Gertie Grossmann

Lung surfactant and the pathogenesis of neonatal bronchiolar lesions induced by artificial ventilation.

Summary: Premature newborn rabbits, obtained by hysterotomy on day 27 of gestation, were tracheotomized immediately after birth and treated with intermittent positive pressure ventilation (IPPV) for 16–60 min. Tidal volume was registered by means of a body plethysmograph and adjusted to 10 ml/kg and the insufflation pressure required to maintain this tidal volume was recorded. One group of animals received, by tracheal tube, a deposit of 50 μl homologous surfactant suspension, prepared by centrifugation of lung wash from adult rabbits (the phospholipid content of the surfactant suspension was 8.4 mg/ml, its lecithin content 6.9 mg/ml); littermates with empty tracheal tubes served as controls. The mean quasistatic compliance of the lung-thorax system was higher in surfactant-treated animals than in controls (0.42 ± 0.12 and 0.27 ± 0.04 ml/cm H<2<O Kg, respectively; <P< < 0.002). Alveolar expansion, determined morphometrically in histologie sections, was increased in animals receiving surfactant, in comparison with controls. Lung sections from control animals revealed widespread necrosis and desquamation of bronchiolar epithelium, whereas such lesions were scarce or absent in surfactant-treated animals. Our findings indicate that lung compliance of the premature neonate can be increased by deposition of surfactant in the upper airways before the onset of ventilation, and that deposition of surfactant prevents the development of bronchiolar epithelial lesions in premature neonates subjected to IPPV.Speculation: The possibility that administration of supplementary surfactant might serve as a prophylaxis against RDS and against epithelial lesions induced by artificial ventilation should be further evaluated in animal experiments and the clinical application of analogous prophylactic measures considered, once synthetic surfactant suspensions with optimal phospholipid (or phospholipid-protein) composition have been defined.

Inactivation of Exogenous Surfactant by Pulmonary Edema Fluid

ABSTRACT: Modified natural porcine surfactant was mixed with edema fluid sampled from the airways of hyperoxia-exposed adult rabbits. By varying the concentration of surfactant lipids (10, 25, and 50 mg/mL) and edema fluid proteins (0–280 mg/mL), we obtained a series of preparations with protein to surfactant lipid weight ratios ranging from 0 to 11.2. The surfactant activity of these various mixtures was analyzed with a pulsating bubble (at a lipid concentration of 10 mg/mL) or in experiments on immature new born rabbits (at lipid concentrations of 25 or 50 mg/mL). For the latter purpose, animals were delivered at a gestational age of 27 d and ventilated with a standardized sequence of insufflation pressures after receiving 0.1 mL of the surfactant-edema sample into the airways at birth. Nearly complete in vitro inhibition of surfactant (markedly delayed film adsorption and a minimum surface tension of 23 mN/m during pulsation) was observed at a protein to surfactant lipid ratio of 4.5. Under in vivo conditions, nearly complete surfactant inhibition (tidal volumes reduced to less than 20% of the values for littermates ventilated with the same pressure after receiving surfactant without admixture of edema fluid) was documented at a protein to surfactant lipid ratio of 11.2. Our data suggest that the functional properties of an immature neonatal lung, in which serum proteins tend to leak into the airspaces after the onset of ventilation, depend on the stoichiometric relation between surfactant lipids and inhibitory proteins in the lung liquid.

Experimental Neonatal Respiratory Failure Induced by a Monoclonal Antibody to the Hydrophobic Surfactant-Associated Protein SP-B

ABSTRACT: The present experiments were designed to test whether selective blocking of the surfactant-associated hydrophobic polypeptide SP-B (8.7 kD) would interfere with lung function during neonatal adaptation. A MAb to porcine SP-B was produced by hybridoma cell line (8B5E); this antibody cross-reacts with rabbit SP-B. Six mg of MAb to SP-B, dissolved in 0.2 mL of saline, was instilled into the airways of near-term newborn rabbits (gestational age 29 d), before the onset of ventilation. Control animals received the same amount of nonspecific rabbit IgG in saline, or were untreated. The animals were ventilated for 120 min with a standardized tidal volume (10 mL/kg). The specific antibody caused a prominent, immediate decrease in lung-thorax compliance, associated with acute inflammatory and exudative lung lesions including hyaline membranes. IgG alone had no such effects. Our data suggest that the MAb to SP-B inhibits surfactant function in the neonatal period by blocking one of the mechanisms responsible for fast adsorption of the surfactant phospholipids to the alveolar air-liquid interface. In addition, an acute inflammatory reaction is probably triggered in the lung parenchyma by the immune reaction.

Lung-Thorax Compliance in the Artificially Ventilated Premature Rabbit Neonate in Relation to Variations in Inspiration: Expiration Ratio

Summary: Surfactant-deficient premature newborn rabbits obtained by hysterotomy on day 27 of gestation were tracheostomized at birth, kept in a multichambered pressure-constant body plethysmograph, and subjected to intermittent positive pressure ventilation using a standardized insufflation pressure (30 cm H2O). A sequence of various frequencies (20, 40, and 60/min) and inspiration:expiration (I:E) ratios (1:4, 1:2, 1:1, 2:1, and 4:1) were applied, and the effect of these various respirator settings on tidal volume (VT) and flow was evaluated by means of a Fleisch tube connected to the body plethysmograph. Irrespective of respirator frequency, increasing I: E ratio from the basic setting of 1:1 resulted in increased VT; decreasing I:E ratio had the opposite effect. There was a nearly linear relation between variations in I:E ratio and VT, but the slope of the regression line was steeper at frequencies 40 and 60/min than at 20/min. At a frequency of 20/min, values (X ± S.D.) for lung-thorax compliance at I:E ratios of 1:4 and 4:1 were 0.50 ± 0.26 and 0.99 ± 0.42 ml/cm H2O·kg, respectively. Corresponding figures for frequency of 60/min were 0.21 ± 0.10 and 0.73 ± 0.36 ml/cm H2O·kg. At the two higher frequencies and low I:E ratios (≤1:1), the duration of the inspiration phase was not sufficient to provide the maximal degree of lung expansion attainable with this insufflation pressure under static conditions. At frequency of 60/min and I:E ratio of 4:1, the expiration was short enough to prevent zero flow before onset of inspiration.Speculation: The wet lungs of premature neonates with surfactant deficiency are not ventilated effectively with a conventional inspiration:expiration ratio of 1:1, or less. However, by increasing inspiration: expiration ratio to as much as 4:1, the viscosity of the fluid in the airways can be overcome, and the lungs can then be ventilated with a lower insufflation pressure. This alternative setting of the respirator should reduce the risk of long-term complications, such as bronchopulmonary dysplasia, in surfactant-deficient babies treated with artificial ventilation in the neonatal period.

Combined effects of surfactant substitution and prolongation of inspiration phase in artificially ventilated premature newborn rabbits.

Summary: Premature newborn rabbits, delivered by hysterotomy on day 27 of gestation, were tracheotomized at birth, kept in body plethysmographs, and subjected to pressure-generated ventilation at a working pressure of 25 cm H2O, 100% O2, and frequency 40/min. Thirty-seven animals received 50 μl of heterologous surfactant (phospholipid content 40 mg/ml) via the tracheal cannula before onset of artificial ventilation, eight were ventilated with a positive end-expiratory pressure (PEEP) of 6 cm H2O, and 44 served as controls. All animals were ventilated in a randomized sequence of 2-min periods with 20, 40, 60, or 80% inspiration time. After the experiment the trachea was clamped at end-inspiration and the lungs fixed by immersion in formalin. Plethysmograph recordings of tidal volume revealed that lung-thorax compliance was low in control animals, even at inspiration time 80% (mean ± S.E. = 0.17 ± 0.03 ml/cm H2O·kg). In animals treated with surfactant or PEEP, compliance was significantly improved at all ventilator settings. The highest mean compliance values, obtained at 60% inspiration time were 0.91 ± 0.07 and 0.73 ± 0.14 ml/cm H2O·kg in surfactant- and PEEP-treated animals, respectively. Compliance of surfactant-treated animals was significantly higher than that of PEEP-treated animals at inspiration time 40% (0.85 ± 0.07 versus 0.52 ± 0.13 ml/cm H2O·kg; P < 0.05). The relative volume of the alveolar compartment, determined morphometrically in histologic sections and expressed as the alveolar expansion index (Ia), was significantly higher in surfactant-treated animals than in controls (1.60 ± 0.12 versus 0.74 ± 0.06; P < 0.005), but not improved in animals ventilated with PEEP. In animals receiving surfactant, Ia increased with the duration of the inspiration phase, from 0.99 ± 0.10 at 20% to 1.95 ± 0.22 at 80% inspiration time. There was also histologic evidence of enhanced recruitment of aerated alveoli in surfactant-treated animals ventilated with prolonged inspiration time.Speculation: The air expansion of the premature neonatal lung can be enhanced to a significant degree by treatment with surfactant in combination with appropriate prolongation of the inspiration phase. Such a therapeutic regimen might be useful in the management of newborn infants with severe respiratory distress syndrome, requiring artificial ventilation; however, because excessive prolongation of the inspiration phase could have adverse effects on pulmonary hemodynamics and lead to hypoventilation with respiratory acidosis, the setting of the ventilator should be carefully adjusted with respect to the therapeutic response in patients with respiratory distress syndrome who are treated with supplementary surfactant.

Exogenous porcine surfactant (Curosurf) is inactivated by monoclonal antibody to the surfactant‐associated hydrophobic protein SP‐B

A monoclonal antibody to the surfactant‐associated hydrophobic protein SP‐B was added at various concentrations to a standard preparation of porcine surfactant (Curosurf 10 mg/ml), and surface properties were evaluated with pulsating bubble. Retarded adsorption of surfactant was observed at antibody concentrations 0.5 mg/ml and significantly increased values for minimum surface tension were observed at antibody concentrations 1 mg/ml. In vivo effects of the antibody were tested in immature newborn rabbits ventilated with a standardized sequence of insufflation pressures. Animals receiving 0.1 ml surfactant (80 mg/ml) mixed with antibody at concentrations 4 mg/ml had low tidal volumes, poor lung stability in pressure‐volume recordings, poor alveolar expansion in histological sections and widespread epithelial necrosis in peripheral airways. Admixtures of IgG had no such effects. We conclude that this monoclonal antibody inactivates exogenous porcine surfactant, probably by preventing fast adsorption of surfactant lipids to the alveolar air‐liquid interfaces.

Surfactant treatment and ventilation by high frequency oscillation in premature newborn rabbits: effect on survival, lung aeration, and bronchiolar epithelial lesions.

ABSTRACT: Premature rabbit neonates delivered at gestational age 27 days were ventilated by high frequency oscillation for 60 min with 100% O2, using a frequency of 7-8 Hz, 50% inspiration time and mean airway pressures of 6-8 cm H2O. Twenty-five animals received bovine surfactant (2 ml/kg body weight; phospholipid concentration 85-100 mg/ml) in the tracheal cannula before onset of ventilation, and 22 littermates served as controls. In the surfactant-treated group, average tidal volume was about 10 times larger than in controls, yet only 15% of the estimated dead space. Judged from ECG recordings, the treated animals also had a much higher survival rate: 96 versus 5% (p < 0.001). Morphometrically, mean alveolar volume density was increased in the surfactant-treated animals in comparison with controls: 0.65 ± 0.08 versus 0.37 ± 0.08 (x ± SD; p < 0.005). Bronchiolar epithelial lesions were found in all control animals and were severe in almost all cases. In the surfactant-treated group, epithelial lesions were absent in 12, mild in 11, and fairly prominent in two animals. We conclude that after treatment with surfactant, the premature newborn rabbit can be ventilated adequately with high frequency oscillation at comparatively low mean airway pressures and that surfactant replacement effectively reduces the development of epithelial lesions in conducting airways during high frequency oscillation.

Inhibition of exogenous surfactant in ventilated immature newborn rabbits.

Immature newborn rabbits were treated at birth by tracheal instillation of porcine surfactant (100 microliters, phospholipid concentration 80 mg.ml-1), to which [14C]dipalmitoylphosphatidylcholine had been added as a marker. They were kept in a body plethysmograph/pneumotachygraph system at 37 degrees C. During a 120 min period of artificial ventilation with a peak insufflation pressure of 20 cm H2O, there was a gradual decrease in tidal volumes (36%.h-1). This decrease was correlated to an elevation of minimum surface tension (r = 0.81; P less than 0.01) and to a prolongation of the adsorption rate (r = 0.80; P less than 0.01) of surfactant recovered by lung lavage from the same animals. There was also correlations between duration of ventilation and minimum surface tension (r = 0.56; P less than 0.01), and between duration of ventilation and adsorption rate (r = 0.73; P less than 0.01). The surface properties of phospholipids extracted from the lavage fluid were similar to those of the original surfactant preparation. Our data suggest that, in immature newborn rabbits subjected to artificial ventilation, exogenous surfactant may become inactivated, probably due to protein leakage into the airspaces.

Immunochemical and Immunohistochemical Evaluation of Lung Permeability in Ventilated Newborn Rabbits

These experiments were designed to quantify the vascular-to-alveolar leakage albumin in the neonatal lung and to analyze the distribution of leaking airspaces in the lung parenchyma. Immediately after delivery, newborn rabbits with gestational age 27-29 days received an intravenous injection of human albumin as a marker and were ventilated for 15 min with standardized tidal volume (10 ml/kg). After the period of ventilation the lungs were either lavaged via the airways or fixed for histological studies. The median amount of albumin in lung lavage fluid, determined by immunodiffusion, was 4.8% of the injected dose after 27 days, 1.3% after 28 days, and 0.4% after 29 days of gestation; it was inversely correlated with the compliance of the respiratory system (r = -0.78; p less than .001). Immunohistochemical examination of lung section revealed that the leak was not diffuse; even in animals with gestational age 27 days it involved only a median of 48% of total alveoli. The median amount of alveoli containing the label fell to 6% after 28 days and to 0% after 29 days gestation, correlating inversely with the compliance of the respiratory system (r = -0.53; p less than 0.01). We suggest that our experimental model is useful for histological demonstration of serum proteins leaking into the airpaces under experimental conditions and for evaluating the effect of therapeutic regiments on neonatal lung permeability.

Passive expiratory flow-volume recordings in immature newborn rabbits. Effect of surfactant replacement on the time constant of the respiratory system.

Immature newborn rabbits with a gestational age of 27 days were paralyzed and kept in body plethysmographs. They were ventilated for 10 min with a tidal volume of approximately 10 ml/kg, with or without previous surfactant treatment via the airways. Tidal volumes and flow were recorded with a pneumotachograph connected to the body plethysmograph, and the expiratory time constant of the respiratory system (trs) was determined from flow-volume diagrams. The values of trs after 10 min were significantly higher in surfactant-treated animals than in controls (50 +/- 7 vs. 23 +/- 4 ms; p less than 0.002), indicating stabilization of the alveoli. There was also a close correlation between trs and the compliance values calculated from tidal volumes and ventilator pressure (r = 0.80; p less than 0.001), as well as between trs and the alveolar volume density in histological lung sections, determined by automated image analysis (r = 0.71; p less than 0.001).