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PubMed1990

Ventricular stroke work loss: validation of a method of quantifying the severity of aortic stenosis and derivation of an orifice formula.

Because aortic stenosis results in the loss of left ventricular stroke work (due to resistance to flow through the valve and turbulence in the aorta), the percentage of stroke work that is lost may reflect the severity of stenosis. This index can be calculated from pressure data alone. The relation between percent stroke work loss and anatomic aortic valve orifice area (measured by planimetry from videotape) was investigated in a pulsatile flow model. Thirteen valves were studied (nine human aortic valves obtained at necropsy and four bioprosthetic valves) at stroke volumes of 40 to 100 ml, giving 57 data points. Valve area ranged from 0.3 to 2.8 cm2 and mean systolic pressure gradient from 3 to 84 mm Hg. Percent stroke work loss, calculated as mean systolic pressure gradient divided by mean ventricular systolic pressure x 100%, ranged from 7 to 68%. It was closely related to anatomic orifice area with an inverse exponential relation and was not significantly related to flow (r = -0.15). An orifice formula was derived that predicted anatomic orifice area with a 95% confidence interval of +/- 0.5 cm2 (orifice area [cm2] = 4.82 [2.39 x log percent stroke work loss], r = -0.94, SEE = 0.029). These results support the clinical use of percent stroke work loss as an easily obtained index of the severity of aortic stenosis.

Aortic Valve↗
PubMed2004

Doppler and immunohistochemical evaluation of decidual spiral arteries in early pregnancy.

OBJECTIVE: The purpose of this study was to estimate spiral artery subchorionic flow at 8-11 gestational weeks (GW) by Doppler ultrasound and then to analyze these vessels in the decidua basalis using histologic, morphometric and immunohistochemical analyses. METHODS: Subchorionic spiral arteries were evaluated in 5 women scheduled for aspiration at 8-11 GW. Flow velocity waveforms were sought using color and pulsed Doppler, and the diastolic/systolic (D/S) index was calculated. Transcervical biopsy specimens and aspiration products were thoroughly examined to investigate the structure of the spiral artery at the implantation site using cytotrophoblastic and arterial smooth muscle cell immunohistochemical markers (anti-cytokeratin 7 and anti-actin monoclonal antibodies). Spiral artery cross-sectional inner areas were measured and compared with the D/S index in each case. RESULTS: Low-impedance pulsatile flow could be detected below the trophoblastic ring in all cases. Complete obstruction of a spiral artery lumen was never observed and cytotrophoblastic cells were incorporated into the vessel wall starting from the perivascular cuff. CONCLUSION: Both techniques evidenced that decidual spiral arteries in the placental bed are not completely obstructed at 8-11 GW.

Actins↗
PubMed1997

Acceleration mapping by Fourier acceleration-encoding: in vitro study and initial results in the great thoracic vessels.

Acceleration mapping can be conducted by replacing the bipolar gradient pulse of a velocity mapping sequence by a tripolar pulse. However, since the acceleration encoding pulse is longer, the image quality is altered by the requirement of a long echo time. Since Fourier encoding velocity imaging has been shown to be robust, this velocity mapping method was transformed into an acceleration mapping method. Four steps of the tripolar acceleration encoding gradient pulse were applied successively; acceleration was then obtained by Fourier transform after zero-filling. The accuracy of the method was assessed with a phantom giving a pulsatile flow. Acceleration maps of the ascending aorta and pulmonary artery were obtained in 10 healthy volunteers. The acceleration values measured were in the range of known physiologic values. The feasibility of Fourier encoding acceleration imaging was also demonstrated in four patients.

Adolescent↗
PubMed1999

Prosthetic heart valve evaluation by magnetic resonance imaging.

OBJECTIVE: To evaluate the potential of magnetic resonance imaging (MRI) for evaluation of velocity fields downstream of prosthetic aortic valves. Furthermore, to provide comparative data from bileaflet aortic valve prostheses in vitro and in patients. METHODS: A pulsatile flow loop was set up in a 7.0 Tesla MRI scanner to study fluid velocity data downstream of a 25 mm aortic bileaflet heart valve prosthesis. Three dimensional surface plots of velocity fields were displayed. In six NYHA class I patients blood velocity profiles were studied downstream of their St. Jude Medical aortic valves using a 1.5 Tesla MRI whole-body scanner. Blood velocity data were displayed as mentioned above. RESULTS: Fluid velocity profiles obtained from in vitro studies 0.25 valve diameter downstream of the valve exhibited significant details about the cross sectional distribution of fluid velocities. This distribution completely reflected the valve design. Blood velocity profiles in humans were considerably smoother and in some cases skewed with the highest velocities toward the anterior-right ascending aortic wall. CONCLUSION: Display and interpretation of fluid and blood velocity data obtained downstream of prosthetic valves is feasible both in vitro and in vivo using the MRI technique. An in vitro model with a straight tube and the test valve oriented orthogonally to the long axis of the test tube does not entail fluid velocity profiles which are compatible to those obtained from humans, probably due to the much more complex human geometry, and variable alignment of the valve with the ascending aorta. With the steadily improving quality of MRI scanners this technique has significant potential for comparative in vitro and in vivo hemodynamic evaluation of heart valves.

Adult↗
PubMed2005

Retinal haemodynamics in patients with age-related macular degeneration.

OBJECTIVE: To investigate whether there is an association between the magnitude of retinal haemodynamic abnormalities in patients with age-related macular degeneration (AMD) and the degree of severity of the AMD. METHODS: A retinal laser Doppler system (Canon CLBF 100) was used to measure retinal arterial haemodynamic parameters in 25 eyes of 25 patients with AMD and nine eyes of nine age-matched control subjects. Severity of AMD was classified into Mild (n=11), Moderate (n=7), or Severe (n=7). The pulsatility ratio (PR), the pulsatility index (PI), and the resistivity index (RI) were determined. RESULTS: PR, PI, and RI in the patients with AMD were each significantly higher than in the control group, and increased monotonically with increasing severity of AMD. However, there were no differences in mean blood velocity, arterial diameter, or blood flow rate among the groups. This suggests that the increased blood flow pulsatility in the retinal arteries of the eyes with AMD is not due to increased distal vascular resistance, but instead is likely due to a loss of compliance in the arterial vasculature leading to the eye. CONCLUSION: Our results suggest that an increasing vascular rigidity in the systemic arterial circulation is directly associated with an increasing severity of AMD.

Aged↗
PubMed1999

Image artifacts due to a time-varying contrast medium concentration in 3D contrast-enhanced MRA.

The purpose of this work was to study image effects due to time-varying contrast medium concentration in contrast-enhanced three dimensional (3D) magnetic resonance angiography (MRA) images. Two different simulation models (1D and 3D) and two different contrast medium variation schemes were used. Phantom measurements were also performed. Experiments were performed for several different bolus timings. Similar sequence and image object parameters were used in both simulations and measurements (TE/TR 2. 1/7.8 mses, flip angle 30 degrees, T1/T2 1200-80/150-40 msec, flow velocity 100 cm/sec). A small variation in bolus timing yielded large variations in the appearance of the image effects, especially if the center of k-space was sampled in the vicinity of rapid contrast medium concentration variation. For a typical bolus injection in a patient, a severe signal loss but only minor ringing and edge artifacts appeared if the bolus injection was poorly timed. Effects of pulsatile flow were minor. The 3D model proved to be a useful tool in these studies. J. Magn. Reson. Imaging 1999;10:919-928.

Aorta↗
PubMedDate not supplied

Clinical use of the abiomed BVS 5000 as a pulsatile extracorporeal membrane oxygenation unit.

The traditional extracorporeal membrane oxygenation circuit uses a centrifugal pump. These pumps require close monitoring and are subject to complications. In addition, they do not take advantage of the potential benefits of pulsatile flow. These extracorporeal membrane oxygenation circuits use a single pump with an inline oxygenator. If cardiac failure persists after respiratory recovery has occurred, removal of the oxygenator requires an additional procedure to convert the patient to biventricular support. This report describes a circuit in which an oxygenator is connected to a pulsatile ventricular assist device. Single and dual circuit configurations are illustrated. Recommendations for pulmonary care during support are also described.

Angioplasty↗
PubMedDate not supplied

A system for in-vitro characterization of heart valve bioprostheses under accelerated fatigue conditions and under physiologic conditions.

An accelerated fatigue testing system and a pulse duplicator (heart simulator) were used in a set-up in which pressure differences and pulsatile flow rates across prosthetic heart valves, as well as machine rates, could be measured using a real-time on-line data-acquisition system. With this information available, an immediate in-vitro characterization of the fluid dynamics of prosthetic heart valves could be obtained under both physiologic and accelerated conditions. In addition to the fatigue tester and the pulse duplicator, a signal conditioner, a DC amplifier, an analog-to-digital converter, and a digital microcomputer comprised the essential hardware. For the purpose of this study, special acquisition software was developed. By means of the same computational algorithms, all quantitative fluid dynamics data could be calculated using information from both the pulse duplicator and the fatigue tester, so that direct comparisons and correlations could be approached. Pressure difference-flow rate relationships for the two machines were comparable.

Bioprosthesis↗
PubMed1996

In vitro flow mapping of regurgitant jets. Systematic description of free jet with laser Doppler velocimetry.

BACKGROUND: Color Doppler and magnetic resonance imaging give pictures of abnormal jets within which the respective contribution of fluid mechanics and image artifacts are difficult to establish because of current technical limitations of these modalities. We conducted the present study to provide numerical descriptions of the velocity fields within regurgitant free jets. METHODS AND RESULTS: Laser Doppler measurements were collected in rigid models with pulsatile flow conditions, giving several series of two-dimensional flow images. The data were studied with the use of two-dimensional or M-mode flow images as well as regular plots. Numerical descriptions validated in steady flow conditions were tested at the various times of the cycle. In these free jets, the momentum was conserved throughout the cycle. The transverse velocity profiles were approximately similar. A central laminar core was found at peak ejection and during the deceleration. Its length (l = 4.08 d-0.036 mm, r = .99) and its diameter (d) were proportional to the orifice diameter. At peak ejection, the velocity decay was hyperbolic, and the transverse velocity profiles were clearly gaussian. The different relations that were tested could be combined in a single formula describing the velocity field: V(x,y,t peak) = V(O,O,t peak).4.(d/x).10(-45(y/x)2) (r = .92). CONCLUSIONS: These in vitro measurements demonstrated the presence of a central laminar core and similar transverse velocity profiles in free turbulent jets. This allowed us to validate a series of numerical relations that can be combined to describe the velocity fields at peak ejection. On the other hand, further studies are needed to describe the various singularities often encountered in pathology.

Heart Valve Diseases↗
PubMedDate not supplied

Gender and age effects on pulsatile ocular blood flow.

PURPOSE: To examine gender and age effects on pulsatile ocular blood flow (POBF). METHODS: Normal subjects, 152 females and 107 males, were separated into younger (40-50) and older (50-60) age groups. RESULTS: For younger women, mean POBF (15.3 +/- 3.7 microl/s) was significantly different (p < 0.01) than for older women (13.8 +/- 3.5 microl/s), younger men (13.2 +/- 3.3 microl/s), and older men (13.3 +/- 3.1 microl/s). The mean POBFs for each of the latter three groups were not significantly different (p > 0.41) from one another. The four groups showed no significant differences in intraocular pressure (p > 0.07) or refraction (p > 0.46). Pulse rate for younger women was significantly higher (p < 0.05) than for the older two groups, but there were no significant pulse rate differences (p > 0.08) between other groups. POBF was not correlated with IOP (r2 < 0.04), refraction (r2 < 0.009) or pulse rate (r2 < 0.04). CONCLUSION: Gender and age play an important role in POBF.

Adult↗
PubMed1976

Pulsatile blood-flow in arterial grafts.

The distensibility of arterial wall is an important factor in the haemodynamics of pulsatile blood-flow. Autogenous-vein grafts have a dynamic response to the arterial pressure pulse (compliance) which approaches that of normal arterial wall, whereas synthetic prostheses are generally incompliant, or become so shortly after implantation. Although synthetic grafts have little effect on steady-state flow, their lack of compliance greatly interferes with pulsatile flow and this may be an important factor in explaining their lack of success as replacements for medium and small sized arteries.

Arterial Occlusive Diseases↗
PubMed1993

The renin-angiotensin-aldosterone system and hematologic changes during pulsatile and nonpulsatile cardiopulmonary bypass.

The effects of pulsatile and nonpulsatile cardiopulmonary bypass using a roller pump on levels of vasoactive hormones and hematologic changes were studied in 32 patients subjected to elective primary coronary artery bypass graft surgery. Seventeen patients had nonpulsatile perfusion (nonpulsatile group) and 15 patients had pulsatile perfusion (pulsatile group) during the period of cardiac arrest. Vasoactive hormones (plasma renin, angiotensin II, aldosterone, epinephrine, and norepinephrine) were measured in these patients. In order to clarify hematologic changes, plasma free hemoglobin, number of platelets, platelet factor 4, and beta-thromboglobulin were measured. There were no significant differences between the pulsatile and nonpulsatile groups with regard to vasoactive hormones and damage of platelets. In the pulsatile group, however, the rise of plasma free hemoglobin levels was significantly higher than that in the nonpulsatile group during and after cardiopulmonary bypass. We did not see the benefit of pulsatile perfusion using a roller pump on vasoactive hormones. Evidence of increased hemolysis with pulsatile flow was demonstrated in our cases.

Aldosterone↗
PubMed1997

MR angiography of aneurysm models of various shapes and neck sizes.

PURPOSE: To investigate the signal intensity of lateral and terminal saccular aneurysm models with differing neck sizes using three-dimensional time-of-flight (TOF) MR angiography with various imaging parameters. METHODS: The study included four lateral and four terminal saccular aneurysm models with pulsatile flow. The height and fundus diameter were 10 mm; the neck diameters were 2.5 mm, 5 mm, 7.5 mm, and 10 mm, respectively. Each aneurysm model was examined with fast imaging with steady-state precession MR sequences with parameters of 20-140/7 (repetition time/echo time) and flip angles of 10 degrees to 30 degrees. Signal intensity was measured and compared among the models. RESULTS: Three-dimensional TOF MR angiography with the shorter repetition time and/or larger flip angle showed weaker signal intensity in the aneurysm models. Stronger signal intensity was obtained in the terminal saccular aneurysm models and/or the models with a wider neck than in the lateral saccular aneurysm models and/or the models with a narrower neck. In some aneurysm models, longer repetition times produced greater signal intensity than that of background brain models, but not in aneurysms with narrow necks. CONCLUSION: Noncontrast 3-D TOF MR angiography delineated terminal saccular aneurysms and/or aneurysms with wider necks and did not delineate lateral saccular aneurysms and/or aneurysms with narrower necks. Longer repetition times are recommended to allow the spins flowing into the aneurysms to recover.

Artifacts↗
PubMed1980

Flow disturbance at the distal end-to-side anastomosis. Effect of patency of the proximal outflow segment and angle of anastomosis.

We investigated the flow disturbance that occurs at the distal end-to-side anastomosis. Clear plastic model end-to-side anastomoses were constructed with inlet angles of 15 degrees and 45 degrees. Flow patterns were visualized with steady and pulsatile flow using a dye-injection technique. Multiple lateral pressure measurements were made in the region of the anastomosis. A laser Doppler anemometer was used to measure near-wall velocity. Flow disturbance was minimal when the inlet angle was low and the proximal outflow segment occluded. Patency of the proximal outflow segment or a high inlet angle may result in areas of boundary-layer separation, with corresponding adverse pressure gradients at the anastomosis. These separation regions are characterized by low near-wall velocity, which may contribute to anastomotic hyperplasia.

Blood Circulation↗
PubMed1995

Preferential use of venovenous extracorporeal membrane oxygenation for congenital diaphragmatic hernia.

Acute respiratory failure (ARF) secondary to congenital diaphragmatic hernia (CDH), unresponsive to maximal medical management, has traditionally been treated with venoarterial (VA) extracorporeal membrane oxygenation (ECMO). Venovenous (VV) ECMO offers several benefits over VA ECMO including preserved pulmonary blood flow, preservation of the carotid artery, and pulsatile flow. However, use of the VV modality has not been widespread because of concerns of the cardiac instability during bypass, and because only one double-lumen (DL) catheter size is available in the United States. The authors hypothesize that VV ECMO is a safe and effective treatment for CDH, symptomatic at birth, and report a single institution experience of preferential VV use for CDH. Over an 18-month period, 14 patients with CDH were placed on ECMO after maximal medical management failed, including high-frequency ventilation and nitric oxide in some cases. Ability to place the 14 Fr DL catheter was the sole criteria for VA or VV selection. Nine patients were successfully placed on VV and 5 on VA; no VV patient required conversion to VA. The two groups of patients were similar with respect to degree of illness, birth weight, EGA, time on and age at start of ECMO. Overall survival for this series was 64%: 66% in the VV group and 60% in the VA group. Two patients in the VV group were found to have congenital heart disease incompatible with life, were withdrawn from therapy and allowed to die, and are listed as treatment failures. The authors conclude that CDH patients receive adequate oxygenation and show hemodynamic stability on VV ECMO.(ABSTRACT TRUNCATED AT 250 WORDS)

Extracorporeal Membrane Oxygenation↗
PubMed1990

Effects of isosorbide dinitrate on the pattern of arterial blood flow in healthy human subjects.

1. Blood velocity measurements have been made in the superficial femoral artery, 10 cm downstream of the common femoral artery bifurcation, in healthy human subjects, using a multi-channel Doppler ultrasound device. 2. In a randomized double-blind protocol, the effects of isosorbide dinitrate were examined during a 2 h period. 3. The changes induced by isosorbide dinitrate include: (i) an increase in the width of the artery and a reduction in brachial arterial blood pressure, implying relaxation of arterial smooth muscle; (ii) an increase in reverse flow and a decrease in time-averaged mean velocity associated with a relatively small decrease of the velocity excursion during the cardiac cycle, implying an increase in flow pulsatility; and (iii) an alteration of the flow pattern both in the core and near the vessel walls.

Adult↗
PubMed2000

An in vitro study of the hinge and near-field forward flow dynamics of the St. Jude Medical Regent bileaflet mechanical heart valve.

The most widely implanted prosthetic valve is the mechanical bileaflet. Recent clinical experiences suggest that some designs are more prone to thromboembolic episodes than others. This study evaluated the hinge flow and near-field forward flow of the new St. Jude Medical Regent bileaflet mechanical heart valve. Laser Doppler velocimetry measurements were conducted within the hinge and near-field forward flow regions of the Regent valve. These pulsatile flow velocity measurements were animated in time to visualize the flow fields throughout the cardiac cycle. During forward flow, a recirculation region developed in the inflow pocket of the Regent hinge but was subsequently abolished by strong backflow during valve closure. Leakage velocities in the hinge region reached 0.72 m/s and Reynolds shear stresses reached 2,600 dyn/cm2. Velocities in the near-field region were highest in the lateral orifice jet, reaching 2.1 m/s. Small regions of separated flow were observed adjacent to the hinge region. Leaflet motion through the Regent hinge creates a washout pattern which restricts the persistence of stagnation zones in its hinge. Based upon the results of these studies, the hematological performance of the Regent series should be at least equivalent to the performance of the Standard series.

Biomedical Engineering↗
PubMed2006

The National Heart, Lung, and Blood Institute Pediatric Circulatory Support Program.

Options for the circulatory support of pediatric patients under the age of 5 years are currently limited to short-term extracorporeal devices, the use of which is often complicated by infection, bleeding, and thromboembolism. Recognizing this void, the National Heart, Lung, and Blood Institute solicited proposals for the development of novel circulatory support systems for infants and children from 2 to 25 kg with congenital or acquired cardiovascular disease. Five contracts were awarded to develop a family of devices that includes (1) an implantable mixed-flow ventricular assist device designed specifically for patients up to 2 years of age, (2) another mixed-flow ventricular assist device that can be implanted intravascularly or extravascularly depending on patient size, (3) compact integrated pediatric cardiopulmonary assist systems, (4) apically implanted axial-flow ventricular assist devices, and (5) pulsatile-flow ventricular assist devices. The common objective for these devices is to reliably provide circulatory support for infants and children while minimizing risks related to infection, bleeding, and thromboembolism. The devices are expected to be ready for clinical studies at the conclusion of the awards in 2009.

Child, Preschool↗