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Pulsatile Flow (pulsatile + flow)
Selected AbstractsThe Importance of dQ/dt on the Flow Field in a Turbodynamic Pump With Pulsatile FlowARTIFICIAL ORGANS, Issue 9 2009Fangjun Shu Abstract Fluid dynamic analysis of turbodynamic blood pumps (TBPs) is often conducted under steady flow conditions. However, the preponderance of clinical applications for ventricular assistance involves unsteady, pulsatile flow,due to the residual contractility of the native heart. This study was undertaken to demonstrate the importance of pulsatility and the associated time derivative of the flow rate (dQ/dt) on hemodynamics within a clinical-scale TBP. This was accomplished by performing flow visualization studies on a transparent model of a centrifugal TBP interposed within a cardiovascular simulator with controllable heart rate and stroke volume. Particle image velocimetry triggered to both the rotation angle of the impeller and phase of the cardiac cycle was used to quantify the velocity field in the outlet volute and in between the impeller blades for 16 phases of the cardiac cycle. Comparison of the unsteady flow fields to corresponding steady conditions at the same (instantaneous) flow rates revealed marked differences. In particular, deceleration of flow was found to promote separation within the outlet diffuser, while acceleration served to stabilize the velocity field. The notable differences between the acceleration and deceleration phases illustrated the prominence of inertial fluid forces. These studies emphasize the importance of dQ/dt as an independent variable for thorough preclinical validation of TBPs intended for use as a ventricular assist device. [source] An investigation of pulsatile flow in a model cavo-pulmonary vascular systemINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 11 2009K. Chitra Abstract The complexities in the flow pattern in a cavo-pulmonary vascular system,after application of the Fontan procedure in the vicinity of the superior vena cava, inferior vena cava, and the confluence at the T-junction,are analysed. A characteristic-based split (CBS) finite element scheme involving the artificial compressibility approach is employed to compute the resulting flow. Benchmarking of the CBS scheme is carried out using standard problems and with the flow features observed in an experimental model with the help of a dye visualization technique in model scale. The transient flow variations in a total cavo-pulmonary connection (TCPC) under pulsatile conditions are investigated and compared with flow visualization studies. In addition to such qualitative flow investigations, quantitative analysis of energy loss and haemodynamic stresses have also been performed. The comparisons show good agreement between the numerical and experimental flow patterns. The numerically predicted shear stress values indicate that the pulsatile flow condition is likely to be more severe than steady flow, with regard to the long-term health of the surgically corrected TCPC. Copyright © 2008 John Wiley & Sons, Ltd. [source] MRA of intracranial aneurysms embolized with platinum coils: A vascular phantom study at 1.5T and 3TJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 1 2008Shingo Kakeda Abstract Purpose To analyze the influence of matrix and echo time (TE) of three-dimensional time-of-flight (3D TOF) magnetic resonance angiography (MRA) on the depiction of residual flow in aneurysms embolized with platinum coils at 1.5T and 3T. Materials and Methods A simulated intracranial aneurysm of the vascular phantom was loosely packed to maintain the patency of some residual aneurysmal lumen with platinum coils and connected to an electromagnetic flow pump with pulsatile flow. MRAs were obtained altering the matrix and TE of 3D TOF sequences at 1.5T and 3T. Results The increased spatial resolution and the shorter TE offered better image quality at 3T. For the depiction of an aneurysm remnant, the high-spatial-resolution 3T MRA (matrix size of 384 × 224 and 512 × 256) with a short TE of ,3.3 msec were superior to the 1.5T MRA obtained with any sequences. Conclusion 3T MRA is superior to 1.5T MRA for the assessment of aneurysms embolized with platinum coils; the combination of the 512 × 256 matrix and short TE (3.3 msec or less) seems feasible at 3T. J. Magn. Reson. Imaging 2008;28:13,20. © 2008 Wiley-Liss, Inc. [source] Reverse flow facial artery as recipient vessel for perforator flapsMICROSURGERY, Issue 6 2009D.D.S., Frank Hölzle M.D., Ph.D. In perforator flaps, anastomosis between flap and recipient vessels in the neck area is often difficult due to small vessel diameter and short pedicle. The aim of this study was to investigate whether the retrograde flow of the distal, paramandibular part of the facial artery would provide sufficient pressure and size to perfuse perforator flaps. Before and after occlusion of the contralateral facial artery, retrograde and anterograde arterial pressure was measured on both sides of the facial artery in 50 patients. The values were compared with the mean systemic arterial pressure. Diameters of facial arteries in the paramandibular region and perforator flap vessels were evaluated by morphometry. Arterial pressure in the distal facial artery with retrograde flow was 76% of the systemic arterial pressure. The latter equaled approximately the anterograde arterial pressure in the proximal end of the facial artery. Mean arterial pressure of the facial arteries decreased after proximal occlusion of the contralateral facial artery, which was not significant (P = 0.09). Mean diameter of the distal facial arteries in the mandibular region was 1.6 mm (range 1.3,2.2 mm; standard deviation 0.3 mm; n = 50), that of the perforator flap arteries 1.3 mm (0.9,2.6 mm; 0.4 mm; n = 20). Facial arteries, based on reverse flow, successfully supported all 20 perforator flaps. Retrograde pulsatile flow in the distal facial artery sustains perforator flaps even if the contralateral facial artery is occluded. Proximity of the distal facial arteries to the defect compensates for short pedicles. Matching diameters of the arteries are ideal for end-to-end anastomosis. © 2009 Wiley-Liss, Inc. Microsurgery, 2009. [source] Comparison of Perfusion Quality in Hollow-Fiber Membrane Oxygenators for Neonatal Extracorporeal Life SupportARTIFICIAL ORGANS, Issue 4 2010Jonathan Talor Abstract Perfusion quality is an important issue in extracorporeal life support (ECLS); without adequate perfusion of the brain and other vital organs, multiorgan dysfunction and other deficits can result. The authors tested three different pediatric oxygenators (Medos Hilite 800 LT, Medtronic Minimax Plus, and Capiox Baby RX) to determine which gives the highest quality of perfusion at flow rates of 400, 600, and 800 mL/min using human blood (36°C, 40% hematocrit) under both nonpulsatile and pulsatile flow conditions. Clinically identical equipment and a pseudo-patient were used to mimic operating conditions during neonatal ECLS. Traditionally, the postoxygenator surplus hemodynamic energy value (SHEpost, extra energy obtained through pulsatile flow) is the one relied upon to give a qualitative determination of the amount of perfusion in the patient; the authors also examined SHE retention through the membrane, as well as the contribution of SHEpost to the postoxygenator total hemodynamic energy (THEpost). At each experimental condition, pulsatile flow outperformed nonpulsatile flow for all factors contributing to perfusion quality: the SHEpost values for pulsatile flow were 4.6,7.6 times greater than for nonpulsatile flow, while the THEpost remained nearly constant for pulsatile versus nonpulsatile flow. For both pulsatile and nonpulsatile flow, the Capiox Baby RX oxygenator was found to deliver the highest quality of perfusion, while the Minimax Plus oxygenator delivered the least perfusion. It is the authors' recommendation that the Baby RX oxygenator running under pulsatile flow conditions be used for pediatric ECLS, but further studies need to be done in order to establish its effectiveness beyond the FDA-approved time span. [source] In Vivo Assessment of a New Method of Pulsatile Perfusion Based on a Centrifugal PumpARTIFICIAL ORGANS, Issue 2 2010Jesús Herreros Abstract The aim of this study was to assess platelet dysfunction and damage to organs after extracorporeal circulation using a pump based on a new method that adds a pulsatile flow to the continuous flow provided by a centrifugal pump. The continuous component of the total flow (2,3 L/min) is created by a Bio-Pump centrifugal pump, while the pulsatile component is created by the pulsating of an inner membrane pneumatically controlled by an intra-aortic counterpulsation balloon console (systolic volume of 37.5 mL in an asynchronous way with a frequency of 60 bpm). Six pigs were subjected to a partial cardiopulmonary bypass lasting 180 min and were sacrificed 60 min after extracorporeal circulation was suspended. The hematological study included the measurement of hematocrit, hemoglobin, leukocytes, and platelet function. The new pump did not significantly alter either platelet count or platelet function. In contrast, hematocrit and hemoglobin were significantly reduced during extracorporeal circulation (approximately 5% P = 0.011, and 2 g/dL P = 0.01, respectively). The leukocyte count during extracorporeal circulation showed a tendency to decrease, but this was not significant. In general, the short-term use of the new pump (4 h) did not cause any serious morphological damage to the heart, lung, kidney, or liver. The results suggest that the hemodynamic performance of the new pump is similar to a conventional centrifugal pump and could therefore be appropriate for use in extracorporeal circulation. [source] Optimizing the Circuit of a Pulsatile Extracorporeal Life Support System in Terms of Energy Equivalent Pressure and Surplus Hemodynamic EnergyARTIFICIAL ORGANS, Issue 11 2009Choon Hak Lim Abstract:, The nonpulsatile blood flow obtained using standard cardiopulmonary bypass (CPB) circuits is still generally considered an acceptable, nonphysiologic compromise with few disadvantages. However, numerous reports have concluded that pulsatile perfusion during CPB achieves better multiorgan response postoperatively. Furthermore, pulsatile flow during CPB has been consistently recommended in pediatric and high-risk patients. However, most (80%) of the total hemodynamic energy generated by a pulsatile pump is absorbed by the components of the extracorporeal circuit and only a small portion of the pulsatile energy is delivered to the patient. Therefore, we considered that optimizations of CPB unit and extracorporeal life support (ECLS) system circuit components were needed to deliver sufficient pulsatile flow. In addition, energy equivalent pressure, surplus hemodynamic energy, and total hemodynamic energy, calculated using pressure and flow waveforms, were used to evaluate the pulsatilities of pulsatile CPB and ECLS systems. [source] The Importance of dQ/dt on the Flow Field in a Turbodynamic Pump With Pulsatile FlowARTIFICIAL ORGANS, Issue 9 2009Fangjun Shu Abstract Fluid dynamic analysis of turbodynamic blood pumps (TBPs) is often conducted under steady flow conditions. However, the preponderance of clinical applications for ventricular assistance involves unsteady, pulsatile flow,due to the residual contractility of the native heart. This study was undertaken to demonstrate the importance of pulsatility and the associated time derivative of the flow rate (dQ/dt) on hemodynamics within a clinical-scale TBP. This was accomplished by performing flow visualization studies on a transparent model of a centrifugal TBP interposed within a cardiovascular simulator with controllable heart rate and stroke volume. Particle image velocimetry triggered to both the rotation angle of the impeller and phase of the cardiac cycle was used to quantify the velocity field in the outlet volute and in between the impeller blades for 16 phases of the cardiac cycle. Comparison of the unsteady flow fields to corresponding steady conditions at the same (instantaneous) flow rates revealed marked differences. In particular, deceleration of flow was found to promote separation within the outlet diffuser, while acceleration served to stabilize the velocity field. The notable differences between the acceleration and deceleration phases illustrated the prominence of inertial fluid forces. These studies emphasize the importance of dQ/dt as an independent variable for thorough preclinical validation of TBPs intended for use as a ventricular assist device. [source] Quantitative Analysis of Pulsatile Flow Contribution to UltrafiltrationARTIFICIAL ORGANS, Issue 1 2009Ki Moo Lim Abstract We evaluated the quantitative contribution of pulsatile flow to ultrafiltration (UF) in terms of fluid power, membrane stretch, and reduction of membrane layering. An in vitro comparison of the UF rate using pulsatile and roller pumps was performed with distilled water and bovine whole blood. The mean transmembrane pressure (TMPm) and UF rate were higher with the pulsatile pump for the same mean flow rate: 6.6 mm Hg and 21.1 mL/min higher on average for distilled water and 34.2 mm Hg and 31.4 mL/min higher on average for blood. The average UF rate was 8.4 mL/min higher with the pulsatile pump for the same TMPm with bovine blood. However, the relationship between the UF rate and the TMPm was independent of the flow configuration for distilled water. We showed that the higher UF rate in the pulsatile pump is mainly due to greater fluid power and reduction of membrane layering, while the membrane stretch was not an important factor. [source] Effects of Left Ventricular Assist Device on Cardiac Function: Experimental Study of Relationship between Pump Flow and Left Ventricular Diastolic FunctionARTIFICIAL ORGANS, Issue 9 2001Akira Saito Abstract: The left ventricular assist device (LVAD) with centrifugal pump has two characteristics. One is a pump flow wave of the centrifugal pump, consisting of the pulsatile flow of the native heart and the nonpulsatile flow of the centrifugal pump. The other is that the centrifugal pump fills from the native heart not only in the systolic phase, but also in the diastolic phase. In the case of the apex outlet LVAD with centrifugal pump, blood flows from the left atrium through the left ventricle to the pump. Pump flow is regulated by preload, and preload is regulated by diastolic hemodynamics. The aim of this study is to analyze the relationship between pump flow and the diastolic hemodynamics of the native heart. Ten anesthetized intact pigs were studied after placement of an LVAD. Data were recorded with the LVAD off (control) and the LVAD on. The assist rate was changed to 25%, 50%, and 75%. The indexes of left ventricular (LV) diastolic function included LV myocardial relaxation (time constant of isovolumic pressure decay [Tau] and maximum negative dP/dt[LV dP/dt min]) and LV filling (peak filling rate [PFR], time to peak filling rate [tPFR], and diastolic filling time [DFT]). Stroke volume decreased significantly in 75% assist. LV end-systolic pressure decreased significantly in 50% and 75% assist. LV end-diastolic volume decreased as assist rate increased, but there were no significant changes. Stroke work decreased significantly in 50% and 75% assist. LV dP/dt min decreased significantly in 50% and 75% assist. Tau prolonged as assist rate increased, but there were no significant changes. DFT shortened significantly in 75% assist. PFR increased significantly in 75% assist. tPFR shortened significantly in 50% and 75% assist. In this study, LV relaxation delayed as an increasing of pump assist rate, but it suggested a result of reduction of cardiac work. Also, it was suggested that LVAD increases the pressure difference between the left atrium and the left ventricle in the diastolic phase. This phenomenon is due to the filling of the left ventricle. In this study it was suggested that as pump assist rate increases, it is more effective to keep cardiac function in the diastolic phase. [source] Using One Rotary Blood Pump to Produce Separate Pulsatile Circulations in the Upper and Lower Halves of the BodyARTIFICIAL ORGANS, Issue 8 2000Takashi Isoyama Abstract: Separate systemic circulations with pulsatile flow were obtained using 1 rotary blood pump as a left ventricular assist device. The outlet of the pump was divided into 2 conduits, 1 connected to the upper half of the body and the other connected to the lower half. An electric actuator that clamped the 2 outlet conduits alternately provided pulsatile flows. An in vitro experiment showed that the pulsatility phases of the upper and lower halves of the body were complementary with pulsatile flow, and an in vivo experiment showed that controlled flow distributions of continuous flows could be obtained. [source] FLUID FLOW IN DISTENSIBLE VESSELSCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 2 2009CD Bertram SUMMARY 1Flow in single vascular conduits is reviewed, divided into distended and deflated vessels. 2In distended vessels with pulsatile flow, wave propagation and reflection dominate the spatial and temporal distribution of pressure, determining the shape, size and relative timing of measured pressure waveforms, as well as the instantaneous pressure gradient everywhere. Considerable research has been devoted to accessing the information on pathological vascular malformations contained in reflected waves. Slow waves of contraction of vessel wall muscle, responsible for transport of oesophageal, ureteral and gut contents, have also been modelled. 3The pressure gradient in a vessel drives the flow. Flow rate can be predicted both analytically and numerically, but analytical theory is limited to idealized geometry. The complex geometry of biological system conduits necessitates computation instead. Initially limited to rigid boundaries, numerical methods now include fluid,structure interaction and can simultaneously model solute transport, thus predicting accurately the environment of the mechanosensors and chemosensors at vessel surfaces. 4Deflated vessels display all phenomena found in distended vessels, but have additional unique behaviours, especially flow rate limitation and flow-induced oscillation. Flow rate limitation is widespread in the human body and has particular diagnostic importance in respiratory investigation. Because of their liquid lining, the pulmonary airways are also characterized by important two-phase flows, where surface tension phenomena create flows and determine the patency and state of collapse of conduits. 5Apart from the vital example of phonation, sustained self-excited oscillation is largely avoided in the human body. Where it occurs in snoring, it is implicated in the pathological condition of sleep apnoea. [source] | ||||||||||