smaller than 2mm are reconstructed from available morphometric and distensibility data and rearranged by applying Murray's Laws. Implementation of morphometric data to reconstruct the branching pattern and applying Murray's Laws to every vessel bifurcation simultaneously, lead to an accurate vascular tree reconstruction. The reconstruction algorithm generates full arterial tree topography down to the first capillary bifurcation. Geometry of each order of the vascular tree is generated separately to minimize the construction and simulation time. The node-to-node connectivity along with the diameter and length of every vessel segment is established and order numbers, according to the diameter-defined Strahler system, are assigned. During the simulation, we used the averaged flow rate for each order to predict the pressure drop and once the pressure drop is predicted, the flow rate is corrected to match the computed pressure drop for each vessel. The final results for 3 cardiac cycles is presented and compared to the clinical data

A Numerical Model for Simulation of Blood Flow in Vascular Networks

An accurate study of blood flow is associated with an accurate vascular pattern and geometrical properties of the organ of interest. Due to the complexity of vascular networks and poor accessibility in vivo, it is challenging to reconstruct the entire vasculature of any organ experimentally. The objective of this study is to introduce an innovative approach for the reconstruction of a full vascular tree from available morphometric data. Our method consists of implementing morphometric data on those parts of the vascular tree that are smaller than the resolution of medical imaging methods. This technique reconstructs the entire arterial tree down to the capillaries. Vessels greater than 2 mm are obtained from direct volume and surface analysis using contrast enhanced computed tomography (CT). Vessels smaller than 2mm are reconstructed from available morphometric and distensibility data and rearranged by applying Murray's Laws. Implementation of morphometric data to reconstruct the branching pattern and applying Murray's Laws to every vessel bifurcation simultaneously, lead to an accurate vascular tree reconstruction. The reconstruction algorithm generates full arterial tree topography down to the first capillary bifurcation. Geometry of each order of the vascular tree is generated separately to minimize the construction and simulation time. The node-to-node connectivity along with the diameter and length of every vessel segment is established and order numbers, according to the diameter-defined Strahler system, are assigned. During the simulation, we used the averaged flow rate for each order to predict the pressure drop and once the pressure drop is predicted, the flow rate is corrected to match the computed pressure drop for each vessel. The final results for 3 cardiac cycles is presented and compared to the clinical data

Dynamic relationship of diffusing capacity and pulmonary alveolar vascular recruitment during exercise in chronic obstructive pulmonary disease

Empirical thesis.Bibliography: pages 188-205.Chapter 1. Introduction -- Chapter 2. Review of the literature -- Chapter 3. Methodology -- Chapter 4. Study I. Influence of resting lung diffusion on exercise capacity in patients with COPD -- Chapter 5. Study II. Alveolar-capillary reserve during exercise in patients with COPD -- Chapter 6. Study III. Influence of dietary nitrate supplementation on gas exchange and exercise performance in patients with COPD -- Chapter 7. Conclusion, limitations, novel aspects, future direction, list of findings -- Appendices -- Bibliography.Chronic Obstructive Pulmonary Disease (COPD) is a leading cause of global morbidity and mortality. COPD has multiple etiologies. Irreversible pulmonary-alveolar capillary damage is one of them which can be assessed by diffusing capacity of the lungs for carbon monoxide (DLCO).The primary objective was to study the use of DLCO in predicting exercise limitation in COPD. The secondary objective was to evaluate the role of dietary nitrate precursor (beetroot juice) in improving alveolar gas exchange, pulmonary vascular function, and exercise intolerance in COPD. A third (mainly exploratory) aim was to study the expansion of pulmonary gas exchange surface area during exercise and its correlation with pulse wave velocity (PWV) as a surrogate of arterial stiffness.32 patients with mild to severe COPD were tested. Cycle ergometry on day 1 was performed. DLCO, noninvasive indices of gas exchange, pulmonary vascular capacitance, cardiac eutput (Qc), Exhaled nitric oxide (exNO), and other respiratory variables were measured before and after ergometry. Patients were randomized to 8 days of beetroot juice or placebo and on day 8 the above protocol was repeated. Effects of high nitrate juice intake on indices of arterial stiffness (Appendix D) were studied by aortic PWV and central aortic pressure (cAP) before and after exercise.Only the single breath DLCO relative to Qc and body weight were significant resting predictors of exercise intolerance. COPD patients who did expand gas exchange surface area during exercise relative to Qc had a more preserved exercise capacity. Beetroot juice showed a (non significant) trend in improving exercise performance and pulmonary gas exchange surface area. The juice significantly lowered blood pressure, increased exNO and improved the patient overall wellbeing through objective scoring. The juice did not affect PWV before exercise in this cohort, but there was an effect of dietary nitrate on brachial systolic and pulse pressure, aortic pulse pressure and reflection magnitude determined from cAP.The three sets of novel experiments showed that exercise limitation in COPD is affected by alveolar-capillary gas exchange impairment attributed to impairment of pulmonary capillary recruitment. DLCO is a good measure of pulmonary vascular health and exercise intolerance in COPD. Dietary nitrate did neither significantly improve alveolar gas exchange nor improve indices of arterial stiffness in this cohort, though positive trends were observed.Mode of access: World wide web1 online resource (206 pages) colour illustration

A Numerical Model for Simulation of Blood Flow in Vascular Networks

An accurate study of blood flow is associated with an accurate vascular pattern and geometrical properties of the organ of interest. Due to the complexity of vascular networks and poor accessibility in vivo, it is challenging to reconstruct the entire vasculature of any organ experimentally. The objective of this study is to introduce an innovative approach for the reconstruction of a full vascular tree from available morphometric data. Our method consists of implementing morphometric data on those parts of the vascular tree that are smaller than the resolution of medical imaging methods. This technique reconstructs the entire arterial tree down to the capillaries. Vessels greater than 2 mm are obtained from direct volume and surface analysis using contrast enhanced computed tomography (CT). Vessels smaller than 2mm are reconstructed from available morphometric and distensibility data and rearranged by applying Murray's Laws. Implementation of morphometric data to reconstruct the branching pattern and applying Murray's Laws to every vessel bifurcation simultaneously, lead to an accurate vascular tree reconstruction. The reconstruction algorithm generates full arterial tree topography down to the first capillary bifurcation. Geometry of each order of the vascular tree is generated separately to minimize the construction and simulation time. The node-to-node connectivity along with the diameter and length of every vessel segment is established and order numbers, according to the diameter-defined Strahler system, are assigned. During the simulation, we used the averaged flow rate for each order to predict the pressure drop and once the pressure drop is predicted, the flow rate is corrected to match the computed pressure drop for each vessel. The final results for 3 cardiac cycles is presented and compared to the clinical data

A Numerical Model for Simulation of Blood Flow in Vascular Networks

An accurate study of blood flow is associated with an accurate vascular pattern and geometrical properties of the organ of interest. Due to the complexity of vascular networks and poor accessibility in vivo, it is challenging to reconstruct the entire vasculature of any organ experimentally. The objective of this study is to introduce an innovative approach for the reconstruction of a full vascular tree from available morphometric data. Our method consists of implementing morphometric data on those parts of the vascular tree that are smaller than the resolution of medical imaging methods. This technique reconstructs the entire arterial tree down to the capillaries. Vessels greater than 2 mm are obtained from direct volume and surface analysis using contrast enhanced computed tomography (CT). Vessels smaller than 2mm are reconstructed from available morphometric and distensibility data and rearranged by applying Murray's Laws. Implementation of morphometric data to reconstruct the branching pattern and applying Murray's Laws to every vessel bifurcation simultaneously, lead to an accurate vascular tree reconstruction. The reconstruction algorithm generates full arterial tree topography down to the first capillary bifurcation. Geometry of each order of the vascular tree is generated separately to minimize the construction and simulation time. The node-to-node connectivity along with the diameter and length of every vessel segment is established and order numbers, according to the diameter-defined Strahler system, are assigned. During the simulation, we used the averaged flow rate for each order to predict the pressure drop and once the pressure drop is predicted, the flow rate is corrected to match the computed pressure drop for each vessel. The final results for 3 cardiac cycles is presented and compared to the clinical data

Fluid-structure interaction investigation of spiral flow in a model of abdominal aortic aneurysm

The presence of a spiral arterial blood flow pattern in both animals and humans has been widely accepted. The effect of spiral flow on physiological processes associated with abdominal aortic aneurysm (AAA) development and progressions can provide valuable information. The purpose of this study is to investigate the influence of spiral flow on haemodynamic changes in an elastic AAA model by implementing a coupled fluid–structure interaction (FSI) analysis. The results showed that an increase in the intensity of spiral flow resulted in an increase in maximum wall shear stress (WSS) and a decrease in maximum wall stress; however, the spiral flow effect on the WSS was higher than the wall stress. It was also shown that not taking into consideration the effect of spiral flow in modelling of AAA can underestimate the magnitude of WSS by up to 30% and overestimate the magnitude of wall stress by up to 11%. The presence of spiral flow within AAAs is associated with beneficial and detrimental effects. The beneficial effects are to reduce the wall stress and the size of regions with low WSS which in turn reduce the risk of rupture, endothelial dysfunction and the development of atherosclerosis. However, the increase in magnitude of WSS is seen as the detrimental effect of spiral flow.9 page(s

Correlation of Stroke Volume Measurement between Sonosite Portable Echocardiogram and Edwards Flotrac Sensor-Vigileo Monitor in an Intensive Care Unit

Purpose Stroke volume (SV) is a parameter that is being recognized as an endpoint in fluid resuscitation algorithms. Its role is now being realized as an important variable in hemodynamic assessment in various clinical scenarios such as septic and cardiogenic shocks. Direct measurement of stroke volume (SV) and its novel corollary, stroke volume variation (SVV) derived by proprietary software, are preferred over mean cardiac output (CO) measurements because they render a more accurate reflection of hemodynamic status independent of heart rate. Flotrac-Vigileo monitor (FTV) (Edwards Lifesciences, Irvine, CA, USA) is a system that uses a complex algorithm analyzing arterial waveform to calculate SV, SVV, and CO. We assessed the feasibility of obtaining SV measurements with a portable echocardiogram and validated its accuracy with the FTV system in mechanically ventilated patients in our intensive care unit (ICU). Furthermore, we emphasized the importance of hemodynamic measurements and familiarity with critical care echocardiography for the intensivists. Methods Ten patients who were on mechanical ventilation were studied. A femoral arterial line was connected to the FTV system monitoring SV and CO. A portable echocardiogram (M-Turbo; Sonosite, Bothell, WA) was used to measure SV. CO was calculated by multiplying SV by heart rate. No patient had arrhythmia. We used biplane Simpson's method of discs to calculate SV in which subtraction of end-systolic volume from end-diastolic volume yields the SV Results The comparison of simultaneous SV and CO measurements by echocardiography with FTV showed a strong correlation between the 2. (For SV, y = 0.9545x + 3.3, R 2 = 0.98 and for CO, y = 0.9104x + 7.7074, R 2 = 0.97). Conclusions In our small cohort, the SV and CO measured by a portable echocardiogram (Sonosite M-Turbo) appears to be closely correlated with their respective values measured by FTV. Portable echocardiography is a reliable noninvasive tool for the hemodynamic assessment of the critically ill. Its results need further validation with gold standard measures in a larger cohort of patients. However, our results suggest portable echocardiography could be an attractive tool in assessment of different hemodynamic scenarios in the critically ill