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: ΔfHb/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: ΔfHb/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 η < 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. The study supports theories on mechanical hemolysis predicting a hemolysis at shear levels of less than 500N/m2 depending on exposure time.

With the methods used it was possible to develop a pump with very low hemolysis potential. For further reduction of blood trauma and correlated thrombus formation basic studies on cell damage in recirculating blood and also advanced flow studies in rotary pumps would be desirable.

Microspheres Based Detoxification System: In Vitro Study and Mathematical Estimation of Filter Performance

Because of the closed plasma (secondary) circuit in the Microspheres based Detoxification System (MDS), a convective blood purification system, the same amount of filtrated plasma is backfiltrated into the blood circuit. Therefore, there is no direct way to determine the ultrafiltrate production rate, which is an important factor of efficiency. The only possible way to estimate the filtration properties of the filter is to consider pressure values. In this study the pressure distribution in the filter was investigated in vitro. To explain the results and to calculate inaccessible parameters, a mathematical model was estabilshed which also considered the asymmetric behaviour of the filter membrane. The result was a linear pressure gradient, agreement with the measurements was reasonably good (calculated primary pressure loss differes <13% from measured value when using mean measured filter resistance as model parameter). Linear pressure distribution offers the possibility of easily calculating the filtration length, a parameter which can be used to estimate the filter condition. The comparison between calculated filtration and backfiltration rates offers an instrument of control for these values.

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, AID interface and PC. Continuous EMG-recording was performed in all cases. Simultaneous recording of muscle tension and EMG revealed a close correlation (lrl=0.95, p < 0.0001) between 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.

Human ECGs corrupted with real CPR artefacts in an animal model: generating a database to evaluate and refine algorithms for eliminating CPR artefacts

AIM

For the analysis of ECG rhythms during ongoing CPR, single- or two-channel methods have been proposed to eliminate artefacts from the CPR-corrupted ECG. To refine, test and evaluate these algorithms with a realistic data set, we introduce an animal model with which we created an extended database of human ECGs with real CPR artefacts.

MATERIAL AND METHODS

In a pig model real CPR-related artefacts were added to annotated human emergency ECGs. Via a special catheter placed in the oesophagus, ECG sequences (duration>10s) were fed in close to the dead pig's heart. The resulting surface potential was recorded on the thorax without and during ongoing chest compressions, which were monitored using a miniature force sensor.

RESULTS

The animals served as a vehicle for human ECGs, making it possible to create a database in which 918 real human ECG sequences (437 shockable and 481 non-shockable) were corrupted with CPR-induced artefacts. The achieved signal-to-noise ratios (SNR) ranged from -17 to +15 dB, sensitivity was 93.5% and specificity was 50.51%. The fed-in ECG and the uncorrupted surface ECG correlated almost perfectly (r=0.926+/-0.081; n=918), indicating negligible signal distortion due to the dead pig itself.

CONCLUSION

As the generated database includes both the original and the corrupted ECG covering a wide range of SNRs as well as the compression force signal, it provides an extended data set to evaluate the reconstruction performance of CPR artefact-removal algorithms.

Effect of cardiac tamponade on plasma concentrations of atrial natriuretic peptide (ANP) in calves

To study the effect of cardiac tamponade on plasma concentrations of atrial natriuretic peptide (ANP) female calves received an infusion of 450 ml of 0.9% saline into the pericardial space. This was accompanied by a parallel rise in both, right atrial pressure (from 4.5 +/- 2.6 mm Hg to 14.1 +/- 3.8 mm Hg (p less than 0.01] and in intrapericardial pressure (from 0.4 +/- 2.0 mm Hg to 12.9 +/- 3.9 mm Hg (p less than 0.01] and a fall in cardiac output from 11.4 +/- 1.9 l/min to 8.5 +/- 2.4 l/min (p less than 0.01). Plasma concentrations of ANP remained unchanged in 7 of 9 experiments. During these seven experiments plasma concentrations of renin and aldosterone increased from 0.65 +/- 0.27 X 10 E-4 GU/ml to 1.04 +/- 0.43 X 10 E-4 GU/ml (p less than 0.01) and from 2.7 +/- 0.9 ng/dl to 11.4 +/- 6.1 ng/dl (p less than 0.01), respectively. On two occasions, which were characterized by an excessive fall in cardiac output (to less than 40% of initial values) cardiac tamponade was followed by an extensive rise in the plasma concentrations of ANP, renin and aldosterone. These results indicate that an increase in intra-atrial pressure per se is not the decisive factor in the control of ANP secretion. Since atrial transmural pressure does not change during cardiac tamponade ANP concentrations are, as a rule, unaltered by that condition. An increase in plasma ANP is seen only during preshock hemodynamic conditions possibly due to a reduced intra-atrial volume.

Influence of fatty acid composition in mammalian erythrocytes on cellular aggregation

The rheologic properties of red blood cells (RBC) are determined by humoral and cellular factors. Fatty acid composition of the RBC phospholipid bilayer is one factor influencing membrane fluidity this could affect RBC aggregation because of a higher bias of RBC deformability. The present investigation was performed to investigate a possible relationship between fatty acid composition and erythrocyte aggregation using animals with high RBC aggregation (horse and pig) and animals with immeasurable RBC aggregation (sheep). Horse and pig showed similar distribution of the four major components palmitoleic acid (C16:0), stearic acid (C18:0), oleic acid (C18:1n9), and linoleic acid (C18:2n6). The sheep's saturated fatty acids C16:0 and C18:0 were decreased, whereas unsaturated oleic acid (C18:1n9) showed a two fold increase in comparison to horse and pig. It can be assumed that the fatty acid bilayer is a minor factor influencing erythrocyte flexibility due to its influence on membrane fluidity and therefore there might be an existing link to erythrocyte aggregation. The sheep has relatively dense erythrocytes with low cell volumes. Therefore, the absence of aggregation might be postulated to arise from geometric factors against the expected effect of unsaturated fatty acids on membrane fluidity, the higher level of unsaturated fatty acids in ovine erythrocytes over that found in horse and pig was surprising. The present result, which accords with former studies, indicates that the geometric factor given by the intracellular skeleton overrides any effect of membrane composition on aggregation in sheep.

Animal experiments with ultra-high molecular weight polyethylene (UHMW-PE) stabilised with alpha-tocopherol used for articulating surfaces in joint endoprostheses

Numerous investigations proved the impressive suitability of alpha-tocopherol as a stabilizer for ultra-high molecular weight polyethylene (UHMW-PE) used for endoprostheses. Regarding the biocompatibility of this new biomaterial, in-vitro celltoxicity tests gave no hint for a cyto- or genotoxic activity. In this study, animal experiments are carried out to further ensure the biocompatibility of this biomaterial. Thin UHMW-PE-films (20 x 6 x 0.23 mm3) were implanted subcutaneously into rats. Morphology and reactivity of surrounding connective tissue against either pure UHMW-PE material or UHMW-PE containing alpha-tocopherol were studied at timed intervals (2 weeks, 3 month, and 6 month after operation) in 3 groups of animals, each group comprising 10 animals. Parallel to these tests, material changes were investigated in these 3 groups of 10 animals at the same intervals after operation with the help of infrared spectroscopy (FTIR). Within the implantation time, no noteworthy oxidative degradation could be observed. The amount of lost alpha-tocopherol due to diffusion is low enough to ensure a lifetime stabilisation of the UHMW-PE. The implants were all well tolerated and definitely encapsulated already 2 weeks after operation. Presence or absence of alpha-tocopherol in the implants did not evince morphological differences. Therefore, negative consequences were not manifest in the presence of alpha-tocopherol.

Fetal and juvenile animal hemorheology

The study provides information on the blood fluidity in healthy, juvenile sheep and rabbits during growth (n = 18), and shows also data from fetal rabbits and cats. In the fetal rabbit (n = 3) and cat (n = 2), whole blood viscosity (WBV; LS30, Contraves, Switzerland) and plasma viscosity (PV; OCR-D, Paar, Austria) was low (WBV (0.7 s(-1)): rabbit: 3.28/3.00/2.44; cat: 7.87/10.88; WBV (94 s(-1)): rabbit: 2.57/2.48/2.39; cat: 2.75/3.73 mPa s) (PV: rabbit: 1.10/1.10/1.05; cat: 1.27/1.39 mPa s), which was associated with a low plasma protein concentration and a low erythrocyte count despite a high erythrocyte volume. After parturition, blood viscosity increased in rabbits in parallel with hematocrit, while MCV decreased (WBV (0.7 s(-1)): 9.28 (8.07/10.88); WBV (94 s(-1)): 3.67 (3.62/3.82); PV: 1.15 (1.15/1.25) mPa s). In contrast, in the sheep, whole blood and plasma viscosity decreased after delivery (WBV (0.7 s(-1)): 1.31 (0.94/1.88); WBV (94 s(-1)): 2.45 (2.43/2.85) PV: 1.24 (1.23/1.29) mPa s). Hematocrit and MCV decreased, while erythrocyte count increased under these circumstances. In summary, whole blood viscosity was similar among fetal sheep, rabbits, and cats and is diminished compared to adult individuals to guarantee an optimal oxygen supply during a period of life in which the oxygen maintainance of the child depends on the health and the environment of the mother. However, during growth, blood viscosity rose in rabbits, while it continuously decreased in the sheep. At an unknown time point this fall in blood viscosity in lambs must reverse, since adult sheep again show a higher blood viscosity than juvenile lambs at the age of 2 months.

Large interarcuate spaces in the cervical vertebral column of the tyrolean mountain sheep

Large interarcual spaces have been described between the arcus vertebrae C5/C6 and C6/C7 in the cervical vertebral column of Nubian goats. This aperture enables direct access to spinal cord and rootlets without the need to perform a hemilaminectomy. The present study was performed in order to determine whether these large interarcual spaces can also be found in the vertebral column of the Tyrolean mountain sheep, as this small ruminant, which is anatomically very similar to the Nubian goat, is frequently used for experimental purposes at the Surgical University Clinic in Austria. The carcasses of 10 sheep (six females, four males; range of age: 2.5-6 years, range of weight: 52-89 kg) were dissected and the vertebral column was exposed. All 10 sheep showed elliptic openings between the fourth cervical and the first thoracal vertebrae. Three sheep had additional openings between the first and the second thoracal vertebrae. All openings were covered solitarily by the ligamentum flavum and under this ligamentum lay the spinal cord without any further osseous or ligamentous protection. These findings are not mentioned in the common textbooks of veterinary anatomy and deserve attention, as they can be a step forward towards non-traumatic experimental surgery on the spinal cord.

Activation of nuclear factor-kappa B significantly contributes to lumen loss in a rabbit iliac artery balloon angioplasty model

BACKGROUND

To investigate the contribution of inflammation to postangioplasty lumen loss, we used an adenoviral gene therapy approach to inhibit the central inflammatory mediator nuclear factor-kappaB (NF-kappaB) by overexpression of its natural inhibitor, IkappaBalpha.

METHODS AND RESULTS

The adenovirus carrying human IkappaBalpha was applied immediately after balloon dilatation by a double-balloon catheter in a rabbit iliac artery restenosis model. Immunohistochemistry of IkappaBalpha revealed that mainly smooth muscle cells of the media but also cells of the adventitia were transduced and expressed the transgene IkappaB alpha for >/= 8 days. At this time point, intercellular adhesion molecule-1 (30%) and monocyte chemotactic protein-1 (50%) expression, as well as recruitment of macrophages into the wounded area (90%), were significantly reduced in IkappaB alpha-treated vessels. In addition, expression of inhibitor of apoptosis proteins was reduced and the percentage of apoptotic cells was increased compared with control-treated contralateral vessels. Animals killed 5 weeks after treatment exhibited a significantly reduced degree of lumen narrowing (P<0.02) on the side treated with adenovirus IkappaBalpha. The lumen gain of approximately 40% was due to positive remodeling.

CONCLUSIONS

From these data, we conclude that balloon angioplasty-induced activation of NF-kappaB contributes to lumen loss likely via induction of an inflammatory response and a decrease in the rate of apoptosis. These data show for the first time that inflammation mediated by NF-kappaB is involved in postangioplasty lumen narrowing. Specific and more potent inhibitors of NF-kappaB might therefore be a useful therapeutic measure to improve clinical outcome after balloon dilatation.

Biocompatibility and performance of the Wallstent and several covered stents in a sheep iliac artery model

PURPOSE

To compare the biocompatibility and performance of various stent-grafts to those of a bare stent in an ovine model with a subchronic (3 months) endpoint.

MATERIALS AND METHODS

Three different types of stent-grafts (ePTFE/nitinol, n = 8; polyester/nitinol, n = 8; and polycarbonate urethane/cobalt-alloy, n = 8) and a bare stent as a control (Ni-Co-Ti-steel-alloy, n = 8) were implanted in the iliac arteries in eight female sheep. One type of each stent-graft was implanted per animal, two implants at each side. The implantation sites for each type varied from animal to animal. Angiographic control and intravascular ultrasound (IVUS) imaging were performed before and after implantation, after 2 months, and before explantation at 3 months and were used to characterize patency and to assess intimal hyperplasia. After 3 months, the implants were retrieved and subjected to histologic evaluation (after methacrylate embedding, cutting, and histologic staining) to characterize the biologic response.

RESULTS

Implantation was technically successful in all procedures. At 2 and 3 months after implantation, all segments in which stents had been implanted were patent. Marked neointima formation was found in the polyester-covered stent-graft that showed significant luminal narrowing of 50%, compared to the ePTFE-covered (24%) and polycarbonate urethane-covered endoprostheses (22%), as well as the bare stent (Wallstent; 9%; P < .001). A minimal inflammatory vessel wall reaction was demonstrated for the polyester-covered and ePTFE-covered endoprostheses; the polycarbonate urethane-covered stent-graft's response was demonstrable but not significantly different from that of the Wallstent. At 3 months, the ePTFE-covered stent-graft showed incomplete (>90%) endothelial coverage; in the other endoprostheses, complete but partially immature endothelialization was found.

CONCLUSION

All stent-grafts induced an inflammatory vessel wall reaction with neointimal hyperplasia. The polyester-covered endoprosthesis caused a marked reaction with 50% luminal stenosis. Endothelialization was retarded with the ePTFE-covered stent-graft. The bare stent performed best in regard to neointimal formation and caused the least inflammatory response.

Epinephrine application via an endotracheal airway and via the Combitube in esophageal position

OBJECTIVE

To compare plasma concentrations and cardiovascular effects of epinephrine after application via a conventional endotracheal airway and via the esophageal lumen of a new emergency airway, the esophageal tracheal Combitube.

DESIGN

Prospective, randomized study.

SETTING

Center for Biomedical Research, University of Vienna.

SUBJECTS

Fourteen juvenile swine received either an endotracheal tube (Group A) or a Combitube in esophageal position (Group B).

INTERVENTIONS

In Part I of the study, epinephrine was administered during spontaneous beating of the heart; in Part II, epinephrine was administered during cardiopulmonary resuscitation, using a ten-fold higher dosage in Group B, respectively.

MEASUREMENTS

Plasma epinephrine levels were measured 1, 2, 3, 5, 7, 10, 15, and 30 mins after application. Systolic arterial blood pressure and cardiac output in Part I, and end-tidal CO2 and coronary perfusion pressure in Part II were recorded.

MAIN RESULTS

In Part I, increased levels of plasma epinephrine and systolic arterial pressure were maintained significantly longer in Group B when compared with Group A. In Part II, no significant differences between the groups were found with regard to plasma epinephrine levels and hemodynamic variables.

CONCLUSION

Epinephrine applied via the esophageal lumen of the Combitube in a ten-fold higher dosage has similar effects on plasma epinephrine levels and hemodynamic variables compared to endotracheal administration.

Neovascularisation of the testes by experimental omentotesticulopexy

With the currently used surgical procedures, surgical correction of extreme forms of high undescended testes is associated with an atrophy rate of 10% to 30%. In this experimental study in two groups of Sprague-Dawley rats of pubescent age, we examined whether fixation (pexy) of an omental flap on the testis (omentotesticulopexy = OMTX) permits preservation of the viability of the parenchyma. A left-sided OMTX was performed in group 1 with the animals under general anaesthesia. An omental flap was prepared. The tunica albuginea of the testis planned for OMTX was pierced with a needle (26 x 23 G) within an area with a diameter of 1 cm; a puncture distance of 2 mm was used. The omental flap was then fixed using absorbable monofilament 6-0 interrupted sutures. Six weeks later the spermatic vessel was transected at this site. The right testis was left untouched throughout the procedure; it remained in situ. In group 2 only the spermatic vessel on the left side was severed. The right testis was not manipulated and remained in situ. After a total of 10 weeks both testes were removed from all rats and fixed in formalin. Standardised haematoxylin and eosin staining was performed and histological sections were obtained. The size of the testicles, Leydig-cell count, viability, and calcified areas within the tissue were determined for all testicles. Student's t-test was used for statistical evaluation. The study showed that OMTX leads to neovascularisation in the area of fixation and that viability can be preserved within this area.

Microspheres based detoxification system: in vitro study and mathematical estimation of filter performance

Because of the closed plasma (secondary) circuit in the Microspheres based Detoxification System (MDS), a convective blood purification system, the same amount of filtrated plasma is backfiltrated into the blood circuit. Therefore, there is no direct way to determine the ultrafiltrate production rate, which is an important factor of efficiency. The only possible way to estimate the filtration properties of the filter is to consider pressure values. In this study the pressure distribution in the filter was investigated in vitro. To explain the results and to calculate inaccessible parameters, a mathematical model was established which also considered the asymmetric behaviour of the filter membrane. The result was a linear pressure gradient, agreement with the measurements was reasonably good (calculated primary pressure loss differs <13% from measured value when using mean measured filter resistance as model parameter). Linear pressure distribution offers the possibility of easily calculating the filtration length, a parameter which can be used to estimate the filter condition. The comparison between calculated filtration and backfiltration rates offers an instrument of control for these values.