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Biomedical subjects

U Windberger

Publications and source records attributed to U Windberger.

15 recordsLinked to original sources
PubMed1996

Coefficient of variation: a powerful Doppler ultrasonographic parameter for detection of renal artery stenosis.

The aim of our study was to objectively compare the effectiveness of various Doppler parameters in the diagnosis of renal artery stenosis. In three sheep, variable degrees of renal artery stenosis were induced and renal segmental arteries were investigated using pulsed Doppler sonography. In each animal the standard deviation of the instantaneous peak velocity within one cardiac cycle normalized by the mean peak velocity (coefficient of variation) had significantly higher normalized regression coefficients (k* = -0.215, average of three animals) when compared to resistive index (k* = -0.090) and acceleration index (k* = -0.069). In each individual animal, coefficient of variation detected lower pressure gradients (6.3 mm Hg, average value) than did resistive index (13.4 mm Hg) or acceleration index (17.3 mm Hg). The coefficient of variation may detect the presence of pressure gradients in renal artery stenosis more accurately than acceleration index or resistive index.

Animals↗
PubMed1996

Impact of glutaraldehyde on calcification of pericardial bioprosthetic heart valve material.

BACKGROUND: This study was conducted to investigate the impact of the preservation method of bioprosthetic heart valve materials on calcification rates and biocompatibility of the biologic tissue. METHODS: In subcutaneous rat implants, conventionally preserved bioprosthetic heart valve material was compared with bovine pericardium that was treated with L-glutamic acid to reduce residual glutaraldehyde released from the fixed tissue. Both these methods were compared with bovine pericardium that was stabilized by a dye-mediated photooxidation reaction without glutaraldehyde. Biocompatibility of these biomaterials was tested in vitro using human endothelial cell cultures. RESULTS: Conventionally preserved bovine pericardium with a high amount of glutaraldehyde incorporated into the tissue resulted in severe calcification 63 days after subcutaneous implantation in rats (165.4 +/- 20 mg Ca2+/g dry weight). Postfixation treatment with L-glutamic acid, which reduces free, unbound aldehyde groups, showed a significant decrease in calcification (89.6 +/- 14 mg Ca2+/g dry weight). Glutaraldehyde-free preservation by dye-mediated photooxidation showed no calcification after 63 days of subcutaneous implantation (1.0 +/- 0.4 mg Ca2+/g dry weight). Regular endothelial cell proliferation was observed on photooxidized and L-glutamic acid-treated tissue, whereas conventionally treated tissue caused endothelial cell death. CONCLUSIONS: This study underlines the detrimental role of glutaraldehyde in the calcification process of bioprosthetic heart valve materials and emphasizes alternative preservation methods that reduce or avoid the use of glutaraldehyde.

Animals↗
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↗
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↗
PubMed1994

The viscoelasticity of blood and plasma in pig, horse, dog, ox, and sheep.

There is little data on blood viscosity in different animals. Therefore a comparison was performed between five species by an in-vitro method using oscillatory flow. At shear rates from 1 to 150/sec the viscous and the elastic component of the complex blood viscosity was highest in pig, followed by horse, dog, ox, and sheep. Plasma viscosity and plasma density were similar in dog and sheep and were higher in ox. The differences in whole blood viscosity were obviously related to the variable interspecies hematocrit, and may also be influenced by different aggregation tendencies. Aggregation in ox was low despite a high plasma fibrinogen. It seems that erythrocytes in sheep and ox remain separately suspended in a relative dense plasma. This may indicate that formation of microthrombi is less likely to occur in ox and sheep than in pig, horse, and dog.

Animals↗
PubMed1993

Dissociation of hemodynamic and renal effects of i.v. alpha-hANF (99-126) in conscious calves.

The effects of i.v. human atrial natriuretic factor (alpha-hANF [99-126]) was investigated in 5 conscious calves (age 4 months, weight 94 +/- 14kg) with constant fluid (300 ml/h) and sodium intake over a period of 24 hours before and during the 3 hours of experimentation. We administered 200 micrograms, 400 micrograms and 800 micrograms ANF at hourly intervals. Immediately (+2 min) after the i.v. injection the peptide's serum-concentration rose from, basal 13 +/- 3 to 802 +/- 191 (200 micrograms), 1707 +/- 419 (400 micrograms) and 3483 +/- 878 pmol/l (800 micrograms) (p < 0.0001), respectively. Mean arterial pressure decreased from, basal, 108 +/- 18 to 85 +/- 17, 76 +/- 16 and 69 +/- 18 mmHg (p < 0.0001), and central venous pressure decreased from, basal, 5.1 +/- 3 to 1.2 +/- 1, 0.4 +/- 1 and 0.8 +/- 2 mmHg (p < 0.001). Heart rate increased from, basal, 66 +/- 5 to 84 +/- 23, 111 +/- 29 and 114 +/- 13 b/min (p < 0.001). Following the administration of ANF the urine volume decreased from, basal, 261 +/- 145 to 195 +/- 72, 121 +/- 41 and 102 +/- 33 ml/h (p < 0.0041). The urinary sodium excretion rates decreased from, basal, 50 +/- 17 to 30 +/- 13, 22 +/- 10 and 19 +/- 10 mmol/h (p < 0.007), and the potassium excretion rates decreased from, basal, 43 +/- 19 to 39 +/- 16, 26 +/- 11 and 23 +/- 10 mmol/h (p < 0.0047). Endogenous clearance of creatinine (basal: 182 +/- 30 ml/min) did not change (260 +/- 84, 218 +/- 66 and 224 +/- 76 ml/h) following i.v. ANF. Inspite of this marked fluid retention, the hematocrit, expressed as relative change, was increased by 7.5%, 11.8% and 10.4%. In 2 calves we additionally measured an increased whole blood and plasma density possibly indicating increased liquid permeation to an extravascular compartment. Thus, in calves the hemodynamic effects of ANF are comparable to those seen in man. However, the failure of ANF to stimulate diuresis and natriuresis indicates a dissociation of hemodynamic and renal effects of ANF in calves.

Animals↗
PubMed1993

[Laparoscopic colon surgery--from experiment to initial clinical experience].

The technique of Laparoscopic resection of the colon sigmoideum was practised in an experimental model before starting a clinical program of laparoscopic colonic surgery. Until now, two resections of the colon sigmoideum, one ileocecal resection, one right colectomy, one Hartmann's procedure and one transversostomy have been performed laparoscopically. Three patients had colonic carcinoma. One sigmoid resection had to be converted to open surgery and this patient underwent relaparotomy because of postoperative ileus. The postoperative course of the other patients was uncomplicated. The promising initial experience demonstrates that laparoscopic colonic surgery is feasible, although further studies have to prove advantages and indications, especially with respect to oncology.

Adolescent↗
PubMed1992

Cardiac function, morphology and chromosomal aberrations in a calf with ectopia cordis cervicalis.

A male calf with ectopia cordis cervicalis inferior was investigated clinically, hemodynamically, and morphologically from the 3rd day of age until slaughter at the age of 22 months. Arterial hypertension (mean AOP 140 mm Hg), concentric myocardial hypertrophy and good ventricular contractility with normal valve function were found. Normal clinical condition at rest (cardiac output 48 l/min in the 600 kg bullock), but cyanosis and dyspnea during physical exercise were observed. Variations in the large vessels, such as persistence of the right cranial caval vein and one common pulmonary vein emptying into the left atrium, were found. Abrupt caliber differences of large arterial vessels together with a right angled aortic arch were observed, presumably contributing to increased afterload. The cytogenetic analysis showed the presence of a small marker chromosome leading to a chromosome number of 61 in a fraction of metaphases (mosaicism). Moreover, chromosome breakages were observed in many cells. From the 5 cows which were inseminated, 3 became pregnant. Ectopia cordis was not observed in any offspring. We conclude that in this animal compensated cardiac insufficiency with peripheral hypertension was established.

Animals↗
PubMed1991

Mesh-constricted varicose and dilated veins used as arterial bypass grafts.

To avoid non-autogenous vascular prostheses in coronary and peripheral vascular procedures, otherwise unusable dilated, varicose or thin-walled veins can be implanted as naturally endothelialized grafts after being calibrated by insertion into mesh tubes. In six sheep the 14 mm diameter jugular vein was inserted into a 12 cm long, 6 mm diameter Dacron mesh tube and implanted as a femoropopliteal graft. On the contralateral side the femoral vein with a maximal diameter of 7 to 8 mm was implanted. At control angiography after two months all grafts were patent, none of the wrapped grafts showed wrinkles or signs of anastomotic hyperplasia. Segments of wrapped veins were casted in paraffin under physiological pressure and cut transversely. In all cases the vein wall was pressed against the mesh tubes without forming folds. Mesh-wrapped varicose veins were used for three femorocrural and seven femoropopliteal reconstructions. All grafts showed a smooth flow surface at control angiography. Indentations occurred only at sites where thick-walled side branches had been ligated rather than oversewn. One popliteo-pedal reconstruction occluded after two months and one patient with a crural reconstruction died two months after surgery with a patent graft. The remaining grafts were patent after 11 (2-32) months. Oversized veins can be considerably constricted by tubes without forming wrinkles. By this technique varicose veins can be used as bypass grafts and in general vein grafts can be matched in size to the recipient vessel.

Aged↗
PubMed1990

A method for constricting large veins for use in arterial vascular reconstruction.

A satisfactory biologic graft can be created if dilated, but otherwise unusable veins are wrapped with a constrictive mesh tube. The purpose of this study was to determine whether a resorbable constrictive tube creates an appropriately sized vascular graft by induction of neoarterial wall growth. In 8 sheep a 5 cm segment of the carotid artery was resected and the external jugular vein inserted as a tubular graft. The vein was either wrapped with a polydioxanon (PDS) reinforced polyglactin (Vicryl) mesh (n = 4), a Vicryl mesh (n = 4), or a Dacron mesh tube (n = 3) to achieve a diameter reduction to 7 mm. Or the vein was used without reinforcement (n = 3). At angiography after 6 months the unreinforced veins had a diameter of 19 mm (range 15-22). The Vicryl reinforced veins measured 9.4 (8.5-10) mm, but 3 of 4 developed aneurysmatic dilatations at sites of valve sinuses with a mean diameter of 19 (15-21) mm. PDS reinforced veins measured 7.4 mm (7.1-7.9). Two of 4 had minor aneurysms of 13 and 16 mm. The two remaining PDS reinforced grafts were indistinguishable from the native artery. Dacron tubes reduced the vein size reliably to 7.6 (7.5-7.9) mm, but showed narrowing at the proximal anastomoses (PDS 7.2 +/- 0.4, Dacron 6.1 +/- 0.4, p = 0.016). PDS wrapping reduced maximal graft diameter to 10.9 +/- 4 mm as compared to that of the native vein, 18.7 +/- 3.5 (p less than 0.05). Resorbable meshes can reduce the diameter of a venous graft by strengthening the vessel wall.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Sustained heart failure induced by repeated microsphere injections for left ventricular assist device testing.

A subacute to chronic heart failure model was established to test left ventricular assist device (LVAD) systems. Five calves were anesthetized and instrumented. Heart failure was induced by daily injection of polystyrene microspheres (37-70 microns) into a left coronary catheter. The last three animals had an atrio-aortic pulsatile LVAD implanted. Cardiac output (CO) decreased from 12 to 5.5 L/min, and SV from 120 to 60 ml, whereas left atrial pressure (LAP) increased from 12 to 25 mmHg within 10 to 20 days in the two animals without LVAD support. Both animals stopped eating and drinking. The LVAD experiments were terminated after 5, 10, and 11 days. Cardiac function was determined during daily pump-off tests. After repeated microsphere injections, LAP increased to 30 and 50 mmHg, and CO decreased to 4 and 6 L/min without pump support. Daily stepwise microsphere injections induce a sclerotic cardiomyopathy in a safe and reliable manner.

Animals↗
PubMedDate not supplied

Improved biocompatibility by postfixation treatment of aldehyde fixed bovine pericardium.

Long-standing release of locally cytotoxic aldehyde concentrations is responsible for lack of spontaneous endothelialization and increased calcification of glutaraldehyde fixed bovine pericardium. Postfixation treatment with amino acids made in vitro endothelialization of bioprosthetic heart valves possible. Such treated pericardium calcified significantly less (13 +/- 4 micrograms/mg dry weight) than did conventionally processed pericardium (114 +/- 25 micrograms/mg) after 63 days of subcutaneous implantation in rats. To test the ability for spontaneous in vivo endothelialization, 5 sheep had 6 mm grafts made from postfixation treated pericardium (PTP) implanted into the carotid artery, compared to PTFE grafts on the contralateral side, which spontaneously endothelialize in animal models. In a pregnant animal, both grafts occluded. All remaining pericardial grafts remained patent, but one additional PTFE graft occluded and another one was stenosed. The area covered with red thrombus was significantly smaller in the PTP grafts (3.05 +/- 3.9%) than in the PTFE grafts 42 +/- 14% (p = 0.0036); TEM and SEM showed endothelial cells growing directly on the PTP, but only on myofibroblasts in PTFE grafts. Postfixation treatment of glutaraldehyde fixed pericardium aids spontaneous endothelialization and decreases tissue calcification.

Animals↗