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Biomedical subjects

W Trubel

Publications and source records attributed to W Trubel.

At least 37 records · Page 2Linked to original sources
PubMed1994

Changes following in vitro endothelial cell lining of ePTFE prostheses: late morphologic evaluation of six failed grafts.

This paper describes the morphologic appearance during long term follow-up of in vitro endothelialised ePTFE grafts (IVECL) implanted in patients with crural reocclusions. Between June 1989 and December 1990, 13 femorocrural IVECL bypasses were implanted. Follow-up angiograms demonstrated stenoses in the middle of the graft in six patients. Two of these patients developed symptoms, and the grafts were biopsied approximately 1.5 years after implantation during a patchplasty procedure. The remaining four patients with asymptomatic stenoses refused elective reoperation and suffered a graft occlusion 53 to 619 days after implantation, all leading to amputation. Biopsy specimens and explanted grafts were examined with standard and electron microscopy. Both biopsies demonstrated multiple layers of degenerating myofibroblasts (MFB). The four explanted grafts also showed altered MFB in addition to necrosis of the graft surface. No endothelial cells were seen on any of the preparations. Long term follow up of IVECL protheses in the crural position has demonstrated that it is possible to lastingly bind cells on an artificial surface. Whether the MFB found are a substitute of lost endothelial cells, or are an end product of metaplastic and/or degenerative alterations, can only be clarified through further biopsy studies.

Arterial Occlusive Diseases↗
PubMed1994

Intraoperative control following femorodistal revascularization: angioscopy is superior to angiography.

Intraoperative angioscopic control was performed in an early series of 27 patients undergoing peripheral vascular surgery. The majority were complex or re-do operations; reversed saphenous vein and PTFE-grafts were used as bypass material exclusively. Angioscopic findings were compared to conventional angiography with respect to the detection of technical problems leading to further surgical procedures. Angioscopy was feasable in 92.5%, it failed twice due to irrigation problems, which was before we used a dedicated angioscopy roller-pump. In 6 patients relevant findings requiring further surgical manipulations were only detected angioscopically, in 2 patients such findings were detected by angioscopy as well as by angiography. Such findings included technical problems (graft rotation [n = 1], anastomotic narrowing [n = 2]), balloon catheter injuries after thromboembolectomy (n = 2) and residual thrombi after local thrombectomy (n = 3); 5 of these patients had undergone previous vascular procedures in the same operation field. After local correction (n = 5) or placement of a new bypass (n = 3) there was no early graft failure. This early angioscopic experience confirmed previous reports that satisfactory visualization and specific recognition of angiographically unsuspected problems after peripheral reconstructions can be obtained by intraoperative angioscopic control. This was seen very distinctively in more complex and re-do operations, which we see as the cases most needing routine angioscopic control.

Aged↗
PubMed1994

The Vienna implantable centrifugal blood pump.

Because of the inherent disadvantages of membrane pumps, rotary pumps have been increasingly investigated in recent years. As a result of improving biocompatibility, extended assistance with implantable devices is of special interest. Questions arise concerning shear stress, blood traumatization, design of seals, and specific control conditions. In their development of an implantable impeller pump, the Vienna group studied the minimization of hemolysis and thrombus formation by means of numerical simulation, visualization, and in vitro blood evaluation. The latter was revealed to be the most powerful tool for pump evaluation. With optimization of geometry, a hemolysis of in vitro: IH = 0.008; MIH = 0.58; and in vivo: 2.1 to 3 mg% plasma-free hemoglobin could be obtained. For proper control and physiological adaptation, a controller based on a nonlinear and a fuzzy strategy was developed. Furthermore, a method for evaluation of the contractility of the assisted heart during nonpulsatile support was tested by computer simulation. This paper summarizes the evaluation methods used and provide an overview of the results of pump and controller design.

Animals↗
PubMed1994

Cardioprotection by nifedipine cardioplegia during coronary artery surgery.

In a double-blind, placebo-controlled, randomized clinical study, the cardioprotective effect of nifedipine (Adalat, Bayer) as an adjunct to St. Thomas' cardioplegia was investigated in 24 patients undergoing coronary artery bypass grafting. Nifedipine at a dosage of 200 micrograms or placebo was added to each 1000 ml of St. Thomas solution, under strict light protection. ECG and haemodynamic data, including cardiac output measurements, serum calcium levels, creatine phosphokinase, (CK) CK-MB and lactate were measured during and after the operation. Additional cardioprotective effects were demonstrated in the nifedipine group by a significantly lesser reduction of the cardiac index after cardiopulmonary bypass and lower post-operative CK and CK-MB serum levels (P < 0.05). The incidence of ischaemia and cardiac arrhythmias was significantly higher in the placebo group on the post-operative ECG.

Arrhythmias, Cardiac↗
PubMed1993

Minimization of hemolysis in centrifugal blood pumps: influence of different geometries.

Centrifugal blood pumps are of substantial importance for intraoperative extracorporeal circulation and for temporary cardiac assist. Their development and improvement raises many specific questions, especially on mechanical blood properties, flow distribution, and the resulting biocompatibility. In this comprehensive study the influence of various pump geometries on blood trauma was investigated. For this purpose analytical calculations, hydrodynamic performance, numerical simulation, in vitro hemolysis tests and in vivo experiments were used. The gap between rotor and housing was found to be crucial showing a distinct minimum of hemolysis at a gap of 1.5 mm (in vitro increase of plasma free hemoglobin per 100 ml plasma an hour: delta fHb/hour = 2.4 +/- 0.83 mg%/h at 1.5 mm versus 12 +/- 2.2 mg%/h at 2.5 mm; p < 0.05). Housing diameter and shape of the vanes were of less importance for blood traumatization (d = 60 mm: delta fHb/hour = 6.36 +/- 1.8 mg%/h; d = 70 mm: fHb = 7.1 +/- 1.9 mg%/h; straight radial vanes: 5.2 +/- 1.8 mg%/h; straight inclined vanes: 6.8 +/- 1.2 mg%/h; flexed vanes: 6.1 +/- 2.0 mg%/h). Three animal experiments confirmed the optimization of geometry, with a mean fHb of 2.5 to 3.2 mg% in steady state. Hydrodynamic efficiency revealed to be a necessary, but not a sufficient and sensitive criterion for hemolysis minimization (e.g. changes of eta < 10% for changes of fHb > 500%). Numerical simulation gives an improved insight in flow distribution, but can not yet be applied for quantification of blood trauma.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

[Aneurysma spurium after iatrogenic arterial puncture--incidence, risk factors and surgical therapy].

Due to the markedly increased number of arterial punctures performed during diagnostic angiography and angioplasty procedures for cardiac and peripheral vessel disease, the complication of false aneurysms after arterial puncture has gained increasing significance. The incidence of false aneurysms after puncture reported in the literature ranges from 0.05-2%. However, careful sonographic follow-up may reveal an incidence twice as high. The goal of this retrospective investigation of 28 patients with false aneurysms was to elucidate risk factors leading to failure of spontaneous closure of the arterial site, as well as to examine the symptoms and clinical course of such patients. Pseudoaneurysms became manifest, depending on the method of puncture, on average 16.4 days after the procedure. The highest risk was seen in adipose patients (18 pts., 64.3%). In these patients the number of tangential and multiple vessel punctures was also highest. Further risk factors were local vessel sclerosis, hypertension, diabetes mellitus, poor general condition, and disturbances of blood coagulation. The typical clinical findings were seen in only 13 patients. In 3 patients blood loss was the predominant symptom. Twelve further pseudoaneurysms (42.8%) were found incidentally at follow-up. The diagnosis was made in all patients sonographically. In 1 patient it was initially identified as an incidental finding at angiography. In 25 cases simple vessel reconstruction was possible (stitch or patch). In 3 cases (10.7%) a more extensive procedure involving vessel replacement was necessary. Severe postoperative complications included local infection (in 2 patients, 1 of whom also had a recurrent false aneurysm) and arterial bleeding necessitating surgical intervention (1 patient).(ABSTRACT TRUNCATED AT 250 WORDS)

Aneurysm, False↗
PubMed1992

The use of mesh-tube-constricted dilated or varicose veins as arterial bypass conduit.

In general, dilated and varicose veins are not used as arterial bypass grafts despite their physiological endothelial lining. A uniform small diameter may be achieved by inserting such veins into mesh tubes. To test the degree to which dilated veins can be constricted without forming folds, in-vitro and experimental investigations were performed before such composites were used for clinical reconstructive surgery. Ovine jugular veins with a diameter of 15 mm were inserted into 6 mm tubes. After casting in paraffin wax none of the specimens showed folds on the flow surface. In 12 sheep pairs of mesh-constricted jugular veins and native femoral veins were implanted as femoropopliteal bypass grafts. Six animals were killed at 6 months and 6 at one year. All bypasses remained patent and none showed signs of obstruction caused by folds or anastomotic hyperplasia at angiographic control. Intimal hyperplasia was significantly reduced from 416 +/- 143 microns in the midportion of native vein grafts to 231 +/- 76 microns (p = 0.0001 paired t-test) in constricted veins as well as at the anastomoses (358 +/- 256 microns vs. 180 +/- 73 microns; p = 0.008). Partially or totally mesh-tube-constricted varicose veins were used for infrainguinal reconstructions in 19 patients and for coronary revascularization in 3. All grafts showed an even calibration at control angiography. As constriction does not lead to internal folds, varicose or dilated veins may be used successfully as bypass grafts after insertion into mesh tubes. The external reinforcement reduces the intimal hyperplasia within the graft and also reduces anastomotic hyperplasia.

Aged↗
PubMed1992

Noninvasive monitoring of rotary blood pumps: necessity, possibilities, and limitations.

Although rotary blood pumps do not contain an inherent mechanism for adaptation to physiological flow necessities, hitherto only a few efforts have been made to obtain robust monitoring and control methods. This paper discusses the necessity of noninvasive monitoring of such pumps and the crucial points of sensor selection and development. A strategy of monitoring atrial pressure out of the data obtained by the collapse of the atrial wall around the inflow cannula and initial results on animal tests and computer simulation of this method are discussed. This approach might lead to reliable and demand-responsive controllers, if some basic criteria are fulfilled.

Atrial Function↗
PubMed1992

Diminished release of atrial natriuretic factor in calves with a total artificial heart.

Venous hypertension after total artificial heart (TAH) replacement, a common problem in humans as well as experimental animals, is thought to be related to reduced release of atrial natriuretic factor (ANF) due to atrial damage. To verify this hypothesis, we stimulated the release of ANF in 6 calves before (-7 days) and after TAH replacement (+25, +50, +80, and +100 days) by the rapid (+ = 10 min) infusion of 2 L of Ringer's solution. In normal calves (-7 days) this procedure induced a rise in plasma concentration of ANF from 18.5 +/- 12 to 31.6 +/- 12 pmol/L (p < 0.05). After TAH the ANF release continuously decreased (analysis of variance, p < 0.02). Thus, ANF increased by 9.8 +/- 9.3, 6.8 +/- 17.5, 0.4 +/- 5.2, and 0.5 +/- 3.2 pmol/L at days 25, 50, 80, and 100, respectively. The central venous pressure increased by 3.4 +/- 1.5 mm Hg (before TAH) and by 6 +/- 2.9 mm Hg (after TAH) during this procedure. A decrease in plasma concentrations of aldosterone, most likely due to extracellular volume expansion and a decrease in total protein plasma concentrations and in hematocrit due to the dilution of blood, was seen in each experiment. Necropsy demonstrated massive atrial dilatation and myocardial dystrophy with atrial fibrosis. ANF granules were present to a small extent in every calf. We conclude that rapid intravenous infusion is an adequate stimulus to release ANF in normal calves. After TAH implantation the release of ANF by high venous pressure declines although ANF granules are still present in the damaged atrial stumps. Therefore, the loss of stimulated ANF could contribute to the observed increase in venous pressure in TAH calves although other pathophysiologic mechanisms cannot be excluded.

Aldosterone↗
PubMed1991

Prosthetic bypass and flow reversal in the dissecting thoraco-abdominal aortic aneurysm.

In 1981 Carpentier and Co-workers introduced an alternative surgical procedure for great dissecting thoraco-abdominal aortic aneurysms, departing from the resection and the orthotopic implantation of a prosthesis (graft inclusion technique). Compression of the aneurysmatic false lumen from the inside under stepwise thrombosis of the aneurysmal sac with conservation of the main arterial origins was achieved by prosthetic bypass of the diseased vascular part and a flow reversal in the dissected aortic region by an oblique suture across the aortic lumen after the origin of the left subclavian artery. This procedure, distinguished by rather little effort and few complications (bleeding, ischaemic spinal cord damage) is described for all stages of dissecting thoracal aortic aneurysms. In the last 2 years this operation was performed in our department on 4 patients (1 m. 3 f) suffering from an acute dissecting thoraco-abdominal aortic aneurysm (Stanford type B). 2 patients died in the early postoperative period, one from a redissection close to the proximal anastomosis, the other due to the critical cardiac situation. 2 patients could be followed up postoperatively 10 and 27 months. In both cases no signs of minor perfusion of the spinal cord, the kidneys, or the mesenterial organs were observed. In both cases a partial thrombosis of the aneurysmal sac with intact blood stream to the major vessels in these regions could be demonstrated by sonography, angiography or DSA, and computer tomography. The concept of flow reversal proved to be an alternative to major resection procedures.

Aged↗
PubMed1991

The new small Viennese total artificial heart: experimental and first clinical experiences.

For bridging to transplantation, a new small total artificial heart (TAH) design has been developed. Function of the two membrane pumps (filling volume left: 87 ml, and right: 75 ml; four mechanical disc valves and screwed connectors) for orthotopic implantation were studied in calf experiments. A calf survival up to 180 days was achieved without problems by pumping with a rate of 117 +/- 2.4 beats/min and a cardiac output of 7.4 +/- 0.7 L/min. For bridging to transplantation, the New Small Viennese TAH was implanted into a small 45-year-old patient (height 160 cm, weight 75 kg) with end-stage coronary heart disease. The patient deteriorated suddenly [mean aortic pressure: 38 mm Hg; cardiac output (CO): 1.8-2.1 L/min; anuria and multiple organ failure] while waiting for a donor heart. Even though his pericardial space was not enlarged, no fitting problems appeared. By using pumping rates of 104.3 +/- 8.7 beats/min, a cardiac output of 5.8 +/- 0.63 L/min was achieved (free hemoglobin was 4.1 +/- 0.48 mg/dl). Even though blood circulation was reestablished, after a TAH duration of 12 days, multiple organ failure persisted, and TAH bridging had to be stopped. In November 1989, a 50-year-old deteriorating transplant candidate with idiopathic cardiomyopathy was bridged for 6 days. Adjusting the heart rate to 86.5 +/- 11.2 beats/min, a CO of 6.84 +/- 0.46 L/min was achieved (free hemoglobin was 5.9 +/- 1.7 mg/dl). Because of chronic liver dysfunction, the patient developed severe icterus while on the TAH, and it took 2 months after heart transplantation to achieve physiological bilirubin concentrations. The patient recovered fully and remains in excellent condition.

Animals↗
PubMed1991

Timing for implantation and transplantation in mechanical bridge to transplantation.

The implantation of a mechanical blood pump in a deteriorating candidate for heart transplantation is indicated in general if the cardiac index is less than 1.9 L/min/m2 despite maximal inotropic support. Deterioration of end organ function may be taken as a second factor indicating the need for mechanical support as patients with acute onset of shock may react differently from patients with chronic deterioration. Preoperative need for dialysis largely reduces the chances of long-term survival. The time on support should be long enough to normalize or at least improve secondarily damaged organ systems, but with time infectious and thromboembolic complications will increase. So optimal periods for artificial heart support range between two days and four weeks. Age less than 40 years is a positive predictor for outcome in TAH bridging. The general guidelines, however, do not preclude a favourable outcome in complicated cases, as we show in our own series.

Adult↗