A FINITE ELEMENT METHOD FOR NEUTRON NOISE ANALYSIS IN HEXAGONAL REACTORS

The early detection of anomalies through the analysis of the neutron noise recorded by incore and ex-core instrumentation gives the possibility to take proper actions before such problems lead to safety concerns or impact plant availability. The study of the neutron fluctuations permits to detect and differentiate anomalies depending on their type and possibly to characterize and localize such anomalies. This method is non-intrusive and does not require any external perturbation of the system. To effectively use the neutron noise for reactor diagnostics it is essential to accurately model the effects of the anomalies on the neutron field. This paper deals with the development and validation of a neutron noise simulator for reactors with different geometries. The neutron noise is obtained by solving the frequency-domain two-group neutron diffusion equation in the first order approximation. In order to solve this partial differential equation a code based on a high order finite element method is developed. The novelty of this simulator resides on the possibility of dealing with rectangular meshes in any kind of geometry, thus allowing for complex domains and any location of the perturbation. The finite element method also permits automatic refinements in the cell size (h-adaptability) and in its polynomial degree (p-adaptability) that lead to a fast convergence. In order to show the possibilities of the neutron noise simulator developed a perturbation in a hexagonal two-dimensional reactor is investigated in this paper.

ADAPTIVE TIME-STEP CONTROL FOR THE MODAL METHOD TO INTEGRATE THE MULTIGROUP NEUTRON DIFFUSION EQUATION

The distribution of the power inside a reactor core can be described by the time dependent multigroup neutron diffusion equation. One of the approaches to integrate this time-dependent equation is the modal method, that assumes that the solution can be described by the sum of amplitude function multiplied by shape functions of modes. These shape functions can be computed by solving a _-modes problems. The modal method has a great interest when the distribution of the power cannot be well approximated by only one shape function, mainly, when local perturbations are applied during the transient. Usually, the shape functions of the modal methods are updated for the time-dependent equations with a constant time-step size to obtain accurate results. In this work, we propose a modal methodology with an adaptive control time-step to update the eigenfunctions associated with the modes. This algorithm improves efficiency because of time is not spent solving the systems to a level of accuracy beyond relevance and reduces the step size if they detect a numerical instability. Step size controllers require an error estimation. Different error estimations are considered and analyzed in a benchmark problem with a out of phase local perturbation.

Inhibitory effect of biofilm-forming Lactobacillus kunkeei strains against virulent Pseudomonas aeruginosa in vitro and in honeycomb moth (Galleria mellonella) infection model

Biofilms correspond to complex communities of microorganisms embedded in an extracellular polymeric matrix. Biofilm lifestyle predominates in Pseudomonas aeruginosa, an opportunistic Gram negative pathogen responsible for a wide spectrum of infections in humans, plants and animals. In this context, anti-biofilm can be considered a key strategy to control P. aeruginosa infections, thereby more research in the field is required. On the other hand, Lactobacillus species have been described as beneficial due to their anti-biofilm properties and their consequent effect against a wide spectrum of pathogens. In fact, biofilm-forming Lactobacilli seem to be more efficient than their planktonic counterpart to antagonise pathogenic bacteria. In this work, we demonstrated that Lactobacillus kunkeei, a novel Lactobacillus species isolated from honeybee guts, can form biofilms in vitro. In addition, the L. kunkeei biofilm can, in turn, inhibit the formation of P. aeruginosa biofilms. Finally, we found that L. kunkeei strains attenuate infection of P. aeruginosa in the Galleria mellonella model, presumably by affecting P. aeruginosa biofilm formation and/or their stability. Since L. kunkeei presents characteristics of a probiotic, this work provides evidence arguing that the use of this Lactobacillus species in both animals (including insects) and humans could contribute to impair P. aeruginosa biofilm formation.

Fluorescence probes for prokaryotic and eukaryotic cells using Re(CO)3+complexes with an electron withdrawing ancillary ligand

Re(CO)₃⁺complexes with an ancillary ligand present an electron withdrawing effect suitable for cell imaging.

Profilin sensitisation in a Mediterranean population

BACKGROUND

Sensitisation to pan-allergens has become an interesting tool for the study of the allergenic profile of different populations. Profilins are one of the most common pan-allergens to be studied because they are responsible for a large number of sensitisations and are clearly related to cross-reactivity and co-sensitisation.

OBJECTIVES

The objective of this study was to investigate the profile of sensitisation to profilins and to correlate it with sensitisation to foods and pollens.

METHODS

Six hundred and fifty-four consecutive patients were skin-prick tested with a battery of common allergens including pollens, epithelia, mites and moulds and profilin and divided into three groups depending on their sensitisation profile (non-atopic, atopic with pollinosis and atopic without pollinosis). Patients with symptoms were challenged and diagnosed with the offending food extracts. Profilin sensitisation was identified and analysed in detail.

RESULTS

According to the classification of the population, the prevalence of profilin sensitisation was estimated at 2.9% in patients suffering respiratory allergy, 4.2% in atopic patients, and 5.9% in pollen-sensitised individuals. Positive association was observed between pollen (except Cupressus and olive) and profilin but not with moulds, mites or epithelia. With respect to foods, positive association was only observed between profilin and melon sensitisation. Lastly, in terms of symptoms, positive association was only observed between profilin sensitisation and OAS.

CONCLUSION

Profilin sensitisation seems to be a marker of pollen-related poly-sensitisation in our area. Pan-allergen diagnosis seems to be an essential tool for developing and improving selection of the correct treatment for allergic patients.

Differential expression of CD30 on CD3 T lymphocytes in patients with systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune systemic disease caused as a result of an imbalance of Th1-/Th2-type cytokines. The soluble form of CD30 (CD30s) released from peripheral blood cells has been described as a marker of active disease in Th2-type immune response as in SLE. However, the expression of CD30 on CD3 T lymphocytes from patients with SLE has not been studied yet. Therefore, we have addressed our study to attempt this issue, studying CD30 expression by flow cytometry on CD3 T lymphocytes and CD4/CD8 subsets in samples from SLE patients mainly with lupus nephritis. In parallel, we have determined the production of the cytokines IL-4 (Th2), IFNγ (Th1), IL-10 and TGFβ by intracellular staining. Differences between positive CD30 T cells in healthy controls and patients with SLE were found, with a higher percentage of CD30-expressing T cells in patients with SLE (P = 0.001). In contrast to healthy controls, CD30 was mainly expressed on CD8 T cells from patients with SLE. The intracellular cytokine staining showed that TGFβ is the main cytokine expressed in CD3 T cells from patients with SLE. In addition to this, we have found a positive correlation between CD30-expressing T cells and IL-4, IFNγ, and immunosuppressive cytokines (IL-10 and TGFβ) (P < 0.05). These results suggest that CD30 could play a role in the pathogenesis of SLE and its expression on CD3 T lymphocytes is not restricted only to Th2-type response.

Mycophenolate as induction therapy in lupus nephritis with renal function impairment

BACKGROUND

Mycophenolate (MF) is effective as induction therapy for lupus nephritis (LN) in patients with normal renal function; however, little is known about its role in patients with impaired renal failure. The purpose of this study was to evaluate the response to MF in LN and its association with baseline renal function.

METHODS

Data were obtained for 90 patients from 12 Spanish renal units who were receiving MF as induction therapy for LN. Patients were classified into 2 groups: group 1 (estimated glomerular filtration rate [eGFR] ≥60 ml/min/1.73 m(2)) and group 2 (eGFR <60 ml/min/ 1.73 m(2)). The primary outcome measure was the percentage of patients who achieved any response and its relationship with initial eGFR. The secondary outcome measures were the percentage of patients who achieved a complete response (CR) or partial response (PR) and the appearance of relapses during treatment and side effects.

RESULTS

At initiation of MF treatment, there were no differences in the main parameters between group 1 (n = 63; eGFR 87 ± 23 ml/min/ 1.73 m(2)) and group 2 (n = 27; eGFR 44 ± 12 ml/min/1.73 m(2)). Exposure to prednisone and MF was similar. The percentages of patients who achieved a response in groups 1 and 2 were, respectively, 69.2 and 43.8% at 6 months and 81.3 and 73.7% at 12 months. CR was more frequent in group 1, whereas PR was similar in both groups. Four patients relapsed and side effects were unremarkable.

CONCLUSIONS

MF is effective and safe as induction therapy for LN, and response is even achieved in patients with baseline renal impairment.

[Comorbidity, anemia and response to erythropoiesis stimulating agents in chronic hemodialysis]

INTRODUCTION

Patients treated with haemodialysis have a high prevalence of co-morbidity that induces a elevate mortality risk. On the other hand, these patients have anaemia whose treatment is based in erythropoiesis stimulating agents. To date there are not enough studies to determine if co-morbidity alters erythropoietin response and the relationship between co-morbidity, response to treatment of anaemia and resistance to erythropoiesis-stimulating agents.

OBJECTIVES

We have the following objectives: i) to study the prevalence of associated diseases in patients treated with haemodialysis in our Hospital Unit and to evaluate the co-morbidity Charlson Index, ii) to know the degree of anaemia control, dose and response to erythropoiesis-stimulating agents, and iii) to determine the relationship with co-morbidity and anaemia treatment.

PATIENTS AND METHODS

We designed a retrospective study in stable haemodialysis treated patients. We calculated the Charlson co-morbidity index adjusted to age and we analysed levels of haemoglobin in the 6 months before study, dose of erythropoiesis-stimulating agents and its resistance index defined as doses of erythropoiesis-stimulating agents/weight (kg)/week/haemoglobin (g/dL). The different variables included in Charlson index were considered as independent variables and the index to repose to erythropoiesis-stimulating agents as a dependent variable, using bivariant and multivariate statistical analysis.

RESULTS

We included 58 patients (31 males and 27 females), median age of 69.5 years (range 24-88), mean haemodialysis 83.7 months. Mean Charlson index was 7.4 +/- 2.8 (range 2-13). Comorbidity-age Charlson index was 2 in 3.4% of patients; 10.3% had 3 or 4 points; 43.2% between 5 and 7 and 43,1% 8 or more. Mean haemoglobin levels was 11,7+/-1,2 g/dL. Mean erythropoiesis-stimulating agents dose was 163.7+/-114.5 IU/kg/week and resistance index 14.1+/-9.7. Most of patients (57%) had a IRE value higher than 10. Fourteen patients (24%) had haemoglobin less than 11 g/dL, and 3 of them (5.1%) received erythropoiesis-stimulating agents more than 300 IU/kg/week. Nine subjects (15.5%) was treated with high dose of erythropoiesis-stimulating agents (>300 IU/kg/week): 3 of them had Hb>or=11 g/dL and 6 had Hb<11 g/dL. We did not found that the intensity of Charlson index is related with the degree of anaemia control or response to erythropoiesis-stimulating agents.

CONCLUSIONS

Although the co-morbidity index is high and the response to erythropoiesis-stimulating agents is inadequate. In our study there is not relationship between these conditions.

[Factors which influence phosphorus removal in hemodialysis]

BACKGROUND

The sustained elevation of phosphorous among patients with end-stage renal failure is associated with elevated mortality rates. Phosphate binding agents are usually necessary to control serum phosphate levels. Phosphate removal during dialysis is limited largely due to the intracellular location of most inorganic phosphorous. The membrane surface, the frequency and the duration of therapy have proved to be very important factors in the serum phosphate control. THE AIM of our work is to investigate the influence on phosphate removal of factors that normally participate in the haemodialysis session: Plasma phosphate level (Php), treatment duration, membrane surface, high or low-flux membranes, the vascular access, dialysate flux , the volume of blood passing through the dialyzer (L) in each dialysis session and the blood flow during the first hour of dialysis. On 16 patients, we also had the possibility of comparing phosphate removal with 1.8 m(2) high-flux haemodialysis, 1.8 m(2) on-line hemodiafiltration and the on-line technique with the new Helixone dialyzer Fresenius Fx100.

METHODS

108 haemodialysis patients, 62% men, 38% women aged 21-82 years (61+/-14;mean+/-sem),) were selected for the study. Mean treatment time 4.14+/-0.41 hours (range 3.5-5 hours). The vascular access was an arterio-venous fistula in eighty five (78%) and a double lumen tunnelled catheter 23 (22%). Patients were studied under their normal every day conditions. High-flux membrane was used by 31 (30%) patients and low-flux membrane by 77 (70%). Membrane surface was: 1.7 m2:17 (16%); 1.8 m2:77 (71%); 2,1 m2:14 (13%). Dialysate flux was: 500 ml/min. 55 patients; 700 ml/min: 53 patients. In 16 out of 108 patients we had the possibility of using on-line hemodiafiltration with ultrapure bicarbonate-buffered dialysate. Phosphate mass removal (MPO4) was calculated using the formula:MPO4=0.1 t-17+50 Cds 60+11Cb 60 (1), where t is treatment time in minutes, Cds60 and Cb60 are phosphate concentrations in dialysate and plasma measured at 60 min from the beginning of hemodialysis in mg/dl, and MPO4 is the estimated phosphate removed in mg/treatment.

RESULTS

We found a good correlation between phosphate removal and serum phosphate levels (p=0.01), but not with the membrane surface or treatment duration. Phosphate removal was 640+/-180 mg/session with low-flux membrane and 700+/-170 mg/session with high-flux membrane (p=0.280). The MPO4 was 720+/-190 mg/treatment in patients with a AV fistula and 620+/-180 in patients with a tunnelled catheter (p=0.023). We found a good correlation between phosphate removal and the volume of blood (L) that passed the dialyzer in each session (r=0.001) but we did not find a correlation between phosphate removal and KT/Vurea, the dialysate flux or the ultra filtration. On-line technique did not increased the MPO4(733+/-280 mg, p=0.383). The on-line technique with the new dialyzer (Fresenius Fx100), increased the phosphate removal to 759+/-199 mg/session (p=0.057).

CONCLUSION

Phosphate removal during dialysis is influenced by Plasma phosphate levels, the volume of blood that passed the dialyzer and the vascular access. Uniformity on time and membrane surface could explain the abs cense of influence in our case. The ultra filtration, dialysate flux, membrane permeability or on-line hemodiafiltration does not influence the phosphate removal. The new membrane helixone with 2,1 m2 (Fresenius Fx100) increases phosphate removal probably because the membrane surface is higher.

[CA-P control in haemodialysis and K/DOQI guidelines]

BACKGROUND

The publication in 2003 of the K/DOQI Clinical Practice Guidelines for Bone Metabolism and Disease in Chronic Kidney Disease recommended targets levels for serum iPTH, Ca, P, and CaxP product. However, many patients do not achieved these target ranges. It is necessary to known the percentage of patients out of range in order to prevent the development of bone disease and to reduce mortality and morbidity.

OBJECTIVES

To know the degree of control of Ca-P metabolism in haemodialysis patients in our haemodilalysis facilities and the achievement of target levels recommended by K/DOQI Guidelines.

PATIENTS AND METHODS

We have retrospectively investigated in 190 prevalent haemodialysis patients (males 58.2%, ratio M/F 1.4, mean age 70 years, range 17-87 years, at least 3 months in haemodialysis) the serum levels of Ca, albumin-corrected serum Ca, P, CaxP product and iPTH in all analitycal determinations performed in 2004. In each patient we have obtained the average (and median) of these serum markers. Cut-off levels were carried out following the recommendations of the K/DOQI Guidelines.

RESULTS

The average of serum Ca and albumin-corrected serum Ca is normal (means +/- SD = 8.9 +/- 0.6 mg/dL and 9.2 +/- 0.7 mg/dL, respectively); however, 53.7% has normal values, 9.1% hypocalcemia and 37.1% hypercalcemia. The average of serum P is also normal (mean +/- SD = 5.0 +/- 1.3 mg/dL); however, only 57.2% has normal values, and 11.7% has hypophosphoremia and the remaining 31, 1% hyperphosphoremia. The CaxP product is normal (mean +/- SD = 46.3 +/- 13.3 mg2/mL2), 4.9% with low values and 23.4% with high values. The median of serum iPTH is 253 pg/mL, but only 31.1% of them have normal values, 25.1% low range values and 43.7% has hyperparathyroidism; 9.3% with iPTH higher than 800 pg/mL. The percentage of patients with hyperphosphoremia is higher in the group with iPTH higher than 300 pg/mL (23.3% vs. 40%, chi2, p= 0.006). In patients with PTHi in normal range, 3.6% have low CaxP product and the remaining 17.8% high CaxP product. Overall, only 25% of patients falls within recommended ranges for all indicators of mineral metabolism and 17% has all serum markers outside these recommendations.

CONCLUSIONS

The degree of control of mineral metabolism in haemodyalisis patients if clearly insufficient and a large percentage of them do not achieved the recommended serum targets recommended by K/DOQI Guidelines. This groups of patients are exposed to a increased risk for oseous and cardiovascular morbimortality. The analysis of adequacy must be performed with percentage of patients out of range in order to apply new therapeutical strategies.

A prospective and multicenter safety-monitoring study of a short up-dosing schedule of immunotherapy with a mass-units-standardized extract of mites

A prospective, multicenter pharmacovigilance study was carried out to evaluate the safety of a new 7-dose treatment schedule of subcutaneous immunotherapy as opposed to the conventional 13 doses normally recommended. The study was carried out in 14 centers and included 261 patients (children and adults) with respiratory allergic disease due to sensitization to mites (Dermatophagoides pteronyssinus and/or farinae). A total of 2290 doses were administered under the direct supervision of the participating specialists. One hundred and ten reactions in 63 patients (24.1%) were recorded, representing 4.8% of the total doses administered. Most of the reactions (98) were local. Only 12 were systemic (0.5% of the administered doses) and occurred in 10 patients (3.8% of the sample). Ten reactions reverted quickly with rescue medication. The maintenance dose had to be lowered in one patient and another patient was withdrawn from the study after suffering two asthmatic crises after two consecutive doses. In view of the results obtained, we can conclude that the new schedule shows an acceptable tolerance profile and does not present a greater risk of reactions than the conventional scheme of 13 doses using an identical extract. Moreover, the new schedule represents substantial savings in the number of doses and visits required to reach the maintenance dose.

Intraoral mandibular distraction osteogenesis: special attention to treatment planning

PURPOSE

To demonstrate our experience using internal devices for unidirectional distraction osteogenesis in treating different mandibular hypoplasias (with or without maxillary deformities). An algorithmic table for diagnosis, and treatment planning is presented.

PATIENTS AND METHODS

Twenty internal distraction devices were used in 16 patients with mandibular hypoplasia. Deficiency in length of the mandible was calculated on three-dimensional computed tomography scans. The device was activated by a transcutaneous pin on the fifth postoperative day. Distraction was achieved at rates of 0.5 mm/12 h. After a variable period of consolidation the devices were removed. Mean follow-up was 18 months.

RESULTS

Successful distraction osteogenesis was achieved in all patients. No premature consolidation or pseudoarthrosis was observed. Improvement of facial aesthetics was produced in all cases. Final occlusion was excellent in those cases where no simultaneous maxillary deformity was present. Orthodontic treatment was applied in all cases. Results remained stable one year postoperatively.

CONCLUSIONS

The occlusal results obtained in this series show that we can plan distraction as a definitive treatment in cases with isolated mandibular hypoplasia. When an additional maxillary deformity is present, mandibular distraction must be performed first if indicated, but a maxillary procedure will be necessary later.

Peritoneal sodium mass removal in continuous ambulatory peritoneal dialysis and automated peritoneal dialysis: influence on blood pressure control

BACKGROUND/AIM

Sodium and water retention is common in peritoneal dialysis patients and contributes to cardiovascular disease. As peritoneal sodium removal depends partly on dwell time, and automated peritoneal dialysis (APD) often uses short dwell time exchanges, the aim of this study was to compare the 24-hour peritoneal sodium removal in APD and standard continuous ambulatory peritoneal dialysis (CAPD) patients and to analyze its possible influence on blood pressure control.

METHODS

A total of 53 sodium balance studies (30 in APD and 23 in CAPD) were performed in 36 stable peritoneal dialysis patients. The 24-hour net removal of sodium was calculated as follows: M = ViCi - VdCd, where Vd is the 24-hour drained volume, Cd is the solute sodium concentration in Vd, Vi is the amount of solution used during a 24-hour period, and Ci is the sodium concentration in Vi. Peritoneal sodium removal was compared between APD and CAPD patients. Residual renal function, serum sodium concentration, daily urinary sodium losses, weekly peritoneal Kt/V and creatinine clearance, 4-hour dialysate/plasma creatinine ratio, proportion of hypertonic solutions, net ultrafiltration, systolic and diastolic blood pressures, and need for antihypertensive therapy were also compared between the groups.

RESULTS

Peritoneal sodium removal was higher (p < 0.001) in CAPD than in APD patients. There were no significant differences in residual renal function, serum sodium concentration, urinary sodium losses, peritoneal urea or creatinine clearances, 4-hour dialysate/plasma creatinine ratio, or proportion of hypertonic solutions between groups. The net ultrafiltration was higher in CAPD patients and correlated strongly (r = 0.82; p < 0.001) with peritoneal sodium removal. In APD patients, peritoneal sodium removal increased significantly only in those patients with a second daytime exchange. The systolic blood pressure was higher (p < 0.05) in APD patients, and the proportion of patients with antihypertensive therapy was also higher in APD patients, although no significant relationship between blood pressure values and amount of peritoneal sodium removal was found.

CONCLUSIONS

The 24-hour sodium removal is higher in CAPD than in APD patients, and there is a trend towards better hypertension control in CAPD patients. As hypertension control and volume status are important indices of peritoneal dialysis adequacy, our results have to be considered in the choice of the peritoneal dialysis modality.

[Diagnostic and clinical course features of lupus membranous glomerulonephritis]

BACKGROUND

Lupus membranous glomerulonephritis (LMG) is sometimes difficult to distinguish from idiopathic membranous glomerulonephritis (IMG) and little is known about its natural history.

METHODS

We have performed a retrospective study of 16 patients with LMG, types Va ("pure" LMG) (8 patients) and Vb (mesangial proliferation) (8 patients). Analytical and clinical characteristics were analyzed in each case at the onset of the disease and during follow-up.

RESULTS

At the time of diagnosis, 7 patients (43%) did not present any extrarenal manifestations of systemic lupus erythematosus (SLE). Nephrotic syndrome was the most common clinical presentation (81%). 14 patients (87%) showed positive antinuclear antibodies (ANA), but at low titres (< 1/300); anti-DNA antibodies were positive only in 3 cases (18%) and hypocomplementemia was observed in 2 (12%). The most relevant histological findings were the presence of Clq deposits (83%) and subendothelial and mesangial deposits. Treatment consisted of corticosteroids, adding immunosuppression when no response was obtained in 2-3 months. In recent years, an angiotensin-converting enzyme inhibitor (ACEI) was added before immunosuppression. At the end of the study, 6 patients (42%) developed chronic renal insufficiency and 8 (58%) renainea with normal renal function. Actuarial renal survival was 100% at 5 years and 75% at 10 years. The evolution towards a non-nephrotic range proteinuria throughout the follow-up was the only parameter significantly associated with a good prognosis.

CONCLUSIONS

LMG can present without extra-renal symptoms of SLE and even with very poor expression of its serological markers. Almost half of the patients (42%) developed chronic renal insufficiency. The evolution towards a non-nephrotic range proteinuria correlated with the maintenance of a normal renal function.

Familial microscopic hematuria caused by hypercalciuria and hyperuricosuria

We report 12 patients belonging to five different families in whom persistent isolated microhematuria was associated with hypercalciuria and/or hyperuricosuria. Four patients had episodes of gross hematuria, three patients had passed renal stones, and a history of nephrolithiasis was obtained in four of the families (80%). Calcium oxalate and uric acid crystals were commonly observed in the urine sediments. Urinary erythrocytes had a normal appearance on phase-microscopic examination. Reduction of calciuria and uricosuria by thiazide diuretics, allopurinol, forced fluid intake, and dietetic measures led to a persistent normalization of urine sediment with complete disappearance of hematuria. Determination of calcium and uric acid urinary excretions should be included in the study of familial hematuria.

Secondary (AA-type) amyloidosis in patients with polymyalgia rheumatica

Several cases of systemic amyloidosis associated with polymyalgia rheumatica (PMR) or giant-cell arteritis (GCA) have been described. Nevertheless, the type of amyloid deposit has not been characterized in most of them. Here we report on two patients with PMR (one with associated GCA) who developed nephrotic syndrome and end-stage renal failure caused by massive amyloid deposition. Immunohistochemical analysis showed that the amyloid deposits were of AA type (secondary amyloidosis) in both cases.

Results of the biocompatible osteoconductive polymer (BOP) as an intersomatic graft in anterior cervical surgery

Eighty-two patients operated on in our Department between 1989 and 1995 with an anterior cervical approach for soft and hard cervical disc herniations and cervical stenosis were included in this study. In 41 cases a heterologous intersomatic bovine graft (Surgibone) was used. Another 41 patients underwent surgery with a biocompatible osteoconductive polymer (BOP) as intervertebral graft. Both groups were retrospectively reviewed and compared with the objectives of evaluating the biodynamic behaviour of the grafts in the intersomatic space, the complications which appeared (specially those related to the grafts), the bone fusion rate achieved and the clinical outcome of the patients. The results of our study show that the BOP group presented a higher tendency to intersomatic space collapse 6 months after discectomy. There were no differences in the general surgical complications between both groups, but those related directly to the graft were significantly higher in the BOP group. The vast majority of the graft complications recorded had no clinical correlation. Without a strict radiological follow-up such complications would never have been discovered. Bone fusion in the BOP group was significantly slower and worse. Finally, the clinical outcome in both groups did not show any significant difference.

In vivo and in situ ischemic tissue characterization using electrical impedance spectroscopy

The investigation of processes of ischemia in different organ tissues is very important for the development of methods of protection and preservation during surgical procedures. Electrical impedance spectroscopy was used to distinguish between different tissues and their degree of ischemia. We describe mathematical methods used to adjust experimental data to Cole-Cole models for one-circle and two-circle impedance loci and a study of the main parameters for representing the behavior of ischemia in time. In vivo and in situ postmortem measurements of different tissues from pigs are shown in the 100 Hz to 1 MHz range. The Cole parameters that best characterize the ischemia are R0 and fc.

Passive transmission of ischemic ST segment changes in low electrical resistance myocardial infarct scar in the pig

OBJECTIVES

To analyze the passive electrical properties of a healed infarction and assess their role on transmission of contiguous ischemic ST segment potential changes.

METHODS

We measured tissue resistivity (omega cm) at 1 kHz and the epicardial ST segment during 1 h of proximal reocclusion of the left anterior descending (LAD) coronary artery in 12 anesthetized pigs with one-month-old transmural infarction elicited by LAD ligature below the first branch. The impedance spectrum (1 to 1000 kHz) of normal and infarcted myocardium was measured in seven other pigs with similar infarctions. Electrical transmission of current pulses (30 microA) in infarcted tissue and in test solutions was also investigated.

RESULTS

The infarct scar has a lower than normal resistivity (110 +/- 30 omega cm vs. 235 +/- 60 omega cm, p < 0.0001) and, unlike the normal myocardium, resistivity and phase angle of the scar did not change at increasing current frequencies, reflecting no capacitative response. LAD reocclusion induced a resistivity rise (510 +/- 135 omega cm, p < 0.01) and a ST segment elevation (0.6 +/- 0.7 to 9.5 +/- 5.1 mV, p = 0.002) in the ischemic peri-infarction zone, whereas the infarcted area showed ST segment elevation (0.5 +/- 0.5 to 3.8 +/- 2.6 mV, p = 0.03) with no resistivity changes. Potential decay of both ST segment and current pulses in the scar and in 0.9% NaCl solution was less than 1 mV/mm. Transmural deposition of connective tissue was seen in the center of the infarction.

CONCLUSIONS

A one-month-old transmural infarction is a low resistance, noncapacitative medium that allows a good transmission of current pulses and of ST segment potential changes generated by contiguous peri-infarction ischemia.

Differential uptake of myocardial perfusion radiotracers in normal, infarcted, and acutely ischemic peri-infarction myocardium

OBJECTIVES

We measured the uptake of technetium-99m tetrofosmin (99m Tc) and thallium-201 (201 TI) in areas of healed transmural myocardial infarction and in the regions of acute peri-infarction ischemia.

METHODS

Anesthetised pigs with a 1-month old transmural infarction elicited by permanent ligature of the left anterior descending (LAD) coronary artery below the first branch underwent one hour of proximal LAD occlusion followed by injection of 99m Tc-tetrofosmin and 201TI either in the left atrium (GI, n= 19) or in the jugular vein (GII, n = 6). Twelve other pigs (GIII) with similar acute peri-infarction ischemia received 99m Tc-tetrofosmin and 201Tl into the left ventricle during cardiocirculatory arrest to rule out the effect of coronary collaterals. Radiotracer counting was determined in samples from normal, acute ischemic and necrotic regions.

RESULTS

Uptake of 99m Tc-tetrofosmin and 201 Tl was greater in the infarct scar (median % of normal tissue: 20 for 99m Tc and 8.6 for 201 Tl in GI; 22 and 15 in GII) than in acute ischemic myocardium (3.2 and 2.5 in GI; 6.4 and 3.3 in GII). Radiotracer injection in arrested hearts (GIII) depicted a similar pattern (median % of injected dose: 6.2 for 99m Tc and 10 for 201Tl in the scar; 2.3 and 4.0 in acute ischemia; 2.9 and 3.5 in normal tissue). The infarcted region showed connective tissue and lack of viable myocardium.

CONCLUSION

A 1-month old infarct scar with no viable myocardial tissue can take up significant fractions of 99mTc-tetrofosmin and 201Tl even in the absence of coronary collateral perfusion. Data suggest that the infarct scar can extract these radiotracers from the intraventricular blood.

Changes in myocardial electrical impedance induced by coronary artery occlusion in pigs with and without preconditioning: correlation with local ST-segment potential and ventricular arrhythmias

BACKGROUND

Myocardial ischemia increases tissue electrical resistivity leading to cell-to-cell uncoupling, and this effect is delayed by ischemic preconditioning in isolated myocardium. Alterations in myocardial resistivity elicited by ischemia in vivo may influence arrhythmogenesis and local ST-segment changes, but this is not well known.

METHODS AND RESULTS

Myocardial impedance (resistivity [omega x cm] and phase angle [degrees]), epicardial ST segment, and ventricular arrhythmias were analyzed during 4 hours of coronary artery occlusion in 11 anesthetized open-chest pigs; these were compared with 13 other pigs submitted to a similar coronary occlusion preceded by ischemic preconditioning. Myocardial resistivity rose slowly during the first 34+/-7 minutes of occlusion (237+/-41 to 359+/-59 omega x cm), increased rapidly to 488+/-100 omega x cm at 60 minutes, and reached a plateau value (718+/-266 omega x cm, ANOVA; P<.01) at 150+/-69 minutes. By contrast, phase-angle changes began after 17 minutes of ischemia (-3.0+/-1.6 degrees to -4.2+/-1.2 degrees at 29+/-8 minutes) and evolved faster thereafter (-12.5+/-5.3 degrees at 144+/-56 minutes). Marked changes in myocardial impedance were observed during the reversion of ST-segment elevation that occurred 1 to 4 hours after occlusion, but impedance changes were less apparent during the early ST-segment recovery seen at 15 to 35 minutes of ischemia. The second arrhythmia peak (30+/-5 minutes) coincided with the fast change in tissue impedance, and both were delayed (P<.05) by ischemic preconditioning.

CONCLUSIONS

A rapid impairment of myocardial impedance occurs after 30 minutes of coronary occlusion, and its onset is better defined by shift in phase angle than by rise in tissue resistivity. Phase 1b arrhythmias are associated with marked impedance changes, and both are delayed by preconditioning. Reversion of ST-segment elevation is partially associated with impairment of myocardial impedance, but other factors play a role as well.

Local repolarization abnormalities induced by transcatheter radiofrequency ablation in pigs

Radiofrequency (RF) ablation alters action potential repolarization of myocardial cells and, theoretically, this should induce ST-T segment changes in the ECG. Since these ECG abnormalities have been rarely reported in patients submitted to RF ablation we assess the ability of the procedure to cause ST-T segment changes in local electrograms. Epicardial ECG mapping was performed in 17 anesthetized open chest pigs submitted to endocardial (n = 9) or to epicardial (n = 8) unipolar radiofrequency ablation (500 kHz, 20 W for 5-10 s). To characterize the cellular electrophysiological alterations induced by RF ablation transmembrane action potentials were recorded at various distances from the ablation lesion; these were compared with seven control pigs. Endocardial RF ablation induced a transient (< 5 min) change of 6.1 +/- 2.4 mV in T wave amplitude (baseline: 12.8 +/- 5.6 mV, P < 0.001) in 141 out of 269 epicardial electrodes. T wave changes were associated with shortening in local activation time (20.1 +/- 2.3 ms at baseline vs 18.5 +/- 2.5 ms at 60 s after ablation, P = 0.03). RF current caused persistent St segment elevation at the center of the ablation lesion with no transmural expansion. Intracellular potentials along a 2-6 mm wide myocardial band bordering the RF lesion lower amplitude (101 +/- 7.0 mV vs 71 +/- 23 mV, P < 0.01) and shorter duration (254 +/- 44 ms vs 156 +/- 29 ms, P < 0.01) than control hearts. The center of the ablation lesion was electrically unexcitable. We concluded that RF ablation alters cellular electrophysiology in small areas surrounding the ablation lesion and this causes short-lasting transmural changes in T 3 wave amplitude and nontransmural ST segment elevation.