Résumé
OBJETIVO: Para melhorar as propriedades mecânicas e imunogênicas, o glutaraldeído é utilizado no tratamento do pericárdio bovino que é utilizado em biopróteses. A liofilização do pericárdio bovino tratado com glutaraldeído diminui os radicais aldeído, com provável redução do potencial para calcificação. O objetivo deste estudo é avaliar os efeitos da liofilização em biopróteses valvares de pericárdio bovino como mecanismo protetor na diminuição da disfunção estrutural valvar. MÉTODOS: Foi realizado o implante de biopróteses de pericárdio bovino tratado com glutaraldeído, liofilizadas ou não, em carneiros de 6 meses de idade, sendo os animais eutanasiados com 3 meses de seguimento. As biopróteses foram implantadas em posição pulmonar, com auxílio de circulação extracorpórea. Um grupo controle e outro grupo liofilizado foram avaliados quanto ao gradiente ventrículo direito/artéria pulmonar (VD/AP) no implante e explante; análise quantitativa de cálcio; inflamação; trombose e pannus. O nível de significância estabelecido foi de 5%. RESULTADOS: O gradiente médio VD/AP, no grupo controle, no implante, foi 2,04 ± 1,56 mmHg e, no grupo de liofilização, foi 6,61 ± 4,03 mmHg. No explante, esse gradiente aumentou para 7,71 ± 3,92 mmHg e 8,24 ± 6,2 mmHg, respectivamente, nos grupos controle e liofilização. O teor de cálcio médio, após 3 meses, nas biopróteses do grupo controle foi 21,6 ± 39,12 µg Ca+2/mg de peso seco, em comparação com um teor médio de 41,19 ± 46,85 µg Ca+2/mg de peso seco no grupo liofilizado (P = 0,662). CONCLUSÃO: A liofilização de próteses valvares com pericárdio bovino tratado com glutaraldeído não demonstrou diminuição da calcificação neste experimento.
OBJECTIVE: Glutaraldehyde is currently used in bovine pericardium bioprosthesis to improve mechanical and immunogenic properties. Lyophilization is a process that may decrease aldehyde residues in the glutaraldehyde treated pericardium decreasing cytotoxicity and enhancing resistance to calcification. The aim of this study is to evaluate bioprosthetic heart valves calcification in adolescent sheep and to study the potential of lyophilization as a mechanism to protect calcification. METHODS: Two groups were evaluated: a control group in which a bovine pericardium prosthetic valve was implanted in pulmonary position and a lyophilized group in which the bovine pericardium prosthetic valve was lyophilized and further implanted. Sixteen sheeps 6 months old were submitted to the operation procedure. After 3 months the sheeps were euthanized under full anesthesia. RESULTS: Six animals of the control group reached 95.16 ± 3.55 days and six animals in the lyophilized group reached 91.66 ± 0.81 days of postoperative evolution. Two animals had endocarditis. Right ventricle/pulmonary artery (RV/PA) mean gradient, in the control group, at the implantation was 2.04 ± 1.56 mmHg, in the lyophilization group, the RV/PA mean gradient, at the implantation was 6.61 ± 4.03 mmHg. At the explantation it increased to 7.71 ± 3.92 mmHg and 8.24 ± 6.25 mmHg, respectively, in control and lyophilization group. The average calcium content, after 3 months, in the control group was 21.6 ± 39.12 µg Ca+2/mg dry weight, compared with an average content of 41.19 ± 46.85 µg Ca+2/mg dry weight in the lyophilization group (P=0.662). CONCLUSION: Freeze drying of the bovine pericardium prosthesis in the pulmonary position could not demonstrate calcification mitigation over a 3 month period although decreased inflammatory infiltration over the tissue.
Sujets)
Animaux , Bovins , Bioprothèse/effets indésirables , Calcinose/prévention et contrôle , Prothèse valvulaire cardiaque/effets indésirables , Test de matériaux/méthodes , Péricarde/composition chimique , Artère pulmonaire/chirurgie , Calcinose/anatomopathologie , Fixateurs/pharmacologie , Lyophilisation/méthodes , Glutaraldéhyde/pharmacologie , Modèles animaux , Péricarde/ultrastructure , Répartition aléatoire , Ovis , Statistique non paramétriqueRésumé
The bovine pericardium has been used as biomaterial in developing bioprostheses. Freeze-drying is a drying process that could be used for heart valve's preservation. The maintenance of the characteristics of the biomaterial is important for a good heart valve performance. This paper describes the initial step in the development of a bovine pericardium tissue freeze-drying to be used in heart valves. Freeze-drying involves three steps: freezing, primary drying and secondary drying. The freezing step influences the ice crystal size and, consequently, the primary and secondary drying stages. The aim of this work was to investigate the influence of freezing rates on the bovine pericardium tissue freeze-drying parameters. The glass transition temperature and the structural behaviour of the lyophilized tissues were determined as also primary and secondary drying time. The slow freezing with thermal treatment presented better results than the other freeze-drying protocols.
O pericárdio bovino é um material utilizado na fabricação de biopróteses. A liofilização é um método de secagem que vem sendo estudado para a conservação de válvulas cardíacas. A preservação das características do biomaterial é de fundamental importância no bom funcionamento das válvulas. Este artigo é a primeira etapa do desenvolvimento do ciclo de liofilização do pericárdio bovino. Liofilização é o processo de secagem no qual a água é removida do material congelado por sublimação e desorção da água incongelável, sob pressão reduzida. O congelamento influencia o tamanho do cristal de gelo e, consequentemente, a secagem primária e secundária. O objetivo deste estudo foi verificar a influência das taxas de congelamento nos parâmetros de liofilização do pericárdio bovino. Determinou-se a temperatura de transição vítrea e o comportamento estrutural do pericárdio bovino liofilizado. Determinou-se o tempo da secagem primária e secundária. O protocolo de liofilização utilizando-se congelamento lento com annealing apresentou os melhores resultados.
Résumé
Mechanical assist ventricular devices have been used in the treatment of low cardiac output syndrome. These devices can be generically grouped in pulsatile and nonpulsatile. There is a great controversy about the advantages and disadvantages of each one of these groups. The objective of this paper is to evaluate the influence of the centrifugal pump used for left ventricular assistance on the coronary and carotid flow in dogs with normal heart. The efficacy of the simultaneous use of an intraaortic balloon pump to compensate the possible deleterious effects of the circulatory assistance with continuous flow was analysed. Fifteen dogs with a mean weight of 16.3 kg were studied. Hemodynamic evaluation included serial measurements of pressures of the right atrium, pulmonary capillary wedge, pulmonary artery, systemic arterial circulation and heart rate. Cardiac output was measured and the following derived hemodynamic parameters were calculated: cardiac index, systolic index, systemic vascular resistance and pulmonary vascular resistance. Carotid and coronary blood flow were obtained by electromagnetic tranducers. The parameters were analysed in four situations: S1. Standard situation; S2. Test situation - the centrifugal pump as a left ventricular assist device; S3. Test situation - the centrifugal pump associated with intraaortic balloon pump; S4. Final situation, where the intraaortic balloon is turned off to confirm its influence. The hemodynamic evaluation didn't show significant statistic changes in the analysed parameters in the four situations. In relation to the coronary flow, however, the use of circulatory isolated assistence with centrifugal pump (S2 and S4) displayed a reduction (24.6 per cent ñ 6.1) in relation to the standard situation - S1 as much as to the associated intraaortic balloon - S3 (p = 0.0079); S1 and S3 showed similar coronary flow. In relation to the carotid flow, the profile analysis suggests the existence of a difference between the multiple situations, but it is not significant (p = 0.0582)...