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Biomedical subjects

H Reul

Publications and source records attributed to H Reul.

At least 109 records · Page 6Linked to original sources
PubMed1988

In vitro stress measurements in the vicinity of six mechanical aortic valves using hot-film anemometry in steady flow.

Based on hot-film anemometry, point velocity measurements in the total cross sectional area 1 and 2 diameters downstream of: Björk-Shiley Standard, Convex-Concave and Monostrut, Hall-Kaster (Medtronic-Hall), St. Jude Medical and Starr-Edwards Silastic Ball aortic valves were made. The spatial distribution of Reynolds Normal Stresses (RNS) was visualized three-dimensionally in order to point out where and to what extent the highest RNSs were found. The measurements were made in steady flowing glycerol mixture at flow rates 10, 20 and 30 l. min-1 corresponding to mean velocities of 27, 54 and 81 cm s-1. The highest maximum RNS values were around 250 Nm-2 and were found downstream of the Björk-Shiley Monostrut and Starr-Edwards Ball valves. The lowest maximum RNSs were found downstream of the St. Jude Medical and Hall-Kaster (Medtronic-Hall) valves (125-140 Nm-2). The Starr-Edwards valve had the highest mean RNS (117 Nm-2) followed by the Björk-Shiley Monostrut (87 Nm-2). These simplified measurements of artificial heart valve performances concerning RNS, enhance the interpretation of results in more complicated flow models not to say in vivo.

Aortic Valve↗
PubMed1988

Turbulent stress measurements downstream of six mechanical aortic valves in a pulsatile flow model.

In a pulsatile flow model aortic Björk-Shiley Standard, Convex-Concave and Monostrut valves were investigated together with the Hall-Kaster (Medtronic-Hall), St Jude Medical and Starr-Edwards Silastic Ball valve using hot-film anemometry. Three-dimensional visualization of average systolic Reynolds normal stresses (RNS) reflected the design of the valves. Mean average RNS were used for comparison of the fluid dynamic performance along with Velocity Energy Ratio (VER100) and Turbulence Energy Ratio (TER) as a relative turbulence intensity for pulsatile flow. Mean average RNS ranged from 13.2 to 37.6 Nm-2 for all the valves with the highest levels for the Björk-Shiley Standard and Starr-Edwards Ball valve and lowest values for the St Jude Medical valve and with the Hall-Kaster (Medtronic-Hall), Björk-Shiley Convex-Concave and Monostrut valves in between.

Aortic Valve↗
PubMed1988

Three-dimensional visualization of velocity fields downstream of six mechanical aortic valves in a pulsatile flow model.

Velocity fields downstream of 27 mm Björk-Shiley Standard, Björk-Shiley Convex-Concave, Björk-Shiley Monostrut, Hall-Kaster (Medtronic-Hall), St. Jude Medical and Starr-Edwards Silastic Ball aortic valves were studied in a pulsatile mock circulation. Stroke volume was 70 cm3 and frequency 71 min-1 and 88 min-1. Fluid velocity was measured by a catheter mounted hot-film anemometer probe in a glycerol water mixture one and two diameters downstream of the aortic valve. Velocity fields were dynamically visualized by a three-dimensional technique and revealed qualitative independence of frequency. All profiles were flat in the acceleration phase of systole. From peak systole and throughout the systolic deceleration phase profiles characteristic of the individual valves appeared. The pivoting and tilting disc valves caused a skewed velocity profile with highest velocities downstream of the major orifice and lowest velocities downstream of the minor orifice. The differences between the three investigated Björk-Shiley valves were remarkable. The St. Jude Medical valve generated velocity peaks downstream of the two major orifices and the central slit, and lower velocities in the hinge areas. A rather flat profile with central hollowing was seen downstream of the Starr-Edwards Ball valve. All velocity profiles were more or less dampened two diameters downstream.

Aortic Valve↗
PubMed1988

Model studies at mechanical aortic heart valve prostheses--Part I: Steady-state flow fields and pressure loss coefficients.

In a 3:1 scaled model of the human aorta models of the Omniscience, Björk-Shiley Convexo-Concave, Björk-Shiley Monostrut, Medtronic-Hall, Duromedics (Hemex) and the Saint Jude Medical heart valve prostheses are studied in steady flow representing the systolic peak flow phase. Detailed flow visualization experiments show flow separations at all inner ring surfaces as well as at most of the occluders. The resulting stagnation areas increase the risk of thrombus accumulation. Flow separations also stimulate vortex formation and turbulent mixing at the downstream jet boundaries and thus may intensify blood damage by turbulent shear stresses. The different influences of struts and occluder guides on the flow around the occluders are discussed. The effects of the individual valve components on the flow fields are analyzed and correlated with the resulting pressure losses.

Aortic Valve↗
PubMed1988

In vitro comparison of aortic heart valve prostheses. Part 1: Mechanical valves.

The hydrodynamic performance of a series of mechanical heart valve prostheses is measured in the aortic position. All experiments are performed in an electrohydraulic, computer-controlled pulse duplicator simulating the left side of the human circulatory system. Testing conditions are set according to a Food and Drug Administration interlaboratory comparison protocol with cardiac outputs of 3.0, 4.5, 6.5, and 8.0 L/min at a constant heart rate of 70 beats/min. Mean systolic pressure differences, volume losses, and energy losses, as well as dimensionless pressure losses and energy loss coefficients, are calculated from the recorded pressure, volume, and flow tracings. The results of 10 mechanical heart valve prostheses (eight tilting disc valves and two bileaflet valves) are presented and their clinical relevance is discussed.

Aortic Valve↗
PubMed1987

Three-dimensional visualization of axial velocity profiles downstream of six different mechanical aortic valve prostheses, measured with a hot-film anemometer in a steady state flow model.

Hot-film anemometry was used for in vitro steady-state measurements downstream of six mechanical aortic valve prostheses at flow rates 10, 20 and 30 l.min-1. Three-dimensional visualizations of velocity profiles at two downstream levels were made with the valves rotated 0 and 60 degrees in relation to the sinuses of valsalvae. The velocity fields downstream of the disc valves were generally skew with increasing velocity gradients and laminar shear stresses with increasing flow rates. Furthermore, increased skewness of the velocity profiles was noticed when the major orifices of the disc valves were towards the commissure than when approaching a sinus of valsalvae. The velocity profiles downstream of the ball valve were generally flat but with considerably more disturbed flow, consistent with the findings in turbulent flow.

Aortic Valve↗
PubMed1987

[Combined treatment of hypopharyngeal carcinoma].

From 1978 through 1984, 120 patients with hypopharyngeal carcinomas were treated cooperatively by the University Hospitals of Erlangen. 120 out of these patients were men and 6 women. 96 patients (80%) suffered from cervical lymph node metastases, 91 (76%) were already in UICC stage IV. There were two cases with stage I, eight cases (7%) with stage II, and 19 cases (16%) with stage III. Among the 116 patients treated by causal therapy, 70 (60%) reached complete remission (CR), 34 (29.5%) partial remission (PR), and 12 (10.5%) were non-responders (NC,P). The cumulative survival at five years was 14% in 120 patients and 24% in 70 patients after CR. None of the patients with PR or NC survived more than two years. 111 patients were irradiated. Group 1: radiotherapy alone (41 patients), group 2: surgery and radiotherapy (47 patients), group 3: chemotherapy and radiotherapy (19 patients). The medium treatment period was 76, 107, and 141 days, respectively. The cumulative survival at five years was 3% in group 1, 28% in group 2, the survival at three years in group 3 was 14%. The results of postoperative radiotherapy, amounting to 36%, were better than the rate of 20% achieved by preoperative radiotherapy and surgery. A survival at five years of 46% was obtained after transoral microlaryngoscopic laser resection and postoperative irradiation, which was therefore superior to conventional operation techniques combined with radiotherapy (16%). Moreover, better functional and cosmetic results were achieved with this method. The prognosis is unfavorably influenced by a high stage, lymph node manifestations, and dedifferentiated tumor histology.

Adult↗
PubMed1984

In-vitro wall shear measurements at aortic valve prostheses.

Wall shear distributions during the cardiac cycle at the valve rings of Starr-Edwards, Björk-Shiley and Lillehei-Kaster aortic valves are measured and compared with thresholds reported for shear-induced trauma of blood components. Further, for the disk valves, the influence of pulse rate on wall shear stresses is evaluated. Hot film anemometry with flush-mounted wall shear probes is used as measurement technique in a pulsatile flow mock circuit. The experimental systolic data support the better hemodynamic characteristics of the disk valves over the ball valve also with respect to the threshold shear stresses of flow induced blood trauma. These results are confirmed by postoperative clinical studies, where lower LDH-values are found with the disk than with the ball valves. During diastole, however, high shear stresses are measured and calculated at the valve ring of the Björk-Shiley prosthesis, which can be referred to the non-overlapping closing mechanism. This result is discussed with respect to the often observed thrombus formation at the disk downstream of the smaller orifice of the Björk-Shiley valve.

Aortic Valve↗
PubMed1982

Portable artificial kidney with advantages of hemodialysis, hemofiltration, and hemoperfusion.

The FDA (filtration, dialysis, absorption) system developed in the present study operates on the principle of simultaneous filtration of blood and dialysis against its purified filtrate, the filtrate being purified by a multi-adsorption system. The filtration of blood is done using a hemofilter which permits clearance of solutes up to 50,000 daltons and easy removal of excess fluid overload under minimal osmotic imbalance conditions. The clearance of small solutes in the above pure-convective filtration process is enhanced by returning the purified filtrate to the hemofilter which introduces an additional diffusive mass transport to the otherwise pure-convective process. The purification of the filtrate is done by 3 kg charcoal and 450 gm of cation exchanger in the Ca++ and Na+ form. Sufficient urea binding is achieved by raising the post-treatment urea level from 50 mg% to 150 mg% which may be justified as the blood urea level below 300 mg% was found to be nontoxic by others. By this procedure, about 40 gm urea is removed per treatment by 3 kg charcoal and 3 to 4 liters of excess fluid discarded. Three kg of charcoal is found to bind an adequate amount of phosphate, thus eliminating the use of phosphate binders, such as alumina, which is a toxic material. The ion exchangers in the Ca++ and Na+ form bind an adequate amount of K+ without altering Na+ and Ca++ levels. The filtrate purification cartridge can be easily regenerated and sterilized, if necessary, thus making it inexpensive. A comparison of the FDA system with other systems clearly showed that it has the advantages of HD, HF, and HP while the major disadvantages of HD, HF, and HP are eliminated in the FDA system.

Anion Exchange Resins↗