INTRODUCTION: Studies comparing high frequency oscillatory and conventional ventilation in acute respiratory distress syndrome have used low values of positive end-expiratory pressure and identified a need for better recruitment and pulmonary stability with high frequency. OBJECTIVE: To compare conventional and high frequency ventilation using the lower inflection point of the pressure-volume curve as the determinant of positive end-expiratory pressure to obtain similar levels of recruitment and alveolar stability. METHODS: After lung lavage of adult rabbits and lower inflection point determination, two groups were randomized: conventional (positive end-expiratory pressure = lower inflection point; tidal volume=6 ml/kg) and high frequency ventilation (mean airway pressures= lower inflection point +4 cmH2O). Blood gas and hemodynamic data were recorded over 4 h. After sacrifice, protein analysis from lung lavage and histologic evaluation were performed. RESULTS: The oxygenation parameters, protein and histological data were similar, except for the fact that significantly more normal alveoli were observed upon protective ventilation. High frequency ventilation led to lower PaCO2 levels. DISCUSSION: Determination of the lower inflection point of the pressure-volume curve is important for setting the minimum end expiratory pressure needed to keep the airways opened. This is useful when comparing different strategies to treat severe respiratory insufficiency, optimizing conventional ventilation, improving oxygenation and reducing lung injury. CONCLUSIONS: Utilization of the lower inflection point of the pressure-volume curve in the ventilation strategies considered in this study resulted in comparable efficacy with regards to oxygenation and hemodynamics, a high PaCO2 level and a lower pH. In addition, a greater number of normal alveoli were found after protective conventional ventilation in an animal model of acute respiratory distress syndrome.

OBJETIVOS: Este modelo experimental foi desenvolvido para analisar os efeitos da restrição nutricional e da hiperoxia, durante 11 dias, sobre o peso e a morfometria pulmonares, em coelhos prematuros. MÉTODOS: Após cesárea, coelhos New Zealand White com idade gestacional de 28 dias foram randomizados nos seguintes grupos: dieta controle e ar ambiente, dieta controle e hiperoxia (> 95% O2), restrição nutricional e ar ambiente e restrição nutricional e hiperoxia (>95% O2). A restrição nutricional foi obtida com uma redução em 30% de todos os nutrientes da dieta controle. As lâminas de pulmão foram coradas com hematoxilina-eosina, resorcina-orceína modificada e picrosírius, sendo posteriormente realizada a análise morfométrica RESULTADOS: Observou-se um menor ganho de peso no grupo restrição nutricional e hiperoxia (p < 0,001) a partir do quarto dia e, no grupo restrição nutricional e ar ambiente (p < 0,001), a partir do sexto dia de vida, em relação aos respectivos grupos controles. A restrição nutricional reduziu o número de alvéolos (p < 0,001) e o depósito de colágeno (p < 0,001). A hiperoxia produziu uma redução do número de alvéolos (p < 0,001) e do depósito de colágeno (p < 0,001), além de maiores intercepto linear médio (p < 0,05) e espessamento de septos inter-alveolares (p < 0,001). A restrição nutricional associada à hiperoxia intensificou a redução do número de alvéolos (p < 0,001) e do depósito de colágeno (p < 0,001). CONCLUSÕES: A restrição nutricional intensificou as alterações morfométricas pulmonares produzidas pela hiperoxia, especialmente em relação à alveolização e depósito de colágeno.

OBJECTIVES: To analyze the effects of nutritional restriction and hyperoxia on lung weight and pulmonary morphometry in premature rabbits during the first 11 days of life METHODS: New Zealand White rabbits were delivered by C-section at 28 days' gestational age and randomized into four groups: control diet and room air, control diet and hyperoxia (> 95% O2), nutritional restriction and room air and nutritional restriction and hyperoxia (> 95% O2). Nutritional restriction was achieved by reducing all nutrients by 30% in comparison with the control diet. Lung tissue slides were stained with hematoxylin-eosin, modified resorcin-orcein and picrosirius, before morphometric analysis was performed. RESULTS: From the fourth day onwards, less weight was gained by the nutritional restriction and hyperoxia group (p < 0.001) and from the sixth day on, by the nutritional restriction and room air group (p < 0.001), in comparison with their respective control groups. Nutritional restriction decreased alveoli number (p < 0.001) and collagen deposition (p < 0.001). Hyperoxia was responsible for reductions in number of alveoli (p < 0.001) and collagen deposition (p < 0.001), in addition to higher mean linear intercept values (p < 0.05) and thickening of alveolar septa (p < 0.001). When nutritional restriction was associated with hyperoxia, the reductions in number of alveoli (p < 0.001) and of collagen deposition (p < 0.001) intensified. CONCLUSIONS: Nutritional restriction intensified the changes of pulmonary architecture findings caused by hyperoxia, in particular through alterations to alveolarization and collagen deposition.

OBJETIVO: Estudar a imunogenicidade e a estabilidade do surfactante de origem porcina produzido pelo Instituto Butantan. MÉTODO: Experimento imunogenicidade: 16 coelhos da raça New-Zealand-White (Peso de 1000g) foram divididos em grupos de 4 animais. Cada grupo foi designado para receber: a) Surfactante do Butantan, b) Survanta® (Abbott Laboratories), c) Curosurf (Farmalab Chiesi) e d) nenhum tratamento com surfactante. Os surfactantes foram administrados via intratraqueal e o sangue dos animais foi coletado antes, 60 e 180 dias após a administração do surfactante. O soro obtido foi analisado quanto a presença de anticorpos anti-surfactante pelo método ELISA (enzyme-linked immunosorbent assay). Experimento estabilidade: O surfactante do Butantan usado neste experimento tinha sido armazenado por um ano em refrigerador (4 a 8°C) e sua estabilidade foi analisada em condições distintas de experimentação, usando o modelo de coelho prematuro. RESULTADOS: Experimento imunogenicidade: Nenhum dos surfactantes analisados determinou a produção de anticorpos contra seus constituintes. Experimento estabilidade: Os resultados deste estudo demonstraram que o surfactante do Instituto Butantan mostrou eficácia semelhante a do Curosurf após ter sido submetido à condições adversas ao longo do tempo. A eficácia foi demonstrada através da complacência pulmonar dinâmica, pressão ventilatória e da curva pressão-volume. CONCLUSÃO: Os resultados deste estudo demonstraram que o surfactante do Instituto Butantan pode representar um tratamento alternativo de reposição de surfactante.

PURPOSE: To study the immunogenicity and the stability of the porcine pulmonary surfactant preparation produced by the Instituto Butantan. METHOD: Immunogenicity assay: Sixteen New-Zealand-White rabbits (1000 g body weight) were divided into 4 study groups. Each group was assigned to receive either a) Butantan surfactant, b) Survanta® (Abbott Laboratories), c) Curosurf® (Farmalab Chiesi), or d) no surfactant. The surfactants were administered intratracheally, and the animals were collected immediately before and 60 and 180 days after surfactant administration. Sera were assayed for the presence of antisurfactant antibodies by enzyme-linked immunosorbent assay (ELISA). Stability assay: The Butantan surfactant used in this assay had been stored for one year in the refrigerator (4 to 8ºC) and its stability was evaluated in distinct assay conditions using a premature rabbit model. RESULTS: Immunogenicity assay: None of the surfactants analyzed triggered antibody immune responses against their components in any of the animals. Stability assay: The results of this study demonstrate that Butantan surfactant was as effective as Curosurf when both were submitted to the adverse circumstance of short- and long-term storage at room temperature. A similar level of efficacy for the Butantan surfactant, as compared to Curosurf was demonstrated by the pulmonary dynamic compliance, ventilatory pressure, and pressure-volume curve results. CONCLUSION: The results of our study demonstrate that Butantan surfactant may be a suitable alternative for surfactant replacement therapy.

OBJETIVO: Avaliar os efeitos de duas diferentes doses de surfactante exógeno sobre a mecânica pulmonar e sobre a regularidade da expansão do parênquima pulmonar em coelhos recém-nascidos. MÉTODO: Coelhos recém-nascidos foram traqueostomizados e randomizados em quatro grupos de estudo: grupo-Controle, sem aspiração de mecônio; grupo MEC, com aspiração de mecônio e sem tratamento com surfactante exógeno; grupos S100 e S200, ambos com aspiração de mecônio e tratados respectivamente com 100 e 200 mg/kg de surfactante exógeno (produzido e fornecido pelo Instituto Butantan). Os animais dos 4 grupos foram ventilados por 25 minutos. A mecânica pulmonar foi avaliada a partir dos valores de complacência dinâmica, pressão ventilatória, volume-corrente e volume pulmonar máximo (curva P-V). A análise histológica foi feita calculando-se o diâmetro alveolar médio (Lm) e o índice de distorção através do desvio padrão do Lm. Utilizou-se ANOVA One Way com a = 0,05. RESULTADOS: Após 25 minutos de ventilação, os valores de complacência dinâmica (ml/cm H2O.kg) foram: 0,87± 0,07 (Controle); 0,49±0,04 (MEC*); 0,67±0,06 (S100) e 0,67±0,08 (S200) e de pressão ventilatória (cm H2O): 9,0± 0,9 (Controle); 16,5±1,7 (MEC*); 12,4±1,1 (S100) e 12,1±1,5 (S200). Ambos os grupos tratados tiveram padrão de expansão do parênquima mais homogêneo em relação aos animais não tratados: índice de distorção de 7,5± 1,9 (Controle); 11,3±2,5 (MEC*); 5,8±1,9 (S100) e 6,7±1,7 (S200) (*p < 0,05 vs outros grupos). CONCLUSÕES: Animais tratados com surfactante mostraram melhora significativa da mecânica pulmonar e maior homogeneidade do padrão de expansão pulmonar comparados ao grupo não tratado. Não houve influência das doses de surfactante utilizadas.

OBJECTIVE: To evaluate the effects of 2 different doses of exogenous surfactant on pulmonary mechanics and on the regularity of pulmonary parenchyma inflation in newborn rabbits. METHOD: Newborn rabbits were submitted to tracheostomy and randomized into 4 study groups: the Control group did not receive any material inside the trachea; the MEC group was instilled with meconium, without surfactant treatment; the S100 and S200 groups were instilled with meconium and were treated with 100 and 200 mg/kg of exogenous surfactant (produced by Instituto Butantan) respectively. Animals from the 4 groups were mechanically ventilated during a 25-minute period. Dynamic compliance, ventilatory pressure, tidal volume, and maximum lung volume (P-V curve) were evaluated. Histological analysis was conducted using the mean linear intercept (Lm), and the lung tissue distortion index (SDI) was derived from the standard deviation of the means of the Lm. One-way analysis of variance was used with a = 0.05. RESULTS: After 25 minutes of ventilation, dynamic compliance (mL/cm H2O · kg) was 0.87 ± 0.07 (Control); 0.49 ± 0.04 (MEC*); 0.67 ± 0.06 (S100); and 0.67 ± 0.08 (S200), and ventilatory pressure (cm H2O) was 9.0 ± 0.9 (Control); 16.5 ± 1.7 (MEC*); 12.4 ± 1.1 (S100); and 12.1 ± 1.5 (S200). Both treated groups had lower Lm values and more homogeneity in the lung parenchyma compared to the MEC group: SDI = 7.5 ± 1.9 (Control); 11.3 ± 2.5 (MEC*), 5.8 ± 1.9 (S100); and 6.7 ± 1.7 (S200) (*P < 0.05 versus all the other groups). CONCLUSIONS: Animals treated with surfactant showed significant improvement in pulmonary mechanics and more regularity of the lung parenchyma in comparison to untreated animals. There was no difference in results after treatment with either of the doses used.