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PubMed1992

[Experimental study on hemodynamic and cardiac effects of counterpulsatile blood flow assisted IABP for acute left ventricular failure].

The purpose of this study is to evaluate the effect of newly developed balloon pumping system with synchronized blood flow assist for acute left ventricular failure. In 21 mongrel dogs with left heart failure following left coronary artery ligation, counterpulsatile flow assisted IABP (CFA-IABP) was instituted changing the flow rate from 5% to 70% of the aortic flow at control. The following results were obtained. 1) CFA-IABP significantly increased aortic, carotid, and coronary sinus flows as well increased aortic pressure and endocardial viability ratio, and also reduced left atrial pressure, LVEDP and myocardial oxygen uptake at the low flow assist of about 20% of aortic flow at control. 2) In high flow assist of more than the 50%, the effect of CFA-IABP was present but limited. 3) There was no change of hemodynamics and cardiac function at the timing of CFA method during the diastolic phase. 4) There was no statistically significant difference between CFA and constitute (non-pulsatile) flow assist, but CFA tended to much improve hemodynamics and cardiac function.

Acute Disease↗
PubMed1978

Analysis of the effects of pulsatile capillary blood flow and volume on gas exchange.

Blood flow into the pulmonary capillaries and the volume of blood within the capillary bed are both pulsatile with the cardiac cycle. We have developed a quantitative model of diffusional gas exchange in the lung to investigate the effects of coupling between these two time-varying parameters on lung O2 and CO2 exchange. For normal man breathing room air at rest, the computed results agree well with previous predictions for the constant flow and volume case, and for the case of pulsatile flow alone. When coupled time-varying pulmonary capillary blood flow and volume are included, using the best data available in the literature to define these parameters, diffusional O2 exchange is improved over the cases of pulsatile flow or volume alone, and closely approximates that obtained for the hypothetical constant flow and volume case. CO2 exchanges, and O2 exchange during hypoxia, are not affected by pulsatile flow and/or volume. These results suggest that O2 exchange is efficient in the presence of coupled blood flow and blood volume pulsations as they exist in the lung capillaries, and that these conditions may be optimal for gas exchange under certain physiological (or pathological) conditions.

Blood Volume↗
PubMed1981

Pulsatile pressure and flow in an arterial aneurysm simulated in a mathematical model.

The pressure and flow patterns within arterial aneurysms are little known. In the present work the equations describing pulsatile flow, the Navier-Stokes equations, are solved numerically using the finite element method with a computer. The solutions of the Navier-Stokes equations are obtained at 24 points in time during the cardiac cycle. At selected instants in time, the solutions are presented as velocity vectors, streamlines and isobars. The results demonstrate a vortex formation during most of the cycle. The pressure within the aneurysm is nearly constant. At the downstream end of the expansion, high pressure gradients are found.

Aneurysm↗
PubMed1996

Volumetric flow estimation in vivo and in vitro using pulsed-Doppler ultrasound.

The measurement of volumetric blood flow in small vessels in vitro and in vivo poses a significant technological challenge. In this study, two pulsatile flow models were developed, one with a 3.2-mm lumen diameter and one with a 12.7-mm lumen diameter, to assess the accuracy of volumetric flow estimation of two pulsed-Doppler devices, a Crystal Biotech VF1 20-MHz system with either a cuff-mounted or a needle-mounted probe and an Advanced Technology Laboratories Ultramark 9 High Definition Imaging system with a 5-MHz linear array transducer. The VF1 volumetric flow error was measured in the 3.2-mm phantom over a variety of pulsatile and continuous waveforms. The accuracy of the VF1 was also tested in porcine femoral and renal arteries. VF1 volumetric flow error ranged from 4.8% to 54.3% in the in vivo studies. The ATL demonstrated similar volumetric flow errors in the porcine femoral artery (approximately 3.2 mm diameter), but these errors were reduced to < or = 17.4% in the 12.7-mm-diameter in vitro flow model.

Animals↗
PubMed1992

Hemodynamic aspects of obliterative processes in peripheral blood vessel--rigid and soft narrowing.

Hemodynamic aspects of obliterative processes in peripheral blood vessels were studied on a mechanical model built of distensible tubing, with a fixed peripheral resistance, through which citrated blood was circulated by pulsatile flow. Hemodynamics of progressive focal stenosis, elongated soft stenosis, and elongated rigid stenosis were assessed. By the use of a hydrodynamic model and a series of in vitro experiments, we have measured the pressure and flow characteristics, and calculated the pressure and energy losses for the various stenotic sites. The critical stricture was found to be larger for a rigid stenosis than a soft stenosis. The length of the stenosis was also an important factor. Increasing the length of a rigid stenosis, for example, by 50 percent resulted in an increase of 25 percent in the flow through the stenosis. The energy dissipation was determined as a preferred indication for several parameters such as: pressure drop, pulsed flow, pulse rate, and the geometry and mechanical properties of the stenosis.

Arterial Occlusive Diseases↗
PubMed1991

Studies of fluids simulating blood-like rheological properties and applications in models of arterial branches.

We studied several non-Newtonian fluids to determine how closely they simulate the flow behavior of human blood. The viscous and viscoelastic properties of these fluids were compared with human blood samples in steady flow and transient flow Couette viscometers and in an oscillatory tube flow viscoelasticity analyzer. We examined: 1) A polyacrylamide suspension (Separan AP30 and AP45) to which we added 4% isopropanol and 0.01% magnesium chloride. 2) A suspension of 2% Dextran with 16% by weight biconcave disc-shaped particles simulating red blood cells. 3) 40% ghost cells prepared according to Dodge in Tri (hydroxymethyl) aminomethane. These ghost cells were used to simulate the two-phase flow behavior of blood. 4) A suspension of 5% Dextran (70,000) with 12% polystyrene particles (diameter of 1 micron) and 10 mMol calcium chloride. All these fluids closely approximate the flow behavior of blood and can be used in a variety of different experimental situations. To measure velocity distribution using a laser-Doppler-anemometer, we used fluids #1 and #3 in a rigid T-junction simulating the first septal branch of the left descending coronary artery. The measurements were done in steady and pulsatile flow experiments at different flow rate ratios. The fluids showed large differences in velocity profiles compared to Newtonian fluids.

Arteries↗
PubMed2006

An apparatus for studying the response of cultured endothelial cells to stresses.

In order to simulate the hemodynamic environment of human arteries in vivo, we designed a laminar flow apparatus which can precisely simulate the normal stress and shear stress to which cultured endothelial cells are exposed. Under both normal and abnormal physiological conditions, this apparatus can accurately control and adjust the values of normal stress and shear stress and the frequency of pulse waves, as well as the amplitude of pulsatile flow. This in vitro apparatus provides an experimental platform for studying the response of the biological characteristics of cultured endothelial cells in a hemodynamic environment.

Blood Flow Velocity↗
PubMed2006

Steady flow generation in microcirculatory systems.

In this paper we explore the mechanical generation of steady-non pulsatile-flow in microfluidic systems. The rationale of the paper is inspired in the example of cardiovascular systems where at the microscale (i.e. capillaries) the flow is steady rather than pulsatile to optimize performance. We present a solution to the generation of steady flow in engineered microfluidic systems either in open or closed loop configurations via the use of disc pumps. The disc pump consists of a flat rotating disc and utilizes both viscous drag and centrifugal force to achieve pumping. Experiments using single loop and double loop microfluidic systems are presented to characterize the disc pump. Continuous flow generated by the disc pumps can be used to separate particles based on size using recirculating loops and for extraction of small particles without disturbing the concentration of bigger particles. The potential impact of this technology includes sample separation and extraction techniques into portable microfluidic labs-on-a-chip, and long term culture systems for cells in suspension.

Biomimetic Materials↗
PubMed2002

Validation of the coupling of magnetic resonance imaging velocity measurements with computational fluid dynamics in a U bend.

Magnetic resonance imaging (MRI) can be used in vivo in combination with computational fluid dynamics (CFD) to derive velocity profiles in space and time and accordingly, pressure drop and wall shear stress distribution in natural or artificial vessel segments. These hemodynamic data are difficult or impossible to acquire directly in vivo. Therefore, research has been performed combining MRI and CFD for flow simulations in flow phantoms, such as bends or anastomoses, and even in human vessels such as the aorta, the carotid, and the abdominal bifurcation. There is, however, no unanimity concerning the use of MRI velocity measurements as input for the inflow boundary condition of a CFD simulation. In this study, different input possibilities for the inflow boundary conditions are compared. MRI measurements of steady and pulsatile flow were performed on a U bend phantom, representing the aorta geometry. PAMFLOW (ESI Software, Krimpen aan den Ussel, The Netherlands), an industrial CFD software package, was used to solve the Navier-Stokes equations for incompressible flow. Three main parameters were found to influence the choice of an inflow boundary condition type. First, the flow rate through a vessel should be exact, since it proves to be a determining factor for the accuracy of the velocity profile. The other decisive parameters are the physiology of the flow profile and the required computer processing unit time. Our comparative study indicates that the best way to handle an inflow boundary condition is to use the velocities measured by MRI at the inflow plane as being fixed velocities. However, before using these MRI velocity data, they first should be corrected for the partial volume effect by filtering and second scaled in order to obtain the correct flow rate. This implies that a reliable flow rate measurement absolutely is needed for CFD calculations based on MRI velocity measurements.

Aorta↗
PubMed1996

A 3D-LDA study of the relation between wall shear stress and intimal thickness in a human aortic bifurcation.

A realistic model experiment on hemodynamics was performed to study correlations between wall shear stresses measured in a cast model of the aortic bifurcation and intimal thickness at each corresponding site of the native blood vessel from which the cast had been made. An elastic model of a 54 year old human aortic bifurcation was made of a polyurethane elastomer using a dipping method, and was perfused with Newtonian or non-Newtonian fluid under physiologic pulsatile flow condition. Local flow velocities were measured with an optical-fibered, 3-dimensional laser Doppler anemometer (3D-LDA) to determine wall shear stresses. Distribution of intimal thickness was determined using histological specimens of the native blood vessel. The results obtained are: 1) Non-Newtonian fluid rheology increased wall shear stresses; 2) Positive correlations were observed between intimal thickness and the maximum instantaneous wall shear stress, and 3) However, if we take only the data from the circumference at the level of the flow divider tip, there were negative correlations between them.

Aorta↗
PubMed1994

[The value of duplex sonography after orthotopic liver transplantation. Experience with 44 patients].

In a prospective study, 44 patients (11 women, 33 men) who had received orthotopic liver transplants underwent a total of 196 consecutive duplex Doppler ultrasound examinations. The aim of the study was to evaluate the correlation between the pulsatile flow index (PFI) and the damping index (DI) as far as complications as rejection or cholangitis were concerned. The patients were examined five times each on average. The PFI and DI were measured in the hepatic artery, the portal vein and the hepatic veins. The findings were compared with the clinical course (cholangitis, rejection) and the histomorphological diagnosis as determined in biopsy specimens. In biopsy-proven rejection episodes, the sensitivity of the PFI in the hepatic artery was 69.4%, the specificity 72.2%. The sensitivity of the DI in the hepatic vein was 89.4%, the specificity 89.1%. Combining the two, specificity was more than 90%. PFI and DI in the portal vein bore no apparent relation to clinical course or histomorphological diagnosis. We found duplex Doppler ultrasound extremely beneficial in determining the timing and indication for liver biopsy. In addition, this simple examination, which can be performed as often as desired, accurately shows the transplanted liver's response to measures taken to counter rejection.

Adult↗
PubMed1994

Differences in the longterm effect of timolol and betaxolol on the pulsatile ocular blood flow.

In the past several years the effect of longterm glaucoma therapy on ocular hemodynamics has taken on increased interest. This interest has been sparked by studies demonstrating differential effects of various beta-blockers on visual function, and the possible contributory role of ocular blood flow. In the present study, the pulsatile ocular blood flow (POBF), as derived by the Langham OBF system, was measured prior to treatment and then tracked throughout a one-year period of beta-blocker therapy (betaxolol 0.5% or timolol 0.5%) in 25 glaucoma patients. Results of the two treatments were compared, and indicated that, whereas both betaxolol- and timolol-treated patients had similar significant reductions in the IOP, the effect of the two treatments on the POBF differed. In timolol-treated patients, the POBF decreased significantly over the 12-month observation period, whereas in betaxolol-treated patients it remained stable.

Adult↗
PubMed2000

Superior gluteal artery in the extended iliofemoral approach.

OBJECTIVE: To determine the incidence of superior gluteal artery injury following fracture of the acetabulum and to determine whether the combination of a superior gluteal artery injury and the use of an extended iliofemoral approach to the acetabulum creates abductor muscle necrosis. DESIGN: Prospective protocol, consecutive cases. SETTING: A consecutive series from the referral practice of the senior author plus seven cases from the practices of two other authors. PATIENTS: Two hundred twenty-seven patients with fractures of the acetabulum were treated operatively between November 1992 and January 1995. Forty-one were treated with the use of the extended iliofemoral approach. Preoperative angiograms were not performed for any of the patients. All fractures involved the posterior column, and all but two fractures had displacement of the greater sciatic notch. The average displacement of the notch was 2.5 centimeters (range 6 to 60 millimeters). INTERVENTION: All patients were treated with open reduction and internal fixation via the extended iliofemoral approach. Intraoperative Doppler examination of the superior gluteal artery was performed before and after reduction and fixation of the posterior column. MAIN OUTCOME MEASURE: Wound complications, abductor manual muscle testing, hip range of motion. RESULTS: Pulsatile flow was confirmed in forty of forty-one patients. All patients were followed for a minimum of six months with an average follow-up of 1.4 years. At most recent follow-up, no patients had evidence of complete loss of abductor function. Sixty-three percent of patients had achieved Grade 4 of 5 motor strength, and 25 percent of them had achieved normal motor strength. CONCLUSIONS: No instances of superior gluteal artery laceration and only one instance of superior gluteal artery thrombosis were encountered in these forty-one patients despite significant fracture displacement involving the sciatic notch. The incidence of superior gluteal artery injury was significantly less than would be expected from previous studies. Massive abductor necrosis resulting from superior gluteal artery injury combined with an extended approach has been described primarily in animal and cadaver studies. Although arteriograms are useful in the control of hemodynamic instability, we cannot support the recommendation of preoperative angiographic study of all patients undergoing acetabular fracture surgery via an extended approach. In one case, an extended iliofemoral approach was tolerated in a patient with absent superior gluteal artery flow.

Acetabulum↗
PubMed1994

Magnetic resonance velocity imaging using a fast spiral phase contrast sequence.

Time-resolved velocity imaging using the magnetic resonance phase contrast technique can provide clinically important quantitative flow measurements in vivo but suffers from long scan times when based on conventional spin-warp sequences. This can be particularly problematic when imaging regions of the abdomen and thorax because of respiratory motion. We present a rapid phase contrast sequence based on an interleaved spiral k-space data acquisition that permits time-resolved, three-direction velocity imaging within a breath-hold. Results of steady and pulsatile flow phantom experiments are presented, which indicate excellent agreement between our technique and through plane flow measurements made with an in-line ultrasound probe. Also shown are results of normal volunteer studies of the carotids, renal arteries, and heart.

Blood Flow Velocity↗
PubMedDate not supplied

Fistula of stapes footplate caused by pulsatile cerebrospinal fluid in inner ear malformation.

Congenital malformations of the inner ear are well described, though the combination with cerebrospinal fluid (CSF) leaks remains controversial. In this paper a case of a bilateral Mondini malformation with a CSF otorrhea on one side is reported. The malformed stapes contains a perforation in the middle of the footplate and associated thinning analogous to a pothole in a mountain stream. The histological findings support the hypothesis of pulsatile flow of CSF as origin of the perforation of the footplate.

Cerebrospinal Fluid Otorrhea↗
PubMed1989

Impedance monitoring for subcutaneous free flap transfers.

The assessment of thoracic blood flow by electrical impedance is a well-established technique. In an application of this a small electrode array has been developed in which an alternating electric current is passed through a subcutaneous free flap and the induced voltage across a small volume measured. A graphical display of this changing voltage illustrates the pulsatile flow through the flap, allowing continuous assessment of perfusion on a beat by beat basis. The electrode array is such that it can be placed in close contact with muscle without interface problems and can assess its viability. It is non-invasive and easily removed. We have found this accurate, easily interpreted by inexperienced staff, and a considerable reassurance in the postoperative period.

Humans↗
PubMed2006

Coil reduction of the right ventricular cavity in a boy with pulmonary atresia, intact ventricular septum, and an aneurysmal coronary sinusoid.

Coronary sinusoids are often found in patients with pulmonary atresia and intact ventricular septum. We report on a 4-year-old boy with such pathology in whom, after completion of the Fontan-circulation, the pulsatile flow through a major sinusoid significantly increased the size of a coronary artery up to aneurysmal dimensions. Because percutaneous closure of the sinusoid was unsuccessful, the right ventricular cavity was partially obliterated with coils. This resulted in a significant decrease of right ventricular stroke volume, regression of the pulsatility and of the coronary size, with good clinical result at 1.5 years of follow-up.

Child, Preschool↗
PubMed2006

Computational fluid dynamics modeling of intracranial aneurysms: effects of parent artery segmentation on intra-aneurysmal hemodynamics.

PURPOSE: The purpose of this study is to show the influence of the upstream parent artery geometry on intraaneurysmal hemodynamics of cerebral aneurysms. METHODS: Patient-specific models of 4 cerebral aneurysms (1 posterior communicating artery [PcomA], 2 middle cerebral artery [MCA], and 1 anterior communicating artery [AcomA]) were constructed from 3D rotational angiography images. Two geometric models were constructed for each aneurysm. One model had the native parent vessel geometry; the second model was truncated approximately 1 cm upstream from the aneurysm, and the parent artery replaced with a straight cylinder. Corresponding finite element grids were generated and computational fluid dynamics simulations were carried out under pulsatile flow conditions. The intra-aneurysmal flow patterns and wall shear stress (WSS) distributions were visualized and compared. RESULTS: Models using the truncated parent vessel underestimated the WSS in the aneurysms in all cases and shifted the impaction zone to the neck compared with the native geometry. These effects were more pronounced in the PcomA and AcomA aneurysms where upstream curvature was substantial. The MCA aneurysm with a long M1 segment was the least effected. The more laminar flow pattern within the parent vessel in truncated models resulted in a less complex intra-aneurysmal flow patterns with fewer vortices and less velocity at the dome. CONCLUSIONS: Failure to properly model the inflow stream contributed by the upstream parent artery can significantly influence the results of intra-aneurysmal hemodynamic models. The upstream portion of the parent vessel of cerebral aneurysms should be included to accurately represent the intra-aneurysmal hemodynamics.

Blood Flow Velocity↗