PubMed Health⌕ Search

Biomedical subjects

H Schima

Publications and source records attributed to H Schima.

At least 19 recordsLinked to original sources
PubMed1992

[A measuring device for calculating electrical impedance of the heart in clinical conditions].

Changes in the electrical impedance of tissue can indicate structural changes. This suggests a technique for the noninvasive detection of allograft rejection after heart transplantation. The direct electrical connection to the heart and the application of a measuring current to the myocardium requires a high standard of safety. A device was developed for measuring cardiac impedance using a sinusoidal current of 20 microA at a frequency of 15 kHz. The control logic ensures a slow current onset and also an immediate cessation in case of conductor fracture or excessive voltage. Initial results in patients with normal recovery after heart transplantation revealed a rapid drop in impedance to about 70% of the initial value in the 1st 48 hours and then a stable course. In the sole rejection episode observed so far, the impedance increased again to 85% of the initial value. This paper discusses the technical safety requirements and the design of the device, and presents initial results of clinical examinations.

Cardiography, Impedance↗
PubMed1992

A modular mock circulation for hydromechanical studies on valves, stenoses, vascular grafts and cardiac assist devices.

P6vices for hydrodynamic simulation are required in a variety of studies such as device evaluation, cardiovascular modeling and for student training. Most studies today use different, incompatible circuits, which must be redesigned for every new application. To obtain a universal apparatus, a unitized system with standard connectors was developed. Three types of connectors were selected: 1" flange connectors, 1/2" tubing connectors and Luer-connectors with a 2 mm lumen. The complete system consists of reservoirs, throttles, valve holders, adapters for Doppler ultrasound probes, and converters to link these basic diameters. The apparatus can be driven by membrane, centrifugal and geared pumps. The system has successfully been used in echocardiographic studies of stenosis and valvular insufficiency, for pulse propagation in vascular grafts, and to test the hydraulic performance of cardiac assist devices. Flow rates between 0.1 and 30 l/min and pressure gradients up to 250 mmHg were achieved. In practical use, the system can be adapted to suit various investigations, with minimal expense. Standardization of the parts and connectors results in simple documentation and good reproducibility.

Blood Circulation↗
PubMed1992

Mechanical bridge to transplantation with the Vienna heart in TAH and LVAD configuration.

The Vienna heart uses a vacuum formed, pellethane pulsatile ventricle and is available in left ventricular assist (LVAD) and total artificial heart (TAH) configurations. This device was used as mechanical support of the failing heart in nine patients intended for heart transplantation. In two patients with cardiomyopathy an orthotopic TAH was implanted; one survived despite severe preoperative ischemic liver damage, and the other died of sepsis. In seven patients an atrio-aortic LVAD was implanted; six had suffered an acute myocardial infarction with cardiogenic shock, and one could not be weaned off bypass. Three patients survived. These included one 65-year-old with incipient ARDS at operation, and a 40-year-old with preoperative liver and kidney insufficiency who was transplanted in septicemia. In this patient the septic focus, natural and artificial heart, were removed at transplantation. Four patients died. In one we were unable to establish satisfactory circulation, one died after failure of the transplanted heart, one suffered a lethal cerebral embolism and one developed multi-organ failure after repeated attacks of ventricular fibrillation. With the Vienna heart sufficient circulatory support could be established with cardiac outputs between 6 and 8 l/min for the TAH and 3.5 to 4.5 l/min for the LVAD. With this type of support an overall survival rate of 44% could be achieved. Mechanical hemolysis was not a clinical problem and no device failure occurred.

Cardiomyopathies↗
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↗
PubMed1991

[Successful bridge transplantation with the Vienna artificial heart].

The Vienna Heart, a pulsatile artificial ventricle, vacuum-formed from Pellethane has been used successfully as total artificial heart (TAH) and left ventricular assist device (LVAD) to bridge over patients in terminal heart failure. A 50 year-old patient with cardiomyopathy had to be resuscitated and was transferred in cardiogenic shock, with impaired renal and liver function. 6 days after orthotopic implantation of a Vienna TAH a suitable donor organ was found and the patient was transplanted. 7 weeks later he was discharged and is alive and well now. A 40-year-old patient was transferred in cardiogenic shock 22 days after recurrent anterior infarction. Due to renal failure he was on haemofiltration. Congestive liver failure caused a severe coagulation disorder so a Vienna LVAD was implanted without the use of extracorporeal circulation. Despite development of septicaemia he was transplanted 24 days later. It was thought that either the ventricular thrombus or the LVAD was the septic focus. All consecutive blood cultures have been negative and he was discharged 6 weeks later. To our knowledge, case 1 represents the first successful bridging with a non-Jarvic TAH. The second case shows that sepsis is not necessarily a contraindication to heart transplantation.

Adult↗
PubMed1990

Mechanical simulation of shear stress on the walls of peripheral arteries.

In the last few years many attempts were made to line artificial vascular grafts with in vitro grown endothelial cell layers and thereby to minimize the risk of thromboembolism. However, adherence and resistance against shear stress forces were not tested under physiological pulsatile shear stress forces. In this paper, a mock-circulation apparatus is described, which simulates various forms of pulsatile shear stress, and which at the same time meets the requirements of cell cultivation. It can be sterilized and needs less than 700 ml of culture medium for priming. The generated flow profile can be adapted to a wide range of shear stress and also to different viscosities of used media. To take account of the different viscosities of culture medium and blood, a computerized calculation of the shear stress pattern was performed. Using the results of this computer model, the flow pattern was modified to obtain normal physiological shear stress when using culture medium. Results of pulse generation and simulation for the superficial femoral artery are presented.

Arteries↗
PubMed1990

Vacuum generation in pneumatic artificial heart drives with a specially designed ejector system.

To improve the filling characteristics of pneumatically driven membrane artificial hearts (AHs), a vacuum is applied during diastole. This paper describes an ejector system for AH-drivers based on the Venturi effect, which was designed for this purpose. It provides vacuums of more than -40 mmHg at flow rates up to 50 l/min requiring a supplying primary gas pressure of less than 150 kPa (1140 mmHg). Under normal working conditions, the necessary supply flow was less than 5l/min. The device is small, cheap, quiet and fail-safe, and has been evaluated successfully in experimental and clinical use.

Heart, Artificial↗
PubMed1989

Clinical total artificial heart bridging: Viennese strategy and experiences.

Worldwide the clinical use of total artificial hearts (TAH) for bridging the time until heart transplantation (HTX) has become part of HTX programs. At our clinic, TAH bridging has been performed in five deteriorating HTX candidates since 1986. Four patients suffered from dilative CMP and one patient from a large anterior wall infarction. Three times the ellipsoid heart and twice the Berlin TAH were implanted. After TAH implantation, the conditions of all patients improved. The accompanying dysfunctions of kidneys and other vital organs, which were due to cardiogenic shock, could be restored in the three patients who underwent subsequent HTX. Bridging periods lasted from 9 to 13 days. Two patients, however, could not be transplanted because of infection. Although three patients could be bridged until transplantation and were in good clinical conditions, the longest survival following two-stage HTX was 40 days. In the future, complications like infection, bleeding, and transplant rejection have to be prevented to improve the long-term results of Viennese TAH bridging.

Aged↗
PubMed1989

Control of the total artificial heart: new aspects in human versus animal experience.

Control strategies for total artificial heart application have generally been based on experience with healthy animals. Human patients in a bad state of health who have impaired organ functions and who are subjected to intensive care procedures can develop atypical hemodynamic behavior. In these patients, both unstable and hyperstable behavior of the vascular resistance were observed. Therefore, regulation of cardiac output (CO) by pressure parameters only was avoided and CO was adjusted to obtain an appropriate O2-utilization (O2U). Intending to keep the O2U within ranges of 20-25%, we obtained cardiac indexes between 3.3 and 4.4 L/m2/min (CO 6-8 L/min), which is higher than other cardiac indexes reported. A CO of 10.5 L/min was even necessary to obtain an O2U of 30% in a septic patient. This strategy caused a stable driving management and led to a rapid hemodynamic stabilization and general improvement of the patients' condition. Results indicate that it is also very important to monitor metabolic parameters for appropriate driver adjustment as well, especially in the early postoperative phase, and that O2-U is a sensitive and useful parameter for this purpose.

Animals↗
PubMed1989

Use of fibrin glue as a substrate for in vitro endothelialization of PTFE vascular grafts.

The shear stress resistance of cultured human endothelium was investigated on 6 mm polytetrafluoroethylene vascular grafts. Endothelial cell attachment was promoted by precoating the grafts with fibrin glue, which contained human fibronectin and inhibitors of fibrinolysis (aprotinin and tranexam acid). To evaluate the possible effect of fibrinolysis on cell detachment, seven grafts were lined with adult human saphenous vein endothelial cells (AHSVEC) and 11 with fibrinolytically almost inactive human umbilical vein endothelial cells (HUVEC). Endothelial cell seeding was performed in a microprocessor-controlled rotation device, allowing a low inoculum of 12 X 10(4) endothelial cells/cm2. Grafts were then cultivated for 9 days to enable the maturation of the cytoskeleton, before they were exposed to pulsatile shear stress for 48 hours. A mock circulation simulated the flow patterns and the wall shear forces of the femoral artery. After a 3-hour seeding process, 45% of AHSVEC and 43% of HUVEC were attached to the fibrin matrix, forming a confluent monolayer. After 24 hours of perfusion, a cell loss of 23% in AHSVEC- and of 42% in HUVEC-lined grafts was encountered. In spite of a further cell loss during the following 24 hours of perfusion, the majority of the graft surface was still covered by endothelial cells. Therefore we conclude that fibrin glue is a suitable substrate for the formation of a shear stress-resistant endothelial cell monolayer on polytetrafluoroethylene vascular grafts.

Aprotinin↗
PubMed1988

Control of perfusion pressure and flow in isolated heart bioassays.

Bioassays using isolated animal hearts are important tools for the investigation of cardiac behaviour, but to obtain accurate results a proper perfusion circuit has to be designed. In particular, biophysical studies of contractile and vascular behaviour require a perfusion circuit which permits the adjustment of several experimental parameters within wide ranges. It must also be able to maintain the stability of these parameters when the behaviour of the isolated organ undergoes major changes. To meet this requirement, we have developed a perfusion circuit which makes it possible to control either the perfusion pressure or the coronary flow, with a high degree of precision. There is an electronic controller which satisfies the requirements of a variety of safety and experimental requirements and guarantees a well-defined perfusion system. Computer simulation of the interaction between the perfusion circuit and the heart identified the basic elements of this time-variable, nonlinear system.

Animals↗
PubMed1987

Total artificial heart bridging: a temporary support for deteriorating heart transplantation-candidates--methods and results.

Since 1975 at the 2. Dept. of Surgery, University of Vienna, Austria, artificial circulation devices and artificial hearts have been constructed and in experimental use. We started a clinical heart transplantation (HTX) program in 1984, and up to now more than 40 HTXs have been performed. Since May 1986, 3 patients--all suffering from end stage dilatative cardiomyopathy--received total artificial heart (TAH) as a temporary support until HTX was possible. Two of them were transplanted after 9 and 10 days. The third patient, who additionally suffered from a postinfarctial lung abscess and had to undergo an indispensable lobectomy contemporary with TAH implantation, could not be transplanted due to an incurable infection, which he died of after 22 days on TAH. The temporary TAH implantation proved to be a valuable measure preventing life-threatening circulatory deterioration. After restoration of a sufficient circulation by the implanted system, the patients' general conditions improved and the concomitant dysfunctions of kidneys, brain, and other vital organs, due to cardiogenic shock, could be rectified in those two patients, who underwent transplantation. Thromboembolic complications were observed only in the third patient, who developed a small infarction in the anterior lobe of the left hemisphere caused by cerebral embolism after 3 weeks of TAH pumping. The use of TAH is liable to severe, even lethal, complications. At present it should be used only as a last resort. If a donor heart is not available, this measure can be a real chance to save the patient's life.

Adult↗