Biomedical subjects

I Millán

Publications and source records attributed to I Millán.

At least 19 recordsLinked to original sources

PubMed2006

Hysteresis of a biomaterial: influence of sutures and biological adhesives.

We studied the changes in energy consumption of samples of calf pericardium, when joined or not joined by sutures and adhesives, by means of hysteretic cycles. Sixty-four samples were subsequently subjected to tensile stress until rupture. An overlapping suture sewn in the form of a rectangle presented an acceptable mean resistance to rupture of over 10 MPa, although lower than the mean values in an unsutured control series where the mean resistance surpassed 15 MPa. The contribution of an acrylic adhesive to the resistance to rupture was negligible. The sutured samples that were reinforced with adhesives and had not been subjected to hysteretic cycles prior to rupture showed an anisotropic behavior. This behavior appeared to be lost in all the samples that underwent hysteretic cycles. We found an inflection point in the stress/strain curve following the stepwise increase in the load, with a value greater than and proximate to the final load applied. This inflection should be analyzed by means of microscopy. Finally, the mathematical relationship between the energy consumed and the stress applied, the strain or deformation produced and the number of cycles of hysteresis to which the samples were subjected was established as the ultimate objective of this study. The bonding systems provoked a greater consumption of energy, with the greatest consumption corresponding to the first cycle in all the series assayed. An equation relating the energy consumption in a sample to the number of hysteretic cycles to which it was subjected was obtained. Its asymptote on the x-axis indicates the energy consumption for a theoretical number of cycles, making it possible to estimate the durability of the sample.

Animals↗

PubMed2006

Durability of a cardiac valve leaflet made of calf pericardium: fatigue and energy consumption.

We studied the mechanical behavior of membranes of calf pericardium, similar to those employed in prosthetic valve leaflets, when subjected to tensile fatigue. The objective was to assess its durability, as a fundamental property of cardiac bioprosthesis, and analyze the energy consumption. For this purpose, the authors built a hydraulic simulator to subject a spherical valve leaflet made of calf pericardium to cyclic stress mimicking cardiac function. A total of 522 assays were performed in 40 samples, subjected to cyclic pressures greater than 6 atm, and 482 subjected to pressures ranging between 2 and 6 atm. The mathematical expression that establishes the relationship between the pressure exerted and the frequency was obtained. If we assume that the function is continuous, this equation provides the range of fatigue tolerated for a given number of cycles. Using the optimal values (the five highest values per series), the expression was found to be y = 9.95x(-0 1214) (R(2) = 0.955), where x represents the frequency in cycles per second and y the pressure in atmospheres. In addition, we established the mathematical relationship between the energy consumed and the frequency, which was a function of the pressure exerted, regardless of the region or zone from which the samples had been obtained. The methods of manual and morphology-based selection employed produced widely dispersed results. When a mechanical criterion was included, the similarity in the energy consumed during fatigue testing markedly improved the correlation, with a coefficient of determination between paired samples of R(2) = 0.7477. A mechanical criterion, such as energy consumption, can help to improve sample selection and produce more consistent results. Finally, we obtained the mathematical expression that relates the energy consumed to the pressure exerted and the number of cycles per second to which the valve leaflet was subjected. This procedure enables us to establish the limit to the energy that a biomaterial can consume over a period of time during which it is subjected to a working pressure and, thus, calculate more precisely its durability.

Animals↗

PubMed2006

[A long-term comparative study of calcitriol versus alphacalcidol in patients with secondary hyperparathyroidism on hemodialysis].

UNLABELLED: Calcitriol has traditionally been the most widely used treatment for secondary hyperparathyroidism (SHPT) in uremic patients. There are currently no crossover equivalence studies of alphacalcidol versus calcitriol establishing which of the two derivatives is more active and better tolerated. The objective of this study was to compare the long term effect on control of PTH of similar doses of alphacalcidol versus calcitriol in the treatment of SHPT in these patients. METHODS: We conducted a retrospective study on 21 hemodialysis patients with stable SHPT of varying severity treated with intravenous calcitriol. In July 2002, the pharmacy of the reference hospital decided to substitute calcitriol for alphacalcidol based on the similarity of the two drugs. The conversion was made substituting a similar amount of drug. Mean absolute serum levels and percentage change in PTH, calcium and phosphorus were compared between the two periods and at 0, 3, 6, 9, 12 and 15 months after starting treatment with alphacalcidol. Student's t-test for paired means was used to compare the values between the two periods. RESULTS: In the calcitriol period, mean PTH levels were 275.2 +/- 111.7 pg/ml. The mean dose of drug used was 1.7 +/- 0.8 mcg postdialysis, and serum calcium and phosphorus levels were 10.1 +/- 0,5 mg/dl and 5,2 +/- 0,9 mg/dl, respectively (p < 0.01). Mean dialysate calcium content was 2,9 +/- 0,3 mEq/l. In the alphacalcidol period, PTH increased (441.6 +/- 178.3 pg/ml) (p < 0.001) and the percentage of patients with PTH < 300 pg/ml decreased (24% at the end of the period), in spite of significantly increasing the mean drug dose (2,3 +/- 0,9 mcg postdialysis) (p < 0.05). Serum calcium levels did not show significant differences (10.2 +/- 0.7 mg/dl) (p = NS), but phosphorus control was improved (4,7 +/- 0,5 mg/dl) (p < 0.01). The percentage of patients with PTH < 300 pg/ml decreased progressively from the start of treatment with alphacalcidol from 75% to 24% at the end of follow-up. Our results seem to suggest that the dose of alphacalcidol and calcitriol are not equivalent and we need to increase the dose of alphacalcidol to obtain a similar result to calcitriol on suppression of PTH in uremic patients with SPTH.

Adult↗

PubMed2005

[Improvements in lung preservation: 3 years' experience with a low-potassium dextran solution].

OBJECTIVE: Lung preservation quality is a crucial factor in the success of a lung transplant. In October 2000 we stopped using Euro-Collins (EC) lung preservation solution and began using a low potassium dextran solution (Perfadex [PER]). The objective of the present study was to assess outcome with the 2 solutions. MATERIAL AND METHODS: We analyzed the results of 68 lung transplants in which PER was used and compared the results with those of a historical control group consisting of the same number of transplants in which EC was used. RESULTS: There were no significant differences in the ages and diagnoses of the recipients in the 2 groups. Waiting list time was longer in the PER group. The most frequent cause of donor death in the EC group was craniocerebral trauma (62%), whereas in the PER group it was cerebral hemorrhage (54%). In the PER group more double lung transplants were performed than in the EC group (78% and 53% respectively; P=.002). There were no differences in the use of extracorporal circulation or ischemia time between the 2 groups. Early graft function, based on the patient's oxygenation index (ratio of PaO2 to inspired oxygen fraction [FiO2]) on arrival at the intensive care unit, was similar in the 2 groups. The incidence of severe graft failure (PaO2/FiO2<150 mm Hg) was significantly lower in the PER group than in the EC group (16% and 37% respectively; P=.01). No significant differences in hours of mechanical ventilation or postoperative mortality between the 2 patient series were found. CONCLUSIONS: Use of the newer lung preservation solution --PER-- led to a 50% lower incidence of severe ischemia-reperfusion graft injury during the early recovery from lung transplantation.

Adolescent↗

PubMed2004

Resistance to tensile stress of a bioadhesive utilized for medical purposes: Loctite 4011.

Sutures are the materials presently employed to secure and give shape to the valve leaflets of cardiac bioprostheses. Their high resistance and low degree of elasticity in comparison with the calf pericardium of which the leaflets are made generates internal stresses that contribute to the failure of the bioprostheses. Biological adhesives are bonding materials that have begun to be utilized in surgery, although there is a lack of experience in their use with inert tissues or bioprostheses. We report our study of Loctite 4011, a biological glue composed of a cyanoacrylate that has been employed for medical purposes, in which samples of pericardium bonded with this adhesive were subjected to uniaxial tensile stress. The samples were glued in such a way as to leave an overlap of 1 cm2 between the surfaces of the tissue. The series included 83 samples: 12 tested 24 h after bonding, 17 after 45 days, 17 after 90 days, 19 after 106 days and 18 after 152 days. The samples subjected to deferred trials were preserved using three types of chemical substances: glutaraldehyde, glycerol or saline plus antibiotics. The mean resistance to rupture of the series tested 24 h after gluing was 0.15 MPa (1.47 machine kg). This resistance remained nearly unchanged, regardless of the preservation solution employed, for at least 152 days, the time at which the study ended. The stress-strain curves demonstrated a high degree of elasticity throughout the 152 days, a finding that was not influenced by the preservation solution. This adhesive showed a considerable resistance to tensile stress, although probably insufficient to replace sutures. However, it maintained a surprisingly high degree of elasticity in the samples. Perhaps the time has come to combine these two elements, sutures and adhesives, to improve the elasticity of the structure without a loss of resistance, and increase the durability of bioprostheses.

Animals↗

PubMed2004

[Impact of a quality program in hemodialysis].

UNLABELLED: One of the requirements of a health care quality management system is to be able to established clinical performance measures (CPM) for its key organisation processes. We described some of the performance measurement that has been used in our hemodialysis unit, since the implementation in the year 2001, of a Quality Management System (QMS). We analyze and compare the effect that the introduction of a ISO 9002 based QMS had in our CPM during the period 2001-2002 (post QMS) vs. the two previous years -1999-2000- (pre QMS). METHODS: We defined several CPM for assessment of hemodialysis adequacy and medical management that covered : Anemia, iron status renal osteodystrophy, hemodialysis prescription and nutritional status , follow up of the established guidelines for vascular access care and prevention of nosocomial infections water quality and general performance outcome like annual crude mortality rate and hospitalization (express as hospital days/patient year). RESULTS: No significant difference was found between both periods regarding annual crude mortality( pre QMS 8.37% vs post QMS 8.95%) or the hospitalization rate ( pre 0.47 patient-days vs. post 0.52 patient-days) . There was a significant difference after implementation of the quality system in the average hemoglobin levels (pre 11.3 +/- 1.5 vs. post 11.9+ +/- .5 p <0,001). Ferritin levels (pre 220 +/- 162 vs. post 313 +/- 373 p<0.01), albumin levels (pre 3.61 +/- 0.46 vs. post 3.82 +/- 0.56 p<0.001) and KTV>1.2 (pre 1.41 +/- 0.26 vs. post 1.50 +/- 0.33 p<0.001). The transferring saturation index (TSI) was unchanged (pre 27.98 +/- 14.39 vs.. post 29.4 +/- 16.66 p=0.11). There was a significant decrease in the average PTH levels (pre 234.9 +/- 285 vs. post 174 +/- 174 p< 0.0001) PTH>300 pg/ml (pre 23.7% vs. post 16.4% p<0.001) calcium levels (pre 10.02 +/- 0.99 vs. 9.83 +/- 0.88 p<0.001), phosphorus (pre 5.50 +/- 1.55 vs. post 5.01 +/- 1.47 p<0.001) as well as serum calcium levels >11 mg/dl (pre 14.6% vs. post 11% p<0.001) and phosphorus >6 g/dl (pre 34% post 21.5% p<0.001). Although the average serum potassium levels decrease (pre 5.51 +/- 0.85 vs. post 5.40 +/- 0.87), the percentage of patients with potassium over 6.5 meq/l was similar in both periods (pre 11.5% vs. post 10. 1%). The number of native A-V vascular access was similar in both periods and above the current DOQI Recommendations. Nevertheless, there was a gradual decrease in native A-V fistula, associated with an increase on the use of permanent catheters. The number of incident patients with a permanent catheter as the only vascular access for hemodialysis increased from 0% in the year 1999, 2000 and 2001 to 6.98% in 2002. There was no hepatitis B and C seroconversión detected in both periods. CONCLUSION: From our study we concluded that regular follow-up of quality performance measurement associated with an ongoing corrective action, promotes an improvement of the outcome measures results.

Blood Chemical Analysis↗

PubMed2004

[Evaluation of health-related quality of life (HRQL) based on information from Coop/Wonca sheets in hemodialysis patients].

UNLABELLED: There has been increasing interest to find instruments to assess the HRQL quickly and easily in daily clinical practice. The main objective of this study is to measure the HRQL inhemodialysis patients using the Coop-Wonca Charts and to analyse whether they can be a useful instrument to assess the patient functional status and the HRQL in this population. METHODS: A descriptive cross-sectional study was performed between March 2003 and May 2003 in 163 hemodialysis patients (106 males and 57 females). The HRQL has been measured according to the validated Spanish version of the Coop-Wonca Charts. The questionnaire has nine different scales with a single-item. The answers score from 1 to 5 with the higher scores indicating the worst health or functional problems. RESULTS: The filling middle time of Coop-Wonca charts was less than five minutes. The charts were easily understood for the patients and can be self-administered. The dimensions of "Physical fitness" (3.66 +/- 0.8) and "Overall health" (3.43 +/- 0.8) showed the higher score, and the item aSocial activities) showed the lower scores (better quality of life) (1.98 +/- 1.3). The factors related to the worse health state are the variables: sex (females), the comorbility (diabetes and/or hepatopathy), the labour status (retired) and the way of transport (taxi/ambu lance). The time in hemodialysis was an independent variable and showed the worse score in the "general quality of life" (p < 0.05) and in the "perception of pain" (p < 0.01). The way of transport used (ambulances) was also an independent variable with worse scores for the dimensions "Physical fitness" (p < 0.01), "Daily activities" (p < 0.05) and "Health status" (p < 0.05). The older patients showed a worse score in the dimension "Physical fitness" (p < 0.01) and the patients with more than prescribed medicines scored worse in "Social activities" (p < 0.01). Males (p < 0.05), widows and single (p < 0.05) scored worse in social support. CONCLUSIONS: The Coop-Wonca Charts could be a good instrument to measure of HRQL in the HD patients. Their application is easy, fast (less than 5 minutes), easily understood, and can be self-administered.

Activities of Daily Living↗

PubMed2003

Production of intracellular IL-2, TNF-alpha, and IFN-gamma by T cells in B-CLL.

BACKGROUND: Recent evidence indicates that the slowly expanding population of CD5(+) B cells that characterizes B-cell chronic lymphocytic leukemia (B-CLL) could be related to defects in the response to cytokine produced by T cells that regulate apoptosis. We studied the intracellular expressions of interleukin-2 (IL-2), tumor necrosis factor-alpha (TNF-alpha), and interferon-gamma (IFN-gamma) in T-helper 1 cells (Th1 response) of B-CLL. METHODS: Peripheral blood mononuclear cells from 21 healthy individuals and purified T cells from 21 early-stage and 15 late-stage B-CLL patients were activated with phorbol myristate acetate and ionomycin. The Th1 cytoplasmic cytokines were evaluated in CD4(+) and CD8(+) T cells by flow cytometry. RESULTS: The percentages of CD4(+) and CD8(+) T cells positive for IL-2 were significantly lower in B-CLL patients than in healthy individuals (P = 0.030 and 0.049, respectively). No significant differences in TNF-alpha or IFN-gamma intracellular expressions were found between patients and healthy individuals. TNF-alpha- and IFN-gamma-expressing CD8 T cells were disease stage dependent, being significantly higher in late-stage patients (P < 0.001 for both cytokines). CONCLUSIONS: Our present observations suggested that Th1 cytokines may be of major importance in the pathogenesis of B-CLL.

Adult↗

PubMed2003

Chronic renal dysfunction after liver transplantation in adult patients: prevalence, risk factors, and impact on mortality.

INTRODUCTION: Although chronic renal dysfunction (CRD) is a common complication among patients undergoing liver transplantation (OLT) its prevalence, risk factors, and impact on outcome have not been well defined. We aimed to assess the incidence of CRD, its associated risk factors and its impact on outcome. PATIENTS AND METHODS: The cohort of 289 consecutive adult first liver transplant patients with posttransplant follow-up longer than 6 months received cyclosporine in 230 patients (153 oil-based and 81 microemulsion formulation), tacrolimus in 55. CRD was defined as serum creatinine levels greater than 1.3 mg/dL for more than 6 months. RESULTS: After a mean follow-up of 67 months, 138 patients (47.8%) displayed CRD. The prevalence of CRD was 30.9%, 41.5%, and 38.9% at 1, 5, and 13 years after OLT, respectively. Twelve patients (4.1%) developed end-stage renal failure. Male gender, older recipient age, pretransplant renal dysfunction and hyperuricemia, posttransplant in-hospital renal dysfunction and hyperuricemia, and renal dysfunction during the first 6 months after OLT were each significantly associated with the development of CRD. Survival was significantly lower (63%) among liver transplant patients with CRD than those without this complication (71%, P=.024). CONCLUSIONS: CRD is an important cause of morbidity after OLT, although end-stage renal disease is infrequent. Because early renal dysfunction is associated with the development of CRD, and decreased long-term patient survival, efforts should be made to avoid early renal dysfunction after liver transplantation.

Adult↗

PubMed2003

Comparison of the mechanical behaviors of biological tissues subjected to uniaxial tensile testing: pig, calf and ostrich pericardium sutured with Gore-Tex.

The purpose of this study was to compare the mechanical behavior of calf pericardium, pig pericardium and ostrich pericardium when subjected to tensile testing. Tensile stress was applied to 108 tissue samples, 36 of each type of tissue, until rupture. Groups of three adjacent strips measuring 12 x 2 cm(2) were cut longitudinally. Each group consisted of an unsutured center sample, or control, and the two contiguous samples, that on the right sutured with Gore-Tex at a 90 degrees angle with respect to the longitudinal axis and that on the left sewn with the same suture material at 45 degrees angle. The sutured samples showed a statistically significant loss of resistance (p<0.001) when compared with the corresponding unsutured tissue. The mean stresses at rupture for sutured ostrich pericardium were 21.81 and 20.81 MPa in the samples sewn at 45 degrees and 90 degrees, respectively, higher than those corresponding to unsutured calf and pig pericardium, 14.0 and 11.49 MPa, respectively, at rupture. The analysis of the stress/strain curve shows a smaller difference between sutured and unsutured ostrich pericardium than those observed in the other two biomaterials. These results demonstrate that, in addition to its greater resistance, ostrich pericardium also presents a less pronounced interaction with the suture material. Its capacity to absorb the shearing stress produced by the suture is greater. This report also confirms that the method of selection using paired samples ensures their homogeneity and makes it possible to predict the behavior of a sample by determining that of the other half of the pair.

Animals↗

PubMed2003

Sutured calf pericardium: influence of the type and angle of the suture on mechanical behavior.

Careful selection of the biological tissue to be used in cardiac bioprostheses and a thorough knowledge of its mechanical behavior, facilitating both the prediction of this behavior and the interactions between the tissue and the other materials employed, is the best approach to designing a durable implant. For this purpose, a study involving uniaxial tensile testing of calf pericardium was carried out. Two sets of three contiguous strips of tissue were obtained from each pericardial membrane, to perform a total of 144 trials. Two samples were sewn with one of four commercially available suture materials: Gore-Tex, nylon, Prolene and silk. In each set of three samples, the center strip remained intact and unsutured to serve as a control, while the left-hand strip was sutured at a 45 degrees angle with respect to the longitudinal axis and the right-hand strip was sewn at a 90 degrees angle. All the samples were tested until rupture. The results demonstrated a significant loss of mean load (p<0.01) in the sutured samples at rupture. The angle of the suture had no influence on these results, although the stress/strain curves showed that, as the tensile stress increased, the mechanical behaviors were less uniform. The rupture of the collagen fibers could explain this phenomenon. The pericardium sutured with Gore-Tex presented a greater strain, or deformation (elongation), at lower levels of stress, regardless of the angle of the suture. The tissue selection criteria, based on the use of paired samples, enabled a correct prediction of the mechanical behavior of the tissue, with excellent correlation coefficients (>0.98) and a high degree of homogeneity in the results.

Journal Article↗

PubMed2002

Mechanical behavior of chemically treated ostrich pericardium subjected to uniaxial tensile testing: influence of the suture.

The mechanical behavior of sutured ostrich pericardium was studied by uniaxial tensile testing. One hundred forty-four tissue specimens were assessed: 96 sutured samples (48 in which a centrally located suture was placed at an angle of 90 degrees with respect to the longitudinal axis, whereas in the remaining 48, a centrally located suture was placed at a 45 degrees angle to the longitudinal axis, in sets of 12 samples each, sewn with sutures made of Gore-Tex, nylon, Prolene, or silk), and 48 unsutured controls. Each group of 24 samples sewn at one angle or the other with the different suture materials was assayed together with a corresponding control group of 12 unsutured samples. The mean tensile strengths in the unsutured controls ranged between 30.16 MPa and 43.42 MPa, whereas those of the sutured sets ranged from 14.68 MPa to 21.91 MPa. The latter presented a statistically significant loss of resistance (p < 0.01) when compared with the unsutured tissue samples. The angle of the suture with respect to the longitudinal axis influenced the degree of shear stress produced by the suture, as well as the behavior of the different suture materials used. The set of samples sewn with Prolene appeared to be that most sensitive to changes in the angle of the suture, whereas tissue sewn at a 45 degrees angle with Gore-Tex presented lower shear stress values in comparison with samples in which the other three materials were used. A method of tissue selection based on morphological and mechanical criteria was used to ensure the homogeneity of the results in such a way that the coefficients of determination (R2) for the stress/strain curve fitting equation ranged between 0.888 and 0.995. This excellent fit made it possible, applying regression analysis, to predict the mechanical behavior of a specimen by determining that of a contiguous tissue sample. Thus, it should be possible, at least theoretically, to characterize the behavior of a specific region or zone of the biomaterial. In conclusion, ostrich pericardium exhibits strong resistance to rupture, even when sutured. The selection method used ensures the homogeneity of the samples and, thus, of the results. The angle of the suture with respect to the longitudinal axis, where the load is centered, determines the shear stress produced by the suture and the mechanical behavior of each suture material.

Animals↗

PubMed2002

The telescoping suture--Part 1: Does this technique improve the mechanical behavior of a biomaterial?: Calf pericardium.

The authors study the mechanical behavior of calf pericardium employed in the construction of cardiac valve leaflets when subjected to telescoping suture, followed by tensile stress until rupture. One hundred twenty pericardial tissue samples were employed, 60 cut from root-to-apex and another 60 cut in transverse direction. Each of these two groups consisted of 12 control samples that were left unsutured and four sets of 12 samples each that were rejoined by telescoping suture using silk, Prolene, nylon or Gore-Tex., and subjected to tensile stress. At the rupture of the sutured tissues, the tensile stress of the suture materials ranged between 57.54 MPa for the series sewn lengthwise with Gore-tex and 114.08 MPa for the series sewn crosswise with silk. At these levels of stress, the deformation of the suture thread was much less marked than that of the calf pericardium, and internal stresses were produced that were difficult for the biomaterial to absorb. There was a loss of real load in all the sutured series when the observed resistance to rupture, expressed in kilograms, was compared with the estimated value. This loss of resistance did not invalidate the telescoping suture technique since the resistance to rupture was still much greater than that associated with suturing the two edges of the cut pericardium together. This report confirms the deleterious role of the shear force generated in the pericardium by the suture.

Animals↗

PubMed2002

The telescoping suture--Part II: A novel method to improve the mechanical behavior of a new biomaterial: ostrich pericardium.

Ostrich pericardium, sutured using a telescoping or overlapping technique, was studied to determine its mechanical behavior. From each of 12 pericardial sacs, four contiguous strips were cut longitudinally, from root to apex, and another four contiguous strips were cut in transverse direction. One of the strips in each set of four was used as an unsutured control and the remaining three were sutured by overlapping 0.5 cm of the tissue and sewing with Gore-tex, Prolene or Pronova. These 96 samples were then subjected to tensile testing along their major axes until rupture. The tensile stresses recorded in the suture materials at the moment tears appeared in the pericardium ranged between 55.99 MPa and 70.23 MPa for Gore-tex in samples cut in the two directions. Shear stress became ostensible at 56 MPa, with clearly evident tears. However, microfracture of the collagen fibers must be produced at much lower stress levels. The comparison of the resistance in kilograms (machine-imposed), without taking into account the sections in which the load was applied, demonstrated only a slight loss of load when the telescoping suture was employed in ostrich pericardium samples. Ostrich pericardium may continue to be an alternative biological material for the construction of heart valve leaflets.

Animals↗

PubMed2001

Ostrich pericardium, a biomaterial for the construction of valve leaflets for cardiac bioprostheses: mechanical behaviour, selection and interaction with suture materials.

The mechanical behavior of ostrich pericardium was studied for the purpose of assessing its utility in the construction of bioprosthetic cardiac valve leaflets. The tissue was tested biaxially using a hydraulic simulator that subjected it to increasing stress until rupture. One hundred eighty trials were performed, 36 with unsutured pericardium and four series of 36 trials each with pericardium sutured with silk, Prolene, nylon or Gore-Tex. The samples were tested in pairs from three different pericardial regions. One sample from each pair (the predictive specimen) was assessed according to morphological and mechanical criteria, while the other (the predicted or selectable specimen) was subjected only to morphological analysis. The findings show that ostrich pericardium treated with glutaraldehyde according to standard methods has an excellent resistance to rupture in biaxial testing, withstanding stresses of up to 100 MPa, and never lower than 30 MPa. Its resistance to rupture is lowered by suturing, a loss that is less pronounced when silk sutures are used. The results with Gore-Tex are very homogeneous and the elastic behavior of the pericardium/suture unit appears to be similar to that of unsutured tissue, suggesting that the interaction between the two biomaterials is minor. Similar results were observed in the series sutured with Prolene and nylon. The use of paired samples makes it possible to closely estimate the mechanical behavior of the tissue in a given zone by determining that of its mate. The statistical study shows that this estimation is not conditioned by the suture employed, thus validating this approach and providing more precise criteria for tissue selection.

Animals↗

PubMed2001

Chemical treatment and tissue selection: factors that influence the mechanical behaviour of porcine pericardium.

Calcification and mechanical failure are the major causes of the loss of cardiac bioprostheses. The chemical treatments used to stabilize the tissue employed are considered to play a fundamental role in the development of these two phenomena, although the problem is multifactorial and the underlying causes are yet to be fully identified. Currently, there is an ongoing search for chemical treatments capable of reducing or eliminating the process of calcification while preserving the mechanoelastic characteristics of the tissue. One of the approaches to this effort is the elimination of the phospholipid component from the biological tissue employed in prosthesis construction. There is evidence that this component may be responsible for the precipitation of calcium salts. The present study compares two delipidating chemical treatments involving chloroform/methanol and sodium dodecyl sulfate (SDS) with the use of glutaraldehyde (GA) alone. For this purpose, porcine pericardial tissue was subjected to tensile strength testing employing a hydraulic simulator. A total of 234 samples were studied 90 treated with GA, 72 treated with chloroform/methanol and 72 treated with SDS. The mean breaking strength was significantly higher in the samples treated with GA (between 43.29 and 63.01 MPa) when compared with those of tissue treated with chloroform/methanol (29.92-42.30 MPa) or with SDS (13.49-19.06 MPa). In a second phase of the study, selection criteria based on morphological and mechanical factors were applied to the pericardial membranes employing a system of paired samples. The mathematical analysis of the findings in one fragment will aid in determining the mechanical behavior of its adjacent twin sample. In conclusion, the anticalcification chemical treatments tested in the experimental model conferred a lesser mechanical resistance than that obtained with GA. On the other hand, the utilization of paired samples was found to be useful in the prediction of the mechanical behavior of porcine pericardial tissue. Nevertheless, in order for our method of selection to be considered the most adequate approach, it will be necessary to validate these findings in dynamic studies involving a real, functional model.

Animals↗

PubMed2001

Porcine pericardial membrane subjected to tensile testing: preliminary study of the process of selecting tissue for use in the construction of cardiac bioprostheses.

The durability of cardiac bioprostheses is limited fundamentally by structural failure due to mechanical fatigue and calcification. In the present report, we analyze, using an in vitro hydraulic simulator to test tensile strength, the mechanical behavior of porcine pericardium for the purpose of establishing the criteria for selecting the biomaterial, taking into account both morphological criteria (thickness and homogeneity of the specimens) and mechanical criteria (stress at breaking point), using the epidemiological model of paired samples. The stress at breakage was found to range widely from 24.07 MPa to 100.29 MPa, although we observed no statistically significant differences when comparing the mean results in the different regions and zones of the pericardium being studies. The application of the selection criteria in the present series resulted in an excellent mathematical fit in terms of the stress/elongation (R2 > 0.95), making it possible to establish, by means of linear regression, the prediction of the tensile strength in one zone on the basis of the values observed in its paired specimen.

Journal Article↗

PubMed2001

A new method for selecting calf pericardium for use in cardiac bioprostheses on the basis of morphological and mechanical criteria.

The durability of existing calf pericardium bioprostheses is limited by phenomena such as mechanical stress and calcification, the factors most frequently implicated in valve failure. Varying the preferred direction of the collagen fibers influences the mechanical behavior of the pericardial membrane. Given this possible variation, a strict control of the selection of the biomaterial employed in the construction of valve leaflets is essential, but a reliable method of selection has yet to be established. This study describes the development of a new system of in vitro selection involving a hydraulic simulator that reproduces the mechanical behavior of pericardial membranes subjected to the stress of continuous flow. By combining morphological criteria such as thickness and homogeneity with those of mechanical behavior, and by selecting paired samples from different parts of the pericardium, we obtained excellent mathematical fits. Linear regression analysis provided the mode of predicting the tensile strength in a given sample when this value had been determined in its twin. The upper zones of calf pericardium, corresponding to either right or left ventricle but at a distance from ligamentous structures, showed the best mean results at rupture (60 MPa) and permitted the most reliable prediction. The expected stress for an elongation of 30% was 1.12 MPa, as was previously observed, with a 95% confidence interval of between 1.11 and 1.14 MPa. These trials, together with the careful selection of the pairs, should help to establish definitive selection criteria.

Journal Article↗