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R Bauernschmitt

Publications and source records attributed to R Bauernschmitt.

36 records · Page 2Linked to original sources
PubMed1998

[Surgery of acute aortic valve endocarditis: prognosis in paravalvular abscess].

The occurrence of paravalvular abscesses in the course of an acute endocarditis of the aortic valve indicates an advanced stadium of the disease. The infection has spread beyond the limits of the valve leaflets, and ongoing destruction of the paravalvular tissue is to be expected, if the endocarditis is continually treated by antibiotics alone. Surgery of acute endocarditis with paravalvular abscess, however, supposedly carries an increased risk of early mortality and late morbidity. The following prospective study was carried out to determine whether a radical surgical approach together with aggressive postoperative antibiotic therapy could help to improve results. Between 1988 and 1995, 138 patients were operated during the acute phase of infective endocarditis; in 102 the aortic valve was involved. Among these, 44 had paravalvular abscesses at the time of surgery. The mean age of both groups was the same, but there was a higher rate of concomitant coronary artery disease, multiple valve involvement, advanced NYHA-class, and staphylococcal disease among the patients with abscesses. All interventions were carried out with cardiopulmonary bypass and cardioplegic arrest. The aortic valve was resected, abscesses were removed, and each part of potentially infected or necrotic tissue was resected as complete as possible, irrespective of the possibility to jeopardize the conduction system or to create large tissue defects. The aortic valve was replaced with a mechanical prosthesis in each case. The postoperative antibiotic regimen was specifically directed against the microorganisms isolated preoperatively; therapy was only modified, if signs of systemic infection did not disappear three days after surgery. The operative mortality was 10% among patients without an abscess and 11% in patients with a paravalvular abscess. Early recurrent endocarditis was recorded in two patients without and in only one patient with an abscess. Late recurrent endocarditis was noted in three patients; none of them had abscesses at the time of surgery. We conclude that the operative risk of acute endocarditis of the aortic valve with a paravalvular abscess does not have to be inevitably higher compared to cases without paravalvular involvement. To achieve these results, it is necessary to use a radical surgical approach and to adjust postoperative antibiotic therapy, if infectious signs do not disappear shortly after surgery.

Abscess↗
PubMed1998

Operation for infective endocarditis: results after implantation of mechanical valves.

BACKGROUND: Operation for acute endocarditis during the active phase violates a basic surgical rule not to implant a foreign body into an infective process, resulting in a high operative mortality and the risk of early recurrent endocarditis. Several investigators analyzing risk factors for perioperative mortality and morbidity presented strategies for more favorable outcomes, but most studies suffer from the drawback of heterogeneous populations observed over a long period of time. METHODS: We present a prospective study on 138 patients operated on from March 1988 to March 1996. Patients were only included if the activity of the infection was proved by positive culture of the valve leaflets or by histologic staining. During the observation period, indication for operation, surgical approach, and postoperative antibiotic therapy were standardized as much as possible. After radical debridement of all parts of infected tissue, valve replacement was carried out with mechanical prostheses. RESULTS: The early mortality was 11.5% overall. High New York Heart Association functional classification, advanced age, and staphylococcal disease were significant risk factors for early mortality. The site of infection, multiple valve involvement, and prosthetic valve endocarditis did not affect the outcome. Early recurrent endocarditis was recorded in only 3 patients of the entire series. CONCLUSIONS: In case of acute infective endocarditis, valve replacement with mechanical prostheses is a safe procedure, if radical operation and aggressive postoperative antibiotic therapy are performed. For further improvements of the results, earlier operation is advisable in patients with rapidly progressive cardiac deterioration and in most cases of staphylococcal endocarditis.

Acute Disease↗
PubMed1997

Spinal cord protection using hypothermic cardiocirculatory arrest in extended repair of recoarctation and persistent hypoplastic aortic arch.

OBJECTIVE: In recurrent coarctation collateral circulation may not be sufficient to maintain adequate perfusion of the lower body during the period of surgical repair. Different techniques such as interposition of a Gott-shunt, use of left heart bypass or hypothermic cardiocirculatory arrest are used to prevent spinal cord injury. METHODS: Twenty-eight operations for recurrent coarctation were performed in 26 patients following end-to-end anastomosis (58%), patch plasty (21%), subclavian flap aortoplasty (14%) and graft interposition (7%). Associated cardiac defects were present in 77% of the patients. Eleven patients who had adequate (> 50 mmHg) distal perfusion pressure during a test occlusion were operated on using simple cross-clamping (group I, mean age 8.5 +/- 3.8 years). In group I, end-to-end anastomosis was performed in nine patients and graft interposition in two patients. In 17 cases (including two patients from group I) with insufficient collateral circulation and with persistent hypoplasia of the arch, hypothermic cardiocirculatory arrest was used (group II, mean age 12.8 +/- 9.6 years). In group II end-to-end anastomosis was performed in three patients and graft interposition in 14 patients. Mean bypass-time was 116 +/- 36 min and arrest-time 33 +/- 16 min. Hypothermic cardiocirculatory arrest was begun when nasopharyngeal temperature was below 20 degrees C, corresponding to a rectal temperature of 24 +/- 3 degrees C. RESULTS: Hypothermic cardiocirculatory arrest allowed open reconstruction of the arch and/or complete or partial replacement of the arch and the coarctation segment. In-hospital mortality was 0 and 5.9% in group I and II, respectively. The one patient who died in group II had simultaneous correction of an anomalous pulmonary venous connection and death was unrelated to the method of coarctation repair. Reversible laryngeal nerve paresis was observed in two patients in group II, no other neurologic complications were observed in either group. Postoperative gradients over the repair site were less than 20 mmHg by Doppler-echocardiography. Two patients of group I had to have a second, early reoperation because of stenosis at the anastomotic site. Reconstruction of the distal aortic arch was then performed during hypothermic cardiocirculatory arrest. CONCLUSIONS: The use of hypothermic cardiocirculatory arrest in this special indication is a safe method which allows open reconstruction of the coarctation site and the aortic arch and protection of the spinal cord. The need for early reoperation because of inadequate repair may be reduced.

Anastomosis, Surgical↗
PubMed1997

[Surgical treatment of acute endocarditis--which preoperative diagnosis does the surgeon need?].

In a group of 140 patients undergoing operation for acute infectious endocarditis in an 8-year period, the value of preoperative diagnostic procedures was analyzed in a retrospective study. Echocardiography was sufficient to establish the diagnosis in each case, angiography did not add any information about the endocarditis, but detected severe coronary heart disease in 19 patients. Abdominal sonography is mandatory to exclude intestinal foci, while CT scan of the brain only has to be performed in patients with neurologic deficits.

Acute Disease↗
PubMed1997

Hemodynamic consequences of replacing the aorta by vascular grafts simulated in a mathematical model.

OBJECTIVE: Replacing parts of the aorta by a noncompliant vascular prosthesis results in marked alterations of the aortic input impedance and influences arterial hemodynamics. We propose a mathematical model of circulation able to predict hemodynamic changes after simulation of vascular grafting. METHODS: Using a mathematical 128-branch model of the human arterial system a digitized aortic flow wave was chosen as the input signal to this system. After determination of the modules of elasticity of native vascular tissue and customary prostheses in technical experiments, replacement of any part of the aorta with a prosthesis was simulated by increasing the elasticity in the parts desired. RESULTS: During control conditions, the model displayed a physiologic distribution of flow and pressure waves throughout the arterial system. Simulated replacement of the aorta resulted in an increase of pressure amplitude and a partial loss of the aortic "Windkessel" function. Calculation of the aortic input impedance showed an increase of the characteristic impedance, while the peripheral resistance remained unaltered. CONCLUSION: This mathematical model of the arterial circulation proves to be useful to simulate hemodynamic changes after implantation of vascular grafts. The results of the model analysis are consistent with previous work done in experimental setups.

Aorta↗
PubMed1997

Description of the ventriculoarterial interaction dynamics using recurrence plot strategies.

OBJECTIVE: The classical description of ventriculoarterial coupling by calculating the ratio between the effective arterial elastance Ea to the end-systolic elastance Ees does not give insight into the underlying dynamics of the interaction between left-ventricular pressure (LVP) and aortic pressure (AOP) and flow (AOF). The aim of this study was to introduce a state space representation for the ventriculoarterial coupling and to quantify changes of the coupling state. METHODS: A ventriculoarterial state space orbit VAO was defined to be dependent on three variables: VAO = [LVP(t), AOP(t + delta t), AOF(t + delta t)]. Changes in the coupling effect directly or indirectly on the time series of these parameters. They reflect the actual state of the cardiovascular system. The time delay delta t between the LVP and the aortic signals takes respect to the short delay between the heart action and the resulting waves in the arterial tree. The recurrence map of the VAO(i) (i = 1 .. N, N = number of points) is constructed by plotting the index i of every single point on the orbit (x-axis) against the indices of his 10 nearest neighbors (y-axis) in distance. The data were recorded in 9 anaesthetized pigs with a sample frequency of 512 Hz over a period of 6 seconds using piezoelectric pressure sensors and a Doppler flowmeter. A control condition was compared to a total occlusion of the descending aorta as a strong artificial disturbance of ventriculoarterial interaction. The nonlinear parameters percent recurrence, percent determinism and the entropy were calculated from the plot. RESULTS: Periodic crossing points and forbidden zones in all plots identify the nonlinear character of the chosen variables. The recurrent patterns are less rigid for control conditions than for total occlusion. Entropy (2.3% rise) and determinism (24% rise) are significantly (p < 0.003) increased. Total aortic occlusion leads to more complex time correlation patterns. CONCLUSIONS: These results may reflect the loss of an ideal coupling state leading to a more complex deterministic behavior of the overall regulatory system. Because recurrence plots do not impose rigid constraints on data set size, stationarity, or statistical distribution, we hypothesize that this technique might be useful to describe the nonlinear dynamics between left ventricle and arterial system.

Animals↗
PubMed1997

Simulation of human circulation at cardiopulmonary bypass.

This article describes a simulation model of the human circulatory system under extracorporeal circulation. The model is supposed to enable the design of a controller for heart-lung-machines, and to perform simulations of the controllers' behaviour. The controller should be able to control extracorporeal circulation based on the oxygen supply to individual organs. The model contains all important control mechanisms in the human circulation that maintain hemodynamics, and the influences of extracorporeal circulation to them. We considered the renin-angiotensin-system, the arterial local autoregulation and the autonomic nervous system. The behaviour of the most important hormone levels is reproduced. Furthermore, hemodynamics in the arterial tree is modeled with locally distributed pressure and flow parameters in 128 vessel segments to gain knowledge about the oxygen supply position of single internal organs. The influences of the special circumstances of an operation under extracorporeal circulation such as anesthesia or hypothermia are implemented in the model. Simulation results show that our model describes the behaviour of human circulation detailed enough to validate the designed controllers.

Arteries↗
PubMed1997

A mathematical high time resolution model of the arterial system under extracorporeal circulation.

OBJECTIVE: The purpose of the following study was to establish a computer-generated model of the hemodynamic effects of pulsatile extracorporal perfusion describing flow and pressure parameters in the body for any given input flow patterns. METHODS: The human arterial tree was delineated according to a 128-branch model encompassing bifurcations and linear physical properties of the arterial walls. The distribution of flow and pressure waves was calculated based on a refined 3-element windkessel model. Autoregulatory mechanisms of brain and kidneys were implemented. RESULTS: By providing a simulated, "pump-generated" flow curve as the input signal to the system, the model was able to create and display flow and pressure curves at a high time resolution in each part of the systemic circulation including reflection phenomena throughout any observation period chosen. The hemodynamic effects of different pump-flow patterns, age, variations in hematocrit, hypothermia and occlusion of arterial branches, like the renal artery, could be simulated. CONCLUSION: In an attempt to get closer to a mathematically based regulation of heart-lung machines, this model of computer generated extracorporeal circulation provides an initial step. Ongoing research is required for implementation of metabolic conditions and continuous approximation of the model of the real physiologic or pathologic situation.

Arteries↗
PubMed1996

Tricuspid valve reconstruction, a treatment option in acute endocarditis.

Tricuspid valve endocardititis is treated surgically by total valve excision or valve replacement. Both procedures are controversial with regard to the hemodynamic consequences and to the long-term prognosis. In the following, results of tricuspid valve repair in acute infective endocarditis are reported and discussed as an additional treatment option. Between January 1988 and December 1993, 118 patients were operated on for acute valve endocarditis at our institution. Eleven of these patients had tricuspid valve endocarditis, isolated (n = 7) or combined with endocarditis of a left-sided valve (n = 4). In the cases with isolated tricuspid valve endocarditis, the indication for surgery was intractable infection in six and hemodynamically relevant tricuspid insufficiency in one out of seven patients. In all patients with associated left-sided endocarditis, the indication was hemodynamic deterioration. In eight patients the tricuspid valve endocarditis was treated as follows: debridement, vegectomy, patch reconstruction of the cusps, reducing the cusps to two. In three patients reconstruction was not possible because of extensive involvement of all parts of the valve, including the valve ring and the papillary muscles. In these patients primary valve replacement (n = 1) or valve excision with secondary replacement (n = 2) was performed. In four patients tricuspid reconstruction was combined with mitral (n = 1), aortic (n = 1) or double valve replacement (n = 2). Postoperatively, signs of infection vanished in all surviving patients (n = 10) and tricuspid valve endocarditis healed without recurrences. Implanted prosthetic material did not lead to recurrent infection. One patient died early postoperatively after valve excision, in septic shock and multi-organ failure. In seven patients late echocardiographic follow-up showed tricuspid regurgitation grade 0 in three patients, I in two, II in one and III in one. Our results suggest that valve repair is a reasonable treatment option for tricuspid valve endocarditis in all cases with localized infection of the valve. Only if extensive valve destruction excludes valve repair, would we now favor primary valve replacement over simple valvulectomy. In all other cases primary valve reconstruction is the treatment of choice for tricuspid valve endocarditis, if surgery is indicated.

Acute Disease↗
PubMed1996

Surgical treatment of acute endocarditis of the aortic valve with paravalvular abscess: considerations justifying the use of mechanical replacement devices.

OBJECTIVE: Early recurrency after surgery for acute endocarditis is a life-threatening complication. Allograft valves are supposed to have a higher resistance to recurrent infection, thus several authors claim them to be the replacement device of choice in cases of aortic endocarditis. However, allografts have two major drawbacks: their availability is limited, and most of the patients require reoperation for graft calcification of degeneration. Until now there has been no prospective study analysing whether early recurrency after surgery of acute endocarditis is associated with the mechanical valve per se or with factors related to the surgical technique or postoperative care. PATIENTS AND METHODS: We present a prospective study on 36 consecutive patients with acute endocarditis of the aortic valve with paravalvular abscesses. In this series, there were 5 women and 31 men with a mean age of 50.3 years. All patients were operated before a course of antibiotic therapy was completed. Abscesses were radically resected and the cavities closed either with direct suture or, if not possible, with Dacron patches. For aortic valve replacement, a mechanical valve was used in every patient. RESULTS: The early mortality in this series was 14%, only one patient experienced recurrent endocarditis and underwent reoperation. The results compare well with those achieved after valve replacements with allograft valves. CONCLUSION: We conclude that, even in cases of acute endocarditis, replacement of the aortic valve with a mechanical device is an acceptable alternative to the allograft, if radical surgical debridement and adequate antibiotic therapy are performed.

Abscess↗
PubMed1995

[Surgical therapy of acute tricuspid valve endocarditis: indications, technique and results].

Tricuspid valve endocarditis is treated by antibiotics alone in the majority of the cases. However, intractable infection or hemodynamic compromise may warrant surgery. In those cases total valve-excision or valve-replacement had been the most common surgical procedures. Both are controversial in regards to the hemodynamic consequences and to the long-term prognosis. In the following, results of tricuspid valve repair in acute infective endocarditis are reported and discussed as an additional treatment option. Between January 1988 and December 1993, 118 patients were operated for acute valve endocarditis at our institution. Eleven of these patients had tricuspid valve endocarditis, isolated (n = 7) or combined with endocarditis of a left-sided valve (n = 4). In the cases with isolated tricuspid valve endocarditis, the indication for surgery was intractable infection in 6 and hemodynamically relevant tricuspid-insufficiency in 1 out of 7 patients, respectively. In all patients with associated left-sided endocarditis, the indication was hemodynamic deterioration. In 8 patients the tricuspid valve endocarditis was treated as follows: Debridement, vegectomy, patch-reconstruction of the cusps, bicuspidalization. In 3 patients reconstruction was not possible because of extended involvement of all parts of the valve, including the valve ring and the papillary muscles. In these patients, primary valve-replacement (n = 1) or valve-excision with secondary replacement (n = 2) was performed. In 4 patients tricuspid-reconstruction was combined with mitral- (n = 1), aortic- (n = 1) or double-valve replacement (n = 2).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Increased resistance against shortening in myocardium from recipient hearts of 7 patients transplanted for dilated cardiomyopathy.

UNLABELLED: The contractile behaviour of demembranized atrial and ventricular myocardium of 7 patients transplanted for end-stage heart failure (ESHF) was analyzed. Atrial muscle specimens of patients undergoing coronary artery bypass surgery (n = 9) and pig papillary muscle were used as reference preparations (n = 9). Extreme care was taken for dissection and mounting the muscle fibres (0.3 x 6 mm) in order to keep the passive series compliance small. Calcium sensitivity, cross-bridge cycling rate (estimated by the force-clamping technique and calculation of the shortening velocity at zero load [Vmax]) and isometric force development were measured. Analysis on light- and electronmicroscopic level was carried out. RESULTS: 1) Calcium sensitivity was not altered in ESHF patients; 2) the velocity of the force generating process (cross-bridge cycling rate) was normal in ventricular and reduced in atrial ESHF myocardium, 3) maximum isometric force development was reduced in ventricular, but not in atrial myocardium of ESHF patients, and 4) Vmax was significantly reduced in ventricular and atrial ESHF myocardium (p < 0.0001). Perimysial and endomysial fibrosis was present in ventricular, not in atrial myocardium of ESHF patients. CONCLUSION: A normal cross-bridge cycling rate in left-ventricular ESHF myocardium combined with a decreased capability of muscle shortening indicates the presence of a resistance against shortening localized either on the cross-bridge level or/and due to intra- and pericellular fibrosis. Left-ventricular contractile dysfunction in patients with end-stage heart failure may be related to a normal contractile apparatus contracting within an abnormal intracellular or interstitial environment.

Animals↗
PubMed1992

Contractile behaviour of skinned papillary muscle in mitral valve disease.

The contractile behaviour of Triton-X 100 skinned left ventricular papillary muscle from 19 patients undergoing cardiac surgery for mitral valve stenosis: n = 6, mitral valve incompetence: n = 7, or combined mitral valve disease: n = 6 was analyzed. At supramaximal activation the "vibration induced force clamping technique" was used for isometric analysis of time course and extent of isometric postvibration force recovery. Afterloaded contractions were applied for extrapolation of the maximum shortening velocity at zero load (Vmax). The Calcium sensitivity was analysed by variation of the free EGTA-buffered Calcium concentration at a passive resting force of 2 mN at 26 degrees C. In different types of mitral valve disease the characteristics of isometric force development were unaltered in terms of maximum force development, force per square mm, Calcium sensitivity and the time course of isometric contraction after force clamping. However the capability to shorten as expressed by Vmax was reduced in mitral valve incompetence (3.87 +/- 0.37 ML/s) as compared with mitral valve stenosis (5.29 +/- 0.35 ML/s) or combined mitral valve disease (4.83 +/- 0.51 ML/s). The ratio between the inverse value of Vmax and the time constant of isometric force development after force clamping was significantly different in mitral valve incompetence as compared with other types of mitral valve disease (p < 0.0001). These data argue for the presence of different resistances against shortening in various types of mitral valve disease, due to altered cross-bridge cycling characteristics or to morphological factors.

Adult↗
PubMed1991

Analyzing contractile responses in demembranized pig papillary muscle fibres: the influence of calcium, resting force, and temperature.

The influence of calcium, resting force and temperature on the contractile behaviour in isolated demembranized ("skinned") pig papillary muscle fibers (n = 36) was analysed. Demembranisation excludes the influence of any membrane related processes on the contractile response as the myofilaments are in direct contact with the bathing medium. Resting force (1 mN-9 mN), temperature (22 degrees C or 32 degrees C) and pCa 7.0-4.3 were varied and the contractile response was analyzed by studying the time constant and the extent of post vibration force recovery (PVFR) of the activated preparations (the vibration method). Additional constant-load experiments and detection of sarcomere-length were carried out. There was an inverse-linear relationship between time constants of post vibration force recovery and maximum shortening velocity as estimated by constant load experiments. Resting force affected the extent of force development but not the time constant of post vibration force recovery and modulated the pCa-force relationship without altering the calcium concentration required for half-maximal activation (calcium sensitivity). In contrast lowering the bath temperature from 32 degrees C to 22 degrees C caused a significant leftward shift of the pCa-force relationship potentially due to changes of the contractile filaments' calcium sensitivity. The effect of temperature on the myocardial contractile system is of special interest as hypothermia is frequently used in cardiac surgery. Analysis of alterations of the contractile proteins' calcium sensitivity during the rewarming period of the patient may provide further insight in the pathophysiology of reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Actins↗