PubMed Health⌕ Search

Biomedical subjects

H Reul

Publications and source records attributed to H Reul.

At least 37 records · Page 2Linked to original sources
PubMed1998

Holographic interferometry and in vitro calcification: comparing pericardial versus porcine bioprostheses.

BACKGROUND AND AIMS OF THE STUDY: Structural valve deterioration of bioprostheses is mainly caused by progressive calcification. It has not yet been convincingly demonstrated whether pericardial or porcine bioprostheses are more prone to calcification. METHODS: A previously described in vitro test protocol consisting of non-destructive holographic interferometry, which permits quantitative deformation analysis of heart valves and accelerated dynamic calcification in vitro was used to evaluate five stented pericardial bioprostheses of different sizes and design (three or two leaflets) from one manufacturer. The extent of calcification was assessed after up to 20 x 10(6) cycles in the valve tester by microradiography, and areas of calcification were compared by holographic interferometry using computerized image processing. Calcification was confirmed by EDX-analysis and Von Kossa staining. Results were compared with in vitro testing of 25 porcine bioprostheses from different manufacturers. RESULTS: The tested pericardial bioprostheses had an individual distribution of mechanical stresses detectable by holographic interferometry, which resulted in different calcification of valve leaflets. A strong correlation between calcification and stress distribution was found (correspondence of affected areas: 82.3 +/- 10.1%, r = 0.97). Variability in calcification and stress distribution, respectively, of pericardial valves compared well with our findings for porcine prostheses. Overall, the extent of leaflet calcification was not statistically different for pericardial and porcine bioprostheses (p = 0.21). CONCLUSIONS: The biological material of bioprostheses (pericardial versus porcine) does not seem to be the crucial factor in the calcification process. Mechanical stresses detectable by holographic interferometry have a more pronounced impact and predict calcification of individual prostheses, at least in the in vitro setting.

Animals↗
PubMed1998

In vitro evaluation of the long-body On-X bileaflet heart valve.

BACKGROUND AND AIMS OF THE STUDY: In order to optimize the length-to-diameter ratio, a series of circular aluminum rings with flared inlet and varying ring lengths, with internal diameters corresponding to that of 19 mm replacement prosthetic heart valve orifices, were tested in a steady-flow hydraulic system. The study aim was to determine the ring length-to-internal diameter ratio that produces the best hydraulic efficiency (i.e. lowest pressure gradient) within the physiologic flow rate range. METHODS: Each ring was tested at flow rates of 10, 15, 20, 25 and 30 l/min and length-to-diameter ratio effect on hydraulic efficiency determined experimentally. The hydraulic effect was most significant for a ratio of about 0.6, with an increase to 1.2 providing little additional benefit. Thus, a ratio of about 0.6 was considered optimum in terms of hydraulic efficiency and incorporated into the design of the On-X bileaflet mechanical heart valve (BHV) series. An in vitro hydrodynamic study of the smallest (19 mm) and largest (25 mm) clinical On-X aortic valves was performed at two independent laboratories. Standard St. Jude Medical BHVs were used as the study controls. RESULTS: Steady-flow experiments showed that the pressure gradient in the On-X valve was about 50% less than that of the comparable size control. The pulsatile flow study demonstrated a similar pressure gradient advantage. Laser Doppler anemometer velocity profiles taken downstream of the On-X valve at the aortic root showed typical characteristics of bileaflet valves, with three velocity peaks. The peak velocity reached 1.6 m/s for the On-X and 1.75 m/s for the control valve. A recirculating vortex was seen in the sinus cavity during the ejection period. This vortex, found in most aortic valves (including bioprostheses), is believed to provide a beneficial wash-out of the valve region and assist in valve closure. CONCLUSIONS: These two independent studies clearly demonstrated that the elongated valve body and comparably larger flow area helped to improve the valve hydrodynamic performance, which is especially beneficial in the smallest (19 mm) size valve.

Aortic Valve↗
PubMed1998

In vitro thrombogenicity testing of artificial organs.

Thromboembolic complications remain as one of the main problems for blood contacting artificial organs such as heart valves, bloodpumps and others. In vitro evaluation of thrombogenesis in prototypes has not previously been part of the standard evaluation of these devices. In comparison to hemolysis testing, evaluation of the thrombogenic potential is more difficult to perform because of the complexity of the blood coagulation system. We present an in vitro testing procedure that allows the accelerated examination of the thrombogenic potential of different types of blood pumps. Additionally, first results are presented that indicate the reliability of the accelerated clotting test for mechanical heart valves. Results for the centrifugal pump BioMedicus and two microaxial pumps have shown typical thrombus formation at locations such as bearings. The results indicate that the accelerated clotting test is an excellent addition to the much more expensive animal testing of artificial organs or assist devices. In vitro testing permits studies of thrombus formation to be performed at an early stage and at low costs and also facilitates a more precise investigation of device areas known to be potential hot spots for thrombus formation.

Animals↗
PubMed1997

Disturbed intracoronary hemodynamics in myocardial bridging: early normalization by intracoronary stent placement.

BACKGROUND: The purpose of this study was to evaluate the hemodynamic mechanisms leading to myocardial ischemia in patients with myocardial bridging. Myocardial bridging is known to induce angina and even severe myocardial ischemia. METHODS AND RESULTS: In 12 symptomatic patients with myocardial bridges, quantitative coronary angiography was performed to obtain systolic/diastolic vessel diameters within the bridged segments. Coronary flow velocities, flow reserve, and pressures were determined with a 0.014-in Doppler and a 0.014-in pressure microtransducer. In 3 symptomatic patients, coronary stents were implanted and hemodynamic measurements were repeated immediately and after 7 weeks. An in vitro validation of the pressure measurements was performed. Angiography revealed a systolic diameter reduction of 80.6+/-9.2% and a persistent diastolic reduction of 35.3+/-11% within the bridged segment. Diastolic flow velocities (cm/s) were increased (31.5+/-14.3 within versus 17.3+/-5.7 proximal and 15.2+/-6.3 distal, P<.001). Coronary flow reserve distal to the bridge was 2.5+/-0.5. There was an increased peak systolic pressure within the bridged segment (171+/-48 versus 113+/-10 mm Hg proximal, P<.001). Stent placement abolished the phasic lumen compression, the diastolic flow abnormalities, the intracoronary peak systolic pressure, and clinical symptoms. Coronary flow reserve improved to 3.8+/-0.3. CONCLUSIONS: Coronary hemodynamics in myocardial bridges are characterized by a phasic systolic vessel compression with a localized peak pressure, persistent diastolic diameter reduction, increased blood flow velocities, retrograde flow, and a reduced flow reserve. These alterations may explain the occurrence of symptoms and ischemia in these patients. Intracoronary stent placement abolished all hemodynamic abnormalities and may improve clinical symptoms in otherwise unsuccessfully treated patients with myocardial bridges.

Adult↗
PubMed1997

Clinical experience with the MEDOS HIA-VAD system in infants and children: a preliminary report.

BACKGROUND: The need of pediatric cardiac assist is growing because of the complexity of the congenital conditions operated on and the increasing number of pediatric transplantations. We evaluated the newly developed pediatric MEDOS HIA-VAD ventricular assist device. METHODS: The pneumatic paracorporeal ventricular assist device has three left ventricular sizes (10-, 25-, and 60-mL maximum stroke volume) and three right ventricular sizes (9, 22.5, and 54 mL) and can be operated effectively with up to 180 cycles/min. We used this device in 6 consecutive pediatric patients. Intention of treatment was to bridge to transplantation in 3 patients and to aid in recovery from a cardiac operation in 3. Age ranged from 5 days to 8 years. RESULTS: Two children died during assist, 2 were weaned from the system and discharged home, and 2 had successful transplantation. During assist, laboratory variables indicative of impaired renal, hepatic, or pulmonary function normalized or showed a trend toward normalization. Both deaths were related to infection. CONCLUSIONS: With the new MEDOS HIA-VAD ventricular assist device system, pediatric mechanical cardiac assist can be performed successfully. It requires timely implantation, careful monitoring, and adequate size-matched devices.

Antibiotic Prophylaxis↗
PubMed1997

The implantable fuzzy controlled Helmholtz-left ventricular assist device: first in vitro testing.

To perform first experimental tests for validation of a new left ventricular assist device (LVAD) with a high efficiency energy converter, a new pump design and a novel type of perfusion control, a functional labtype, were manufactured. With a stroke volume of 65 ml, a total pump housing volume of 450 ml (including valves and connectors), and a weight of 430 g, it is one of the smallest and lightest implantable pulsatile electromechanical LVADs. Pulsatile operation is generated by a special reduction and displacement gear which transforms a uniform rotational movement of a sensorless, electronically commutated DC motor into a translatory pusher plate movement. A prolonged duration for filling (60% of the cycle time) supports full-empty pumping and consequently a high overall pump efficiency. Active adaptation of output flow to organ perfusion demand is achieved by changing the rotational speed of the motor by means of a sensorless fuzzy controller, which detects preload and afterload induced effects at the motor current input. First in vitro test results obtained within a circulatory mock loop that simulates physiological preloads and afterloads are presented. They comprise preload sensitivity and the function of the novel perfusion controller as well as preload and afterload related flow data. The results prove the feasability of the energy conversion with the novel gear and control concept for an implantable electromechanical pulsatile LVAD.

Animals↗
PubMed1997

A new blood pump for cardiopulmonary bypass: the HiFlow centrifugal pump.

Centrifugal blood pumps are considered to be generally superior to the traditionally used roller pumps in cardiopulmonary bypass. In our institute a new lightweight centrifugal sealless blood pump with a unique spherical thrust bearing and with a magnetic coupling was developed, the HiFlow. The small design makes the pump suitable for applications in complex devices or close to a patient. Hemolysis tests were carried out in which the BioMedicus pump BP-80 and a roller pump were used as reference. The centrifugal pump HiFlow showed the least blood trauma within the group of investigated pumps. In summary, the HiFlow pump concept with its low priming volume and limited contact surfaces shows great potential for clinical applications in cardiopulmonary bypass. Also, the possibility of using the pump as a short-term assist device with an option of a pulsatile driving mode was demonstrated.

Animals↗
PubMed1997

A new in vitro test method for calcification of bioprosthetic heart valves.

To investigate the calcification behavior of different bioprosthetic heart valves and verify possible hypotheses of the etiology of valve calcification, an accelerated pulse tester for bioprostheses was developed, whereby up to ten valves can be tested under identical test conditions. Each valve was mounted in a separate compartment on a piston and cyclically moved through a calcifying solution at frequencies of up to 800/min at 37 degrees C: An appropriate calcifying solution was evaluated by incubation tests of bovine and porcine tissue. Calcification was confirmed by measuring Ca and phosphate depletion by atomic absorption spectroscopy, von Kossa staining, EDAX, and microradiography. The first tests were successfully carried out on porcine valves that had been nondestructively assessed for tissue/stress anomalies by holographic interferometry prior to the calcification test. The tests showed that 75% of irregular fringe pattern areas corresponded to the calcification areas.

Animals↗
PubMed1997

Pre-clinical evaluation of a novel, pneumatic, ventricular assist device (Medos HIA-VAD) under pathophysiological conditions.

To evaluate a new cardiac assist system, the Medos HIA-VAD, we studied the effects of mechanical unloading on regional and global myocardial dysfunction. As a model for the regional temporary contractile dysfunction we chose an anesthetized, open chest preparation in sheep. We occluded the diagonal coronary artery for 15 minutes and reperfused for 90 minutes. Hemodynamic parameters and wall thickening were monitored. Unloading with the 60-ml Medos HIA-VAD was performed either during ischemia (group II) or during reperfusion (group III). The recovery of non-uniformity indicated by post-ejection wall thickening was significantly faster (p < 0.05) in both groups if compared to the non-assisted group (group I) (all groups n = 4). Recovery of systolic wall thickening in the postischemic region in group I was only 76 +/- 12%, while it was 103 +/- 11% and 92 +/- 11% in groups II and III, respectively (p < 0.05). In a canine model of global left ventricular failure, we occluded the left anterior descending coronary artery for 20 min, and after 5 minutes of reperfusion, the circumflex artery for 45 min (group I, n = 5). After 5 min of CX occlusion in group II we performed assisted circulation for 90 min with the 10-ml (n = 5) and the 25-ml (n = 5) Medos HIA-VAD. In group I, no dog survived, in group II, all survived 4 hours of reperfusion (n = 10). Lactate at the end of the experiment was 1.1 +/- 0.9 mmol/L (10-ml, and 1.1 +/- 0.2 mmol/L (25-ml) (p > 0.05 vs. base line). We conclude that the Medos HIA-VAD is a reliable assist device that enhances myocardial recovery and allows sufficient peripheral circulation in the case of cardiogenic shock.

Animals↗
PubMed1996

Comparison of passive and active perfusion catheters: an in vitro study in a pulsatile coronary flow model.

Perfusion balloon catheters are designed to provide continuous transcatheter blood flow and thereby reduce myocardial ischemia during coronary angioplasty. To compare the transcatheter flow rates of active and passive (auto-) perfusion catheters, a well-controlled experimental study was performed in a circulation model that duplicates the phasic, predominantly diastolic flow pattern of the left coronary artery. Mean diastolic coronary driving pressure varied between 20 and 100 mm Hg. For the autoperfusion catheters, a strong relationship between transcatheter flow and diastolic coronary driving pressure was found. For example, a coronary driving pressure of 80 mm Hg provided a coronary flow of 30 ml/min (RX-Perfusion [RP], ACS), 28 ml/min (Speedflow [SF], Schneider), 20 ml/min (Lifestream [LS], ACS), and 19 ml/min (Flowtrack [FT], ACS). Reduction of driving pressure to 40 mm Hg decreased the absolute transcatheter flow, which was now 16 ml/min (RP), 13 ml/min (SF), and 10 ml/min (LS and FT). The relative catheter flow (the ratio of absolute flow to baseline coronary flow rate without a catheter in place), was independent of actual coronary driving pressure and ranged between 21% +/- 1% (RP) and 14% +/- 1% (FT and LS). For the active perfusion system (Coreflo, Leocor, a maximal transcatheter flow of 82 ml/min was found. Using this active perfusion system, the relative catheter flow increased with decreasing coronary driving pressure:80 --> 40 mm Hg: 56% --> 107%. For all catheters, the distal perfusion decreased between 30% (3.0 mm RP) and 50% (3.0 mm LS) by a 0.014-inch guidewire placed through the inner channel of the catheter. Because of the strong relationship between coronary driving pressure and transcatheter flow, the residual flow through all autoperfusion catheters becomes critical (<20 ml/min), when the coronary driving pressure drops below 50 mm Hg. By contrast, active perfusion systems are independent of the actual coronary driving pressure and are therefore advantageous for prolonged dilation in patients with low aortic pressure.

Angioplasty, Balloon, Coronary↗
PubMed1996

In vitro flow dynamics of a new mechanical cardiac valve prosthesis--"tricusp".

The hydrodynamic performance of a newly developed JCL-trileaflet mechanical heart valve prostheses (Tricusp) was measured and compared with some of the currently most used heart valve prostheses types. All experiments were performed in an electrohydraulic, computer-controlled pulse duplicator simulating the left side of the human circulatory system. Testing conditions were set according to a Food and Drugs Administration interlaboratory comparison protocol, with cardiac outputs 3.0, 4.5, 6.5 or 8.0 l/min and a constant heart rate of 70 beats/min. Mean systolic pressure differences, volume and energy losses, dimensionless pressure losses and energy loss coefficients were calculated from the recorded pressure, volume and flow tracings. The results with the Tricusp valve were found to be as good, or even better than those with the currently most used commercially available bileaflet valves.

Heart Valve Prosthesis↗
PubMed1996

In vitro testing of heart valve wear outside of the manufacturers laboratory--requirements and controversies.

BACKGROUND AND AIM OF THE STUDY: Currently, various national and international Standards regulate in vitro and in vivo testing as well as the clinical evaluation of heart valve prostheses. This study concentrates on a single aspect of these protocols: accelerated wear and fatigue testing. METHODS: The differences in the above Standards were appraised and an experimental study was designed to assess the validity of Standard testing conditions with respect to in vivo relevance. An instrumented BSCC tilting disc valve was tested in two different types of fatigue testers and in a separate study in a sheep model. RESULTS: By comparing the obtained results it could be clearly demonstrated that under the current Standard conditions (ISO, CEN, FDA) actual in vivo impact loading cannot be reproduced. Also, the two compared test devices, though operating under the same Standard conditions, generated totally different loading conditions on the test valve. CONCLUSIONS: Based on these findings it is suggested that the actual loading conditions of each valve type should be measured either in vivo in animal models or within a circulatory mock loop which provides physiologic loading conditions, and the test conditions for accelerated wear and fatigue testing should be modified accordingly. Cavitation effects which can be assumed to be associated with high frequency wear testing is another important issue which has to be addressed in future amendments to the Test Standards.

Animals↗
PubMed1996

The heart-Hemopump interaction: a study of Hemopump flow as a function of cardiac activity.

The Hemopump is a useful left ventricular assist device. Because it is a rotary blood pump, the pump performance is not constant and is dependent on the cardiac cycle. We measured the static flow delivered by the pump at varying pressure heads (delta P) in a mock circulation. These data are compared to the pump performance in vivo. On the basis of these results, 5 sheep were instrumented for continuous Hemopump flow measurement as well as left ventricular and aortic pressure measurements. The Hemopump flow was relayed instantaneously to the pressure head. Low filling and ventricular failing (through intravenous administration of a beta-blocker) conditions were applied. The in vivo measured flows also are pressure head dependent, but the flow curve shows hysteresis resulting in a loop during each cardiac cycle. The in vivo peak flows (delta P = 0) are similar to the in vitro data. The in vivo means flows (delta = 50 mm Hg) are similar to the in vitro data for the lower pump speeds but are less than that at the higher pump speeds (3.74 +/- 0.55 L/min in vivo at Speed 7 versus 4.6 L/min in vitro). Low filling interrupts the delta P-flow loop and reduces flow. In the failing ventricle, delta P increases and flow is reduced. The cannula leaks and results in aortic insufficiency (0.36 +/- 0.05 L/min) when the pump is turned off. Several conclusions have been drawn from these tests: Cardiac activity is beneficial for the pump performance as well as when the aortic pressure curve is nonpulsatile; the longer the systolic phase, the higher the pump flow; the pump should never be turned off in clinical use, and filling is important for the pump's performance.

Animals↗
PubMed1996

Hemodynamic system analysis of intraarterial microaxial pumps in vitro and in vivo.

Because of the lack of a sophisticated pump management system, the performance of the Hemopump in patients cannot assessed successfully. To clarify the interrelationship between an intravascular nonpulsatile pump and a pulsating ventricle, an in vitro study was set up under controlled conditions. Before these in vitro experiments, a series of in vivo experiments were performed in sheep using Hp31 cannulae. As anticipated, the resulting pulsatile pump flow was a function of the momentary pressure difference across the pump. This varying pump flow showed a significant flow loop hysteresis, indicating that the pressure difference across the pump is not the only parameter governing momentary pump flow of a rotary pump operating at constant speed in a pulsatile environment. Furthermore, flow in the Hp31 was significantly influenced by the inflow situation, blood supply, size of the ventricular cavity, and shape and position of the inflow cannula within the ventricle. Pulsatile flow conditions with good as well as impaired inflow into the pump were accordingly simulated in vitro to verify the in vivo measurements, to characterize the various inflow conditions, and to discuss methods of improved pump management. As a result of the in vivo and in vitro experiments, one can rely on the measurement of nonpulsatile in vitro flow and pressure differences across the pump to characterize the momentary pump flow for good inflow conditions into the pump. For these situations, the flow hysteresis produced, caused by fluid inertia within the pump and cannula, can be neglected. In contrast, for an impaired inflow situation, the calculated pump flow based on pressure difference measurements can be misleading. Consequently, an improved pump management system is required to adjust the pump speed, the pump performance, to any kind of impaired inflow.

Animals↗
PubMed1996

Quality control of bioprosthetic heart valves by means of holographic interferometry.

BACKGROUND AND AIMS OF THE STUDY: Limited durability of porcine bioprostheses is mainly caused by the progressive development of calcification. We tested the hypothesis that hidden tissue anomalies or unfavorable stress concentrations of commercially available bioprostheses may lead to later calcification and dysfunction. Application of holographic interferometry for non-destructive testing of biological heart valves enables a full-field analysis of heart valves and reveals deformation irregularities of valve tissue. MATERIAL AND METHODS: We developed an accelerated calcification protocol for bioprosthetic heart valves including an accelerated pulsatile valve tester for simultaneous testing of 10 heart valves under identical conditions and a rapid synthetic calcification fluid containing a final Ca x P of 130 (mg/dl)2 in barbital buffer solution. Ten porcine bioprostheses (St. Jude Medical, Bioimplant) were assessed by holographic interferometry and subjected to the pulsatile accelerated calcification process. Distribution and amount of calcification was evaluated by microradiography after 12 x 10(6) and 19 x 10(6) cycles, respectively. Areas of irregular fringe patterns detected by holography as well as areas of calcification were calculated and compared using a personal computer. RESULTS: All tested bioprostheses had localized or extended areas with holographic irregularities and the accelerated valve testing protocol resulted in even macroscopically visible calcifications at various sites. Comparative analysis of the obtained microradiographs revealed that 74.2% +/- 6.0% of calcified leaflet areas lay within the previously detected holographic anomalies. CONCLUSIONS: Our first results show a strong correlation between holographic anomalies and calcification of porcine bioprostheses. We conclude that suitable methods for evaluation and quality control of bioprosthetic heart valves are available and seem to be predictive with regard to valve calcification.

Aortic Valve↗
PubMed1995

Comparison of valvular resistance, stroke work loss, and Gorlin valve area for quantification of aortic stenosis. An in vitro study in a pulsatile aortic flow model.

BACKGROUND: Valvular resistance and stroke work loss have been proposed as alternative measures of stenotic valvular lesions that may be less flow dependent and, thus, superior over valve area calculations for the quantification of aortic stenosis. The present in vitro study was designed to compare the impacts of valvular resistance, stroke work loss, and Gorlin valve area as hemodynamic indexes of aortic stenosis. METHODS AND RESULTS: In a pulsatile aortic flow model, rigid stenotic orifices in varying sizes (0.5, 1.0, 1.5 and 2.0 cm2) and geometry were studied under different hemodynamic conditions. Ventricular and aortic pressures were measured to determine the mean systolic ventricular pressure (LVSPm) and the transstenotic pressure gradient (delta Pm). Transvalvular flow (Fm) was assessed with an electromagnetic flowmeter. Valvular resistance [VR = 1333.(delta Pm/Fm)] and stroke work loss [SWL = 100.(delta Pm/LVSPm)] were calculated and compared with aortic valve area [AVA = Fm/(50 square root of delta Pm)]. The measurements were performed for a large range of transvalvular flows. At low-flow states, flow augmentation (100-->200 mL/s) increased calculated valvular resistance between 21% (2.0 cm2 orifice) and 66% (0.5-cm2 orifice). Stroke work loss demonstrated an increase from 43% (2.0 cm2) to 100% (1.0 cm2). In contrast, Gorlin valve area revealed only a moderate change from 29% (2.0 cm2) to 5% (0.5 cm2). At physiological flow rates, increase in transvalvular flow (200-->300 mL/s) did not alter calculated Gorlin valve area, whereas valvular resistance and stroke work loss demonstrated a continuing increase. Our experimental results were adopted to interpret the results of three clinical studies in aortic stenosis. The flow-dependent increase of Gorlin valve area, which was found in the cited clinical studies, can be elucidated as true further opening of the stenotic valve but not as a calculation error due to the Gorlin formula. CONCLUSIONS: Within the physiological range of flow, calculated aortic valve area was less dependent on hemodynamic conditions than were valvular resistance and stroke work loss, which varied as a function of flow. Thus, for the assessment of the severity of aortic stenosis, the Gorlin valve area is superior over valvular resistance and stroke work loss, which must be indexed for flow to adequately quantify the hemodynamic severity of the obstruction.

Aortic Valve↗
PubMed1995

Fuzzy control concept for a total artificial heart.

The development of an electromechanically driven total artificial heart (Helmholtz-TAH) was initiated in 1990. Anatomical fitting, biocompatibility, and automatic physiologic adaptation of pump output are the basic requirements that characterize the overall TAH concept. For evaluation of these features, a TAH labtype was developed. It provides most features of the conceptual artificial heart and supports in vitro testing of energy conversion, pump behavior, structural parts, sensors, and control concepts. A fuzzy controller has been implemented for adaptation of the pump rate to body perfusion demand by left pump chamber filling detection. This controller will be an important element of a future extensive TAH control system. The implementation is supported by a professional fuzzy control development tool that allows on-line and real time optimization of control strategies for dynamic processes. The first experiments proved the feasibility and the advantages of this fuzzy control concept. The first in vitro test results are presented.

Fuzzy Logic↗