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PubMed1989

[Doppler echocardiographic estimates of pressure gradients in various types of stenoses: usefulness and limitations].

UNLABELLED: In the present study, the accuracy of Doppler estimates of pressure gradients in various types of stenoses was clinically and experimentally evaluated. Fifty-seven patients, including 23 with ventricular septal defect, 15 with aortic or pulmonary valvular stenosis, four with infundibular stenosis, and five with supravalvular aortic or pulmonary stenosis were observed. The peak systolic pressure gradient (dP (C] was obtained at the time of catheterization in all patients. Before catheterization, the maximum velocity was measured by pulsed or continuous Doppler echocardiography and the estimated systolic pressure gradient according to Doppler (dP (D] was calculated by the simplified Bernoulli equation. The experimental model was designed to create pulsatile flow through a stenosis model. Nine different stenotic model types were used, including three orifice-like stenoses and six truncated cones with heights of 10 mm and 20 mm distal to the stenosis. The orifices in their stenoses were 3, 4 and 5 mm, respectively. Glycerin solution containing Sephadex with a viscosity similar to that of blood was used as the circulation medium. Its specific gravity was 1.16 g/cm3. In each stenotic model, the maximum velocity and instantaneous systolic peak pressure gradient were measured at various water flow rates. CLINICAL RESULTS: In patients with ventricular septal defect or valvular stenosis, dP (D) correlated very well to dP (C), with the regression equation, y = 0.87x + 2.79 (r = 0.92) or y = 0.96x + 1.02 (r = 0.99). In the other patients except for three with patent ductus arteriosus, dP (D) overestimated dP (C) by 11 to 71 mmHg, and their post-stenotic areas had gradually widened according to angiographic findings.(ABSTRACT TRUNCATED AT 250 WORDS)

Aortic Stenosis, Subvalvular↗
PubMed2003

Local haemodynamics and shear stress in cuffed and straight PTFE-venous anastomoses: an in-vitro comparison using particle image velocimetry.

OBJECTIVES: To use particle image velocimetry (PIV) to study the haemodynamics and shear stress associated with cuffed and straight PTFE-venous anastomoses. METHODS: Silastic models of a straight and cuffed (Venaflo) PTFE-venous anastomoses were attached to a pulsatile flow 'Berlin Heart' circuit filled with glycerine/water and hollow glass tracer spheres. Instantaneous velocity fields were obtained PIV and shear rates and patterns calculated from frame-by-frame analysis. RESULTS: A high velocity jet struck the anastomotic 'floor' and was deflected toward the venous outflow. Shear stresses near the floor were significantly higher, in the straight anastomosis. Sites of high shear stress correlated well with the known sites of intimal hyperplasia. CONCLUSIONS: A cuffed anastomosis type may be favourable in terms of local haemodynamics so enhancing the long-term patency of PTFE-venous grafts.

Anastomosis, Surgical↗
PubMed1990

[Surgery for postinfarction ventricular septal perforation under hypothermic fibrillatory arrest with pulsatile perfusion].

Surgery were performed by 2 different methods of myocardial protection in 17 patients with postinfarction ventricular septal perforation (VSP) from 1982 to 1989. Ten consecutive operations were performed using hypothermic fibrillatory arrest with pulsatile perfusion (VF group). Pulsatile flow was produced by an intra-aortic balloon pumping device. Other 7 consecutive VSP operations were performed using cardioplegic arrest (CP group). In the VF group, the mean age was 67 years (range 54 to 78 years), and VSP was located in the anterior wall in 7, in the inferior wall in 2, and in the anterior and inferior walls in 1 patients. The operation was performed 2.5 days after the onset of VSP. In the CP group, the mean age was 71 years (range 50 to 78 years), and VSP was located in the anterior wall in 6 and in the inferior wall in 1 patient. The operation was performed 4.7 days after the onset of VSP. Cardiogenic shock developed after septal rupture in 50% of the patients in the VF group and 71% in the CP group (N.S.). Prior to the operation, no significant differences were found in hemodynamic status between the 2 groups. Cardiac index in the VF group was higher than that of the CP group (p less than 0.05) shortly after cardiopulmonary bypass. The operative mortality rate was 10% in the VF group and 57% in the CP group. From these clinical results, hypothermic fibrillatory arrest with pulsatile perfusion can be beneficial as a method of myocardial protection during surgery for VSP and presently this has become the method of choice in our department.

Aged↗
PubMedDate not supplied

A novel miniature ventricular assist device for hemodynamic support.

The HemoDynamics Systems enabler is a new cardiac assist pump that can expel blood from the left ventricle and provide pulsatile flow in the aorta. We evaluated the efficacy of the 18 Fr enabler. The enabler was inserted from the left ventricular apex into the ascending aorta in eight sheep. Heart failure (mild, moderate, and severe) was induced by microsphere injection into the coronary arteries to reduce cardiac output by 10-30%, 31-50%, and more than 50% from baseline, respectively. The enabler was activated, and its flow was increased to approximately 2.0 L/min. Hemodynamic variables were recorded before and after activation. In moderate heart failure, cardiac output and mean aortic pressure increased from 2.3 +/- 0.6 L/min and 59 +/- 12 mm Hg before assist to 2.8 +/- 0.6 L/min and 70 +/- 8 mm Hg at 30 minutes after activation, respectively (p < 0.01). Left atrial pressure decreased from 17 +/- 3 to 13 +/- 4 mm Hg (p < 0.05). Similar findings were observed in mild and severe heart failure. Despite its small diameter, the enabler significantly improved the hemodynamics of failing hearts and may potentially serve as a means of peripheral left ventricular support. Further study is warranted.

Animals↗
PubMed1994

Hydrodynamic performance of the Medtronic Freestyle Aortic Root Bioprosthesis.

The Freestyle Aortic Root Bioprosthesis is comprised of a porcine aortic root preserved in buffered 0.2% glutaraldehyde solution. It is fixed at a pressure sufficient to distend the aortic wall, but the leaflets are fixed with no transvalvular gradient. The bioprosthesis is treated with alpha-amino-oleic acid (AOA) to reduce the potential for leaflet calcification. In order to conduct in-vitro performance studies, a simulated aorta test chamber was developed. The test chamber material formulation can be altered to produce a wide range of desired compliances, while maintaining repeatable dimensional specifications. The test chamber design also allows for performance testing simulating a variety of implant techniques. Both Freestyle and the stented control valves (Hancock Standard Model 242) were mounted within the simulated aortas for these studies. Steady state and pulsatile flow pressure drop studies demonstrated a significantly lower gradient across the Freestyle valve when compared to stented Hancock Standard controls. In addition, the smaller size (19,21,23 mm) Freestyle valves had superior EOA's compared to the Standard St. Jude bileaflet mechanical and Hancock modified orifice (MO) porcine valve designs. The regurgitant volumes were equivalent to the control (Hancock Standard model 242) valves when compared to the Freestyle valves with equivalent flow areas. Additional studies were conducted in order to determine the effects of sizing and configuration on hydrodynamic performance. These studies were performed in four configurations: total root, inclusion, partially scalloped (two sinuses) and fully scalloped valve. These studies demonstrated that both pressure drop and regurgitation are significantly affected by valve sizing and implant technique. Accelerated wear studies were performed on three of each size and six of the largest Freestyle valves. Stented Hancock Standard valves and non-AOA treated Freestyle valves were used as controls. Hydrodynamic performance tests were conducted at intervals throughout the study. No evidence was found to indicate a difference in wear or hydrodynamic performance between the AOA treated and untreated Freestyle valves.

Aorta↗
PubMed1976

Observations on blood flow related electrical impedance changes in rigid tubes.

Mammalian blood in pulsatile flow through a rigid tube has been shown to be anisotropic with regard to its electrical conductivity. When flow increases there is a rise in conductivity in the longitudinal and a fall in the radial direction. These changes are caused by flow-dependent variations in the orientation of the disk-shaped erythrocytes.

Animals↗
PubMedDate not supplied

Poststenotic signal loss in MR angiography: effects of echo time, flow compensation, and fractional echo.

PURPOSE: To evaluate with steady and pulsatile flow the influence of echo time, gradient strength and duration, and flow compensation on the degree of turbulent signal loss, factors that have been implicated in MR angiography's overestimation of the degree of stenosis. METHODS: We examined poststenotic turbulent flow in two models, one that created a turbulent jet and another that simulated a plaque-like stenosis. The pulse sequence used in these experiments allowed for a single variable (flow compensation, echo time, or gradient strength) to be varied without changing the others. RESULTS: Poststenotic signal loss can lead to overestimation of the degree of a stenosis. The area of signal loss in the turbulent jet was influenced by fractional echo and flow compensation, but not by echo time. We found that the dominant mechanism in poststenotic signal loss is related to the strength and duration of the imaging gradients. CONCLUSIONS: Flow-compensated sequences with reduced gradient strength and duration will reduce poststenotic signal loss and may lead to more accurate estimations of the extent of stenotic lesions.

Arterial Occlusive Diseases↗
PubMed2000

The effect of sizing on the hydrodynamic parameters of the Medtronic freestyle valve in vitro.

BACKGROUND: An in vitro model has been established to investigate the effect of sizing on the hydrodynamic characteristics and leaflet motion of the Medtronic Freestyle valve. METHODS: The valves were tested in fresh porcine aortic roots. Two or three different sizes of valves were implanted in the same aortic root one after the other. The compliance of the fresh aortic and the composite roots was measured in the pressure range of 0 to 120 mm Hg, and the composite roots were then tested in a pulsatile flow simulator. The transvalvular gradient and degree of regurgitation were measured and the effective orifice area and performance index were calculated. Leaflet motion was recorded on video. RESULTS: The fresh aortic roots dilated by average 39.4% as the hydrostatic pressure rose from 0 to 120 mm Hg. Implantation of the Medtronic Freestyle valve did not change the distensibility of the aortic root significantly. The sizing protocol did not affect significantly the hydrodynamic performance. However, a significantly lower open leaflet bending deformation was found in the undersized valves. Regurgitation was found only at 2-mm undersized valves. CONCLUSIONS: Leaflet motion of the Medtronic Freestyle valve in vitro was best if 1 mm undersized, and this may be beneficial to long-term durability.

Aorta↗
PubMed1996

Haemodynamic and echocardiographic characteristics of a stentless allograft mitral prosthesis: an in vitro study.

Poor long-term durability and impaired haemodynamic performance are known disadvantages of bioprosthetic heart valves when compared to valve replacement using aortic allografts. A new stentless allograft mitral implant was developed and tested in vitro in a left ventricular model and pulsatile flow system to evaluate hydrodynamic function. Mitral valves were excised from sheep hearts and the mitral annulus reinforced by a strip of ovine pericardium. A patch of expanded polytetrafluoroethylene (ePTFE) was placed above the tips of the remaining papillary muscles. For in vitro evaluation of a total of five valves were investigated in a pulse duplicator. Transvalvular pressure gradients (delta P) were measured over a flow range corresponding to a cardiac output of 5l/min, at a heart rate of 70 beats/min, with a systole accounting for approximately 35% of the cardiac cycle. The systolic ejection period and diastolic filling period in this model were 350 and 510 ms, respectively, and aortic pressure was 120/80 mmHg. The effective orifice area was calculated from measurements of mean pressure drop and root mean square flow. Additionally, valve performance was evaluated by Doppler echocardiography. Results of in vitro studies of a 25 mm stentless allograft mitral implant, which is similar to the valves implanted in a chronic weaning sheep model, revealed a mean(s.d.) delta P of 2.0(1.6) mmHg (range 1.0-4.9 mmHg). The mean calculated effective orifice area was 3.38(0.52) cm(2) (range 2.5-3.8 cm(2)). Doppler echocardiography showed excellent performance of the mitral valve components and valve competence could be achieved. During the in vitro studies no failure caused by tissue rupture was detected. The results of the in vitro studies revealed data for delta P and effective orifice area superior to data obtained for standard 25 mm porcine bioprostheses.

Animals↗
PubMed1988

Hydrodynamic investigation of mechanical bileaflet valves.

For hydrodynamic comparison, 11 mechanical bileaflet valves have been perfused in a mock circulation system under pulsatile flow conditions. Six St. Jude Medical valves with different sizes from No. 21 to No. 31 and five Duromedics prostheses with corresponding sizes from No. 21 to No. 29 have been investigated. Flow, pressure, and orifice area were measured, while cardiac output was varied between 2 and 6 L/min. Insufficiency (I), maximal orifice area (Amax), mean orifice area (A), discharge coefficient (CD), performance index (PI), and efficiency index (EI) were determined. The St. Jude Medical valves show higher values of orifice area when compared with the Duromedics valves. For smaller valve sizes up to No. 25, the values of the orifice area are similar. The Duromedics valves show much lower values of insufficiency; thus, for small valve sizes, the Duromedics prosthesis seems to be superior. For larger valve sizes (No. 27, No. 29, and No. 31), a decision has to be made whether higher insufficiency and higher orifice area of the St. Jude Medical valve or lower insufficiency with lower orifice area is more acceptable.

Heart Valve Prosthesis↗
PubMed2005

In-vitro assessment of the functional performance of the decellularized intact porcine aortic root.

BACKGROUND AND AIMS OF THE STUDY: Tissue-engineered heart valves offer the potential to deliver a heart valve replacement that will develop with the young patient. The present authors' approach is to use decellularized aortic heart valves reseeded in vitro or in vivo with the patient's own cells. It has been reported that treatment of porcine aortic valve leaflets with 0.1% (w/v) sodium dodecyl sulfate (SDS) in hypotonic buffer produced complete leaflet acellularity without affecting tissue strength. The present study aim was to investigate the effect of an additional treatment incorporating 1.25% (w/v) trypsin and 0.1% (w/v) SDS on the biomechanics and hydrodynamics of the aortic root. This treatment has been shown to produce decellularization of both the aorta and valve leaflets. METHODS: Fresh porcine aortic roots were treated to reduce the thickness of their aortic wall, and incubated in hypotonic buffer for 24 h. The leaflets were masked with agarose gel, and the aorta was treated with 1.25% (w/v) trypsin for 4 h at 37 degrees C. The trypsin and agarose were removed and the roots incubated with 0.1% (w/v) SDS in hypotonic buffer for 24 h. Fresh and treated circumferential and axial aortic specimens were subjected to uniaxial tensile testing, while intact porcine aortic roots were subjected to dilation and pulsatile flow testing. RESULTS: Decellularized aortic wall specimens demonstrated significantly decreased elastin phase slope and increased transition strain compared to the fresh control. However, the treatment did not impair tissue strength. Decellularized intact roots presented complete leaflet competence under systemic pressures, increased dilation and effective orifice areas, reduced pressure gradients, physiological leaflet kinematics and reduced leaflet deformation. CONCLUSION: The excellent leaflet kinematics and hydrodynamic performance of the decellularized roots, coupled with the excellent biomechanical characteristics of their aortic wall, form a promising platform for the creation of an acellular valve scaffold with adequate mechanical strength and functionality to accommodate dynamic cell repopulation in vitro or in vivo. This approach can be used for both allogeneic and xenogeneic tissue matrices.

Animals↗
PubMed1997

Multi-purpose mechanical circulatory device.

A mechanical circulatory assist device for long term use outside the hospital setting has been developed. The device can be used for left, right or bi-ventricular support, and several of the developed technologies are applicable for total artificial hearts and non-pulsatile flow systems. The totally implantable device is principally designed for left ventricular support with implantation in the left hemithorax. The system utilizes transcutaneous energy and information transfer sub-systems, and has no percutaneous connections. In vitro durability testing has been conducted for periods from 1-4 years. Bovine experiments have been conducted with sustained circulation for periods form 1.5 to 96 hours. The in vitro and in vivo evaluation to date has demonstrated that the system can function effectively as a totally implantable ventricular assist device. The transcutaneous energy and information transfer sub-systems provided the ability to power, monitor and control the device, without the need for percutaneous connections. Design optimization and chronic in vivo evaluation is planned.

Animals↗
PubMedDate not supplied

Vascular signals from pleura-based lung lesions studied with pulsed Doppler ultrasonography.

Vascular signals arising from pleura-based lung lesions were studied in 50 patients using pulsed Doppler ultrasonography. Twenty-seven had malignant lesions and 23 benign lesions. In 24/27 of the malignant masses, we observed no Doppler signals: in 2 cases, a low-velocity, turbulent, pulsatile flow was demonstrated; in 1 case pulsed Doppler ultrasonography showed only a low-velocity, continuous flow. In 20/23 of the benign lesions, we found 2 types of Doppler signal waveforms: an irregularly pulsatile, venous-like signal, and a regularly pulsatile, arterial-like waveform. The last 8 patients of our series underwent color Doppler ultrasound examination, which demonstrated the presence of arterial and venous vessels in 4 benign lesions and the absence of blood flow in 4 malignant masses. To our knowledge, we report for the first time the ability of obtaining Doppler signals from a variety of lung lesions. The actual clinical relevance of this application requires further studies.

Adult↗
PubMed1995

Determination of the curvatures and bending strains in open trileaflet heart valves.

The leaflets of trileaflet artificial heart valves manufactured from polyurethane, gluteraldehyde-treated porcine aortic valves and pericardial tissue are subject to cyclic stresses and strains which can reduce the lifetime of the implanted valves through leaflet calcification and fatigue failure. A detailed knowledge of the stress state within a valve leaflet throughout a cardiac cycle is desirable in order to improve the geometry of the valve leaflets and ultimately improve the valve performance. An experimental method to evaluate the radius of curvature at the free edge of the open valve leaflet is presented. The technique has been applied to polyurethane trileaflet heart valves manufactured within the authors' laboratory and to commercially available bioprosthetic valves in the fully open position under steady and pulsatile flow conditions. Simple bending theory has been applied to the polyurethane valves to calculate bending stresses and strains at the free leaflet edge based on the measured curvature. The results showed that in the fully open position the highest curvatures occurred at the commissural regions for all the valves analysed. Additional areas of high curvature were present along the free leaflet edge. Average curvatures as high as 0.85 mm-1 were observed at the leaflet commissures for the polyurethane valves with a resultant bending stress of 0.72 MPa. The porcine bioprosthetic valves showed average curvatures as high as 2.5 mm-1 which also occurred at the leaflet commissures. The results of the study have been compared to values of stress obtained from numerical analysis of closed polyurethane valve leaflets reported in the literature.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Comparative study of the hydrodynamic function of the CarboMedics valve.

The hydrodynamic function of each size of the CarboMedics valve was assessed in a pulsatile flow simulator. The mean pressure difference with respect to forward flow, regurgitant volumes, and total energy loss across each valve were analyzed. The results for the 23-mm aortic and 29-mm mitral CarboMedics valves were compared with those for the St. Jude Medical and Björk-Shiley Monostrut valves. Results showed good hydrodynamic function for each CarboMedics valve, although the pressure difference and total energy loss across the 19-mm aortic valve was high. The hydrodynamic function of the CarboMedics valve was comparable with that of the St. Jude Medical valve. Both valves showed similar leakage volumes, which were significantly larger than that for the Björk-Shiley Monostrut valve. On account of this the total energy loss in the Björk-Shiley valve was significantly less than that for the bileaflet valves in the aortic position. Concern remains for the continuing presence of high closed-valve regurgitation in the bileaflet valves.

Aortic Valve↗
PubMed2005

Influence of mimic cardiac rate on hydrodynamics of different mechanical prosthetic cardiac valves in vitro.

OBJECTIVE: To assess the influence of mimic cardiac rate on hydrodynamics of different mechanical prosthetic cardiac valves. METHODS: US-made CarboMedics bileaflet valve, China-made Jiuling bileaflet valve and C-L tilting disc valve were tested via a pulsatile flow simulator in the aortic position. Testing conditions were set at mimic cardiac rates of 55 bpm, 75 bpm, 100 bpm with a constant mimic cardiac output of 4 L/min. The mean pressure differences (deltaP), leakage volumes (L(E)V) and closing volumes (C(L)V) across each valve, and effective orifice areas (EOA) were analyzed. RESULTS: Within physiological range, deltaP, L(E)V, and C(L)V decreased as mimic cardiac rate increased, with a large extent of variance. EOA increased along with an increase in mimic cardiac rate. It was a different response in terms of cardiac rate alteration for different types of mechanical prosthetic cardiac valves. CONCLUSION: Mimic cardiac rate change affects hydrodynamics of mechanical prosthetic cardiac valves. Within physiological range, the hydrodynamic of prosthetic bileaflet valve is better than that of tilting disc valve.

Biomechanical Phenomena↗
PubMed1997

Adenovirus-mediated transfer of tissue-type plasminogen activator gene to human endothelial cells.

BACKGROUND: Seeding of vascular grafts with genetically engineered human endothelial cells (hECs) secreting antithrombogenic or fibrinolytic agents has considerable clinical potential. METHODS: An adenoviral vector was used to transfer the human tissue-type plasminogen activator (htPA) gene to hECs, and the ability of the transduced hECs to secrete htPA was examined. Cultured hECs on plates were incubated with various concentrations of recombinant adenoviruses containing the htPA or LacZ gene for various times to determine the optimal transfer conditions. Transduced hECs were seeded onto fibronectin-coated expanded polytetrafluoroethylene grafts (4 mm in diameter), some of which were exposed to pulsatile flow in vitro. RESULTS: Effective transduction of the htPA gene into hECs (htPAhECs) was achieved with viral soup at a multiplicity of infection of 30 after incubation for 1 day, which yielded 4.8 +/- 0.20 x 10(3) ng/10(6) cells/6 hr htPA antigen on plates (n = 3), 2.2 +/- 2.0 x 10(3) ng/10(6) cells/6 hr on grafts (n = 6), and 6.8 +/- 1.7 x 10(2) ng/10(6) cells/6 hr on perfused grafts (n = 6). The retention of htPAhECs by perfused grafts was 84.0% +/- 3.0%, comparable with the noninfected (82.1% +/- 8.0%) and mock-infected (94.2% +/- 0.4%) hEC values. CONCLUSIONS: By adenoviral vector-mediated gene transfer, 10(2-3)-fold enhancement of htPA secretion was demonstrated, which did not affect cell retention by grafts.

Adenoviridae↗
PubMed2003

Pulsatile perfusion and cardiomyocyte viability in a solid three-dimensional matrix.

BACKGROUND: The manufacture of full thickness three-dimensional myocardial grafts by means of tissue engineering is limited by the impeded cellular viability in unperfused in vitro systems. We introduce a novel concept of pulsatile tissue culture perfusion to promote ubiquitous cellular viability and metabolism. METHODS: In a novel bioreactor we established pulsatile flow through the embedded three-dimensional tissue culture. Fibrin glue served as the ground matrix wherein neonatal rat cardiomyocytes were inoculated. Fluor-Deoxy-Glucose-Positron-Emission-Tomography (FDG-PET) and life/dead assays were employed for comparative studies of glucose uptake resp. cell viability. RESULTS: A solid 8 mm thick structure resulted. Cellular viability significantly increased in the perfused chambers. We observed centripetal migration of the embedded cardiomyocytes to the site of the core vessel. However, cellular viability was high in the periphery of the tissue block too. FDG-PET revealed enhanced metabolic activity in perfused chambers. CONCLUSIONS: The present concept is highly effective in enhancing cellular viability and metabolism in a three-dimensional tissue culture environment. It could be utilized for various co-culture systems and the generation of viable tissue grafts.

Animals↗