Search PubMed⌕ Search

Biomedical subjects

U Losert

Publications and source records attributed to U Losert.

At least 91 records · Page 5Linked to original sources
PubMed1982

[Improved myocardial protection in open heart surgery by massive preoperative insulin supply (author's transl)].

In this study we investigated, whether in addition to cooling and cardioplegia, preventive administration of massive doses of insulin with glucose exerts a protective effect on the myocardium by increasing myocardial glycogen stores and shifting myocardial metabolism towards (primarily anaerobic) glycolysis. Experiments were done on two groups of 5 dogs each (average 27 kg) undergoing experimental extracorporeal circulation (ECC) with 90 min aortic clamping, under cooling and cardioplegia. Cardiac output (CO), systolic ventricular blood pressure (Pventr), heart rate (HR) and mean central venous pressure (CVP) were recorded at LA-levels of 5, 10, 15 and 20 mm Hg before onset of ECC (preop. value), after termination of ECC, and after 2 periods of a 10 min. reperfusion. While the 1st group served as control, the 2nd group received a massive i.v. insulin supply (total 20 U/kg) every 10 min, as well as glucose to keep blood sugar level stable within 60 min. prior to the onset of ECC. It was shown that in the control group after termination of ECC and after 1st reperfusion Pventr and CO were significantly below the preop. values, and only after the 2nd reperfusion within the preop. range. In the insulin group, however, Pventr and CO were already within the preop. range at termination of the ECC. After the 1st and after the 2nd reperfusion CO was in part significantly above the preoperative value. HR and total peripheral resistance (TPR) were not significantly changed. It is concluded that preventive insulin application produces a more vital myocardial cell function immediately after termination of ECC, indicating increased myocardial protection and improved ischaemic tolerance.

Animals↗
PubMed1981

[Measuring intratracheal pressure in sheep fetuses in utero].

In pregnant sheep between the 100th and 138th gestational day the fetal tracheal pressure was measured in utero. For this purpose the uterus was opened and catheters inserted into the trachea and also into the amniotic sac. The average values of the intratracheal pressure during resting periods of the fetus were 9.8 +/- 1.2 mm Hg (1.3 +/- 0.135 kPa). During long periods only maximal pressure changes of 2 mmHg (0.26 kPa) without any greater alterations in pressure were seen, displaying a pressure gradient of 5.3 mmHg (0.7 kPa) between trachea and amniotic sac. Beside this also phases of stronger breathing excursions were observed, the intratracheal pressures ranging between + 25 mmHg and - 10 mmHg (+ 3.3 kPa, - 1.33 kPa) ("physiological gasps") usually starting with positive pressures. After ligature of the umbilical cord similar breathing excursions could be seen, displaying values as cited above, but mostly starting with negative pressures("pathological gasps"). By a short unique electrical stimulation of the isolated fetal ischiadic nerve, only an unique intratracheal pressure change was seen, ranging between + 25 mmHg and - 8 mmHg.

Animals↗
PubMed1980

Evidence that thrombus organizing blood derived cells produce prostaglandin I2-.

An artificial vessel replacement, which is athrombogenic and impermeable for a migration from the adjacent tissue, was implanted end to end into the thoracic aorta of 10 sheep. The center of this tube has a Dacron surface, which is known to trap blood elements. We examined the tissue samples built up by blood derived cells between 2 and 84 days morphologically by means of light microscopy as well as by SEM and TEM. We checked the thrombus fragments of 7 cases for their PGI2-generation using MONCADA's bioassay. In our specimens we found an average activity of 4, 7 pg PGI2 mg/min. The morphological examination revealed different stages of thrombosis and organization consisting of a large number of cells. Macrophages, fibroblast like cells, myofibroblasts as well as endothelial cells and foreign body giant cells around the Dacron fibers could be found. Our experimental design excludes the ingrowth of mesenchymal elements, which suggests that blood derived cells are able to produce PGI2.

Aging↗
PubMed1979

[The research programme "Artificial Heart" at the 2nd Department of Surgery, University of Vienna: a ten year review (author's transl)].

The experimental and clinical results are presented of the research programme "Artificial Heart" carried out by the 2nd Department of Surgery, University of Vienna. In particular, an assessment of the clinical experience in 177 patients with the intra-aortic balloon pump is documented and it is concluded that only limited cardiac support is possible by this pump. In view of this fact more efficient methods of mechanical circulatory support, such as the interaortic auxilliary ventricle, the aortic "Windkessel" ventricle with guiding balloon, and two types of ventriculo-aortic bypass ventricle were tested with regard to their haemodynamic and long-time efficacy. The transatrio-aortic auxilliary ventricle (E-LVAD) was also clinically tested in 11 patients. In conclusion the problems of total mechanical heart replacement are discussed.

Animals↗
PubMed1978

Clinical application of the ellipsoid left heart assist device.

The ellipsoid left heart assist device (E-LVAD) was implanted in eight patients suffering from intraoperative heart failure. It was not possible to remove these patients from extracorporeal circulation following an intracardiac procedure; therefore, implantation of the E-LVAD was performed during extracorporeal circulation. The inflow connector was pushed forward from a purse-string suture on the right superior pulmonary vein, across the mitral valve and into the left ventricle. The outflow connector was joined to the ascending aorta. In two patients, the artificial heart chamber was removed after complete recovery of the circulation; these patients, however, later died. In six other patients, untreatable right heart failure developed and these patients died with the pump in place. It is concluded, therefore, that the right heart must also be mechanically supported during postoperative heart failure.

Adult↗
PubMed1976

[A new design for a totally artificial heart: the ellipsoid heart (author's transl)].

Thromboembolic complications represent the main limiting factor in cardiac replacement by totally artificial hearts in calves at present. Thrombus formation within artificial hearts is caused by the appearance of stagnation areas. The ellipsoid heart eliminates stagnation areas by virtue of its production as a one-piece membrane. The heart is driven pneumatically and functions as a diaphragmatic blood pump. The stroke volume is 178 cm3 and the maximal cardiac output 15.8l/Min. Three acute experiments demonstrated a high degree of haemodynamic efficiency without compression of, or interference with surrounding structures, especially the inferior vena cava or the right atrium.

Animals↗
PubMed1976

[On the application of electric stimulation currents in operations. Concept of a clinically applicable device (author's transl)].

With the use of high voltage electric currents in patients who initally have been anaesthetised, the anaesthesiologist faces new aspects. For this reason basic principles of physical medicine and medical engineering with respect to special problems are described. The majority of impulses current generators used so far do not even comply with the first principal requirement of any therapy namely knowledge of the dose of the agent applied. A system for electric currents crossing the body is outlined, which is characterized by constant current and isovoltage-free outlets in connection with a special ECG-amplifier and a control pattern. This apparatus for the first time guarantees maximal safety in clinical use. First animal experiments demonstrate the possibility of the risk if this method is applied in a inexperienced manner: in all animals ventricular fibrillation could be achieved when the electrodes were used in a position near the heart and there appeared to occur nonspecific reactions when current was directed through the brain (ear acupuncture)

Acupuncture Therapy↗
PubMed1975

[Partial replacement of the heart].

A ventricular-aortic blood pump was constructed for the functional replacement of the left heart. Hemodynamic experiments showed that the device was able to pump the total cardiac output in calves with a body weight under 85 kg. In these cases the myocardial oxygen consumption decreased to 40%. Laboratory findings in 5 longterm experiments revealed a complete adaptation of the body to the artificial organ up to 73 days.

Animals↗
PubMedDate not supplied

Sustained heart failure induced by repeated microsphere injections for left ventricular assist device testing.

A subacute to chronic heart failure model was established to test left ventricular assist device (LVAD) systems. Five calves were anesthetized and instrumented. Heart failure was induced by daily injection of polystyrene microspheres (37-70 microns) into a left coronary catheter. The last three animals had an atrio-aortic pulsatile LVAD implanted. Cardiac output (CO) decreased from 12 to 5.5 L/min, and SV from 120 to 60 ml, whereas left atrial pressure (LAP) increased from 12 to 25 mmHg within 10 to 20 days in the two animals without LVAD support. Both animals stopped eating and drinking. The LVAD experiments were terminated after 5, 10, and 11 days. Cardiac function was determined during daily pump-off tests. After repeated microsphere injections, LAP increased to 30 and 50 mmHg, and CO decreased to 4 and 6 L/min without pump support. Daily stepwise microsphere injections induce a sclerotic cardiomyopathy in a safe and reliable manner.

Animals↗
PubMedDate not supplied

Effect of stationary guiding vanes on improvement of the washout behind the rotor in centrifugal blood pumps.

In centrifugal pumps, there always exists an area of stagnation between the rear of the rotor and the rear housing wall that promotes thrombus formation around the axle. Some current devices overcome the problem by using holes in the rotor plane, leading to increased hydrodynamic losses and shear stress. In this study, a simple apparatus was developed to overcome this problem. Guiding vanes were fixed to the rear housing wall. These vanes decrease the tangential velocity of the fluid and thus the centrifugal force, leading to an increased secondary flow toward the axle. The effect of such vanes was studied in videographic and ultrasound studies. An increase of washout and mixing between the flow layers could be demonstrated (stay time < 200 msec versus several seconds without vanes). In the first animal experiment using nonoptimized vanes, there was no thrombus at the back plane or the seal, and only a small thrombus at the transition between axle and rotor. Hemolysis was slightly elevated (3.2 mg/dl versus 2.5 mg/dl in control experiments). In conclusion, it is highly likely that this simple system will improve the flow characteristics in centrifugal pumps.

Animals↗
PubMedDate not supplied

Compliance and formation of distal anastomotic intimal hyperplasia in Dacron mesh tube constricted veins used as arterial bypass grafts.

Dilated and varicose veins constricted with a Dacron mesh tube were successfully used as arterial bypass grafts to avoid nonautogenous vascular prostheses. Mesh constriction has also been used to adapt the venous graft lumen to the diameters of grafted arteries. The influence of the external mesh on the wall elasticity of such venous grafts and the reactions of the host artery were not investigated. Elastic properties of mesh constricted autologous veins used as arterial grafts in femoropopliteal reconstructions, as well as consecutive formation of distal anastomotic intimal hyperplasia (DAIH), were investigated in this experiment. Twenty-four autologous venous grafts were implanted in 12 sheep. Grafts were left natural (Groups 1 and 3) or were constricted with an external Dacron mesh (Groups 2 and 4); their diameters were left unchanged (Groups 1 and 2) or were matched to the diameter of the host artery (Groups 3 and 4). Wall elasticity of the graft, distal anastomosis, and distal artery were measured by locally applied crystal transducers during surgery and follow-up. Formation and localization of DAIH was evaluated histomorphologically after a median of 8.3 months. Graft wall elasticity was found to be lower (54.6 vs. 147.9, P = 0.006) and overall DAIH was found to be higher in mesh tube grafts (49.42 vs. 20.8 microns, P = 0.001, Mann-Whitney U-test). No differences in elasticity and DAIH formation were observed between grafts with adapted and large diameters. Constriction of venous grafts by a Dacron mesh tube reduces graft wall elasticity and promotes formation of DAIH. To avoid such an increased mismatch in compliance while making use of the advantages of this method, the external mesh tube must not be brought close to the distal anastomotic area itself.

Anastomosis, Surgical↗