Anna B. Roehl

Development of a composite degradable/nondegradable tissue-engineered vascular graft.

The present study aimed to determine the feasibility of constructing a reinforced autologous vascular graft by combining the advantages of fibrin gel as an autologous cell carrier material with the inherent mechanical strength of an integrated mesh structure. It was hypothesized that the mesh and dynamic culture conditions could be combined to generate mechanically stable and implantable vascular grafts within a shorter cultivation period than traditional methods. A two-step moulding technique was developed to integrate a polyvinylidene fluoride (PVDF) mesh (pore size: 1-2 mm) in the wall of a fibrin-based vascular graft (I.D. 5 mm) seeded with carotid myofibroblasts. The graft was cultured under increasing physiological flow conditions for 2 weeks. Histology, burst strength, and suture retention strength were evaluated. Cell growth and tissue development was excellent within the fibrin gel matrix surrounding the PVDF fibers, and tissue structure demonstrated remarkable similarity to native tissue. The grafts were successfully subjected to physiological flow rates and pressure gradients from the outset, and mechanical properties were enhanced by the mesh structure. Mean suture retention strength of the graft tissue was 6.3 N and the burst strength was 236 mm Hg. Using the vascular composite graft technique, the production of tissue engineered, small-caliber vascular grafts with good mechanical properties within a conditioning period of 14 days is feasible.

Neuroprotective properties of levosimendan in an in vitro model of traumatic brain injury

BackgroundWe investigated the neuroprotective properties of levosimendan, a novel inodilator, in an in vitro model of traumatic brain injury.MethodsOrganotypic hippocampal brain slices from mouse pups were subjected to a focal mechanical trauma. Slices were treated after the injury with three different concentrations of levosimendan (0.001, 0.01 and 0.1 μM) and compared to vehicle-treated slices. After 72 hrs, the trauma was quantified using propidium iodide to mark the injured cells.ResultsA significant dose-dependent reduction of both total and secondary tissue injury was observed in cells treated with either 0.01 or 0.1 μM levosimendan compared to vehicle-treated slices.ConclusionLevosimendan represents a promising new pharmacological tool for neuroprotection after brain injury and warrants further investigation in an in vivo model.

Anti-ischemic effects of inotropic agents in experimental right ventricular infarction.

Background: Right ventricular (RV) function is an important determinant of survival after myocardial infarction. The efficacy of reperfusion therapy might be increased by the cardioprotective action of inotropic agents, which are used for symptomatic therapy in situations with compromised hemodynamics. Therefore, we used a porcine model of RV ischemia and reperfusion (IR) injury to study the influence of milrinone, levosimendan and dobutamine on the extent and degree of myocardial injury.

Establishment of a porcine right ventricular infarction model for cardioprotective actions of xenon and isoflurane

Background: Right ventricular (RV) function is an important determinant of post‐operative outcome. Consequences of RV infarction might be limited by pre‐conditioning with volatile anesthetic drugs. Therefore, we used a porcine model of RV ischemia and reperfusion (IR) injury to study the influence of isoflurane and xenon on the extent and degree of myocardial injury.

The role of hypoxia-inducible factor-1α and vascular endothelial growth factor in late-phase preconditioning with xenon, isoflurane and levosimendan in rat cardiomyocytes

OBJECTIVES The protective effects of late-phase preconditioning can be triggered by several stimuli. Unfortunately, the transfer from bench to bedside still represents a challenge, as concomitant medication or diseases influence the complex signalling pathways involved. In an established model of primary neonatal rat cardiomyocytes, we analysed the cardioprotective effects of three different stimulating pharmaceuticals of clinical relevance. The effect of additional β-blocker treatment was studied as these were previously shown to negatively influence preconditioning. METHODS Twenty-four hours prior to hypoxia, cells pre-treated with or without metoprolol (0.55 µg/ml) were preconditioned with isoflurane, levosimendan or xenon. The influences of these stimuli on hypoxia-inducible factor-1α (HIF-1α), vascular endothelial growth factor (VEGF) as well as inducible and endothelial nitric synthase (iNOS/eNOS) and cyclooxygenase-2 (COX-2) were analysed by polymerase chain reaction and western blotting. The preconditioning was proved by trypan blue cell counts following 5 h of hypoxia and confirmed by fluorescence staining. RESULTS Five hours of hypoxia reduced cell survival in unpreconditioned control cells to 44 ± 4%. Surviving cell count was significantly higher in cells preconditioned either by 2 × 15 min isoflurane (70 ± 16%; P = 0.005) or by xenon (59 ± 8%; P = 0.049). Xenon-preconditioned cells showed a significantly elevated content of VEGF (0.025 ± 0.010 IDV [integrated density values when compared with GAPDH] vs 0.003 ± 0.006 IDV in controls; P = 0.0003). The protein expression of HIF-1α was increased both by levosimendan (0.563 ± 0.175 IDV vs 0.142 ± 0.042 IDV in controls; P = 0.0289) and by xenon (0.868 ± 0.222 IDV; P < 0.0001) pretreatment. A significant elevation of mRNA expression of iNOS was measureable following preconditioning by xenon but not by the other chosen stimuli. eNOS mRNA expression was found to be suppressed by β-blocker treatment for all stimuli. In our model, independently of the chosen stimulus, β-blocker treatment had no significant effect on cell survival. CONCLUSIONS We found that the stimulation of late-phase preconditioning involves several distinct pathways that are variably addressed by the different stimuli. In contrast to isoflurane treatment, xenon-induced preconditioning does not lead to an increase in COX-2 gene transcription but to a significant increase in HIF-1α and subsequently VEGF.

Continuous right ventricular volumetry by fast-response thermodilution during right ventricular ischemia: Head-to-head comparison with conductance catheter measurements*

Objective:To evaluate the accuracy of right ventricular ejection fraction and right ventricular end-diastolic volume obtained by volumetric pulmonary artery catheter, using the conductance catheter as reference method. Design:Prospective, comparative study. Setting:Research laboratory of a university hospital. Subjects:Seven young female German landrace pigs. Interventions:Ligation of the distal right coronary artery to induce temporary acute ischemia. Measurements and Main Results:Right ventricular ejection fraction and right ventricular end-diastolic volume were measured simultaneously with a volumetric pulmonary artery catheter and the conductance catheter technique (reference method), in an animal model of acute right ventricular ischemia. Measurements were performed at baseline, during ischemia, and during reperfusion. The methods were compared with Bland-Altman analyses and their diagnostic accuracy to detect ischemia was quantified by receiver operating characteristic curve analysis. For right ventricular ejection fraction measurements, Bland-Altman analysis indicated a bias of −9.9% indicating underestimation by pulmonary artery catheter with limits of agreement ranging from −26% to 6.1%. The data showed a trend for more underestimation at higher right ventricular ejection fraction values. For right ventricular end-diastolic volume, a bias of 31 mL, indicating overestimation by pulmonary artery catheter was found. Limits of agreement ranged from −25 mL to 88 mL. Ischemia induced a decrease in right ventricular ejection fraction and an increase in right ventricular end-diastolic volume, as expected, which was detected by conductance catheter with a significant higher diagnostic accuracy indicated by a receiver operating characteristic area under the curve of 0.98 (p < .001) and 0.92 (p < .001), respectively. Corresponding sensitivity and specificity were 100% and 86%, respectively, for right ventricular ejection fraction conductance catheter (cutoff value = <40%), and 86% and 100% for right ventricular end-diastolic volumeconductance catheter (cutoff value = >94 mL). However, diagnostic accuracy for right ventricular ejection fraction pulmonary artery catheter and end-diastolic volume pulmonary artery catheter to detect ischemia was limited with area under the curve 0.76 (p = .06) and 0.57 (p = .65), respectively. Conclusions:Accuracy of volumetric pulmonary artery catheter in conditions of right ventricular ischemia is low and inadequate for diagnosis of right ventricular ischemia and failure.

The effects of levosimendan on brain metabolism during initial recovery from global transient ischaemia/hypoxia

BackroundNeuroprotective strategies after cardiopulmonary resuscitation are currently the focus of experimental and clinical research. Levosimendan has been proposed as a promising drug candidate because of its cardioprotective properties, improved haemodynamic effects in vivo and reduced traumatic brain injury in vitro. The effects of levosimendan on brain metabolism during and after ischaemia/hypoxia are unknown.MethodsTransient cerebral ischaemia/hypoxia was induced in 30 male Wistar rats by bilateral common carotid artery clamping for 15 min and concomitant ventilation with 6% O2 during general anaesthesia with urethane. After 10 min of global ischaemia/hypoxia, the rats were treated with an i.v. bolus of 24 μg kg-1 levosimendan followed by a continuous infusion of 0.2 μg kg-1 min-1. The changes in the energy-related metabolites lactate, the lactate/pyruvate ratio, glucose and glutamate were monitored by microdialysis. In addition, the effects on global haemodynamics, cerebral perfusion and autoregulation, oedema and expression of proinflammatory genes in the neocortex were assessed.ResultsLevosimendan reduced blood pressure during initial reperfusion (72 ± 14 vs. 109 ± 2 mmHg, p = 0.03) and delayed flow maximum by 5 minutes (p = 0.002). Whereas no effects on time course of lactate, glucose, pyruvate and glutamate concentrations in the dialysate could be observed, the lactate/pyruvate ratio during initial reperfusion (144 ± 31 vs. 77 ± 8, p = 0.017) and the glutamate release during 90 minutes of reperfusion (75 ± 19 vs. 24 ± 28 μmol·L-1) were higher in the levosimendan group. The increased expression of IL-6, IL-1ß TNFα and ICAM-1, extend of cerebral edema and cerebral autoregulation was not influenced by levosimendan.ConclusionAlthough levosimendan has neuroprotective actions in vitro and on the spinal cord in vivo and has been shown to cross the blood–brain barrier, the present results showed that levosimendan did not reduce the initial neuronal injury after transient ischaemia/hypoxia.

Xenon and isoflurane improved biventricular function during right ventricular ischemia and reperfusion

Background: Although anesthetics have some cardioprotective properties, these benefits are often counterbalanced by their negative inotropic effects. Xenon, on the other hand, does not influence myocardial contractility. Thus, xenon may be a superior treatment for the maintenance of global hemodynamics, especially during right ventricular ischemia, which is generally characterized by a high acute complication rate.

Xenon alters right ventricular function

Background: In contrast to other volatile anesthetics, xenon produces less cardiovascular depression with fewer fluctuations of various hemodynamic parameters, but reduces cardiac output (CO) in vivo. Besides an increase in left ventricular afterload and reduction of heart rate, an impairment of the right ventricular function might be an additional pathophysiological mechanism for the reduction of CO. Therefore, we used an animal model to study the effects of xenon as a supplemental anesthetic on right ventricular function, especially right ventricular afterload.

Xenon and isoflurane reduce left ventricular remodeling after myocardial infarction in the rat.

Background:Xenon and isoflurane are known to have cardioprotective properties. We tested the hypothesis that these anesthetics positively influence myocardial remodeling 28 days after experimental perioperative myocardial infarction and compared their effects. Methods:A total of 60 male Sprague–Dawley rats were subjected to 60min of coronary artery occlusion and 120min of reperfusion. Prior to ischemia, the animals were randomized for the different narcotic regimes (0.6 vol% isoflurane, 70 vol% xenon, or intraperitoneal injection of s-ketamine). Acute injury was quantified by echocardiography and troponin I. After 4 weeks, left ventricular function was assessed by conductance catheter to quantify hemodynamic compromise. Cardiac remodeling was characterized by quantification of dilatation, hypertrophy, fibrosis, capillary density, apoptosis, and expression of fetal genes (&agr;/&bgr; myosin heavy chains, &agr;-skeletal actin, periostin, and sarco/endoplasmic reticulum Ca2+-ATPase). Results:Whereas xenon and isoflurane impeded the acute effects of ischemia-reperfusion on hemodynamics and myocardial injury at a comparable level, differences were found after 4 weeks. Xenon in contrast to isoflurane or ketamine anesthetized animals demonstrated a lower remodeling index (0.7±0.1 vs. 0.9±0.3 and 1.0±0.3g/ml), better ejection fraction (62±9 vs. 49±7 and 35±6%), and reduced expression of &bgr;-myosin heavy chain and periostin. The effects on hypertrophy, fibrosis, capillary density, and apoptosis were comparable. Conclusions:Compared to isoflurane and s-ketamine, xenon limited progressive adverse cardiac remodeling and contractile dysfunction 28 days after perioperative myocardial infarction.