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Biomedical subjects

D Westphal

Publications and source records attributed to D Westphal.

At least 19 recordsLinked to original sources
PubMed1992

Two-dimensional color-mapping of turbulent shear stress distribution downstream of two aortic bioprosthetic valves in vitro.

Since artificial heart valve related complications such as thrombus formation, hemolysis and calcification are considered related to flow disturbances caused by the inserted valve, a thorough hemodynamic characterization of heart valve prostheses is essential. In a pulsatile flow model, fluid velocities were measured one diameter downstream of a Hancock Porcine (HAPO) and a Ionescu-Shiley Pericardial Standard (ISPS) aortic valve. Hot-film anemometry (HFA) was used for velocity measurements at 41 points in the cross-sectional area of the ascending aorta. Three-dimensional visualization of the velocity profiles, at 100 different instants during one mean pump cycle, was performed. Turbulence analysis was performed as a function of time by calculating the axial turbulence energy within 50 ms overlapping time windows during the systole. The turbulent shear stresses were estimated by using the correlation equation between Reynolds normal stress and turbulent (Reynolds) shear stress. The turbulent shear stress distribution was visualized by two-dimensional color-mapping at different instants during one mean pump cycle. Based on the velocity profiles and the turbulent shear stress distribution, a relative blood damage index (RBDI) was calculated. It has the feature of combining the magnitude and exposure time of the estimated shear stresses in one index, covering the entire cross-sectional area. The HAPO valve showed a skewed jet-type velocity profile with the highest velocities towards the left posterior aortic wall. The ISPS valve revealed a more parabolic-shaped velocity profile during systole. The turbulent shear stresses were highest in areas of high or rapidly changing velocity gradients. For the HAPO valve the maximum estimated turbulent shear stress was 194 N m-2 and for the ISPS valve 154 Nm-2. The RBDI was the same for the two valves. The turbulent shear stresses had magnitudes and exposure times that might cause endothelial damage and sublethal or lethal damage to blood corpuscules. The RBDI makes comparison between different heart valves easier and may prove important when making correlation with clinical observations.

Aortic Valve↗
PubMed1990

Estimation of turbulent shear stresses in pulsatile flow immediately downstream of two artificial aortic valves in vitro.

Measuring turbulent shear stresses is of major importance in artificial heart valve evaluation. Bi- and unidirectional fluid velocity measurements enable calculation of Reynolds shear stress [formula: see text] and Reynolds normal stress [formula: see text]. tau is important due to the relation to hemolysis and thrombus formation, but sigma is the only obtainable parameter in vivo. Therefore, determination of a correlation factor between tau and sigma is pertinent. In a pulsatile flow model, laser Doppler (LDA) and hot-film (HFA) anemometry were used for simultaneous bi- and unidirectional fluid velocity measurements downstream of a Hall Kaster and a Hancock Porcine aortic valve. Velocities were registered in two flow field locations and at four cardiac outputs. The velocity signals were subjected to analog signal processing prior to digital turbulence analysis, as a basis for calculation of tau and sigma. A correlation factor of 0.5 with a correlation coefficient of 0.97 was found between the maximum Reynolds shear stress and Reynolds normal stress, implying [formula: see text]. In vitro estimation of turbulent shear stresses downstream of artificial aortic valves, based on the axial velocity component alone, seems possible.

Aortic Valve↗
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↗
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↗
PubMed1984

[Biotransformation of monolinuron (N-(4-chlorophenyl)-N'-methyl-N'methoxyurea) in isolated perfused chicken liver].

The biotransformation of radioactively labelled monolinuron (N-(4-chloro[U-14C]phenyl)-N'-methyl-N'-methoxyurea) was studied in the isolated perfused liver of the chicken. After a 4-hr perfusion, 83.1% of the added radioactivity was recovered, 56.6% in the perfusion medium and 26.5% in the liver and bile. The fraction of radioactivity extractable from the perfusion medium into ethyl acetate amounted to 47.8% of the added dose. In addition to monolinuron, five breakdown products were identified in this extract, namely N-(4-chlorophenyl)-N'-hydroxymethyl-N'-methoxyurea, N-(4-chlorophenyl)-N'-methoxyurea, N-(4-chlorophenyl)-N'-methylurea, 4-chlorophenylurea and 4-chloroacetanilide. Of particular interest was the absence of arylhydroxylated monolinuron derivatives, since in monolinuron-metabolism studies in the laying hen 2-hydroxy-4-chlorophenylurea and 3-hydroxy-4-chlorophenylurea were both detected. This differing metabolism corresponds to earlier findings in the rat, in which arylhydroxylated breakdown products were detected only in in vivo studies and not in rat-liver perfusion. Possible reasons for the differing metabolism of monolinuron in vivo and in vitro are discussed.

Animals↗
PubMed1979

[Delayed infections after foreign body inclusion in the maxillofacial region].

Nine cases of so-called late infections following foreign body inclusions due to trauma as well as possible developmental mechanisms were discussed. The question arises as to whether a nonirritating incorporated foreign body should be surgically removed as early as possible to eliminate the possibility of late infection.

Abscess↗
PubMed1979

[Bulbus motility in early and late surgery of orbital floor fractures (author's transl)].

Among 638 patients with fractures of the middle third of the facial skeleton 139 were found to have clinically relevant fractures of the orbital floor. 74 of them were followed up ophthalmologically and by x-ray examination. In 49 patients the results of the operative treatment were judged from a detailed questionnaire. Operation within 2 weeks after the accident yielded better results than later operation. Persisting motility disturbances concerned mainly the upper field of gaze.

Eye Movements↗
PubMed1978

Hypoxemia following the administration of sublingual nitroglycerin.

Nitroglycerin, 0.6 mg sublingually, was given to 27 nonasthmatic subjects with varying degrees of airways dysfunction to determine the effect on arterial oxygenation. In six normal subjects, the partial pressure of oxygen in arterial blood (Pao2) transiently decreased by 9 mm Hg (p less than 0.05) and in eight subjects with only small airways dysfunction, the Pa02 decreased by 14 mm Hg (p less than 0.0001). The alveolar-arterial oxygen gradient on oxygen increased by only 11 mm Hg indicating that the decrease in room air Pao2 was primarily due to worsening ventilation-perfusion mismatch and not to an increase in shunt. Thirteen subjects with advanced obstructive or restrictive lung disease experienced a much lesser decrease in Pao2 of 4 mm Hg. Data are presented on xenon perfusion studies of a dog model of unilateral alveolar hypoxia that suggest the worsening ventilation-perfusion ratio seen in the human subjects after the administration of nitroglycerin could be due to loss of the lung's ability to vasoconstrict in regions of alveolar hypoxia and shift perfusion to better ventilated regions of the lung.

Adult↗
PubMed1978

Testing in vitro of an indirect mutagen (cyclophosphamide) with human leukocyte cultures: Activation by liver perfusion and by incubation with crude liver homogenate.

The indirect mutagen cyclophosphamide was tested in human whole blood cultures with respect to chromosome-breaking activities and suppression of mitotic indices after activation by liver perfusion and crude liver homogenates with and without cofactors. Both methods produced nearly the same effects, with the exception of liver homogenate without cofactors which had only weak metabolic activities.

Animals↗
PubMed1978

[Infected median and lateral neck cysts and fistulas].

During the last 10 years, 50 patients with congenital anomalies of the neck were treated in the Hospital for Oral and Plastic Surgery in Düsseldorf. Acute or chronic infection was observed in one third of the median and lateral cervical cysts and all cervical fistulas. Most of the cysts and fistulas were not diagnosed or considered in the differential diagnosis at the time of referral. The most frequent false diagnoses were: odontogenous abcess, odontogenous fistula, phlegmon of the floor of the mouth, specific lymphoma, abcess of the lymph node.

Adolescent↗
PubMed1978

[Infected dermoid and epidermoid cysts in the maxillofacial region. Differential diagnosis and therapy].

More than 30% of the patients with dermoid and epidermoid cysts treated on an in-patient basis during the last 10 years in the Düsseldorf Hospital for Jaw and Plastic Surgery showed symptoms of acute or chronic inflammation. The difficulties involved in the clinical diagnosis of infected dermoid or epidermoid cysts were illustrated by example cases. Infected dermoid and epidermoid cysts may be mistaken for ondontogenous abscesses, infected atheromas, furuncles, superinfected tumors, and specific inflammations.

Abscess↗
PubMed1977

Sinuscopy for the diagnosis of blow-out fractures.

Between 1973 and 1976 thirty-one patients with the symptoms of a blow-out fracture underwent sinuscopy. In all these cases a precise diagnosis was not possible from the clinical and x-ray findings alone without exploratory surgery. In 28 cases an exact diagnosis could be made using sinuscopy; 21 patients with blow-out fractures underwent reconstructive surgery to the orbital floor. In the remaining 7 cases fracture of the orbital floor was ruled out and the patients were spared more extensive diagnostic procedures. In 3 cases the diagnosis of a fracture could not be definitely established. Exploratory surgery of the orbital floor showed blow-out fractures which needed treatment. These findings were photographed; 5 typical photographs of fractures are presented. Sinuscopy provides a simple and sure method in the diagnosis of blow-out fractures. Its early application is recommended in cases of suspected fractures of the orbital floor, since reconstructive surgery of blow-out fractures yields the best functional results when performed within 2 weeks after the accident.

Adolescent↗