Biomedical subjects

U Losert

Publications and source records attributed to U Losert.

At least 37 records · Page 2Linked to original sources

PubMed1997

L-arginine treatment alters the kinetics of nitric oxide and superoxide release and reduces ischemia/reperfusion injury in skeletal muscle.

BACKGROUND: Constitutive nitric oxide synthase (cNOS) may produce species involved in ischemia/reperfusion (I/R) injury: NO in the presence of sufficient L-arginine and superoxide at the diminished local L-arginine concentration accompanying I/R. METHODS AND RESULTS: During hindlimb I/R (2.5 hours/2 hours), in vivo NO was continuously monitored (porphyrinic sensor), and L-arginine (chromatography), superoxide (chemiluminescence), and I/R injury were measured intermittently. Normal rabbits were compared with those infused with L-arginine 4 mg x kg(-1) x min(-1) for 1 hour. In both groups, approximately 6 minutes into ischemia, a rapid increase of NO from its basal level of 50+/-17 to 115+/-7 nmol/L, P<.005 (microvessels), was observed. In animals not treated with L-arginine, NO dropped below basal to undetectable levels (<1 nmol/L) during reperfusion. In animals treated with L-arginine, the decrease of NO was slower, such that substantial amounts accumulated during reperfusion (25 nmol/L). Decreased NO during I/R was accompanied by increased superoxide, which during reperfusion reached 50 nmol/L without or 23 nmol/L with L-arginine treatment. Calcium-dependent cNOS was a major source of superoxide release (inhibited 70% by L-NMMA and 25% by L-NAME) during I/R. CONCLUSIONS: L-Arginine treatment decreased superoxide generation by cNOS while increasing NO accumulation, leading to protection from constriction (microvessel area, 17.77+/-0.95 versus 11.66+/-2.21 microm2 untreated, P<.0005) and reduction of edema after reperfusion (interfiber area, 16.56+/-2.13% versus 27.68+/-7.70% untreated, P<.005).

Animals↗

PubMed1997

Effects of manual high-impulse CPR on myocardial perfusion during cardiac arrest in pigs.

The aim of the study was to compare the effect of a 30 and 50% duty cycle on coronary perfusion pressure (CPP) and end tidal carbon dioxide (ETCO2) and to determine whether a duty cycle of 30% can be achieved manually. After 3 min of ventricular fibrillation cardiac arrest, pigs were resuscitated in two groups with changing duty cycles every 3 min: group A starting with 50 and then 30%; and group B starting with 30 and then 50%. After administration of epinephrine, duty cycles in group A were 50 and then 30%, in group B initially 30% and then 50% Before administration of epinephrine, no significant differences in CPP between the 30 and 50% duty cycles were found; after epinephrine CPP increased with both duty cycles. ETCO2 did not vary before epinephrine; after epinephrine, there were statistically significant differences but there is doubt regarding the clinical relevance of these differences. Survival was 4/6 in group A and 3/5 in group B (NS). It is possible to perform a manual duty cycle of 30%. However, our data do not support the use of a 30% duty cycle during cardiopulmonary resuscitation (CPR).

Animals↗

PubMed1997

Flow measurement at the pump head of centrifugal pumps: comparison of ultrasonic transit time and ultrasonic Doppler systems.

Determination of blood flow is essential for monitoring rotary blood pumps. However, accurate measurement directly adjacent to the pump housing is difficult because of the highly irregular flow profiles near the fast spinning rotor. Therefore, a specially adapted flow probe based on the ultrasound transit time (USTT) principle was designed to evaluate the flow in centrifugal blood pumps. The probe can be directly mounted at the housing and creates 2 crossed measuring ultrasound beams. The mean value, Qm, of the 2 output signals corresponds to the blood flow and the difference, Qd, correlates to the vorticity of the flow profile in the pump outflow tract. In vitro measurements obtained an accuracy for mean flow values of better than +/-0.6 L/min in extreme working points and for vorticity values even as high as Qd = 3.5 L/min. Because of vorticity, however, the output signal contained considerable noise, and that required the application of a 10 Hz filter. Positioning of the ultrasound (US) beams parallel to the axial direction of the pump was superior to radial positioning. Additional measurement of the flow profile demonstrated that a large vorticity occurred (up to Qd equal to 3.5 L/min), and this vorticity was highly dependent upon the afterload of the pump. In vivo experiments demonstrated the reliability of the method. We concluded that USTT flow measurement can determine blood flow immediately adjacent to the pump housing with sufficient accuracy, and these measurements are superior to those from US-Doppler systems (which cannot handle the vorticity accurately enough) and electromagnetic devices (which lack zero stability).

Blood Flow Velocity↗

PubMed1997

Variable platelet response to low-dose ASA and the risk of limb deterioration in patients submitted to peripheral arterial angioplasty.

A group of 100 patients with intermittent claudication (70 male, 30 female), treated with I00 mg ASA per day, were followed over 18 months after elective percutaneous balloon angioplasty. Platelet function was monitored over a period of 12 months by corrected whole blood aggregometry (CWBA). Upon stimulation by arachidonic acid (AA), adenosine diphosphate (ADP) and collagen, CWBA-results were obtained by an electronic acquisition and evaluation system correcting for hematocrit and platelet count of the blood sample. All patients showed a completely inhibited platelet response to AA stimulation. Comparison of the CWBA-results with clinical parameters revealed that reocclusions at the site of angioplasty occurred exclusively in male patients for which CWBA failed to prove an inhibition of aggregation upon both agonists, ADP and collagen, and for these patients the risk of complication is at least 87% higher (p = 0.0093). Only 40% of male patients show the expected effect of ASA on in vitro platelet aggregation at any given point in time and CWBA is capable of predicting those male patients which are at an elevated risk of reocclusion following peripheral angioplasty.

Administration, Oral↗

PubMed1996

Microspheres based detoxification system: a new method in convective blood purification.

A variety of protein-bound or hydrophobic substances, accumulating as a result of pathologic conditions such as exogenous or endogenous intoxications, are removed poorly by conventional detoxification methods because of low accessibility (hemodialysis), insufficient adsorption capabilities (hemosorption), low efficiency (peritoneal dialysis), or economic limitations (high-volume plasmapheresis). Combining advantages of existing methods with microspheric technology, a module-based system was designed. Major operating parameters of the latter can be modified to allow for adjustment to individual clinical situations. An extracorporeal blood circuit including a plasmafilter is combined with a secondary high-velocity plasma circuit driven by a centrifugal pump. Different microspheric adsorbers can be combined in one circuit or applied in sequence. Thus, a prolonged treatment can be tailored using specially designed selective adsorber materials. Comparing this system with existing methods (high-flux hemodialysis, molecular adsorbent recycling system), results from our in vitro studies and animal experiments demonstrate the superior efficiency of substance removal.

Adsorption↗

PubMed1996

Intraperitoneal cholelithiasis after laparoscopic cholecystectomy--behavior of 'lost' concrements and their role in abscess formation.

UNLABELLED: In two experimental studies we sought preliminary information about the behavior of concrements lost in the peritoneal cavity during laparoscopic cholecystectomy. MATERIALS AND METHODS: In study 1, human gallstones were analyzed using X-ray diffraction, classified in three groups and examined with an ultramicroscope; then they were implanted in the peritoneal cavity of rats. After 8 weeks or 6 months, the animals were sacrificed and the concrements analyzed again as before. The tissues surrounding the calculi were also examined histologically. In study 2, human gallstones were examined with regard to bacterial contamination on the surface or in the middle of the calculi. The cholesterol content was analyzed, and the stones were divided into three groups and implantated in the rats as in the first study. After 8 weeks, the animals were sacrificed and areas with identifiable tissue reactions were examined histologically and microbiologically. RESULTS: The concrements lost their crystalline formation without any relation to their former cholesterol content, as shown by X-ray diffraction as well as ultramicroscopy. Mineralogically, these changes are a certain sign of structural dissolution. Cholesterol stones only caused abscess formations in association with gram-negative bowel germs. Sterile pigment concrements often led to a mesenchymal reaction such as granulomas. Contaminated pigment stones also resulted in extensive abscess formations.

Abscess↗

PubMed1996

[Biocompatibility of polyethylene terephthalate--PET--(Trevira strong)--an in vivo study of the sheep knee].

The anterior cruciate ligament was transected at the femoral origin in the right stifle joint of 25 sheep. The ligaments were re-inserted using the Marshall technique, and reinforced with a 3 mm band made of polyethylene terephthalate--PET--(Trevira hochfest) using the through-the-condyle (TTC) procedure, and re-attached--with a preload of 20 N--to the femoral and tibial condyle with two 4 mm staples. To assess the biocompatibility of the augmentation band, the synovial fluid was analysed for total protein and glucose concentration 2, 6, 24, and 56 weeks after implantation, and a total and differential cell count performed. No significant differences were found before and after implantation of the PET band. No pathological increase in the total protein concentration occurred after implantation (normal range: > 3.0 g/dl), and no significant differences vs. the preoperative analysis were found. No synovitis-signalling decrease in the glucose concentration (normal range: > 40 mg/dl) was observed. The preoperative glucose concentration of 87 +/- 12.84 mg/dl showed no significant difference from the postoperative concentration of 95 +/- 13.58 mg/dl. The cytological examination revealed no increase in the leucocyte counts (normal range: 3 leucocytes/HPF). Neither free nor phagocytosed wear particles were seen.

Animals↗

PubMed1996

Pharmacologically induced heart failure for the evaluation of circulatory assistance.

For the evaluation of the hemodynamic interaction between the natural heart and an assist device, a reversible pharmacological model based on the channel blocker Verapamil under hyperkalemia, was developed for deterioration of left ventricular function. Four calves weighing 70-90 kg underwent standard implantation for left atrioaortal assist (BioMedicus, BP-80), pump anesthesia (oxygen/isoflurane [1%]; 8 mg/kg of BW/h ketamine), and of ventricular demand pacing at 120 bpm. Left atrial pressure (LAP), ventricular pressure (LVP), aortic pressure (AoP), pulmonary arterial (Qpulm) pressures, and graft flow (Qgraft) were monitored. The hemodynamic effects of anesthetic overdose (2% Isoflurane) were compared with those of Verapamil (Isoptin: 0.2 mg/kg BW/h 5 mmol/kg of BW/h of KCl) medication. Both regimens caused a decreased in AoP to < or = 50%. For Isoflurane, a slight reduction in cardiac output (CO) of 10% at a nearly constant LAP and a strong decrease of the peripheral resistance (Rperi) of 35% could be seen where Isoptin caused a significant reduction in CO of 40% at an increased LAP (+25%) and changes in Rperi of < 10%. Because the vascular tonus remains nearly constant, the hemodynamic effects are controllable and reversible (antagonized with calcium chloride); thus we conclude that Verapamil administration under hyperkalemia conditions is a proper model for mimicking congestive heart failure with low systemic side effects.

Anesthetics, Inhalation↗

PubMed1996

Preanal stapler anastomosis in minimally invasive surgery of Hirschsprung's disease.

The purpose of this experimental investigation was to optimize the laparoscopic variant of Swenson-Grob's procedure for treatment of Hirschsprung's disease using a circular stapler to perform the preanal anastomosis and to measure its tightness. Several methods of operative treatment of Hirschsprung's disease are described. In our laparoscopic study four methods were evaluated in 10 15-kg piglets. Swenson-Grobs procedure is one of the methods,which can be performed laparoscopically without any laparotomy and was used in this modification on 4 piglets. The laparoscopically mobilized colorectum was pre- anal prolapsed, preanal resected, and anastomosed in a special technique using a circular stapler. The prolapsed anastomosis was replaced into the abdominal cavity and laparoscopically peritonealized. We controlled the anastomosis position by laparotomy, then cut out the anastomosis and controlled its tightness by manometric air insufflation into the orally and aborally tightened bowel below water. In those 4 animals the position was correct and all anastomoses were tight up to a pressure of 40 mm Hg and more. We conclude that preanal stapler anastomosis improves the minimally invasive variant of Swenson-Grob's procedure to treat Hirschsprung's disease, because it minimizes the risk of anastomotic leakage and follows the rules of minimally invasive surgery, because there is no need of laparotomy.

Anastomosis, Surgical↗

PubMed1995

Influence of hematocrit and platelet count on impedance and reactivity of whole blood for electrical aggregometry.

Previous studies have shown that differing qualities of blood specimen seem to influence whole blood electrical aggregometry (WBEA), making it difficult to standardize the method. The aim of this study was to investigate the impact of hematocrit (HCT) and platelet count (PLC) on in vitro platelet aggregation in citrated whole blood (CWB) in order to compensate for their possible effects on impedance aggregometry. Red blood cells and blood platelets were isolated from fresh citrated whole blood taken from 15 healthy donors (mean age = 26 years) and recombined to 20 physiologically relevant combinations of hematocrit and platelet count (HCT: 20-50, PLC: 100-500). Platelet aggregability was measured using WBEA with three different triggers. A special-purpose software package was used in this study, ensuring proper calibration, acquisition, and evaluation of analogue to digital converted data, allowing the calculation of a set of characteristic parameters of each impedance curve. Most of the linear regressions showed that all parameters significantly depend on HCT and PLC. Furthermore, we found interactions of both variables, making it impossible to focus on the effects of one of the investigated variables only. The outcome of this study is a set of dependences, allowing the calculation of regressions for in vitro aggregation in whole blood, enabling a comparison of blood of any quality with each other, regardless of the variables HCT and PLC. Together with the previously defined dependence of sample age on WBEA data, this step should help to make this technique a more reliable and practicable clinical tool, making it suitable for daily routine investigations.

Adult↗

PubMed1995

Hemodynamic effects of prolonged abdominal insufflation for laparoscopic procedures.

Abdominal insufflation for laparoscopic procedures leads to numerous hemodynamic effects. We focused on blood flow distribution and arterial and venous pressure changes during CO2 insufflation at an intra-abdominal pressure of 12 mm Hg. Three segments of the vascular system were investigated (intrathoracic, cranial extrathoracic, caudal extrathoracic) in supine animals at insufflation, during a 90-minute period of pneumoperitoneum, and at desufflation. Except for instrumentation of the animals, no further surgery was performed. At insufflation (+5 minutes), cardiac output increased from 2.7 +/- 0.5 to 3.3 +/- 1.1 L/min while heart rate decreased from 138 +/- 26 to 128 +/- 17 beats per minute. Increases in jugular venous (from 6 +/- 1 to 11 +/- 4 mm Hg) and atrial (right, from 7 +/- 1 to 12 +/- 3; left, from 12 +/- 4 to 17 +/- 5 mm Hg) pressures occurred uniformly during inspiration. The great variance in atrial pressures during ventilation was not associated with changes in stroke volume, as the effective transmural filling pressures remained nearly constant. The increase in femoral venous pressure occurring during both inspiration and expiration (from 10 +/- 2 to 18 +/- 4 mm Hg) exceeded the increase in right atrial and jugular venous pressures during inspiration. Parallel increases were noted in arterial pressures (carotid, from 119 +/- 15 to 129 +/- 9; femoral, from 122 +/- 16 to 133 +/- 10 mm Hg), left ventricular pressure (from 133 +/- 17 to 143 +/- 10 mm Hg), and carotid and femoral flow (carotid, from 174 +/- 71 to 195 +/- 70; femoral, from 66 +/- 25 to 73 +/- 40 (NS) mL/min).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1995

Compliance mismatch and formation of distal anastomotic intimal hyperplasia in externally stiffened and lumen-adapted venous grafts.

OBJECTIVE: Compliance and formation of distal anastomotic intimal hyperplasia (DAIH) were investigated in externally stiffened venous grafts of varying calibers. METHODS: 36 femoropopliteal reconstructions were performed in 18 sheep. The autologous venous grafts were inserted into tubes made of Dacron mesh to achieve compliance-mismatch and lumen adaptation. Compliance was measured by echotracked ultrasonography and profiles of DAIH were generated from histologic sections harvested after 8.3 months. MAIN RESULTS: The external mesh tube significantly lowered the local compliance of graft and host artery. DAIH appeared extensively in those groups where mesh tube constricted venous grafts met untreated host arteries (p = 0.002). No differences in compliance and DAIH formation were observed when grafts with large and adapted diameters were compared. CONCLUSIONS: For prevention of DAIH the distal venous graft diameter is not important, while the local compliance of an autologous vein is a predictive factor for DAIH formation and thus long-term patency.

Anastomosis, Surgical↗

PubMed1995

An implantable seal-less centrifugal pump with integrated double-disk motor.

Thrombus formation and sealing problems at the shaft as well as the compact and efficient design of the driving unit have been major difficulties in the construction of a long-term implantable centrifugal pump. To eliminate the problems of the seal, motor size, and efficiency, two major steps were taken by modifying the Vienna implantable centrifugal pump. First, a special driving unit was developed, in which the permanent magnets of the motor themselves are used for coupling the force into the rotor. Second, the rotor shaft in the pumping chamber was eliminated by adopting a concept recently presented by Ohara. The rotor is supported by 3 pins, which run on a carbon disk, whose concave shape leads to stabilization. The device has the following specifications: size: 65 mm (diameter) by 35 mm (height), 101 cm3; priming volume 30 cm3, 240 g; and a 6-pole brushless double disk DC motor. The required input power of the described prototype is 15 W at 150 mm Hg, 5 L/min (overall eta = 11%), and has an in vitro index of hemolysis (IH) of 0.0046 g/100 L. The test for in vitro thrombus growth exhibited far less thrombus formation in the new design than in designs with axles. In conclusion, the design of a special driving unit and the elimination of the axle led to the construction of a small pump with very low blood traumatization.

Biomechanical Phenomena↗

PubMed1995

Monitoring of FES-induced muscle activity by continuous EMG-recording.

Functional Electrical Stimulation (FES) requires information on the stimulated muscle for adjustment of the stimulation current, avoidance of muscle fatigue during the conditioning period and long term follow-up. Several applications of chronical FES are in clinical practice, but a system for direct registration of muscle activity under FES still does not exist. In six sheep the right Latissimus Dorsi Muscle (LDM) and Thoracodorsal Nerve were exposed. Stimulation electrodes were applied to each nerve and 3 EMG-applied sensing electrodes were placed into each LDM. The LDM tendon was connected to a force transducer. Burst stimulation was applied and the amplitude was increased from 0 to 4 mA in steps from burst to burst. EMG (M-wave) was amplified and recorded continuously via modified instrumentation amplifier, oscilloscope and tape recorder. Isometric muscle tension was recorded using force transducer, A/D interface and PC. Continuous EMG-recording was performed in all cases. Simultaneous recording of muscle tension and EMG revealed a close correlation (IrI=0.95, p < 0.0001) between the muscle strength and amplitude of the M-wave. Continuous recording of the EMG seems to be a reliable method for direct monitoring of the stimulated muscle. Three intramuscular electrodes can provide enough information to monitor FES induced muscle activity.

Animals↗

PubMed1994

Erb:YAG and Hol:YAG laser osteotomy: the effect of laser ablation on bone healing.

Sixty-nine male Sprague Dawley rats were divided into three groups of 23 animals each and osteotomies were performed in group 1 with a power saw, in group 2 with the Erb:Yag laser, and in group 3 with the Hol:YAG laser. Two animals of each group were sacrificed 1 week, 4, 8, and 12 weeks after operation for histologic investigation, and five animals of each group at 4, 8, and 12 weeks after osteotomy for torque testing. Anterior-posterior (AP) radiographs were taken at the same time points and investigated for callus formation and development of pseudoarthrosis. All tibiae osteotomied with the Hol:YAG laser (group 3) developed pseudoarthrosis within 12 weeks and, therefore, torque testing could not be performed for this group. Biomechanical measurements of bone treated by power saw or Erb:YAG laser osteotomies, respectively, showed no significant statistical difference in the stability of bone between the two groups. Histologic examination after 1 week exhibited fibrous tissue at the site of osteotomy in rats of all three groups and additionally carbonization in rats of group 3. Saw osteotomies resulted in more callus formation than Erb:YAG osteotomies, but both techniques provoked a certain reunion within 8 weeks. Hol:YAG laser-treated osteotomies, however, exhibited formation of dense fibrous tissue, carbonization and no callus formation within 12 weeks. Radiographic pictures showed more callus formation for saw osteotomies as compared to those performed with the Erb:YAG laser. For Hol:YAG laser osteotomies pseudoarthrosis was identified also radiologically.

Aluminum Silicates↗

PubMed1994

The Vienna implantable centrifugal blood pump.

Because of the inherent disadvantages of membrane pumps, rotary pumps have been increasingly investigated in recent years. As a result of improving biocompatibility, extended assistance with implantable devices is of special interest. Questions arise concerning shear stress, blood traumatization, design of seals, and specific control conditions. In their development of an implantable impeller pump, the Vienna group studied the minimization of hemolysis and thrombus formation by means of numerical simulation, visualization, and in vitro blood evaluation. The latter was revealed to be the most powerful tool for pump evaluation. With optimization of geometry, a hemolysis of in vitro: IH = 0.008; MIH = 0.58; and in vivo: 2.1 to 3 mg% plasma-free hemoglobin could be obtained. For proper control and physiological adaptation, a controller based on a nonlinear and a fuzzy strategy was developed. Furthermore, a method for evaluation of the contractility of the assisted heart during nonpulsatile support was tested by computer simulation. This paper summarizes the evaluation methods used and provide an overview of the results of pump and controller design.

Animals↗

PubMed1994

Regenerative potential of abdominal vagal nerves in rats.

After truncal vagotomy, impaired gastric emptying may represent a serious complication. This led us to study the feasibility of a reinnervation of the antrum by microsurgical vagorrhaphy and vagoplasty. Sixty-four rats were randomly assigned to undergo either 1) no operation (control), 2) laparotomy and vagal dissection (sham operation), 3) truncal abdominal vagotomy with nerve segment resection, 4) truncal vagotomy followed by vagorrhaphy, or 5) vagal resection extending to the nerve of Latarjet followed by grafting of the gap using the resected vagal segment (vagoplasty). Six months after surgery, vagal regeneration was assessed by morphometry of the anterior vagus and the antral wall and by recording the gastric emptying of a radiolabeled meal, the contractile response to electrical stimulation of the cervical vagi, and basal and insulin-stimulated acid secretion. After truncal vagotomy, there was a marked degeneration of vagal fibers and no evidence of spontaneous reinnervation. After vagorrhaphy, a recovery of gastric secretory and motor functions as well as morphological data indicated vagal regeneration. After vagoplasty, a partial recovery of gastric motor functions and the morphological appearance suggested a partial vagal reinnervation.

Abdomen↗

PubMed1994

Hemodynamic changes during prolonged laparoscopic surgery.

7 healthy pigs, anesthetized with ketamine/azaperon/thiopentone and ventilated with O2/N2O by volume control, underwent anterior resection of the descending colon by laparoscopic view. During operation of pneumoperitoneum by inflating CO2 to an abdominal pressure of 14 mm Hg was installed. Immediately (+2 min) after the onset of insufflation, both systemic and pulmonary arterial pressure increased. However, pulmonary artery pressure started to decrease after 10 min, whereas systemic arterial pressure remained elevated until the end of the experimental protocol. Left ventricular (LV) pressure and LV dp/dt increased in parallel with the systemic arterial pressure. Peak inspiratory pressure and central venous pressure increased in parallel with the abdominal pressure. Blood gas analysis of arterial and pulmonary blood demonstrated increased pCO2 associated with mild acidosis. Arterial pO2 did not change significantly indicating that the decreased pulmonary distensibility did not endanger the oxygenation. Pulmonary pO2 and pulmonary O2 saturation increased early (+10 min) after start of insufflation and were stable during the 2 h of observation indicating either increased cardiac output or decreased O2 extraction. We conclude that the sharp initial rise of both arterial pressures could be the effect of a mechanical action, whereas sustained hemodynamic alterations would involve complex regulatory mechanisms like an increase of sympathetic activity, baroreceptor control, or a response to acidosis. The acute and, in the systemic circulation, stable increase of ventricular afterload should be considered in patients with underlying cardiac diseases such as ischemic heart disease or valvular dysfunction or in patients taking drugs which interfere with normal compensatory processes.

Animals↗