Pulmonary surfactant will secure free airflow through a narrow tube

Factors influencing airway smooth muscle tone: a comprehensive review with a special emphasis on pulmonary surfactant

A thin film of pulmonary surfactant lines the surface of the airways and alveoli, where it lowers the surface tension in the peripheral lungs, preventing collapse of the bronchioles and alveoli and reducing the work of breathing. It also possesses a barrier function for maintaining the blood-gas interface of the lungs and plays an important role in innate immunity. The surfactant film covers the epithelium lining both large and small airways, forming the first line of defense between toxic airborne particles/pathogens and the lungs. Furthermore, surfactant has been shown to relax airway smooth muscle (ASM) after exposure to ASM agonists, suggesting a more subtle function. Whether surfactant masks irritant sensory receptors or interacts with one of them is not known. The relaxant effect of surfactant on ASM is absent in bronchial tissues denuded of an epithelial layer. Blocking of prostanoid synthesis inhibits the relaxant function of surfactant, indicating that prostanoids might be involved. Another possibility for surfactant to be active, namely through ATP-dependent potassium channels and the cAMP-regulated epithelial chloride channels [cystic fibrosis transmembrane conductance regulators (CFTRs)], was tested but could not be confirmed. Hence, this review discusses the mechanisms of known and potential relaxant effects of pulmonary surfactant on ASM. This review summarizes what is known about the role of surfactant in smooth muscle physiology and explores the scientific questions and studies needed to fully understand how surfactant helps maintain the delicate balance between relaxant and constrictor needs.

High-frequency chest wall oscillation multiple times daily can better reduce the loss of pulmonary surfactant and improve lung compliance in mechanically ventilated patients

BACKGROUND

High-frequency chest wall oscillation (HFCWO) has been widely recognized for its airway secretion clearance effectiveness in critically ill ICU patients.

OBJECTIVES

The purpose of this randomized controlled trial is to validate and compare the effects of different frequencies of HFCWO on oxygenation, lung compliance, and pulmonary surfactant proteins (SPs) in critically ill patients admitted to the intensive care unit (ICU).

METHODS

Sixty patients with severe craniocerebral injury treated with a tracheostomy and mechanical ventilation were randomized into three groups (20 patients in each group): a single group (treated with 30 minutes of HFCWO once daily) and a double group (treated with 30 minutes of HFCWO twice daily), and a blank group (treated without HFCWO). Primary outcome measures included results on several specific proteins (SP-A, SP-B, SP-C, and SP-D) in serum and alveolar lavage fluid. Secondary outcome measures were lung static compliance test and oxygenation.

RESULTS

Patients in both the single and double groups exhibited significant oxygenation and static compliance improvement. Similar results were observed in changes in SPs concentrations in the alveolar lavage fluid. However, a significant reduction of SPs levels was observed in the serum. In the group comparison analysis for the same variables between the single and double group, twice daily HFCWO treatments showed a significantly better result.

CONCLUSION

Compared with HFCWO once daily, HFCWO twice daily is advantageous in patients with tracheostomy and prolonged ventilation, which demonstrated significantly greater effectiveness in improving oxygenation and lung static compliance linked to the increase of and SPs contents in the airways as well as a reduction of SPs shift from airways to the blood.

Liquid plug formation in an airway closure model

The closure of a human lung airway is modeled as an instability of a two-phase flow in a pipe coated internally with a Newtonian liquid. For a thick enough coating, the Plateau-Rayleigh instability creates a liquid plug which blocks the airway, halting distal gas exchange. Owing to a bi-frontal plug growth, this airway closure flow induces high stress levels on the wall, which is the location of airway epithelial cells. A parametric numerical study is carried out simulating relevant conditions for human lungs, either in ordinary or pathological situations. Our simulations can represent the physical process from pre- to post-coalescence phases. Previous studies have been limited to pre-coalescence only. The topological change during coalescence induces a high level of stress and stress gradients on the epithelial cells, which are large enough to damage them, causing sub-lethal or lethal responses. We find that post-coalescence wall stresses can be in the range of 300% to 600% greater than pre-coalescence values, so introduce a new important source of mechanical perturbation to the cells.

Tensiometric and Phase Domain Behavior of Lung Surfactant on Mucus-like Viscoelastic Hydrogels

Lung surfactant has been observed at all surfaces of the airway lining fluids and is an important contributor to normal lung function. In the conducting airways, the surfactant film lies atop a viscoelastic mucus gel. In this work, we report on the characterization of the tensiometric and phase domain behavior of lung surfactant at the air-liquid interface of mucus-like viscoelastic gels. Poly(acrylic acid) hydrogels were formulated to serve as a model mucus with bulk rheological properties that matched those of tracheobronchial mucus secretions. Infasurf (Calfactant), a commercially available pulmonary surfactant derived from calf lung extract, was spread onto the hydrogel surface. The surface tension lowering ability and relaxation of Infasurf films on the hydrogels was quantified and compared to Infasurf behavior on an aqueous subphase. Infasurf phase domains during surface compression were characterized by fluorescence microscopy and phase shifting interferometry. We observed that increasing the bulk viscoelastic properties of the model mucus hydrogels reduced the ability of Infasurf films to lower surface tension and inhibited film relaxation. A shift in the formation of Infasurf condensed phase domains from smaller, more spherical domains to large, agglomerated, multilayer structures was observed with increasing viscoelastic properties of the subphase. These studies demonstrate that the surface behavior of lung surfactant on viscoelastic surfaces, such as those found in the conducting airways, differs significantly from aqueous, surfactant-laden systems.

Pulmonary surfactant in the airway physiology: a direct relaxing effect on the smooth muscle

Beside alveoli, surface active material plays an important role in the airway physiology. In the upper airways it primarily serves in local defense. Lower airway surfactant stabilizes peripheral airways, provides the transport and defense, has barrier and anti-edematous functions, and possesses direct relaxant effect on the smooth muscle. We tested in vitro the effect of two surfactant preparations Curosurf® and Alveofact® on the precontracted smooth muscle of intra- and extra-pulmonary airways. Relaxation was more pronounced for lung tissue strip containing bronchial smooth muscle as the primary site of surfactant effect. The study does not confirm the participation of ATP-dependent potassium channels and cAMP-regulated epithelial chloride channels known as CFTR chloride channels, or nitric oxide involvement in contractile response of smooth muscle to surfactant.By controlling wall thickness and airway diameter, pulmonary surfactant is an important component of airway physiology. Thus, surfactant dysfunction may be included in pathophysiology of asthma, COPD, or other diseases with bronchial obstruction.

Pulmonary fluid flow challenges for experimental and mathematical modeling

Modeling the flow of fluid in the lungs, even under baseline healthy conditions, presents many challenges. The complex rheology of the fluids, interaction between fluids and structures, and complicated multi-scale geometry all add to the complexity of the problem. We provide a brief overview of approaches used to model three aspects of pulmonary fluid and flow: the surfactant layer in the deep branches of the lung, the mucus layer in the upper airway branches, and closure/reopening of the airway. We discuss models of each aspect, the potential to capture biological and therapeutic information, and open questions worthy of further investigation. We hope to promote multi-disciplinary collaboration by providing insights into mathematical descriptions of fluid-mechanics in the lung and the kinds of predictions these models can make.

Acute chlorine gas exposure produces transient inflammation and a progressive alteration in surfactant composition with accompanying mechanical dysfunction

Acute Cl2 exposure following industrial accidents or military/terrorist activity causes pulmonary injury and severe acute respiratory distress. Prior studies suggest that antioxidant depletion is important in producing dysfunction, however a pathophysiologic mechanism has not been elucidated. We propose that acute Cl2 inhalation leads to oxidative modification of lung lining fluid, producing surfactant inactivation, inflammation and mechanical respiratory dysfunction at the organ level. C57BL/6J mice underwent whole-body exposure to an effective 60ppm-hour Cl2 dose, and were euthanized 3, 24 and 48h later. Whereas pulmonary architecture and endothelial barrier function were preserved, transient neutrophilia, peaking at 24h, was noted. Increased expression of ARG1, CCL2, RETLNA, IL-1b, and PTGS2 genes was observed in bronchoalveolar lavage (BAL) cells with peak change in all genes at 24h. Cl2 exposure had no effect on NOS2 mRNA or iNOS protein expression, nor on BAL NO3(-) or NO2(-). Expression of the alternative macrophage activation markers, Relm-α and mannose receptor was increased in alveolar macrophages and pulmonary epithelium. Capillary surfactometry demonstrated impaired surfactant function, and altered BAL phospholipid and surfactant protein content following exposure. Organ level respiratory function was assessed by forced oscillation technique at 5 end expiratory pressures. Cl2 exposure had no significant effect on either airway or tissue resistance. Pulmonary elastance was elevated with time following exposure and demonstrated PEEP refractory derecruitment at 48h, despite waning inflammation. These data support a role for surfactant inactivation as a physiologic mechanism underlying respiratory dysfunction following Cl2 inhalation.

The effect of viscoelasticity on the stability of a pulmonary airway liquid layer

The lungs consist of a network of bifurcating airways that are lined with a thin liquid film. This film is a bilayer consisting of a mucus layer on top of a periciliary fluid layer. Mucus is a non-Newtonian fluid possessing viscoelastic characteristics. Surface tension induces flows within the layer, which may cause the lung's airways to close due to liquid plug formation if the liquid film is sufficiently thick. The stability of the liquid layer is also influenced by the viscoelastic nature of the liquid, which is modeled using the Oldroyd-B constitutive equation or as a Jeffreys fluid. To examine the role of mucus alone, a single layer of a viscoelastic fluid is considered. A system of nonlinear evolution equations is derived using lubrication theory for the film thickness and the film flow rate. A uniform film is initially perturbed and a normal mode analysis is carried out that shows that the growth rate g for a viscoelastic layer is larger than for a Newtonian fluid with the same viscosity. Closure occurs if the minimum core radius, R(min)(t), reaches zero within one breath. Solutions of the nonlinear evolution equations reveal that R(min) normally decreases to zero faster with increasing relaxation time parameter, the Weissenberg number We. For small values of the dimensionless film thickness parameter epsilon, the closure time, t(c), increases slightly with We, while for moderate values of epsilon, ranging from 14% to 18% of the tube radius, t(c) decreases rapidly with We provided the solvent viscosity is sufficiently small. Viscoelasticity was found to have little effect for epsilon>0.18, indicating the strong influence of surface tension. The film thickness parameter epsilon and the Weissenberg number We also have a significant effect on the maximum shear stress on tube wall, max(tau(w)), and thus, potentially, an impact on cell damage. Max(tau(w)) increases with epsilon for fixed We, and it decreases with increasing We for small We provided the solvent viscosity parameter is sufficiently small. For large epsilon approximately 0.2, there is no significant difference between the Newtonian flow case and the large We cases.

Role of lung surfactant in respiratory disease: current knowledge in large animal medicine

Lung surfactant is produced by type II alveolar cells as a mixture of phospholipids, surfactant proteins, and neutral lipids. Surfactant lowers alveolar surface tension and is crucial for the prevention of alveolar collapse. In addition, surfactant contributes to smaller airway patency and improves mucociliary clearance. Surfactant-specific proteins are part of the innate immune defense mechanisms of the lung. Lung surfactant alterations have been described in a number of respiratory diseases. Surfactant deficiency (quantitative deficit of surfactant) in premature animals causes neonatal respiratory distress syndrome. Surfactant dysfunction (qualitative changes in surfactant) has been implicated in the pathophysiology of acute respiratory distress syndrome and asthma. Analysis of surfactant from amniotic fluid allows assessment of fetal lung maturity (FLM) in the human fetus and exogenous surfactant replacement therapy is part of the standard care in premature human infants. In contrast to human medicine, use and success of FLM testing or surfactant replacement therapy remain limited in veterinary medicine. Lung surfactant has been studied in large animal models of human disease. However, only a few reports exist on lung surfactant alterations in naturally occurring respiratory disease in large animals. This article gives a general review on the role of lung surfactant in respiratory disease followed by an overview of our current knowledge on surfactant in large animal veterinary medicine.

The effect of elevated dietary cholesterol on pulmonary surfactant function in adolescent mice

It has been established that phospholipids and cholesterol interact in films of pulmonary surfactant (PS). Generally it is thought that phospholipids increase film stability whereas cholesterol increases film fluidity. To study this further, we modified dietary cholesterol in mice which received either standard rodent lacking cholesterol (sd), or high cholesterol (2%) diet (hc) for 1 month. Phospholipid stability was investigated by a capillary surfactometer (CS), which measures airflow resistance and patency. PS was collected by bronchiolar lavage and centrifuged to obtain the surface-active film (SAF). Results showed that the hc-SAF had significantly more cholesterol than sd-SAF. CS analyses at 37 degrees C showed no significance differences in airflow resistance between hc-SAF and sd-SAF. However, at 37 degrees C, sd-SAF showed greater ability to maintain patency compared to hc-SAF, whereas at 42 degrees C hc-SAF showed patency ability similar to sd-SAF. The results suggested that increased cholesterol in hc-SAF induced less stability in the SAF possibly due to cholesterol's fluidizing effect on phospholipids at physiological temperatures.

Interactions of serum with lung surfactant extract in the bronchiolar and alveolar airway models

Lung surfactant (LS) a lipid-protein mixture is secreted by type-II pneumocytes and prevents alveolar collapse as well as maintains upper airway patency. In certain lung pathophysiology dysfunction of the LS occurs due to leakage of serum derived materials interacting with surfactant at the respiratory air-water interface. Bovine lipid extract surfactant (BLES) with and without foetal calf serum (FCS) were studied as models of bronchiolar airway patency using a capillary surfactometer, and in alveolar (terminal) airway using adsorbed Langmuir films in a surface balance. About 5 wt.% of serum was found to maximally decrease airway patency of BLES by 90%, as well as the surface films ability to reach low surface tension below 25 mN/m. In fact, FCS was found to be about 200-fold more potent inhibitor of the surfactant extract compared to a major serum component, albumin. Also serum but not albumin significantly reduced the gel-phase structures found in BLES films under compression at low amounts (5-10 wt.%), and eventually abolished these organized structures as imaged by fluorescence and atomic force microscopy. This fact suggests that serum caused complete molecular re-organization of the surfactant lipids in films at an air-water interface, and the ability of such films to reduce surface tension or maintain airway patency. The study may provide a novel structure-function disruption model for lung surfactant inactivation in the airways in pathophysiology.

Inhaled lysophosphatidylcholine provokes bronchoconstriction in guinea pigs in vivo

Lysophosphatidylcholine is increased in the airway of bronchial asthma, but its role is not clear. We investigated the role of lysophosphatidylcholine in asthma in anaesthetized, mechanically ventilated guinea pigs. Pressure at the airway opening was measured as an index of bronchial response. Increasing doses of lysophosphatidylcholine (1--10 mg/ml) were inhaled and then bronchoalveolar lavage was carried out. 100 and 200 microg/ml methacholine were inhaled 10 min after inhalation of 2.5 mg/ml lysophosphatidylcholine, 10 mg/ml dipalmitoyl phosphatidylcholine and 10 mg/ml glycerophosphocholine, all of which per se did not change the pressure at the airway opening. Effect of 1.0 microg/kg salbutamol, or 60 mg/kg diphenhydramine on the lysophosphatidylcholine-induced increase in the pressure at the airway opening was investigated. Inhalation of lysophosphatidylcholine dose-dependently increased the pressure at the airway opening and increased bronchial responsiveness to methacholine. On the other hand, inhalation of dipalmitoyl phosphatidylcholine decreased the pressure at the airway opening and decreased bronchial responsiveness to methacholine. Intravenously administered salbutamol, but not diphenhydramine, prevented the lysophosphatidylcholine-induced increase in the pressure at the airway opening. The percentage of leukocytes in bronchoalveolar lavage fluid did not change significantly at least within 20 min after the lysophosphatidylcholine inhalation. Lysophosphatidylcholine causes bronchoconstriction and enhances bronchial responsiveness without inducing leukocyte infiltration in the airway, suggesting that lysophosphatidylcholine may be a new bronchoconstrictor mediator in bronchial asthma.

Effect of surfactant deficiency and surfactant replacement on airway patency in the piglet lung

We investigated the effect of surfactant deficiency on airway patency and the effectiveness of surfactant replacement as either an instilled liquid bolus, a non-hygroscopic aerosol or a hygroscopic aerosol. Small airway patency was assessed in isolated piglet lungs by passing a continuous flow of gas though a cannulated airway. Occlusion was assessed by measuring increases in pressure in the cannula that resulted from airway obstruction. In surfactant-deficient conditions the amount of airway closure increased approximately three-fold. However, administration of exogenous surfactant as an instilled liquid bolus, non-hygroscopic aerosol or a hygroscopic aerosol decreased airway closure such that it was statistically similar to that recorded prior to induction of surfactant deficiency, although the instilled and hygroscopic aerosol surfactant both appeared superior to the non-hygroscopic aerosol. These experiments showed that pulmonary surfactant does have a role in maintaining airway patency and that airway closure induced by surfactant deficiency could be reduced by administration of surfactant in any of the aforementioned forms.

The pattern of surfactant cholesterol during vertebrate evolution and development: does ontogeny recapitulate phylogeny?

Pulmonary surfactant is a complex mixture of phospholipids (PLs), neutral lipids and proteins that lines the inner surface of the lung. Here it modulates surface tension, thereby increasing lung compliance and preventing the transudation of fluid. In humans, pulmonary surfactant is comprised of approximately 80% PLs, 12% neutral lipids and 8% protein. In most eutherian (i.e. placental) mammals, cholesterol (Chol) comprises approximately 8-10% by weight or 14-20 mol% of both alveolar and lamellar body surfactant. It is regarded as an integral component of pulmonary surfactant, yet few studies have concentrated on its function or control. The lipid composition is highly conserved within the vertebrates, except that surfactant of teleost fish is dominated by cholesterol, whereas tetrapod pulmonary surfactant contains a high proportion of disaturated phospholipids (DSPs). The primitive Australian dipnoan lungfish Neoceratodus forsterii demonstrates a 'fish-type' surfactant profile, whereas the other derived dipnoans demonstrate a surfactant profile similar to that of tetrapods. Homology of the surfactant proteins within the vertebrates points to a single evolutionary origin for the system and indicates that fish surfactant is a 'protosurfactant'. Among the terrestrial tetrapods, the relative proportions of DSPs and cholesterol vary in response to lung structure, habitat and body temperature (Tb), but not in relation to phylogeny. The cholesterol content of surfactant is elevated in species with simple saccular lungs or in aquatic species or in species with low Tb. The DSP content is highest in complex lungs, particularly of aquatic species or species with high Tb. Cholesterol is controlled separately from the PL component in surfactant. For example, in heterothermic mammals (i.e. mammals that vary their body temperature), the relative amount of cholesterol increases in cold animals. The rapid changes in the Chol to PL ratio in response to various physiological stimuli suggest that these two components have different turnover rates and may be packaged and processed differently. In mammals, the pulmonary surfactant system develops towards the end of gestation and is characterized by an increase in the saturation of PLs in lung washings and the appearance of surfactant proteins in amniotic fluid. In general, the pattern of surfactant development is highly conserved among the amniotes. This conservation of process is demonstrated by an increase in the amount and saturation of the surfactant PLs in the final stages (>75%) of development. Although the ratios of surfactant components (Chol, PL and DSP) are remarkably similar at the time of hatching/birth, the relative timing of the maturation of the lipid profiles differs dramatically between species. The uniformity of composition between species, despite differences in lung morphology, birthing strategy and relationship to each other, implies that the ratios are critical for the onset of pulmonary ventilation. The differences in the timing, on the other hand, appear to relate primarily to birthing strategy and the onset of air breathing. As the amount of cholesterol relative to the phospholipids is highly elevated in immature lungs, the pattern of cholesterol during development and evolution represents an example of ontogeny recapitulating phylogeny. The fact that cholesterol is an important component of respiratory structures that are primitive, when they are not in use or developing in an embryo, demonstrates that this substance has important and exciting roles in surfactant. These roles still remain to be explored.

A comparison of biologically variable ventilation to recruitment manoeuvres in a porcine model of acute lung injury

Background

Biologically variable ventilation (return of physiological variability in rate and tidal volume using a computer-controller) was compared to control mode ventilation with and without a recruitment manoeuvre – 40 cm H₂O for 40 sec performed hourly; in a porcine oleic acid acute lung injury model.

Methods

We compared gas exchange, respiratory mechanics, and measured bronchoalveolar fluid for inflammatory cytokines, cell counts and surfactant function. Lung injury was scored by light microscopy. Pigs received mechanical ventilation (F_IO₂ = 0.3; PEEP 5 cm H₂O) in control mode until PaO₂ decreased to 60 mm Hg with oleic acid infusion (PaO₂/F_IO₂ <200 mm Hg). Additional PEEP to 10 cm H₂O was added after injury. Animals were randomized to one of the 3 modes of ventilation and followed for 5 hr after injury.

Results

PaO₂ and respiratory system compliance was significantly greater with biologically variable ventilation compared to the other 2 groups. Mean and mean peak airway pressures were also lower. There were no differences in cell counts in bronchoalveolar fluid by flow cytometry, or interleukin-8 and -10 levels between groups. Lung injury scoring revealed no difference between groups in the regions examined. No differences in surfactant function were seen between groups by capillary surfactometry.

Conclusions

In this porcine model of acute lung injury, various indices to measure injury or inflammation did not differ between the 3 approaches to ventilation. However, when using a low tidal volume strategy with moderate levels of PEEP, sustained improvements in arterial oxygen tension and respiratory system compliance were only seen with BVV when compared to CMV or CMV with a recruitment manoeuvre.

Surfactant function in children with chronic airway inflammation

Pulmonary surfactant is necessary to keep the terminal conducting airways patent. It is unknown whether mild to moderate airway inflammation may influence surfactant function and thus contribute to the pathogenesis of chronic airway inflammation in children. To answer this question, 21 children with chronic obstructive bronchitis and 19 asymptomatic children with long-term tracheostomy and increased numbers of neutrophils in their airways were compared with 15 healthy controls. Bronchoalveolar lavage fluid was separated into large surfactant aggregates (LA) and a supernatant containing inhibitory constituents. Surfactant function of LA, recombinations of LA and supernatant, and recombinations of a defined bovine surfactant and supernatant was assessed in a capillary surfactometer. Compared with controls, the function of the LA surfactant was reduced and there was no difference between children with tracheostomy and chronic obstructive bronchitis. The function of LA-supernatant recombinations was poor in all subjects. This may be explained by the well-known protein influx during the lavage procedure. The activity of bovine surfactant-supernatant reconstitutions was impaired in children with tracheostomy. In all surfactant mixtures assessed, surfactant function was inversely correlated to the number of neutrophils in the lavage fluid. Chronic lower airway inflammation with mild or no clinical symptoms is associated with impaired surfactant function. The dysfunction may contribute to airflow restrictions frequently observed in these children.

Eosinophil cationic protein alters pulmonary surfactant structure and function in asthma

BACKGROUND

Impaired surfactant function has been demonstrated in patients with asthma. Inhibitory proteins originating from plasma or inflammatory mediators are good candidates to contribute to this dysfunction. Eosinophils are potent effector cells in asthma, which, on activation, release inflammatory mediators, especially reactive granula proteins such as eosinophil cationic protein (ECP).

OBJECTIVE

Because the potential role of ECP in the inhibition of surfactant function is not known, we tested the hypothesis of whether ECP levels in bronchoalveolar lavage fluid (BALF) of patients with asthma after segmental allergen provocation correlate to surfactant dysfunction. Furthermore, we tested the effect of purified ECP on surfactant function and structure in vitro.

METHODS

Surfactant isolated from BALF of asthmatic patients was assessed for biophysical function with the Pulsating Bubble Surfactometer and the Capillary Surfactometer and correlated to ECP levels. Purified ECP and plasma proteins at various concentrations were incubated with natural surfactant. Surfactant function was studied with the Capillary Surfactometer, and surfactant structure was determined by electron microscopy.

RESULTS

ECP is elevated in BALF from patients with asthma after allergen challenge compared with baseline. ECP levels after allergen challenge correlate well to surfactant dysfunction. In vitro, ECP induces a concentration-dependent inhibition of surfactant function that can be inhibited by antibodies against ECP. ECP is more potent compared with albumin or fibrinogen. Finally, ECP induces severe ultrastructural changes to surfactant vesicles that are more pronounced than changes induced by either fibrinogen or albumin.

CONCLUSIONS

ECP contributes to surfactant dysfunction in asthma, which in turn could lead to airway obstruction.

Surface-lining layer of airways in cystic fibrosis mice

Lung disease is the major cause of death in individuals suffering from cystic fibrosis (CF), with abnormal lung-lining fluids occurring as early as early infancy. However, the precise etiology of CF lung disease is still poorly understood. We investigated the structural components of the airway surface-lining layer in targeted Cftrtm1HGU/Cftrtm1HGU mutant mice and non-CF controls. Five lungs per animal group were fixed by intravascular triple perfusion. The ultrastructure of the surface-lining layer of large and small intrapulmonary conducting airways was systematically investigated according to a standard protocol in transmission and scanning electron micrographs. In both animal groups, the surface-lining layer consisted of an aqueous phase and an osmiophilic film of variable thickness at the air-fluid interface. The aqueous phase usually did extend <1 microm beyond the uppermost tips of the epithelial cells in both animal groups. The aqueous phase of the small airways was slightly more electron dense in Cftrtm1HGU/Cftrtm1HGU than in non-CF mice. Neither the ultrastructure of the surfactant film at the air-fluid interface nor the forms assumed by the osmiophilic structures associated with surfactant turnover in the aqueous layer differed significantly in Cftrtm1HGU/Cftrtm1HGU and non-CF mice. Hence, there were no signs of any ultrastructural abnormalities in the surface-lining layer of young adult Cftrtm1HGU/Cftrtm1HGU mice before infection with CF-related pathogens.

The role of surfactant in asthma

Pulmonary surfactant is a unique mixture of lipids and surfactant-specific proteins that covers the entire alveolar surface of the lungs. Surfactant is not restricted to the alveolar compartment; it also reaches terminal conducting airways and is present in upper airway secretions. While the role of surfactant in the alveolar compartment has been intensively elucidated both in health and disease states, the possible role of surfactant in the airways requires further research. This review summarizes the current knowledge on surfactant functions regarding the airway compartment and highlights the impact of various surfactant components on allergic inflammation in asthma.

Pulmonary surfactant function studied with the pulsating bubble surfactometer (PBS) and the capillary surfactometer (CS)

Two instruments, the pulsating bubble surfactometer (PBS) and the capillary surfactometer (CS), were constructed for a study of pulmonary surfactant's physical properties. The instruments study spherical surfaces as in alveoli (PBS) and cylindrical surfaces as in terminal conducting airways (CS). Phospholipids, pulmonary surfactant's main components, are amphiphilic and, therefore, spontaneously form a film at air-liquid interfaces. When the film in the PBS is compressed to a reduced area during 'expiration', the molecules come closer together. Thereby, a high surface pressure develops, causing surface tension to be reduced more than bubble radius. If these conditions, observed with the PBS are analogous in lungs, alveolar stability would be promoted. The CS was developed for a study of how surfactant has ability to maintain patency of narrow conducting airways. Provided adsorption is extremely fast, a surfactant film will line the terminal conducting airway as soon as liquid blocking the airway has been extruded. During expiration that film will develop high surface pressure (=low surface tension). This will counteract the tendency for liquid to accumulate in the airway's most narrow section. If surfactant is dysfunctioning, liquid is likely to accumulate and block terminal airways. Airway resistance would then increase, causing FEV(1) to be reduced.

Compositional and functional changes of pulmonary surfactant in a guinea-pig model of chronic asthma

Recent studies have found that severe surfactant dysfunction occurs during an asthma attack, but the changes in surfactant in a guinea-pig model of chronic asthma have not been studied. We therefore analysed the surfactant recovered from guinea-pigs after repeated inhalation of ovalbumin to see if the surfactant recovered from chronic asthmatic lungs would be intrinsically altered. Guinea pigs immunized through repeated inhalation of aerosolized ovalbumin (OA) were exposed to the antigen once a week for a month. Twenty-four hours after the last challenge the alveolar wash was recovered. We calculated saturated phosphatidylcholine (Sat-PC) and total protein (TP) pool sizes in alveolar spaces. Surfactant subtype conversion of large aggregate surfactant (LA) to small aggregate surfactant was studied in vitro by means of the surface area cycling technique. The phospholipid composition of LA was analysed by thin layer chromatography and the surface activity of LA was also determined. We found decreased surfactant pool sizes, decreased ratio of Sat-PC to TP in alveolar lavages in asthma groups, and surface activity of the surfactant recovered from asthmatic lungs to be inferior to that of the controls. Accelerated surfactant subtype conversion in vitro was also noted in the lungs of asthmatic animal models. In addition, the changes in phospholipid compositions which were similar to the pattern of acute lung injury suggested that alveolar inflammation might be involved in the pathogenesis of chronic asthma. These results indicate that surfactant is intrinsically abnormal in chronically asthmatic lungs.

Altered airway surfactant phospholipid composition and reduced lung function in asthma

Pulmonary surfactant in bronchoalveolar lavage fluid (BALF) and induced sputum from adults with stable asthma (n = 36) and healthy controls (n = 12) was analyzed for phospholipid and protein compositions and function. Asthmatic subjects were graded as mild, moderate, or severe. Phospholipid compositions of BALF and sputum from control subjects were similar and characteristic of surfactant. For asthmatic subjects, the proportion of dipalmitoyl phosphatidylcholine (16:0/16:0PC), the major phospholipid in surfactant, decreased in sputum (P < 0.05) but not in BALF. In BALF, mole percent 16:0/16:0PC correlated with surfactant function measured in a capillary surfactometer, and sputum mole percent 16:0/16:0PC correlated with lung function (forced expiratory volume in 1 s). Neither surfactant protein A nor total protein concentration in either BALF or sputum was altered in asthma. These results suggest altered phospholipid composition and function of airway (sputum) but not alveolar (BALF) surfactant in stable asthma. Such underlying surfactant dysfunction may predispose asthmatic subjects to further surfactant inhibition by proteins or aeroallergens in acute asthma episodes and contribute to airway closure in asthma. Consequently, administration of an appropriate therapeutic surfactant could provide clinical benefit in asthma.

Function and composition of pulmonary surfactant and surfactant-derived fatty acid profiles are altered in young adults with cystic fibrosis

STUDY OBJECTIVES

To determine whether chronic lung inflammation in young adult patients with cystic fibrosis (CF) alters the composition and function of surfactant and surfactant components in bronchoalveolar secretions.

DESIGN

A prospective, descriptive study.

SETTING

An adult CF center in a tertiary health-care center.

PARTICIPANTS

Thirteen normal volunteer (NV) subjects recruited via local advertising and 15 CF patients recruited from the CF center.

INTERVENTIONS

None.

MEASUREMENTS AND RESULTS

We performed BAL and measured surfactant-associated protein A (SP-A) via enzyme-linked immunosorbent assay in BAL fluid (BALF), and quantitated total phospholipid, phospholipid subclass, and fatty acid subclass content of extracted BALF. We also determined the protein and phospholipid content, SP-A content, and functional characteristics of surfactant isolated from BALF via high-speed centrifugation. The phospholipid-to-protein ratio (milligram/milligram) of surfactant isolated by centrifugation (mean +/- SEM) was 1.01 +/- 0.07 for NV subjects and 2.62 +/- 0.42 for CF patients (p = 0.0001). Minimal surface tension was < 1 dyne.s.cm(-5) in all samples from NV subjects, but 21.9 +/- 0.73 dyne.s.cm(-5) for surfactant from CF patients. Immunoblotting of isolated surfactant revealed a marked decrease in SP-A for CF patients, compared to NV subjects. However, mean concentrations of SP-A in BALF that had not been subjected to high-speed centrifugation to isolate surfactant were not significantly different for CF patients (4.7 +/- 0.8 microgram/mL) vs NV subjects (4.6 +/- 0.2 microgram/mL). Additionally, phospholipid-to-protein ratios (0.32 +/- 0.04 for NV subjects vs 0.10 +/- 0.02 for CF patients; p < 0.0001) in extracted uncentrifuged BALF, and SP-A-to-protein ratios (microgram/milligram) in BALF were significantly depressed (74 +/- 8 for NV subjects vs 16 +/- 3 for CF patients; p < 0.0001). The phospholipid and fatty acid subclass profiles of extracted CF BALF vs NV BALF revealed a decreased mean phosphatidylcholine-to-sphingomyelin ratio (20.7 +/- 10.0 vs 55.2 +/- 8.7; p = 0.002), increased oleic acid content (12.1 +/- 2.3 nmol/mL vs 3.2 +/- 0.9 nmol/mL; p < 0.01), and increased arachidonic acid content (2.2 +/- 0.5 nmol/mL vs 0.6 +/- 0.3 nmol/mL; p < 0.05) for CF patients.

CONCLUSIONS

Altered phospholipid-to-protein ratios and phospholipid subclasses, altered surfactant-derived fatty acid profiles, high minimal surface tension, and decreased association of SP-A with lipid components of isolated surfactant indicate that surfactant components are considerably altered and dysfunctional in lower respiratory tract secretions of CF patients. Surfactant composition and function are altered in CF, and the pattern of phospholipid and surfactant-derived fatty acid subclass alterations in CF are characteristic of ongoing lung injury and may depress surfactant function.

Exogenous surfactant therapy and mucus rheology in chronic obstructive airway diseases

Exogenous surfactant is a specialized biomaterial used for substitution of the lipoprotein mixture normally present in the lungs-pulmonary surfactant. Respiratory Distress Syndrome is a disease of preterm infants mainly caused by pulmonary immaturity as evidenced by a deficiency of mature lung surfactant. Pulmonary surfactant is known to stabilize small alveoli and prevent them from collapsing during expiration. However, apart from alveoli, surfactant also lines the narrow conducting airways of the tracheobronchial tree. This paper reviews the role of this surfactant in the airways and its effect on mucus rheology and mucociliary clearance. Its potential role as a therapeutic biomaterial in chronic obstructive airway diseases, namely asthma, chronic bronchitis, and respiratory manifestations of cystic fibrosis, are discussed. This paper also attempts to elucidate the exact steps in the pathogenic pathway of these diseases which could be reversed by supplementation of exogenous surfactant formulations. It is shown that there is great potential for the use of present day surfactants (which are actually formulated for use in Respiratory Disease Syndrome) as therapy in the aforementioned diseases of altered mucus viscoelasticity and mucociliary clearance. However, for improved effectiveness, specific surfactant formulations satisfying certain specific criteria should be tailor-made for the clinical condition for which they are intended. The properties required to be fulfilled by the optimal exogenous surfactant in each of the above clinical conditions are enumerated in this paper.

Pseudomonas aeruginosa from patients with cystic fibrosis affects function of pulmonary surfactant

Patients with cystic fibrosis are severely affected by an infection with Pseudomonas aeruginosa, a microbe known to synthesize phospholipase C. This study was designed to determine whether that enzyme would affect the function of pulmonary surfactant phospholipids. Mucoid and nonmucoid strains of P. aeruginosa, freshly obtained from patients with cystic fibrosis, were cultured for 12 h on agar plates. The bacteria were suspended in saline solution and then pelleted by centrifugation. The supernatant was used to dilute the surfactant preparation, calf lung surfactant extract, from 35 to 2 mg/mL. Surfactant function, before and after incubation, was examined with a capillary surfactometer, an instrument specifically developed for an evaluation of the ability of surfactant to maintain patency of a narrow glass tube, simulating a terminal conducting airway. Phospholipid hydrolysis was also evaluated biochemically by determining the total content of phospholipids in surfactant before and after incubation. In five experiments, the lipids were separated with thin-layer chromatography, and the phosphorus content was determined in the diacylphosphatidylcholine band before and after incubation for 6, 24, and 48 h. Capillary openness and phospholipid concentration decreased as enzyme concentration and time of incubation increased (p<0.0001). Linear regression showed a significant correlation between time of capillary openness and phospholipid concentration (r = 0.957; p<0.0001). Calf lung surfactant extract hydrolysis was catalyzed by extracts of the bacteria, particularly the nonmucoid, analogous to the catalysis observed with phospholipase C. Surfactant hydrolysis catalyzed by enzymes from P. aeruginosa might severely affect surfactant function provided enzyme concentration is high and time of incubation is long.

Mechanical force-induced signal transduction in lung cells

The lung is a unique organ in that it is exposed to physical forces derived from breathing, blood flow, and surface tension throughout life. Over the past decade, significant progress has been made at the cellular and molecular levels regarding the mechanisms by which physical forces affect lung morphogenesis, function, and metabolism. With the use of newly developed devices, mechanical forces have been applied to a variety of lung cells including fetal lung cells, adult alveolar epithelial cells, fibroblasts, airway epithelial and smooth muscle cells, pulmonary endothelial and smooth muscle cells, and mesothelial cells. These studies have led to new insights into how cells sense mechanical stimulation, transmit signals intra- and intercellularly, and regulate gene expression at the transcriptional and posttranscriptional levels. These advances have significantly increased our understanding of the process of mechanotransduction in lung cells. Further investigation in this exciting research field will facilitate our understanding of pulmonary physiology and pathophysiology at the cellular and molecular levels.

Antigen-induced airway inflammation in atopic subjects generates dysfunction of pulmonary surfactant

If pulmonary surfactant develops a dysfunction, its ability to maintain patency of narrow conducting airways diminishes, which is likely to cause an increased airway resistance. We hypothesized that antigen challenge will cause inflammation in the conducting airways and that this will cause a surfactant dysfunction. Twenty atopic patients underwent bronchoalveolar lavage (BAL) 5 min and 48 h after challenge with antigen in one segment and with saline solution in another. BAL fluid (BALF) cell count, differential, and proteins were determined. Surfactant function was studied with a capillary surfactometer (CS), an instrument specifically designed to evaluate surfactant's ability to maintain patency. Eosinophils increased 80-fold 48 h after antigen challenge and total protein increased from 84 to 241 micrograms/ml (median values). BALF surfactant lost part of its ability to maintain openness of the capillary, from 68.8% to 14.0% (p < 0.05). Protein concentration negatively correlated with percent openness (r = -0.62, p = 0.005). We conclude that the antigen challenge resulted in an inflammatory reaction that caused pulmonary surfactant to lose some of its ability to maintain airway patency and speculate that surfactant dysfunction is probably an important factor contributing to increased airway obstruction in allergen-induced exacerbation of asthma.

Surfactant effects in model airway closure experiments

The capillary instability that occurs on an annular film lining a tube is studied as a model of airway closure. Small waves in the film can amplify and form a plug across the tube. This dynamical behavior is studied using theoretical models and bench-top experiments. Our model predicts the initial growth rate of the instability and its dependence on surfactant effects. In experiments, an annular film is formed by infusion of water into an initially oil-filled glass capillary tube. The thickness of the oil film varies with the infusion flow rate. The instability growth rate and closure time are measured for a range of film thicknesses. Our theory predicts that a thinner film and higher surfactant activity enhance stability; surfactant can decrease the growth rate to 25% of its surfactant-free value. In experiments, we find that surfactant can decrease the growth rate to 20% and increase the closure time by a factor of 3.8. Functional values of a critical film thickness for closure support the theory that it increases in the presence of surfactant.

Dysfunction of pulmonary surfactant in asthmatics after segmental allergen challenge

Increased airway resistance in asthma may be partly due to poor function of pulmonary surfactant. This study investigated the inflammatory changes of bronchoalveolar lavage fluid (BALF) and the performance of BALF surfactant in healthy control subjects (n = 9) and patients with mild allergic asthma (n = 15) before and after segmental challenge. BALF was obtained for baseline values, and 24 h after challenge with saline solution in one lung segment and with allergen in another. Cell counts, phospholipid and protein concentrations, and ratios of small to large surfactant aggregates (SA/LA) were analyzed. Surface tension was determined with a pulsating bubble surfactometer, and the ability of the BALF surfactant to maintain airway patency was assessed with a capillary surfactometer. Baseline values of control subjects and asthmatics were not different. Challenge with saline and antigen raised total inflammatory cells in both control subjects and asthmatics. Allergen challenge of asthmatics, but not of healthy volunteers, significantly increased eosinophils, proteins, SA/ LA, and surface tension at minimum bubble size, and diminished the time the capillary tube is open. In conclusion, allergen challenge in asthmatics induced surfactant dysfunction, probably mainly because of inhibiting proteins. During an asthma attack, narrow conducting airways may become blocked, which might contribute to an increased airway resistance.

Ozone affects breathing and pulmonary surfactant function in mice

The effect on breathing of BALB/c mice immediately following ozone exposure (2 ppm) for 0, 2, 4, 6, and 8 h was studied with a whole body plethysmograph. Whether such exposure affected the normal function of pulmonary surfactant of maintaining airway patency was evaluated with a capillary surfactometer. Respiratory rate in mice that were not exposed was 358+/-16 (mean+/-S.E.) breaths/min and decreased to 202+/-10 after 6 h exposure. The mean pressure change caused by breathing diminished significantly, indicating a reduced tidal volume. BAL fluid from controls maintained patency for 88+/-2% of the study time, 120 s, implying a good surfactant function, but the ozone exposure caused the surfactant to lose its capability of maintaining patency (P < 0.0001). This decaying surfactant function of the BAL fluid coincided with an increasing protein concentration in the fluid of exposed animals (1.46+/-0.14 mg/ml in the 8-h group) as compared to controls (0.44+/-0.04 mg/ml, P < 0.0001). It is concluded that leakage of plasma proteins into the airway lumen was probably the main reason for the surfactant dysfunction, which may have contributed to the altered breathing pattern.

Surfactant dysfunction develops in BALB/c mice infected with respiratory syncytial virus

Recent reports suggest an important role for pulmonary surfactant in maintaining the patency of narrow conducting airways. The hypothesis that surfactant dysfunction is an important factor in respiratory syncytial virus (RSV) infection was tested in a mouse model. Mice, inoculated with either a low or a high dose of RSV, were subjected to bronchoalveolar lavage (BAL), and the fluids were analyzed for percentage of inflammatory cells and concentrations of proteins and phospholipids. After concentration of the surfactant by centrifugation, its function was analyzed with a capillary surfactometer. RSV infection resulted in a dose-dependent disruption of surfactant function (p < 0.0001). BAL fluid supernatants were added to calf lung surfactant extract (CLSE) to examine whether surfactant inhibiting agents were present. Indeed, BAL fluid supernatants of RSV-infected mice disrupted the normal function of calf lung surfactant extract in a dose dependent way (p < 0.0001), indicating the presence of inhibitors. Protein concentrations were increased in BAL fluids of RSV-infected mice versus control mice (p < 0.0001), and were inversely related to surfactant function (r = -0.44, p = 0.0004), suggesting an inhibitory effect of proteins. Protein concentration also correlated with the percentage of inflammatory cells (r = 0.51, p = 0.004). Phospholipid concentrations were not affected by the RSV infection. The results of these studies strongly suggest that a disruption of pulmonary surfactant function, most likely due to inhibition from inflammatory proteins, is important for the pathophysiology of RSV infection.

Dysfunction of guinea-pig pulmonary surfactant and type II pneumocytes after repetitive challenge with aerosolized ovalbumin

BACKGROUND

Asthma symptoms may partially be caused by a surfactant dysfunction. The inflammatory reaction, so characteristic of asthma, involves a protein invasion of airways which harmfully affects the surfactant function. However, mild asthma attacks might also impede the surfactant synthesis in alveolar type II cells.

OBJECTIVE

The present study evaluates the hypothesis that type II pneumocyte metabolic function might be disturbed in a model of mild asthma.

METHODS

Immunized, as well as not immunized control guinea-pigs, were challenged three times at two-day intervals with 0.04% ovalbumin aerosol. Bronchoalveolar lavage (BAL) was performed one day after the last challenge and the fluid was evaluated for surface activity, and content of phospholipids and proteins. Alveolar type II cells were isolated and their ability to incorporate a 3H labeled surfactant precursor was evaluated.

RESULTS

BAL fluid from immunized and challenged animals showed less surface activity (P < 0.01) when compared with BAL fluid from controls, not immunized but challenged. Most likely the reduced surface activity was caused by a 74% increase in the protein concentration (P < 0.05). Isolated type II cells from immunized and challenged animals had 33% less phospholipids than cells from controls (P < 0.05), and phosphatidylcholine synthesis was reduced 35% (P < 0.05).

CONCLUSION

These results suggest that the synthesis, intra-cellular storage, and biophysical activity of surfactant are decreased in an intermittent and mild form of asthma.

Surfactant composition in infants and young children with cystic fibrosis

We tested the hypothesis that the composition of bronchial surfactant is normal in infants with cystic fibrosis (CF) in the absence of active lung disease but that it is altered by lower respiratory tract infection and inflammation. We examined the total phospholipid (PL), disaturated phospholipid (DSP), surfactant protein-A (SP-A), surfactant protein B (SP-B), and surface activity in bronchoalveolar lavage fluid from 27 subjects with CF whose mean age was 22.7 (SD 14.5) mo. Six infants with stridor served as non-CF controls. Twelve of the subjects with CF (CF-I group) had evidence of active pulmonary infection or inflammation which was absent in the remaining 15 subjects (CF-NI group). We found no differences in the surfactant composition or activity between controls and the CF-NI group. In contrast, the DSP/PL ratio was lower in the CF-I subjects than in both the CF-NI subjects (p = 0.05) and controls (p < 0.01) suggesting a disturbance of surfactant function. SP-A concentrations were higher in the CF-I group compared to the other two groups (p < 0.05). These results suggest that the bronchial surfactant of infants with CF is altered following lower airway infection and inflammation and is not a primary abnormality associated with this disorder.

Airway surfactant, a primary defense barrier: mechanical and immunological aspects

Epidemiologic studies have shown strong associations between mortality and morbidity from respiratory and cardiac causes and exposure to fine (PM10), but not coarse, particulates. A plausible mechanistic explanation for these associations is lacking. It has been shown that particles may be retained for an extended period of time in the airways, and that their clearance is inversely proportional to particle size. Such particles are localized in close association with the airway epithelium, and if they consist of low surface energy material, will be coated with an osmiophilic layer, consistent with surfactant. Particles are displaced into this position by surface and line tension forces exerted by the surfactant film at the air-aqueous interface. Particle displacement due to line tension is much greater for smaller particles in the micrometer range. The surface forces acting on the particles leave deep indentations on the epithelial cells. During the displacement process they may come into contact with airway macrophages in the mucous layer and/or dendritic cells situated in the airway epithelium. The smallest particles may even penetrate the mucosa to enter the interstitial compartment. In addition to altering the physical properties of particles, surfactant coatings reduce particle toxicity and enhance phagocytosis by opsonization. We speculate that surfactant acts as a primary defense barrier and plays a role in antigen presentation and elimination at the air-mucus interface of the airways.

Pulmonary surfactant as vehicle for intratracheally instilled tobramycin in mice infected with Klebsiella pneumoniae

1. The use of pulmonary surfactant has been proposed as a vehicle for antibiotic delivery to the alveolar compartment of the lung. This study investigated survival rates of mice with a respiratory Klebsiella pneumoniae infection treated intratracheally with tobramycin using a natural exogenous surfactant preparation as vehicle. 2. At day 1 after infection, animals were injected intratracheally with 20 microliters of the following solutions: (1) a mixture of surfactant (500 micrograms) and tobramycin (250 micrograms); (2) tobramycin (250 micrograms) alone; (3) surfactant (500 micrograms) alone; and (4) NaHCO3 buffer (control, sham-treatment). A fifth group received no treatment (control). Deaths were registered every 12 h for 8 consecutive days. 3. The results show an increased survival in the group receiving the surfactant-tobramycin mixture compared to the group receiving tobramycin alone (P < 0.05), the group receiving surfactant alone (P < 0.01) and the control groups (P < 0.01). It is concluded that intratracheal instillation of surfactant-tobramycin is superior to tobramycin alone in protecting animals from death due to a respiratory Klebsiella pneumoniae infection.

Respiratory mechanics before and after late artificial surfactant rescue

OBJECTIVE

To assess the effect of late administration of synthetic surfactant (Exosurf) on the ventilatory function of premature infants with hyaline membrane disease (HMD).

METHODOLOGY

Prospective non-randomized study in the Neonatal Intensive Care Unit (NICU) of a major referral hospital. The patients included two groups of premature infants with a birthweight between 750 and 2000 g who developed HMD. In group 1 with moderate to severe HMD, 2 x 5 mL/kg doses of Exosurf were given 12 h apart (first dose given at a mean age of 18.7 +/- 3.4 h [mean +/- s.e.m.]). In group 2 with milder HMD, no surfactant was given.

RESULTS

Significant reductions (P < 0.05) in the fraction of inspired oxygen (FIO2) occurred 6 h after surfactant administration (24 h of life) and by 48 h (64 h of life) in group 2. These improvements in gas exchange preceded improvements in passive respiratory compliance which occurred 24 h after surfactant (42 h of life) and by 72 h (88 h of life) in group 2 (P < 0.01). In both groups pulmonary resistance increased and was significant (P < 0.05) by 48 h (66 h of life) in group 1.

CONCLUSIONS

Synthetic surfactant given as late as a mean age 18.7 +/- 3.4 h still improves gas exchange but these early improvements cannot be completely explained by modifications of respiratory compliance.

Surfactant dysfunction develops when the immunized guinea-pig is challenged with ovalbumin aerosol

BACKGROUND

The cause of the airway resistance developing during an asthma attack is not completely understood. Besides bronchospasm and airway oedema a surfactant dysfunction has been suggested as a reason for an increased airway resistance.

OBJECTIVE

This paper aims at examining if indeed surfactant dysfunction develops when an asthma attack is induced in guinea-pigs.

METHODS

Guinea-pigs, immunized against ovalbumin and then challenged (by inhaling the antigen) underwent lung function tests (n = 7) and were compared with seven animals challenged, but not immunized. Lung lavage was carried out in three groups of guinea-pigs: controls, never immunized nor challenged (n = 7), not immunized but challenged (n = 6), immunized and challenged, no lung function test (n = 6). After concentrating the lavage fluid 10 times the surface activity was evaluated with the pulsating bubble surfactometer. The fluid's concentration of phospholipids and proteins was determined as was the phospholipid composition.

RESULTS

The 19 immunized and challenged animals all developed severe respiratory distress, six so seriously that they died. Lung function tests showed significantly increased airway resistance and decreased tidal volume, minute volume, and dynamic compliance. Surface activity of lavage fluid from immunized and challenged animals was significantly reduced when compared with fluid from control animals (P < 0.01). Immunization and challenge had no effect on the lavage fluid's phospholipid concentration or composition, but the proteins were at a higher concentration than in the fluid of the controls (P < 0.01).

CONCLUSION

Proteins leaking into the airways inhibited the surfactant. This, in turn might have caused conducting airways to become blocked by liquid columns, which would increase airway resistance.

Influence of pulmonary surfactant on in vitro bactericidal activities of amoxicillin, ceftazidime, and tobramycin

The influence of a natural pulmonary surfactant on antibiotic activity was investigated to assess the possible use of exogenous surfactant as a vehicle for antibiotic delivery to the lung. The influence of surfactant on the bactericidal activity of amoxicillin was tested against Staphylococcus aureus and Streptococcus pneumoniae, and the influence of surfactant on the activities of ceftazidime and tobramycin was tested against Klebsiella pneumoniae, Pseudomonas aeruginosa, S. aureus, and S. pneumoniae. In vitro antibiotic activity was determined by killing curve studies in media with and without surfactant. Amoxicillin and ceftazidime activities were not changed in the presence of surfactant, except for a decreased killing rate of S. pneumoniae by ceftazidime in medium with additional rabbit serum. In contrast, killing curves with low concentrations of tobramycin (0.25x and 1x the MIC) showed a decreased level of activity of tobramycin against all pathogens tested in the presence of surfactant. With higher tobramycin concentrations (4x the MIC) killing rates were decreased less or were unchanged in the presence of surfactant. Concluding from the results of the study, both amoxicillin and ceftazidime can be combined with surfactant without the loss of activity. For mixing surfactant with tobramycin, dosages should be adjusted to overcome the partial inactivation of tobramycin by surfactant.

Surfactant replacement therapy for non-respiratory distress syndrome neonatal respiratory disease--research or clinical application?

Research studies have highlighted both physiological and pathological evidence to incriminate surfactant abnormality and/or deficiency in many neonatal respiratory diseases. Data from animal models and clinical studies support the concept that surfactant replacement therapy (SRT) may have a role to play in such problems. There is now, therefore, a need to perform further randomized controlled trials to assess the appropriate clinical application of SRT in non-respiratory distress syndrome neonatal respiratory disease.

Exosurf rescue surfactant improves high ventilation-perfusion mismatch in respiratory distress syndrome

OBJECTIVE

To assess ventilation/perfusion (VA/Q) mismatch of the high type, following rescue surfactant therapy for respiratory distress syndrome.

HYPOTHESIS

Surfactant therapy reduces such mismatch.

DESIGN

Randomized, double-blind, placebo-controlled study, assessing VA/Q with the arterial-alveolar difference of CO2 tension (P(a-A)CO2). This difference was determined with capnometry and arterial blood gases, using the equation: P(a-A)CO2 equals arterial CO2 minus alveolar CO2 partial pressure.

SETTING

A level III nursery.

PATIENTS

Ten intubated infants with respiratory distress syndrome.

INTERVENTION

Infants were randomized to each receive two doses of surfactant or two doses of air placebo.

RESULTS

P(a-A)CO2 improved after surfactant and worsened after placebo (P = 0.0021), comparing slopes of 12-hr regression lines. A similar pattern occurred with oxygenation. These changes in P(a-A)CO2 and in oxygenation were minimally correlated within the surfactant group.

CONCLUSION

Exosurf rescue surfactant reduced VA/Q mismatch of the high type, over several hours.