Development of a time-cycled volume-controlled pressure-limited respirator and lung mechanics system for total liquid ventilation.

Total liquid ventilation can support gas exchange in animal models of lung injury. Clinical application awaits further technical improvements and performance verification. Our aim was to develop a liquid ventilator, able to deliver accurate tidal volumes, and a computerized system for measuring lung mechanics. The computer-assisted, piston-driven respirator controlled ventilatory parameters that were displayed and modified on a real-time basis. Pressure and temperature transducers along with a lineal displacement controller provided the necessary signals to calculate lung mechanics. Ten newborn lambs (<6 days old) with respiratory failure induced by lung lavage, were monitored using the system. Electromechanical, hydraulic, and data acquisition/analysis components of the ventilator were developed and tested in animals with respiratory failure. All pulmonary signals were collected synchronized in time, displayed in real-time, and archived on digital media. The total mean error (due to transducers, analog-to-digital conversion, amplifiers, etc.) was less than 5% compared with calibrated signals. Components (tubing, pistons, etc.) in contact with exchange fluids were developed so that they could be readily switched, a feature that will be important in clinical settings. Improvements in gas exchange and lung mechanics were observed during liquid ventilation, without impairment of cardiovascular profiles. The total liquid ventilator maintained accurate control of tidal volumes and the sequencing of inspiration/expiration. The computerized system demonstrated its ability to monitor in vivo lung mechanics, providing valuable data for early decision making.

Prenatal dexamethasone rescues heart hypoplasia in fetal rats with congenital diaphragmatic hernia.

BACKGROUND/PURPOSE: Patients and rats with congenital diaphragmatic hernia (CDH) have lung and heart hypoplasia. Prenatal steroids improve lung hypoplasia in CDH rats. The current study tests the hypothesis that prenatal dexamethasone could rescue heart hypoplasia in rats with CDH. METHODS: Timed pregnant rats received intragastrically either 100 mg nitrofen or oil on day 9.5, and other animals had the same treatment with, in addition, either 0.25 mg/kg dexamethasone intraperitoneally or no treatment on days 19 and 20. Fetuses were recovered on day 21, and heart weight to body weight ratios, heart DNA, protein, and glycogen were measured in fresh specimens. Left-to-right ventricular diameter and aortic-to-pulmonary diameter ratios were measured after formalin fixation. RESULTS: Wet heart weight to body weight, left-to-right ventricular diameter, and aortic-to-pulmonary root diameter ratios, which were lower in fetuses exposed only to nitrofen than in their oil controls, were similar in those exposed to nitrofen plus dexamethasone than in their corresponding oil plus dexamethasone controls. Total heart DNA, which was decreased in fetuses exposed to nitrofen with CDH in comparison with their controls, was increased in those receiving nitrofen and dexamethasone in comparison with theirs. Protein to DNA ratio was decreased in all rats with CDH irrespective of their exposure or not to dexamethasone. Glycogen to DNA ratio was higher in all dexamethasone-treated fetuses than in those without this treatment. No gross histologic differences were seen among groups. CONCLUSIONS: Heart hypoplasia in rats with CDH is in part rescued by prenatal dexamethasone treatment as expressed by increased number of smaller myocytes with higher glycogen content. Prenatal steroids could modify heart involvement in human fetuses with CDH as well.

Heart hypoplasia in experimental congenital diaphragmatic hernia.

BACKGROUND/PURPOSE: Heart hypoplasia is associated with congenital diaphragmatic hernia (CDH) and decisively influences survival rate. This study examines whether nitrofen-exposed fetal rats have heart hypoplasia. METHODS: Pregnant rats received either 100 mg nitrofen or vehicle on gestational day 9.5. The hearts recovered near full term were either formalin fixed for anatomic studies or snap-frozen for biochemical studies. Heart weight, ventricular chamber diameters and aortic-to-pulmonary root diameter ratios were measured in fixed hearts. Protein and DNA were determined in frozen hearts. Analysis of variance (ANOVA) and correlation-regression studies were used for statistical assessment. RESULTS: All control fetuses were normal, whereas 61% of those exposed to nitrofen had CDH. Cardiovascular malformations were found in 73% of CDH and in 50% of non-CDH animals. Wet and fixed heart weights in percent of fetal weight, left-to-right ventricular diameter ratio, and aortic-to-pulmonary root diameter ratio were significantly decreased in fetuses with CDH in comparison with controls. Only wet heart was significantly decreased in nitrofen-treated fetuses without CDH, although all other variables showed a trend in the same direction. Protein to DNA ratios were similar in the three groups. The structure of the myocytes was histologically similar in all groups. CONCLUSIONS: The spectrum of lesions in the nitrofen model of CDH encompasses heart hypoplasia, further validating its use for research on this condition. Heart hypoplasia is related to cardiopulmonary compression, but its presence in treated animals without CDH demonstrates that the teratogen itself participate directly in its pathogenesis, and this finding invites further research on this line.

Thyroid hormones in the pathogenesis of lung hypoplasia and immaturity induced in fetal rats by prenatal exposure to nitrofen.

BACKGROUND/PURPOSE: Nitrofen is believed to act on prenatally exposed fetuses by changing maternal or fetal thyroid hormone physiology. The aim of this study was to determine whether the amounts of circulating and lung tissue T3 and T4 are decreased in rat fetuses with nitrofen-induced pulmonary hypoplasia and diaphragmatic hernia. METHODS: Timed-pregnant rats were given 100 mg of nitrofen in oil on gestational day 9.5, and their fetuses were recovered on the 21st day. Lung weight to body weight ratio was determined. Hormonal studies consisted in measurement of plasma T3, T4, and TSH, and of T3, T4, and DNA in lung tissue. Suitable groups of control fetuses prenatally exposed to oil were used for comparison. RESULTS: The lungs of nitrofen-treated fetuses were hypoplastic and those who had congenital diaphagmatic hernia were even more so. Nitrofen treatment led to decreased plasma T3 and T4 levels without TSH changes. T3 and T4 in lung tissue were apparently decreased in treated fetuses when expressed by weight, but these differences disappeared when expressed by DNA (cell content). CONCLUSIONS: Lung hypoplasia and immaturity induced by nitrofen treatment are not related to decreased levels of thyroid hormones in tissue near term. This should be kept in mind when proposing hormonal treatment for prenatal induction of lung maturation.

Pulmonary surfactant dysfunction in congenital diaphragmatic hernia: experimental and clinical findings.

Experimental and clinical findings indicate immaturity of pulmonary surfactant in congenital diaphragmatic hernia (CDH). Lung histology has shown a decreased amount of lamellar bodies. A low lecithin/sphingomyelin ratio in the amniotic fluid, and decreased concentrations of surfactant protein A and disaturated phosphatidylcholine in the pulmonary tissue and the amniotic fluid have been reported. Furthermore, low compliance and high surface tension have also been found. Evidence of clinical and experimental findings of structural, biochemical and functional pulmonary immaturity in CDH is reviewed. Prenatal administration of corticosteroids to accelerate fetal pulmonary maturation, and the use of early surfactant therapy, should be further evaluated in the clinical management of CDH.

The effects of multiple small doses of exogenous surfactant on experimental respiratory failure induced by lung lavage in rats.

AIM: To test the effect on pulmonary gas exchange and mechanics of multiple small doses of exogenous surfactant as an alternative to bolus delivery in experimental respiratory failure induced by lung lavage. METHOD: After anesthesia, tracheostomy and constant volume ventilation, respiratory failure was induced by lung lavage in 20 rats. Animals were randomly assigned to an untreated control group or two experimental groups. Equal total doses of modified porcine surfactant (200 mg.kg-1 body weight), were given by tracheal instillation, either as a single bolus or in four (50 mg.kg-1 b.w.) fractional doses at 10-min intervals. Arterial pH and blood gases, and peak inspiratory pressure (PIP) were measured. RESULTS: After lavage, a rapid decrease in arterial pH and PaO2, and an increase in PaCO2 and PIP were observed in all animals. In both surfactant-treated groups, PaO2 increased after surfactant instillation, and remained significantly higher than controls throughout the experiment. Arterial pH was significantly higher and PaCO2 significantly lower only in the single bolus group. In the multiple dose group, these levels were similar to those of controls. CONCLUSION: In surfactant-depleted rats with respiratory failure, instillation of four fractional surfactant doses did not result in the same enhancement on gas exchange and PIP, in the following 60 min, as same total dose given by a single bolus.

Lung growth and maturation in the rat model of experimentally induced congenital diaphragmatic hernia.

This paper explores whether, in addition to the previously described lung hypoplasia with arteriolar hypermuscularization present in the nitrofen-induced foetal rat model of congenital diaphragmatic hernia (CDH), there are changes in the respiratory exchange epithelium, consistent with the hypothesis that abnormal surfactant production and/or release could account in part for the respiratory insufficiency in this condition. Foetal lungs from nitrofen-treated rats were obtained on the 21st day of gestation, weighed and processed for light and electron-microscopic studies and compared to controls of the same age. Tissues from 29 control and 26 CDH foetuses were examined. In addition, lungs from 19 foetuses born to nitrofen-treated dams but without CDH were also studied. The lungs from CDH animals were hypoplastic by weight in comparison with control ones and so were those from treated foetuses without CDH. Airway branching was arrested in CDH at the pseudo-glandular stage of development, corresponding to the 16th day of gestation and the very narrow air spaces were lined by generally mature type II pneumocytes rich in glycogen and lamellar bodies corresponding to the 19th day of gestation. This pattern was in contrast to that of the control foetuses which had a normal terminal sac pattern with flat type I pneumocyte lining corresponding to their gestational age. Nitrofentreated animals without CDH had intermediate patterns. These findings support the hypothesis that the surfactant-producing system has the same lesions in this experimental model as in other less-affordable ones, like the foetal lamb one. Further studies on the contribution of this factor to the altered respiratory physiology in CDH using this model are warranted.

The kidney in the fetal rat model of congenital diaphragmatic hernia induced by nitrofen.

This paper explores whether there is a correlation between kidney and lung growths in an experimental model of congenital diaphragmatic hernia (CDH) induced by intragastric administration of Nitrofen (115 mg/kg) in olive oil on time-dated pregnant Wistar rats at the 9th day of gestation. For comparison we used pregnant rats treated with olive oil alone. Twenty-nine normal fetuses from 3 control rats and 24 left CDH fetuses from 6 Nitrofen rats were studied. Fetal (3.6 +/- 0.8 v 4.9 +/- 0.4 g, P < .001) and total lung (2% +/- 0.5% v 2.6% +/- 0.3% of body weight, P < .001) weights were significantly decreased in animals with CDH. Kidneys were also smaller in CDH animals although not significantly (0.7% +/- 0.1% v 0.8% +/- 0.1% of body weight, P = .05) and were also histologically immature. Regression of kidney weight on body weight for both groups yielded regression lines that were identical at analysis of covariance and all data points from the CDH group were within the control group 95% confidence limits. After converting raw data into lung/body and kidney/body weight ratios, no inverse correlation suggesting a feedback mechanism of growth regulation between both organs could be found. Since nitrofen acts through modifications of the thyroid hormone status in both dam and fetus, altered maturation of several organs should be expected although some of them, like the lung, are the leading targets. The present CDH rodent model is probably different from the human malformation in spite of the striking anatomic similarities between them.(ABSTRACT TRUNCATED AT 250 WORDS)

[Pulmonary surfactant in experimental congenital diaphragmatic hernia]. / Surfactante pulmonar en la hernia diafragmatica congénita experimental.

This paper examines the amounts of tensoactive phospholipids in the lung tissue of rat fetuses treated with Nitrofen (TOK) and in control animals. The herbicide led to congenital diaphragmatic hernia (CDH) in some fetuses and to pulmonary hypoplasia (PH) in all. The amounts of phosphatidylcholine (PC), phosphatidylglycerol (PG), phosphatidylinositol (PI) and phosphatidylethanolamine (PE) per gram of fresh lung tissue were significantly increased in comparison with the control animals, those of phosphatidylserine (PS) and sphingomyelin (SM) were also increased, but not significantly. Fetuses with HP alone had intermediate values. These findings are in agreement with our previous demonstration of an excess of type II pneumocytes in this model, and point to the existence of some trouble of the secretion or release of surfactant in it; although they do no clarify whether the amount of alveolar surfactant is in fact decreased.

[Experimental congenital diaphragmatic hernia with pulmonary hypoplasia in a rat model]. / Hernia diafragmatica congenita experimental con hipoplasia pulmonar en un modelo de rata.

Aiming at better understanding the mechanisms of malformation and the pathophysiology of congenital diaphragmatic hernia (CDH) and the pulmonary hypoplasia (PH) associated to it we have developed an experimental model in the Wistar rat fetus according to the following design: Three time-dated pregnant rats had 1 ml of olive oil instilled into the stomach at the 9 1/2 day of gestation (control group) and six more were treated with 115 mg/kg of Nitrofen in olive oil (experimental group). After Cesarean section on the 21st day we recovered 29 normal fetuses from the control and 41 fetuses from the experimental groups. Seventeen of these did not have diaphragmatic defects whereas the remaining 24 had left CDH. Fetuses from treated rats were significantly smaller than control ones and those bearing CDH were even smaller than their littermates. Total wet lung weight was significantly smaller in both subgroups of the experimental group. Histologic studies revealed that: 1) There were some variations in the degree of pulmonary hypoplasia in fetuses with CDH probably related to the size of the defect. 2) The main differences in maturation between lungs in control and experimental groups were in the tubulo-acinar structure. We describe the ultrastructure in both groups. This study recalls that some teratogens may be implicated in the pathogenesis of CDH, and also that PH, which was also present in treated fetuses without CDH, could be the cause rather than the consequence of CDH. In that case, our current therapeutic aims should be reviewed.