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.

Compliance and formation of distal anastomotic intimal hyperplasia in Dacron mesh tube constricted veins used as arterial bypass grafts

Dilated and varicose veins constricted with a Dacron mesh tube were successfully used as arterial bypass grafts to avoid nonautogenous vascular prostheses. Mesh constriction has also been used to adapt the venous graft lumen to the diameters of grafted arteries. The influence of the external mesh on the wall elasticity of such venous grafts and the reactions of the host artery were not investigated. Elastic properties of mesh constricted autologous veins used as arterial grafts in femoropopliteal reconstructions, as well as consecutive formation of distal anastomotic intimal hyperplasia (DAIH), were investigated in this experiment. Twenty-four autologous venous grafts were implanted in 12 sheep. Grafts were left natural (Groups 1 and 3) or were constricted with an external Dacron mesh (Groups 2 and 4); their diameters were left unchanged (Groups 1 and 2) or were matched to the diameter of the host artery (Groups 3 and 4). Wall elasticity of the graft, distal anastomosis, and distal artery were measured by locally applied crystal transducers during surgery and follow-up. Formation and localization of DAIH was evaluated histomorphologically after a median of 8.3 months. Graft wall elasticity was found to be lower (54.6 vs. 147.9, P = 0.006) and overall DAIH was found to be higher in mesh tube grafts (49.42 vs. 20.8 microns, P = 0.001, Mann-Whitney U-test). No differences in elasticity and DAIH formation were observed between grafts with adapted and large diameters. Constriction of venous grafts by a Dacron mesh tube reduces graft wall elasticity and promotes formation of DAIH. To avoid such an increased mismatch in compliance while making use of the advantages of this method, the external mesh tube must not be brought close to the distal anastomotic area itself.

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.

Myocardial protection with Bretschneider cardioplegic solution--an evaluation of full oxygenation

In the present study the effect of oxygenated Bretschneider cardioplegia on high-energy phosphates [adenosine triphosphate (ATP), adenosine diphosphate (ADP) and creatine phosphate (CP)] and hemodynamics was evaluated in the isolated working rabbit heart. Hearts were obtained from 37 adult white Elco rabbits (3,100 +/- 110 g). After a 20-min working period 14 hearts were arrested with Bretschneider cardioplegia (8 degrees C) oxygenated with 98% oxygen (O2) and 2% carbon dioxide in comparison to 14 hearts receiving Bretschneider solution saturated with 98% nitrogen (N2) and 2% carbon dioxide as a control group for either 60 or 90 min (O(2)60, O(2)90, N(2)60, N(2)90 groups, n = 7). Seven hearts were used to determine preischemic baseline values of ATP, ADP and CP, 2 were excluded. The results showed a significantly poorer preservation of high-energy phosphates in hearts receiving oxygenated Bretschneider cardioplegia as compared to hearts receiving nitrogenated cardioplegia (p < 0.05). Postischemic recovery of hemodynamics did not demonstrate any statistically significant differences between the groups. However, the intragroup analysis showed a tendency towards weaker hemodynamic recovery in hearts treated with oxygenated cardioplegia. in contrast to the beneficial effect of oxygenated St. Thomas solution. In conclusion our findings suggest that oxygenated Bretschneider cardioplegia leads to significantly poorer preservation of high-energy phosphates and depressed hemodynamic recovery.

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.

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.

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.

In vitro investigation of thrombogenesis in rotary blood pumps

Thrombus formation at sealing and stagnation areas remains a major problem in the development of rotary blood pumps. Until now, the complex phenomena could only be studied in vivo. In this study, an in vitro mock circulation previously used for hemolysis studies was adapted for thrombosis evaluation. Blood was collected in the slaughterhouse with strict avoidance of air contact and was heparinized (1.5 U heparin/ml blood; activated coagulation time [ACT]: initially, 140-180 s; after collection, 400-600 s). During the test, the ACT decreased gradually. The tests were stopped after 90 to 180 min at an ACT of 1.5 times the initial value. Thrombus formation was observed at the same locations as observed in left-heart assist devices (sealing area, connecting bolts, and stagnant water areas at connectors). The thrombi were similar in shape, color, and histology to those found after 2 to 4 days in vivo. This test provides a valuable tool for evaluating thrombus formation in prototypes and screening tests of different rotary pump designs.

Minimization of hemolysis in centrifugal blood pumps: influence of different geometries

Centrifugal blood pumps are of substantial importance for intraoperative extracorporeal circulation and for temporary cardiac assist. Their development and improvement raises many specific questions, especially on mechanical blood properties, flow distribution, and the resulting biocompatibility. In this comprehensive study the influence of various pump geometries on blood trauma was investigated. For this purpose analytical calculations, hydrodynamic performance, numerical simulation, in vitro hemolysis tests and in vivo experiments were used. The gap between rotor and housing was found to be crucial showing a distinct minimum of hemolysis at a gap of 1.5 mm (in vitro increase of plasma free hemoglobin per 100 ml plasma an hour: delta fHb/hour = 2.4 +/- 0.83 mg%/h at 1.5 mm versus 12 +/- 2.2 mg%/h at 2.5 mm; p < 0.05). Housing diameter and shape of the vanes were of less importance for blood traumatization (d = 60 mm: delta fHb/hour = 6.36 +/- 1.8 mg%/h; d = 70 mm: fHb = 7.1 +/- 1.9 mg%/h; straight radial vanes: 5.2 +/- 1.8 mg%/h; straight inclined vanes: 6.8 +/- 1.2 mg%/h; flexed vanes: 6.1 +/- 2.0 mg%/h). Three animal experiments confirmed the optimization of geometry, with a mean fHb of 2.5 to 3.2 mg% in steady state. Hydrodynamic efficiency revealed to be a necessary, but not a sufficient and sensitive criterion for hemolysis minimization (e.g. changes of eta < 10% for changes of fHb > 500%). Numerical simulation gives an improved insight in flow distribution, but can not yet be applied for quantification of blood trauma.(ABSTRACT TRUNCATED AT 250 WORDS)

Platelet function after total artificial heart replacement: clinical application and experiment

Clinical application of artificial blood pumps for mechanical circulatory support has been hampered by thromboembolic events. The underlying mechanisms are complicated and may differ from patient to patient. Because the calf is commonly used for artificial heart studies, the object was to determine the value of data gained in an animal model. To this end, the average of 10 calf experiments was compared with three clinical applications of an orthotopically implanted total artificial heart in patients with terminal heart failure. Platelet reactivity was investigated in vitro by collagen-induced whole blood aggregometry, radioimmunoassay methods, and scanning electron microscopy over a 10-day period. An analogous periodicity of platelet function was found in human and animal recipients. Improvement of platelet function preceded that of platelet counts in the early postoperative phase. Exaggerated responses to aggregative agents were observed at days 3 and 7. On the basis of our data, we believe that we can comment about the prospective course of the function and number of human platelets, which may contribute to the identification of critical phases of such treatment, during total artificial heart replacement.

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.

Mechanical blood traumatization by tubing and throttles in in vitro pump tests: experimental results and implications for hemolysis theory

Blood has become essential as a test fluid to evaluate hemolysis and biocompatibility of blood pumps in vitro. The blood is usually pumped from a blood bag into a circuit against elevated pressure. A throttle or a length of tubing is used to produce the pressure head. Blood damage caused by the shear stress in these pressure-reducing devices should be minimal. It is not known whether the high but short-lasting shear stress in a throttle is more or less damaging to the blood than the low but long-lasting stress in tubing. In this study, throttles (width 11 mm, minimal height 0.9 mm, length 30 mm; shear stress = 136 N/m2 lasting for 3.23 ms); and tubing (inner diameter 9.5 mm, length 4.5 m, shear stress = 4.5 N/m2 lasting for 3.5 s) were compared at a flow of 5 L/min and a pressure drop of 150 mm Hg. Experiments (n = 10) with bovine blood were performed in two parallel setups using Bio-Medicus pumps BP80. Free hemoglobin in plasma (fHb) and thromboxane B2 (TXB2) were measured. After 6 h, the fHb increase was 31.9 +/- 19.1 mg% for the throttle setup and 32.3 +/- 16.2 for the tubing setup. The TXB2 release was 296 +/- 70 and 305 +/- 54 pg/0.1 ml respectively after 4 h. In summary, no significant differences between the two setups for either fHb or TXB2 could be detected. So the use of a throttle, which requires far less priming volume and a smaller blood-contacting surface while also offering a wider range of adjustment, seems preferable.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro and in vivo endothelialization of glutaraldehyde treated bovine pericardium

In an experimental study, endothelial cell seeding on glutaraldehyde-fixed and detoxified bioprosthetic tissue, suitable for valve fabrication, was investigated in vitro. These findings were compared to spontaneous endothelial cell ingrowth on vascular grafts fabricated from the same materials. Special consideration was given to the quality of cell attachment with regards to improved shear stress resistance in the endothelial layer covering the bioprosthetic surface. On glutaraldehyde detoxified bovine pericardium, in vitro endothelial cell seeding resulted in uninhibited cell proliferation, but the cells were loosely bound to the underlying tissue. In vivo, endothelial cells grew spontaneously over the surface of vascular implants in direct contact with the bioprosthetic material. In contrast to standard fixed bovine pericardium, a significant decrease in thrombotic appositions could be observed. Cells exhibited intensive production of extracellular matrix, which renders the method of spontaneous in vivo cell ingrowth as the most promising approach for further research.

In vitro hematological testing of rotary blood pumps: remarks on standardization and data interpretation

Pump test procedures using blood will have to meet several standards not only to obtain reliable results in vitro but also to allow comparison of results of different investigators. This article reviews some of the issues that should be considered in pump testing, especially referring to the discussions held at the International Workshops on Rotary Blood Pumps in 1988 and 1991. The test loop itself should meet some requirements such as constant physiological temperature, standardized circulating volume, control of pressure and flow, and exact definition of the blood-contacting surface. Specifications have to be made concerning the test fluid blood, including sampling technique, anticoagulation, blood gases, pH, and glucose level. Only fresh blood should be used. Heparin is recommended for anticoagulation because it will be used also in vivo. Different procedures for cleaning and rinsing of plastic materials for reuse are mentioned. Bacterial overgrowth, which can lead to extreme oxygen consumption and acidosis, may be avoided through addition of antibiotics (e.g., gentamicin). To be able to compare data of the different working groups, a new modified index of hemolysis (MIH) has been defined.

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.

Diminished release of atrial natriuretic factor in calves with a total artificial heart

Venous hypertension after total artificial heart (TAH) replacement, a common problem in humans as well as experimental animals, is thought to be related to reduced release of atrial natriuretic factor (ANF) due to atrial damage. To verify this hypothesis, we stimulated the release of ANF in 6 calves before (-7 days) and after TAH replacement (+25, +50, +80, and +100 days) by the rapid (+ = 10 min) infusion of 2 L of Ringer's solution. In normal calves (-7 days) this procedure induced a rise in plasma concentration of ANF from 18.5 +/- 12 to 31.6 +/- 12 pmol/L (p < 0.05). After TAH the ANF release continuously decreased (analysis of variance, p < 0.02). Thus, ANF increased by 9.8 +/- 9.3, 6.8 +/- 17.5, 0.4 +/- 5.2, and 0.5 +/- 3.2 pmol/L at days 25, 50, 80, and 100, respectively. The central venous pressure increased by 3.4 +/- 1.5 mm Hg (before TAH) and by 6 +/- 2.9 mm Hg (after TAH) during this procedure. A decrease in plasma concentrations of aldosterone, most likely due to extracellular volume expansion and a decrease in total protein plasma concentrations and in hematocrit due to the dilution of blood, was seen in each experiment. Necropsy demonstrated massive atrial dilatation and myocardial dystrophy with atrial fibrosis. ANF granules were present to a small extent in every calf. We conclude that rapid intravenous infusion is an adequate stimulus to release ANF in normal calves. After TAH implantation the release of ANF by high venous pressure declines although ANF granules are still present in the damaged atrial stumps. Therefore, the loss of stimulated ANF could contribute to the observed increase in venous pressure in TAH calves although other pathophysiologic mechanisms cannot be excluded.

Effect of stationary guiding vanes on improvement of the washout behind the rotor in centrifugal blood pumps

In centrifugal pumps, there always exists an area of stagnation between the rear of the rotor and the rear housing wall that promotes thrombus formation around the axle. Some current devices overcome the problem by using holes in the rotor plane, leading to increased hydrodynamic losses and shear stress. In this study, a simple apparatus was developed to overcome this problem. Guiding vanes were fixed to the rear housing wall. These vanes decrease the tangential velocity of the fluid and thus the centrifugal force, leading to an increased secondary flow toward the axle. The effect of such vanes was studied in videographic and ultrasound studies. An increase of washout and mixing between the flow layers could be demonstrated (stay time < 200 msec versus several seconds without vanes). In the first animal experiment using nonoptimized vanes, there was no thrombus at the back plane or the seal, and only a small thrombus at the transition between axle and rotor. Hemolysis was slightly elevated (3.2 mg/dl versus 2.5 mg/dl in control experiments). In conclusion, it is highly likely that this simple system will improve the flow characteristics in centrifugal pumps.

Noninvasive monitoring of rotary blood pumps: necessity, possibilities, and limitations

Although rotary blood pumps do not contain an inherent mechanism for adaptation to physiological flow necessities, hitherto only a few efforts have been made to obtain robust monitoring and control methods. This paper discusses the necessity of noninvasive monitoring of such pumps and the crucial points of sensor selection and development. A strategy of monitoring atrial pressure out of the data obtained by the collapse of the atrial wall around the inflow cannula and initial results on animal tests and computer simulation of this method are discussed. This approach might lead to reliable and demand-responsive controllers, if some basic criteria are fulfilled.

Long-Term Results of Nervous Tissue Alterations Caused by Epineurial Electrode Application: An Experimental Study in Rat Sciatic Nerve

In order to evaluate the long-term effects of epineurial electrode application for functional electrical stimulation (FES) the left sciatic nerve of seven rats was exposed. Four ring-shaped stainless steel wire electrodes were sutured to the epineurium of each nerve in the same manner as performed clinically for carrousel stimulation in man. The nerves were reexposed 1 year after implantation and the stimulation threshold to obtain a tetanic contraction in the lower limb was determined for each electrode. Afterwards the animals were sacrificed. The electrodes were excised and cross sections of the sciatic nerve directly at site of the electrodes, 2-mm proximal and 2-mm distal to them were harvested for histologic and planimetric assessment of nerve lesions. The area of damaged neural tissue was expressed as a percentage of the total cross-sectional area within the perineural sheath. The sciatic nerves of the right side served as controls. The values for the stimulation thresholds ranged between 0.1 and 1.0 mA (mean 0.43 mA). By morphometric examination five of seven nerves were seen altered, the altered areas captured between 1% and 4.8% of the total cross-sectional area of the nerves within the perineural sheath. Besides two specimens, all altered nerve segments exhibited distinct signs of nerve fiber regeneration. The clinical implications of the results for long-term electrical stimulation, such as phrenic pacing, are discussed.

[Direct diagnosis of the atherosclerotic vascular wall: possibilities and limits of intravascular ultrasound]

The clinical application of intravascular ultrasound still awaits established criteria for the interpretation of normal and diseased arterial wall structures. The aim of this preclinical study was to evaluate sonographic features of normal and atherosclerotic human arteries in vitro and to correlate these findings with histological cross-sections. Seventy-four segments from 33 human postmortem arteries of various anatomic locations were studied in saline solution using a mechanical 20-MHz transducer in a 6F catheter. In normal arteries, close correlations were found between sonographic and morphometric measurements of total wall thickness (r = 0.89), lumen circumference (r = 0.99), and of lumen area (r = 0.89, all p less than 0.001). Of 29 histologically verified atherosclerotic lesions, 19 were calcified, and all of them were correctly diagnosed with IVUS; however, acoustic shadowing prevented quantitative plaque evaluation. Of 10 fibromuscular lesions, six (60%) were correctly diagnosed with IVUS, using either direct morphologic criteria (n = 4) or indirect signs of vessel wall irregularity (n = 2), while the remainder (n = 4) were missed by IVUS due to a similar echodensity compared with the surrounding tissue. Thus, there was an overall sensitivity of 86% for the detection of atherosclerotic lesions by IVUS. In animal experiments in vivo, the feasibility of high-quality-imaging in pulsatile arteries was confirmed and pathologic changes in vein grafts were visualized. We conclude that IVUS carries the potential to directly assess arterial wall changes in vivo. The method appears very sensitive in the detection of calcified plaque, whereas fibromuscular lesions may often not be readily distinguished from normal surrounding tissue. This may limit the clinical usefulness of IVUS at the present time.

Influence of centrifugal blood pumps on the elasticity of erythrocytes

The influence of centrifugal blood pumps on the elasticity of erythrocytes was tested in an in vitro set-up. Fresh bovine blood was pumped by vaneless and impeller blood pumps with low and high hemolytic potential (1L priming volume, flow 5 L/min versus 150 mmHg, pumping time 6 hours). The elasticity of the red blood cells was measured by laser diffraction. Starting with an elasticity of 238 +/- 39, the overall change during 6 hours was 12 +/- 38 compared to a change of the control value of -13 +/- -58. Even a pump with very high hemolytic potential (Hemolysis index 21.9) did not cause relevant changes of elasticity. It is concluded that 1) elasticity is not a useful parameter to use in the evaluation of centrifugal pumps, and 2) the mechanical trauma caused by centrifugal pumps produces no relevant permanent alteration of the elastic properties of red blood cells, at least under in-vitro conditions.

Biocompatibility of aldehyde-fixed bovine pericardium. An in vitro and in vivo approach toward improvement of bioprosthetic heart valves

Aldehyde-induced side effects limit the clinical usefulness of bioprosthetic heart valves. Treatment of aldehyde-fixed pericardium with L-glutamic acid at pH 3.5 and storage in a nontoxic, bacteriostatic solution resulted in a lower degree of calcification in 63-day subcutaneous implants in rats (13.3 +/- 2 mg calcium per gram dry weight of tissue), as compared with commercially available tissue (169 +/- 24 mg/gm, p less than 0.05). Endothelial cells died within 1 day after seeding on the commercial tissue; however, considerable endothelial cell proliferation was measured, even 14 days after seeding on L-glutamic acid-treated pericardium. Improved biocompatibility of this alternative treatment may be due to stable chemical binding of free, reactive aldehyde groups.

The new small Viennese total artificial heart: experimental and first clinical experiences

For bridging to transplantation, a new small total artificial heart (TAH) design has been developed. Function of the two membrane pumps (filling volume left: 87 ml, and right: 75 ml; four mechanical disc valves and screwed connectors) for orthotopic implantation were studied in calf experiments. A calf survival up to 180 days was achieved without problems by pumping with a rate of 117 +/- 2.4 beats/min and a cardiac output of 7.4 +/- 0.7 L/min. For bridging to transplantation, the New Small Viennese TAH was implanted into a small 45-year-old patient (height 160 cm, weight 75 kg) with end-stage coronary heart disease. The patient deteriorated suddenly [mean aortic pressure: 38 mm Hg; cardiac output (CO): 1.8-2.1 L/min; anuria and multiple organ failure] while waiting for a donor heart. Even though his pericardial space was not enlarged, no fitting problems appeared. By using pumping rates of 104.3 +/- 8.7 beats/min, a cardiac output of 5.8 +/- 0.63 L/min was achieved (free hemoglobin was 4.1 +/- 0.48 mg/dl). Even though blood circulation was reestablished, after a TAH duration of 12 days, multiple organ failure persisted, and TAH bridging had to be stopped. In November 1989, a 50-year-old deteriorating transplant candidate with idiopathic cardiomyopathy was bridged for 6 days. Adjusting the heart rate to 86.5 +/- 11.2 beats/min, a CO of 6.84 +/- 0.46 L/min was achieved (free hemoglobin was 5.9 +/- 1.7 mg/dl). Because of chronic liver dysfunction, the patient developed severe icterus while on the TAH, and it took 2 months after heart transplantation to achieve physiological bilirubin concentrations. The patient recovered fully and remains in excellent condition.

Histological assessment of nerve lesions caused by epineurial electrode application in rat sciatic nerve

The left sciatic nerve of 36 rats was exposed and four ring-shaped stainless steel wire electrodes were sutured to the epineurium of each nerve in the same manner as performed clinically for "carousel stimulation" in man. The rats were sacrificed 10 days (Group 1), 3 weeks (Group 2), or 3 months (Group 3) after implantation. The electrodes were excised, the nerves were embedded in Epon, and semithin sections were obtained for histological and planimetric assessment of lesions caused by the epineurially sutured electrodes. The right sciatic nerves served as controls. The total area of neural tissue within the perineurium was determined at three levels: at the site of the electrodes, 8 mm proximal, and 8 mm distal. The area of neural tissue damaged by the surgical procedure was expressed as a percentage of the total area. In Group 1, nine of 12 nerves showed lesions ranging from 0.39% to 25.39% of the total area of neural tissue, in Group 2 eight of 11 sciatic nerves showed lesions ranging from 0.24% to 13.03% of the total area, and in Group 3 five of 12 nerves showed lesions ranging from 0.21% to 4.96% of the total area. The pathologically altered areas in Groups 2 and 3 exhibited distinct signs of nerve fiber regeneration. The reasons for the decrease in damage from Group 1 to Group 3 and the clinical implications of the results for long-term electrical stimulation are discussed.

First experimental application of multichannel stimulation devices for cardiomyoplasty

The effect of long-term application of epineural electrodes to nerves was investigated in rat experiments. Neural damage reached a maximum of 6% shortly after implantation and decreased to 3% after 1 year. Impedance and threshold of epineural electrode were investigated in sheep experiments for up to 12 months. The mean impedance was in the range of 1 kohm, while the threshold less than 1 mA. The reduction in fatigue produced by multichannel stimulation was demonstrated by sequential isometric contractions of rectus muscles in sheep. The decrease in force was only 10% after 60 minutes of multichannel stimulation as compared to a reduction of 50% for single channel stimulation. Studies of cardiomyoplasty with single channel stimulation confirmed results reported by other investigators. In acute experiments with sheep, we demonstrated fiber-selective stimulation which led to isolated contraction of the left or right distal part or the right proximal part of the latissimus dorsi muscle. Potential advantages in the application of implantable multichannel stimulation devices as compared to single channel stimulation for cardiomyoplasty include: (1) fatigue-free stimulation at submaximal force level; (2) selection of hemodynamically effective electrode combinations; (3) potential for consecutive activation of muscle fiber groups, thereby allowing better simulation of the physiological contraction of the heart muscle; (4) redundancy of electrodes in case of technical failure or dislocation; and (5) stimulation of more than one muscle, if necessary.