Biomedical subjects

U Schütt

Publications and source records attributed to U Schütt.

8 recordsLinked to original sources

PubMed2004

Automatic control of the extra-corporal bypass: system analysis, modelling and evaluation of different control modes.

Automatic control of the blood gas parameters during extracorporeal circulation has the potential to improve the quality of this procedure and to relieve the personnel from a time consuming task. This paper describes a model of the underlying system for a standard clinical set-up and pinpoints the major difficulties which are the variations of the process gains and the blood- and gas-flow dependent dead times and time constants. Scheduled PI-controllers both for the arterial oxygen as well as for the carbon dioxide partial pressure were designed. Scheduling was based on the blood flow rate. These controllers were tested in a simulation environment. The control systems remained stable under all tested operating condition, but if the blood flow rate was changed abruptly rather large load errors occurred. The performance was improved markedly by adding a feed-forward control path which directly influences the actuating signals based on the actual blood flow rate and the hemoglobin contents, variables which are measured anyway. The major conclusion of this study is to use such direct feed-forward compensation even if more sophisticated control algorithms are used.

Algorithms↗

PubMed2004

Automatic control of isolated organ perfusion.

If provided with adequate physiological conditions explanted hearts may continue to operate in the regular beating mode. This property offers the opportunity to substitute extensive animal experiments by investigations on the isolated organs. At the same time it enables the development of an alternative method for the transport of donor hearts for transplantation. Experimental setups for both applications are described in this paper. The focus is laid on the optimisation of handling and effectiveness of these setups by means of automatic control. The method for investigating the controlled system ("plant") for blood gas exchange, and especially the determination of the transfer function for the partial pressure of oxygen are described. The plant was triggered with stepwise changes on the gas side at several operating points. A first order lag element with time delay was chosen as approximation of every transfer function. The parameter 'time delay', 'gain of the plant' and 'time constant' were analysed as to the dependency on blood flow rate, gas flow rate and partial pressure of oxygen at the blood outlet of the oxygenator. As a result an equation was found to calculate the time delay from gas flow rate and blood flow rate. Correlation of gain and time constant with parameters of the plant were obtained, too. The data is used for the design of a controller, adapting to the different operating points of the plant.

Algorithms↗

PubMed2000

Gingerol, isoproterenol and ouabain normalize impaired post-rest behavior but not force-frequency relation in failing human myocardium.

OBJECTIVE: Rest- and stimulation frequency-dependent potentiation of contractile force is blunted in failing human myocardium. These alterations have been related to reduced sarcoplasmic reticulum (SR) Ca(2+)-reuptake and enhanced transsarcolemmal Ca(2+)-elimination by Na+/Ca(2+)-exchange. We investigated whether inotropic interventions that enhance SR Ca(2+)-uptake, or reduce Ca(2+)-elimination by Na+/Ca(2+)-exchange, normalize impaired post-rest and force-frequency behavior in left ventricular muscle strips from failing human hearts. METHODS: We tested the influence of [10]-gingerol which activates SR Ca(2+)-ATPase (10 mumol/l; n = 13), and isoproterenol which activates cAMP-dependent pathways (0.01, 0.1, 1 mumol/l; n = 40) on post-rest and force-frequency behavior. Ouabain which blocks Na+/K(+)-ATPase (0.03 mumol/l; n = 16) was used to test the effects of inhibiting Ca(2+)-elimination by Na+/Ca(2+)-exchange. For comparison, the effects of blocking SR Ca(2+)-uptake by thapsigargin (10 mumol/l; n = 14) were tested. In addition, Ca(2+)-uptake in myocardial homogenates was measured for gingerol (10 mumol/l; n = 6). RESULTS: Gingerol, isoproterenol (0.1, 1 mumol/l) and ouabain exerted significant positive inotropic effects under basal experimental conditions and normalized post-rest behavior. In contrast, force-frequency relation was only slightly improved by gingerol and isoproterenol (0.01 mumol/l). Ouabain and isoproterenol (1 mumol/l) further deteriorated force-frequency relation due to frequency-dependent significant increases in diastolic tension. Thapsigargin exerted negative inotropic effects and significantly deteriorated post-rest and force-frequency behavior. In addition, gingerol increased SR Ca(2+)-uptake significantly in myocardial homogenates. CONCLUSIONS: Inotropic interventions that stimulate SR Ca(2+)-ATPase or inhibit Na+/Ca(2+)-exchange normalize impaired post-rest behavior. Force-frequency behavior is only slightly improved by stimulation of SR Ca(2+)-ATPase but not by inhibition of Na+/Ca(2+)-exchange. This dissociation between post-rest and force-frequency behavior results from diastolic dysfunction at high stimulation rates.

Adult↗

PubMed2000

Single-center experience with the thoratec ventricular assist device.

OBJECTIVE: The Thoratec ventricular assist device (Thoratec Laboratories, Pleasanton, Calif) is widely accepted for univentricular and biventricular support in patients with various indications. The aim of this study is to describe our experience with implantation of the Thoratec ventricular assist device in more than 100 patients. METHODS: From March 1992 to June 1998, 114 patients (98 men and 16 women; mean age, 47.9 years) received the Thoratec ventricular assist device for a mean duration of 44.9 days. The patients were divided into 3 groups. Group 1 included 84 patients in whom the system was applied as a bridge-to-transplant procedure. Group 2 included 17 patients with postcardiotomy cardiogenic shock, and group 3 included 13 patients with cardiogenic shock of other causes. RESULTS: Sixty-eight percent of patients in group 1 survived to transplantation with a posttransplant survival of 88%. The only independent risk factor affecting survival was age more than 60 years. Survivals in groups 2 and 3 were 47% and 31%, respectively. Main complications in all groups were bleeding, multiple organ failure, liver failure, sepsis, and neurologic disorders. CONCLUSIONS: The Thoratec ventricular assist device has proved to be a reliable device for bridge to transplantation and postcardiotomy support. Further studies are required on patient selection and on patient and device management to reduce the incidence of complications in these patient populations.

Adolescent↗

PubMed1999

Bridging to cardiac transplantation with the Thoratec Ventricular Assist Device.

Mechanical circulatory support has become an established procedure for bridging patients to cardiac transplantation. One of the devices available is the Thoratec VAD, which can be applied for univentricular or biventricular support. Between March 1992 and June 1997, 74 patients were bridged with Thoratec VAD to cardiac transplantation. In 67 patients the system was applied exclusively (26 LVAD, 38 BVAD, 3 TAH), in 7 patients subsequently or in combination with another MCS device. 71.6% with exclusive Thoratec application underwent transplantation with a post-transplant survival rate of 90%, 4 patients are still waiting. Transplant rate in LVAD and BVAD patients was 84% and 71.4%, respectively, posttransplant survival 95.2% and 88%, respectively. 28.6% with a combined application of Thoratec and another MCS device survived to be discharged from hospital. Main complications were bleeding, liver failure, multiple organ failure, and infections. In terms of reliability and efficacy the Thoratec VAD is the system of choice for mid-term application in patients bridged to cardiac transplantation.

Equipment Design↗

PubMed1998

Frequency-dependent changes in contribution of SR Ca2+ to Ca2+ transients in failing human myocardium assessed with ryanodine.

We tested the influence of blocking sarcoplasmic reticulum (SR) function with ryanodine (1 microM) on stimulation rate-dependent changes of intracellular Ca2+ transients and twitch force in failing human myocardium. Isometrically contracting, electrically stimulated muscle strips from ventricles of 10 end-stage failing human hearts were used. Muscles were loaded with the intracellular Ca2+ indicator aequorin. At stimulation rates from 0.5-3 Hz, intracellular Ca2+ transients and twitch force were simultaneously recorded before and after ryanodine exposure (37 degrees C). Ryanodine significantly reduced twitch force at 1 Hz by 46 +/- 9% and aequorin light by 57 +/- 10% in failing human myocardium (P < 0.05). The blunted or inverse aequorin light- and force-frequency relation became positive after ryanodine: in failing human myocardium, twitch force and aequorin light before ryanodine did not increase with increasing frequency and force decreased significantly at 3 Hz (P < 0.05). After ryanodine, twitch force (P < 0.05) and aequorin light increased with increasing stimulation frequency and were maximum at 2 Hz. The data indicate that inhibition of SR function significantly reduces twitch force and Ca2+ transients in failing human myocardium, but converts the blunted or inverse Ca(2+)- and force-frequency relation into a positive one. We infer that Ca2+ responsible for approximately 50% of twitch force is derived from the SR and approximately 50% from sarcolemmal Ca2+ influx in failing human myocardium. This sarcolemmal component increases at higher stimulation frequencies.

Calcium↗

PubMed1995

Left ventricular function in heart valve surgery: a multidisciplinary challenge.

Between January 1988 and December 1994, 4,097 patients underwent heart valve replacement at the Heart Center North Rhine-Westfalia, Bad Oeynhausen, 1,388 (33.8%) of them suffered from impaired left ventricular (LV) function. Overall hospital mortality was 2.3% (n = 95). In the poor LV function group it was 1.8% (n = 25). There was a significant increase of mortality from 1.5% in patients younger than 60 years to 4.9% in patients 80 years of age and older. Reoperations and emergency operations showed an additional increase of mortality each: 6.2% and 18.2%, respectively. Medium term survival (maximum 48 months) was assessed in a group of 2,006 patients operated between January 1991 and December 1993. The cumulative mortality for patients with poor LV function (n = 148) was 12.8%, whereas for those with normal LV function it was 6.1%. Our data suggest that left ventricular function is of minor importance as far as primary operative results are concerned. In long term follow up patients with valve replacement and poor LV function show an increased mortality mainly due to cardiac causes.

Adolescent↗

PubMed1993

[Preventive ovariectomy in colorectal cancer].

Between 1975 and 1989 we carried out a total of 567 resections of the colon and rectum and performed a uni- or bilateral ovarectomy in 53 (9.3%) cases. Histopathological findings in the case of 41 (7.2%) patients were unremarkable whereas 8 cases (1.4%) revealed metastases of the colorectal cancer. In the case of 4 patients (0.7%) synchronous ovarian cancer occurred. According to the TNM-scheme primary tumors included T2 in 2 cases, T3 in 5 and T4 in 1 of the cases. Reported figures of ovarian metastases in colorectal cancer vary between 2.0 and 10.3%, we found 2.1% in our series. Prophylactic ovarectomy even in premenopausal patients is indicated if one or both ovaries show pathological findings on laparotomy since infiltrative growth of the tumor can be proved only histologically. In addition we performed bilateral oophorectomy on postmenopausal women as a method of preventing occurrence of other ovarian tumors.

Adult↗