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Biomedical subjects

A Uhlig

Publications and source records attributed to A Uhlig.

14 recordsLinked to original sources
PubMed2001

Pseudoaneurysm complicating homograft aortic valve replacement--two different--courses and strategies.

The courses of two patients with pseudoaneurysm formation following aortic valve replacement using homografts are reported. Both patients had aortic valve replacement due to acute infective endocarditis with paravalvular abscess formation. The first case had an uneventful postoperative course; but on routine echocardiography, a pseudoaneurysm located at the left coronary commissure was found at one year follow-up. As the pseudoaneurysm was completely asymptomatic, the patient was followed up carefully at six months intervals. The second patient also had pseudoaneurysm formation postoperatively, but he presented one year after surgery with fever and elevated leucocyte count. He had surgical revision of the pseudoaneurysm because no other reason for an infection could be found. Four months later he presented again with infection signs and pseudoaneurysm formation. This time, the homograft was completely excised and another homograft was implanted. One year after the final operation, he is now free from re-infection. The two presented courses show that pseudoaneurysms complicating aortic valve replacement should be managed according to attendant circumstances and symptoms.

Adult↗
PubMed2000

Mitral valve surgery utilizing homografts: early results.

BACKGROUND AND AIM OF THE STUDY: Mitral valve repair is superior to prosthetic valve replacement due to preservation of the subvalvular apparatus. We used cryopreserved homografts for mitral valve replacement in selected cases, in whom valve repair would not have been successful. METHODS: Cryopreserved homografts were used in 10 patients (four males, six females; mean age 47 +/- 8 years; range: 27-65 years), for either complete (n = 7) or partial (n = 3) mitral valve replacement. Surgery was indicated due to acute endocarditis (n = 3), stenosis (n = 4) or combined mitral valve disease (n = 3). Transesophageal echocardiography (TEE) was performed to determine correct homograft size; these values were compared with intraoperative measurements of valvular dimensions. The function of the implanted grafts was examined intraoperatively by TEE. Follow up included clinical examination, electrocardiography and echocardiography. RESULTS: All patients survived surgery. Intraoperative TEE revealed mild insufficiency (grade I) in six cases and no insufficiency in four. The papillary muscle-mitral annulus distance was the most reliable preoperative echocardiographic parameter to determine the required homograft. Mean pressure gradients were 3.2 +/- 0.7 mmHg for complete and 2.4 +/- 0.5 mmHg for partial homograft replacement. Sinus rhythm was present in all cases at discharge. Mean follow up was 24 months (range: 6-36 months). At six-month and one-year follow up, the pressure gradients had risen slightly to 3.4 +/- 0.6 mmHg (complete) and 2.8 +/- 0.6 mmHg (partial). To date, four patients had competent grafts, and six presented with an insufficiency (grade I). All patients had normal left ventricular function (EF 65 +/- 6%) at their last follow up; there were no signs of endocarditis during the follow up period. CONCLUSION: Mitral homografts for valve replacement or repair are recommended in selected cases in whom conservative reconstruction techniques are not possible. The avoidance of long-term anticoagulation therapy and preservation of left ventricular geometry are clear advantages to other mitral valve prostheses.

Adult↗
PubMed1999

[Homografts for mitral valve replacement in florid endocarditis--an alternative to prosthetic replacement].

INTRODUCTION: Homografts for valve replacement are indicated in acute valve endocarditis. It is assumed that they possess anti-infective properties. Homografts are an established indication in aortic valve replacement. We present our early results with homografts for mitral valve replacement in acute endocarditis. PATIENTS AND METHODS: Between July 1996 and March 1998 we used cryopreserved homografts for mitral valve replacement in seven patients. In three cases (age 24, 42, and 34 years) the indication was an acute endocarditis with subsequent severe mitral valve insufficiency. The size of the required homograft was measured preoperatively using transesophageal echocardiography. For implantation the technique described by A. Carpentier was used; for stabilization of the mitral anulus a valvular ring (Physio) was implanted. Follow-up was done every six months including clinical and echocardiographical examinations. After the first postoperative year an Ultrafast-CT was done in addition. RESULTS: One patient had complete mitral valve replacement, in the other two cases the diseased parts of the valve were completely excised and the valve was repaired using a partial homograft. There were no perioperative deaths. In the follow-ups, up to 24 months of uneventful homograft function was documented by echocardiography; no insufficiency > degree I was seen on color Doppler echocardiography. At the last follow-up (mean follow-up 16 months, range 12 to 24 months) the average mitral valve orifice was 2.5 +/- 0.5 cm2, the mean pressure gradient 2.8 +/- 0.8 mm Hg. In Ultrafast-CT no morphological abnormalities of the mitral valves and no dilatation of the left ventricle were seen. There were no signs of a recurrence of the endocarditis in any patient during the follow-up period. CONCLUSION: Homografts for mitral valve replacement are an interesting alternative to prosthetic valve replacement, especially in younger patients. In cases with acute endocarditis, in which mechanical prosthesis should not be used, a reconstruction or repair of the mitral valve with preservation of the ventricular geometry is possible even if large parts of the mitral valve are infected.

Adult↗
PubMed1997

Miniaturized ion-selective chip electrode for sensor application.

The performance of miniaturized potentiometric cells, with multilayer, planar ion-selective sensors in aqueous electrolyte solutions, human serum, urine, and whole blood, is presented. The basic steps of the fabrication with silicon technology are summarized. The effect of the contact surface between the internal reference system and the ion-sensitive membrane on the analytical characteristics of potassium- and calcium-sensitive sensors is studied. Silicone rubber-, high molecular weight PVC-, carboxylated PVC and aliphatic polyurethane (Tecoflex)-based solvent polymeric membranes were dispensed into anisotropically etched wells on silicon wafers, and the resulted planar sensors were tested in terms of their ion sensitivity (slopes of the cell voltage-pK or pCa calibration curves), long-term stability, and reproducibility. For the assay of potassium in whole blood, the miniaturized potentiometric cell was built in a flow-through manifold. To achieve the required precision, the flow conditions were optimized and the sensors calibrated periodically. The results prove the feasibility of the new sensor design and satisfy the particularly difficult requirements for the analysis of biological samples.

Biosensing Techniques↗
PubMed1997

Microbiosensors using electrodes made in Si-technology.

The combination of electrochemical transducers made in silicon technology with chemical and biochemical components has been used to manufacture miniaturized sensor structures. Three different types of sensors have been developed and optimized for practical use; (i) an ion-selective sensor, (ii) a glucose enzyme sensor, (iii) a redox-amplifying sensor for immunosensing. The immunodetection based on the redox recycling of mediator molecules is shown for low and high molecular weight analytes. The sensors have been integrated with miniaturized fluidic components and combined with sensor-related electronics and a common microcontroller.

Antigen-Antibody Complex↗
PubMed1995

Immunologic reaction and viability of cryopreserved homografts.

Homograft cell viability after cryopreservation was investigated and cytoimmunologic monitoring was performed during the early postoperative course to research possible immunologic reactions after allograft aortic valve replacement. After cryopreservation, morphologic observations were made, a nonradioactive cell proliferation assay was used, and prostaglandin I2 secretion of the remaining endothelial cells was determined. Cytoimmunologic monitoring was performed daily within the first 3 weeks postoperatively. An increase of the activation index greater than 1 was rated as an immunologic reaction. Maintained metabolic activity of graft endothelial cells after cryopreservation was confirmed by prostaglandin I2 release (9.24 +/- 3.48 ng/cm2 basic release and 20.1 +/- 5.76 ng/cm2 when stimulated with 25 mumol/L Na arachidonic acid). Cell proliferation was indicated after graft incubation with the nonradioactive viability kit (0.27 +/- 0.9 at 450 nm). Cytoimmunologic examinations (n = 861) after homograft implantation showed a more intense activation in patients with ABO-incompatible grafts (activation index 2.1 +/- 1.6, n = 16) than in those with ABO-compatible grafts (activation index 1.3 +/- 0.8, n = 17). In these groups, the duration of activation by cytoimmunologic monitoring was 2.8 +/- 1.5 days and 1.3 +/- 0.6 days, respectively (p < 0.041). No activation was observed in 8 patients after xenograft valve replacement (p < 0.01). Our data indicate that cryopreservation of homograft valves represents a cell- and tissue-protective preservation method. Postoperatively, all homograft valves caused immunologic reactions, which were reversible without immunosuppression treatment.

ABO Blood-Group System↗
PubMed1994

Cytoimmunological monitoring after homograft valve replacement.

Examination results concerning immunological reactions in cryopreserved allograft valves during the early postoperative course are so far not available. Cytoimmunological monitoring (CIM) is a well established method to prove rejection reaction after allograft transplantation and was used in this study. Allograft valves were harvested from patients who underwent heart transplantation, and did not require sterilizing in antibiotic solutions. The valves were dissected, conserved and subsequently frozen to -40 degrees C and stored in a freezing system at -196 degrees C. During the first 3 weeks following allograft implantation, CIM was performed daily. An activation index (AI) was determined from the cytological evaluation of the mononuclear concentrate in the peripheral blood. An increase of the AI > 1 was defined as an immunological reaction. As control we performed 98 CIM examinations in eight patients who underwent bioprosthetic valve replacement in the aortic position. Echocardiography (TTE and TEE) was used postoperatively as function control. Out of 16 patients who underwent cryopreserved aortic valve implantation in the aortic position, 336 CIM-results were obtained. An immunological reaction could be detected in all patients, starting on the 5th day on average. Comparing ABO-compatible (group I, n = 9) with ABO-incompatible (group II, n = 7) allografts, the AI-maximum in group I was 1.4 with a mean duration of 1.5 days. Group II was characterized by more intensive immunoreactions (mean = 2.3) which proved to be even more prolonged (mean = 3.3 days, P < 0.05). Nevertheless it became apparent that all observed immunological events were completely reversible without the need for immunosuppressive drugs.(ABSTRACT TRUNCATED AT 250 WORDS)

ABO Blood-Group System↗
PubMed1994

Integrity and viability of homograft valves.

Since it has been suggested that the leaflet tissue viability influences durability after homologous valve replacement, we compared different harvest and preservation techniques in order to examine the quality and smoothness of homograft conservation. We analyzed human aortic and pulmonary valve leaflets obtained from 'heart-beating donors' (HBD) during heart transplantation and from 'non-heart-beating donors' (NHBD) during coroner's autopsies. Valves were either cryopreserved in liquid nitrogen or stored at 4 degrees C in nutrient medium similar to the procedure reported in our protocols of the homograft bank system. All grafts from NHBD had been antibiotically sterilized for 3 days beforehand. Morphological observations were made using light and electron microscopy and, in order to characterize the endothelial cell viability, a non-radioactive cell proliferation assay was used. The PGI2 secretion of the remaining endothelium was defined as the 6-keto-prostaglandin F1 alpha metabolite by an enzyme immunoassay. Observations in the scanning electron microscope revealed that, after cryopreservation, homografts show an almost confluent endothelium when processed within 24 h after harvest from HBD, but lack endothelial cells when obtained from NHBD. Cryopreserved grafts from NHBD exhibited an altered tissue structure with edema and vacuolization within the spongiosa of the leaflets as well as irreversible cell damage when examined under the light and transmission electron microscope. That the metabolic activity of HBD homografts was maintained was confirmed by proven PGI2 secretion (6150 +/- 1200 pg/3 ml M199 after cryopreservation), whereas specimens from NHBD showed a reduced (1950 +/- 730 pg/3 ml M199) and, after cryopreservation, almost no release (P < 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

[Clinical forms of enzootic pneumonia in calves and their effects on respiration].

Enzootic pneumonia was diagnosed in 160 of 225 bullocks in a livestock fattening unit. Within the first 10 weeks, 51 of those affected contracted the disease a second time after the symptoms had vanished. Acute catarrhal bronchopneumonia were most common (49.3%) during the first outbreak, whereas acute catarrhal purulent bronchopneumonia (39.2%) and chronic pneumonia (29.4%) were most common during the second. Arterial blood gas analysis was undertaken for 33 clinically healthy bullocks and 100 bullocks with clinically diagnosed acute bronchitis, acute catarrhal bronchopneumonia, acute catarrhal purulent bronchopneumonia and chronic pneumonia. The pO2, SATO2 and A-aDO2 levels found in blood from the abdominal aorta of all diseased animals differed significantly from those of healthy animals. The values for animals with distinct catarrhal bronchopneumonia and catarrhal purulent bronchopneumonia showed the greatest differences.

Animals↗