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Langmuir 1986, 2. 664-668
structure with preferential exposure of methyl groups is introduced. Instead of a situation in which there is no vehicle present with sufficiently low surface energy to be surface active, now the methyl groups with a surface tension of 23 dyn/cm (18) are concentrated to the surface. Methylene groups would give a higher surface tension, 28-30 dyn/cm.Is This means that the surface activity of the lamellar liquid crystal which is induced by the long-range ordering will not function against a hydrocarbon with sufficiently low inherent surface tension. The gradually reduced foam stability with increased aliphatic hydrocarbon content illustrates this fact. As shown by Figure 13, addition of water to such hydrocarbons does not increase the surface tension. As 2,2-4-trimethylpentane is added to TEDgDE/ water, the surface tension is gradually reduced and when it reaches a critical point, no foam stability is left. A similar mechanism acts for hexadecane but in this case the low vapor pressure may also lead to some liquid hydrocarbon being present a t the surface to air. In the latter case with a hydrocarbon with a low vapor pressure, the possibility of a layer of solubilized hydrocarbon remaining on the surface of the liquid crystal should also be taken into account. The nature and structure of that layer is unknown. The results strongly indicate the presence of the liquid-crystalline phase at the surface as the decisive element
in the stabilization of the foam but leave no information about the stabilizing action of the liquid-crystalline layer. As a first item, it is essential to point out that the Ross”J2 results show an opposite result for a phase separation with two liquids. The surface free energies are of similar magnitude for the liquid crystal and the liquid, and, hence, it appears reasonable to assume that the enhanced rigidity of the liquid-crystalline phase is responsible for the improved stability of the present foams. In accordance with earlier literature23a monomolecular layer with high vicosity is a sine qua non for the stability of aqueous foams. A surface multimolecular layer of high viscosity should presumably fill the same function. In addition, the prevention of drainage by the viscous liquid-crystalline phase is also an important factor. Our earlier contributions4 demonstrated the enrichment of liquid-crystalline phase in the foam and slower drainage. However, the final conclusions must await further results.
Acknowledgment. Grants from Swedish Board for Technical Development, STU 84-3829, and National Science Foundation, NSF CPE 8213378, are gratefully acknowledged. Registry No. TEDGE, 5274-68-0;isooctane, 540-84-1;benzene, 71-43-2;hexadecane, 544-76-3. (23) Kitchener, J. A. Recent Prog. Surj. Sci. 1964, I , 51.
Method for Assessment of Fetal Lung Maturity1 Dotchi Exerowa,*t Zdravko Lalchev,i Borislav Marinov,§ and Karl Ognyanove Institute of Physical Chemistry, Bulgarian Academy of Sciences, 1040 Sofia, Bulgaria, Department of Biochemistry, University of Sofia, 1421 Sofia, Bulgaria, and Institute of Obstetrics and Gynecology, Medical Academy, Sofia, Bulgaria Received March 7, 1986. I n Final Form: June 4, 1986 A physicochemical method for evaluation of fetal lung maturity is described. The method is baseT on the possibility for spontaneous formation of a stable, with respect to rupture, black foam film (BFF) from mature amniotic fluid (AF). The stable BFF from AF is obtained as a result of a spontaneous processes taking place at the air/liquid interface, the interface which lines the alveolus. While mature AF samples give BFF that are stable for a long time, the foam films from immature AF samples are not stable and invariably rupture under the same conditions. Thus,failure to obtain a stable BFF from AF samples indicates a high risk for development of respiratory distress syndrome (RDS) in the newborn. The technique for detecting foam film rupture and BFF formation from AF samples is microscopic. The results obtained by the new method in a study of 182 samples from normal pregnancies are compared with those from the clinical investigation as well as with the lecithin/sphingomyelin(L/S) ratio of the samples. The BFF method proves to be of a higher diagnostic potential than the L/S ratio; moreover it is fast, is easy to perform, produces simple and unambiguous results, and requires minimal sample volumes. Introduction A series of papers have shown the correlation between lung immaturity and respiratory distress syndrome (RDS).ls2 A number of m e t h d s for prediction of fetal lung maturity by examination of samples from amniotic fluid have been developed (e.g., ref 3-11). Still, “no single test Bulgarian Academy of Sciences. *University of Sofia. Medical Academy-Sofia. Presented at the symposium on “Fluid-Fluid Interfaces: Foams”, 190th National Meeting of the American Chemical Society, Chicago, IL, Sept 8-13, 1985.
*
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of anmiotic fluid has yet been found to be completely reliable, easily performed, and universally applicable”.12 (1) Gluck, L.; Kulovich, M. V.; Borer, R. C., Jr.; et al. Am. J . Obstet. Gynecol. 1~71.109.440. (2) Gluck, L.; Kulovich, M. V. Am. J. Obstet. Gynecol. 1973,115,539. (3) Clements. J. A.: Platzker. A. C. G.: Tiernev. Enel. - , D. F.: et al. N. J. M e d . 1972, 286, 1077. (4)Muller-Tyle, E.; Lempert, S.; Steinbereithner, K.; et d.Am. J. Obstet. Gynecol. 1975, 122, 295. ( 5 ) Tiwary, C. M.; Goldkrand, J. M. Obstet. Gynecol. 1976, 48, 191. (6) Goldkrand, J. W.; Varki, A.; McClurg, S. E. Am. J . Obstet. Gynecol. 1977, 128, 591. ( 7 ) Hallman, M.; Kulovich, M.; Kirkpatrick, E.; et al. Am. J. Obstet. Gynecol. 1976, 125, 613.
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0 1986 American Chemical Society
Langmuir, Vol. 2, No. 5, 1986 665
Method for Assessment of Fetal Lung Maturity We now describe a new method for assessment of fetal lung maturity which takes into account both the total phospholipid amount in the amniotic fluid (AF)and the surface properties of the phospholipid molecules at the airliquid interface. The method is based on fundamental physicochemical investigations in the fielld of the foam films (e.g., ref 13-24). A foam f b is formed when two air bubbles come in contact in a solution of a surface active material ( S A M ) and consists of two adsorbed layers at the air-liquid interface with a water core between them. The behavior of the foam film depends on the amount and the surface properties of the SAM a t the airliquid interface. Above a certain SAM volume concentration (varying for different SAMs) the black foam film (BFF) is always spontaneously obtained; the BFF is stable with respect to rupture and can "live" for hours and days. Below this concentration the foam film is unstable and invariably ruptures in seconds.*&% Addition of 47.5 vol % ethanol t o water solutions decreases the surface tension at the air-liquid interface to 29 dyn per cm.27 As a result, in the case of AF, the addition of ethanol ensures predominant adsorption of the AF phospholipids, especially of dipalmitoyllecithin (DPL) as compared to proteins and other AF constituents, this fact has been made use of in the test of Clements and co-workers? Hence, in the presence of 47.5 vol % ethanol the BFF formation from AF could depend only on the amount of phospholipids in the AF. Concordantly, our preliminary investigations show that in the presence of ethanol the main factors responsible for the formation of BFF from AF are the AF concentrations of electrolyte and phospholipids, especially of lecithin."sW Therefore, and as far as the risk for RDS development in the newborn correlates with the lecithin deficiency in the AF, one may expect to find (at given electrolyte concentration and in (8)Shinitzky. M.; Goldfisher,A.; Buiek, A,; et al. Br. J. Obstet. Cynecol. 1976,83,838. (9) Statland, B. E.;Sher, G.;Freer, D. E.;et al. Am. J. Clin. Pothol.
197R l d.. . .. . ,fig .., S .. (10) Pattle, R. E.; Kratzing. C. C.; Parkinaon. C. E.; et al. Br. J. Obstet. Oyneeol. 1979,86,615. (11) Golde, S.H.; Mosley, G. H. Am. J. Obstet. Cyneeol. 1980, 136, ZLL. (12) OBrien, W. F.;Cefalo, R.C . Am. J. Obatet. Oyneeol. 1980,136, 1 ....2 5 (13) Scheludko, A. Adu. Colloid Interface Sci. 1967.1, 391. (14) Mysela, K. 1.; Shinoda, K.; Frankel, S. Soap Films; Pergamon Presa; New York, 1959. (15) Clunie, I. S.;Gmdman, I. F.; Ingram, B. T. In Surface ond Colloid Science; Wiley London, 1971; p 167. (16) Exerowa, D. Commun. Dep. Chem. (Bufg. Aead. Sei.) 1978, 11, 729. (17) Exerowa, D.: Kashchiev, D.; Balinov, B. Proceedings of the In-
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ternationol Congress of Aspects Mieroseopipues de I'Adhesion et de lo Lubrifimtion; Elsevir: Paris, 1981. (18) Jones, M. N.; Mysels, K. I.; Scholten, P. C. Tram Faraday SOC. 1966.62, 1336. (19) Lyklema, 1.; Maysels.
K. L. J. Am. Chem. Soe. 1965, 87, 2539. (20) Frij, A.; De Feijeter, I. A.; Agterof, W. M. Intermtion Forces in Soap Film. Foam"; Academic Press: London, 1976: p 91. (21) Kashchiev, D.; Exerowa,D. J. Colloid Interface Sei. 1980,77,501. (22) Exerowa, D.; Platikanov. D. Ann. Univ. Sofia, Foe. Chim. 1970/1971,65, 237.
(23) Exerowa. D.; Nikolov, A.; Zscharievs, M . J. Colloid Interface Sei. 1981.81. , , 419. (24) Exerows, D.; Balinov. B.; Nikolova, A,; et al. J. Colloid Interfoee Sei. 1983, 95. 289. (25) Lalchev, Z. Ph.D. Thesis, Bulgarian Academy of Science, 1984. (26) Ererowa. D.; Lalchev, Z.; Kashehiev, D. Colloids Surf. 1984, IO, 112
(27) Guggenheim,E. A. Thermodynamics; North Holland Publishing: Amsterdam, 1959; p 267. (28) Exerows, D.;Lalchev, Z:Marinov, B.; Ognyanov, K.Authorship Certificate No. 50291: Bulg. Inat. for Rational. and Inventions, 1981.
Figure 1. Scheme of the cell for formation and investigation of foam films with diameter 2r from 1 V 2to 5 X em. (a) Glass cylinder-holder of the biconcave drop (diameter 2R = 4 X 10.' em); (d) capillary; (e) layer of the investigated solution; (0bottom of the cell.
Figure 2. Photo of the assembled glass cell for formation and investigation of foam films the presence of 47.5 vol % ethanol) a correlation between the fetal lune maturitv and the BFF formation from AF. In addition, ihe type and stability of the BFF from AF in the presence of ethanol is studied in detail in ow previous
paper^?^.^^ Materials a n d Methods Patients. One hundred eighty-two patients were selected from the Research Institute of Obstetrics and Gynecology a t the Medical Academy-Sofia. Cases of maternal diabetes melitus and hypertensive diseases were not included. None of the mothers received corticosteroid derivatives. Fetal age wa8 computed from size, last normal mehtrual period, and physical and neurological development after birth. The morphological maturity of the newborn was determined by the method of Dubowitz and co-workers,29 including both morphological and neurological signs. The respiratory state of the newborn was determined by the method of HobePo as modified by M a ~ s o n . ~ ' The persons performing the laboratory test were unaware of the clinical status of the donors or of their infants (29) Dubowitz, L. M.
S.;Dubowitz, V.;Goldbera, C. J. Pediatr. ( S t .
666 Langmuir, Vol. 2, No. 5, 1986 7
.
Exerowa et al.
1
,
Figure 3. Photo of the equipment for formation and observation of foam films. (a) Inverted reflected light microscope; (b) ther. mostating jacket; (c) thermostating water outleg (d) glass cell (ef. Figure 2); (e) polyethylene tube connecting the glass cell to the Hg pump; (0 Hg pump for solution aspiration.
Figure 4. Foam films from amniotic fluid at various states: (a) a grey foam film; (b) a grey foam film with growing black spots; (e) a stable black foam film. The grey foam film (a) may rupture indicating immaturity or develop through (b) into (e) to indicate
and the neonatologist was not informed about the laboratory test results. Samples a n d Laboratory Procedure. One hundred eighty-two AF samples (of ca. 5 mL each) were collected between the 26th and 43rd gestational week from 182 women either by transcervical intraamniotic pressure catheter during labor or at the time of amniotomy with the use of transcervical amniocentesis. All samples contaminated with blood or meconium were discarded. Samples were centrifuged at 8OOg for 10 min and the supernatant was devided into two parts: for the lecithin/sphingomyelin (L/S) determination and for the foam film test. Samples were stored at -20 "C and thawed prior to analyses. Lecithin/Sphingomyelin (L/S) Ratio Determination. The L/S ratio of 126 AF samples (111 from the group of 182 samples and additional 15 from abortions) was determined by thin-layer chromatography by the method of Gluck and co-workers.' Values were computed by densitometry with a "Zeiss EP/65-m, reflected light" densitometer. Formation a n d Observation of Foam Films. We used the well-known method of S c h e l ~ d k o 'where ~ the foam film is formed in an appropriate glass cell presented in Figure 1. The glass cylinder (a), which is attached by a capillary (d) to the upper part of the cell, is loaded by merging it into the AF solution. A biconcave drop remains in the cylinder when it is taken out from the solution. Vertical lines closely adjacent to each other are finely cut, "furrowed", onto the inner surface of the glass cylinder to improve The lower part of the cell has a bottom of optical glass (0 above which a layer of the AF solution (e) is spread. The two parts of the cell are connected so that in some time the intracellular air space becomes saturated. The foam film is obtained by aspiration of solution from the drop into the capillary (d) until the upper and the lower meniscus come in contact. The process of foam film formation can he observed through the bottom of the cell on any type of an inverted reflected light microscope (in our case "Epytip", Karl Zeiss-Jena). Figure 2 shows the glass cell assembled, Figure 3 the microscope for foam film observation with a specially constructed thermostating jacket mounted onto it and an
Hg pump by means of which the AF solution is aspirated. Modificationsof the glass cell are possible and other types of microscopes (transmitted or reflected light) may, of course, be employed for foam film observation. The results reported in this paper are obtained with the glass cell and the microscope presented on Figures 2 and 3, respectively. In general, three states of the film are chronologically realized and observed the grey foam film (Figure 4a), the same with black spots growing in it (Figure 4b), and the black foam film (Figure 4c). A t the first two states (Figure 4a,b), the foam film may rupture which, provided other conditions are kept constant, depends only on the concentration and the surface properties of the phospholipids, especially of lecithin, in the AF (e.g., ref 25-28). Procedure of the Method and Detection of the Test Result. Supernatant, 1.0 mL, from the centrifuged AF sample is diluted with 0.7 mL of 0.2 M NaCl and 1.7 mL of 95 vol % ethanol. The final dilution of the A F constituents has to be 3.4X. The glass cylinder is loaded as described above. The cell is assembled, placed on the microscope, and thermoatated for 15 min at 25 OC. Under microscopy control the AF solution is then aspirated by means of the Hg pump from the cylinder (Figure la) into the capillary of the cell (Figure Id) until the image of the foam film appears in the middle of the out-of-focus biconcave drop. The sue of the film may he further adjusted with the aid of the Hg pump to the preferred diameter (2r may he from cm). In the beginning the to 5 X foam film is always thick, but soon it gets spontaneously thinner. Under the reflected light microscope the foam film appears as a colored disk with concentric rings around it (Figure 4a-e). If the AF sample is immature the foam film ruptures (negative test result) within 20 s while its color is still grey (Figure 4a); with mature samples, however, the following always occurs: on the grey background black spots spontaneously appear and grow (Figure 4b) to cover the whole film (positive test result, Figure 4-2). The BFF obtained from mature A F samples is very stable and can "live" for hours and days.25.26,"Thus, after 10 min of centrifugation and 15 min of thermostating, the result is present within only 1-2 min. Besides, the test result is a straightforward and unambiguous one (rupture of the grey foam film within seconds or practically infinite persistance of the BFF). There are several very important conditions under which the method is to he performed. First, the concentration
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(32)Exemwe, D.; Zacharieva, M.;Cohen. Polym. Sei. 1979,257, 1089.
R.;Platikanov, D.
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Method for Assessment of Fetal Lung Maturity Table I. Correlation between Test Results and Clinical Results (182 Samples) no. of with RDS without RDS gest. age, week samules BFF+ BFF- BFF+ BFF26-31 15 0 11 2 2 32-35 34 0 11 20 3 0 0 133 0 36-43 133 total 182 0 22 155 5 0.0% 3.1% false predictions
L
05.-
0
Table 11. Comparison of the L/S Ratio to the Clinical and Test Results (126 Samples)" no. of with RDS without RDS L / S ratio samples BFF+ BFFBFF+ BFF>2.0 82 0 5 76 1 0 6 11 1 1.6-2.0 18 26' 0 25 1 0 11.5 total 126 0 36 88 2 "The L/S ratio of the 38 BFF-negative cases is 1.20 f 0.26; the L/S ratio of the 88 BFF-positive cases is 3.64 f 1.10; P < 0.001
'
calculated by the two-tailed Student t-test. 15 samples with L/S 11.5 are from abortions (17-21 gestation week); the remaining 11 samples are 26-28 gestation week.
of ethanol in the solution is critical; therefor special care is to be taken to maintain it exactly 47.5 vol %. Second, saturation of the adsorbed layers of the foam film with the AF phospholipids is reached for about 10 min, which necessitates the 15 min of thermostating at 25.0 f 0.1 OC. Third, the method may be performed vith a preferred volume of AF (for instance 0.5 mL of AF + 0.35 mL of 0.2 M NaCl + 0.85 mL of 95% ethanol), but the final dilution with respect to the SAM in the AF has to be exactly 3.4fold. This is the dilution derived from a statistically sufficient number of cases (ca. 200), which distinguishes the mature from the immature AF samplesz5(see also the Discussion). It is shown in a special s t ~ d ythat ~ ~at! this ~ ~ dilution the final electrolyte concentration in the examined solution, in spite of its variations among the different AF samples, is always above the critical value for BFF formation.
Results Table I divides the 182 samples into three groups with respect to the gestational week. The clinical resulta showed 22 immature and 160 mature cases. In each of the 22 cases when the newborn developed RDS we observed absence of BFF at the 3.4X dilution. Absence of BFF was, however, observed in five other samples when the newborn did not develop RDS; i.e., we obtained five false negative test results. In 82% of the BFF-negative cases (27) the newborns developed RDS (22); i.e., the absence of BFF indicates a high risk for development of RDS. In each of the 155 cases where BFF was obtained a t the 3.4X dilution, the newborn did not, develop RDS; Le., the formation of BFF indicates fetal lung maturity in 100% of the cases, fully excluding the risk for development of RDS. The L / S ratio of 126 samples was measured and compared to the test and the clinical results (Table 11). There were 82 samples with L/S ratio above 2.0 of which 76 gave BFF and six did not. In five of the latter six cases (L/S was between 2.0 and 2.4) the newborns developed RDS, and one of the BFF-negative results was false; Le., the newborn did not develop RDS (the sample was 34th gestation week with L/S = 2.3). In all of the 76 cases of L/S ratio above 2.0 where the presence of BFF was observed, the newborns did not develop RDS. From the 18 cases with transitional L/S ratios the BFF method gave seven negative and 11positive test results. Accordingly, six of
io
rt 2o
cw,[ rs/m~l
Figure 5. Dependence of the probability (W) for observation of BFF on the concentration of DPL in 3.4fold diluted A F samples in the presence of 47.5 vol % ethanol; electrolyte concentration =7X M; T = 25 O C . Ct is the concentration a t which W = 1; Le., the observation of BFF is 100%.
the seven BFF-negative cases developed RDS; the remaining one as well as the 11 BFF-positive cases did not. Therefore, in the transitional L/S ratios one false negative and no false positive results were obtained. The 26 samples (15 of them are from abortions and were cons; '-red immature without examination for the diagnosis oL .DS) with L/S ratios below 1.5 were, with regard to fetal lung maturity, negative in 25 cases and positive in one; each of these is correctly predicted by the BFF method. Only in one case from this L/S zone did we obtain a BFF, and, correspondingly, the newborn did not develop RDS (the sample was 28 gestation week with L / S = 1.5). There is a statistically significant difference between the L/S ratios of the group of the 38 BFF-negative cases and the group of the 88 BFF-positive cases (see the text below Table 11). Figure 5 shows the dependence of the probability for BFF observation (W) on the concentration of DPL (CDpL) in the 3.4X diluted AF solution (as determined by thinlayer chromatography). It is clear that the BFF is always observed for CDpL > 13 Mg/mL, while for CDpL < 11pg/mL, W = 0; i.e., the films always rupture.
Discussion The BFF method obviously shows a high reliability of the prediction for both the mature and the immature samples. With the 182 samples studied the BFF method gave five false negative test results and no false positive results (Table I). The test results are in good agreement with the L / S ratio method (Table 11). The new physicochemical method is performed on AF in order to evaluate the functionality and the amount of surfactant in the AF. The design of the method makes it extremely sensitive to the amount of phospholipids, especially of lecithin in the AF. A model experiment with individual DPL showed that under the conditions of the method the concentration of DPL a t which a BFF is obtained (Figure 4c-positive test resu?) lies within the interval of the DPL concentrations of mature AF samples and of the absolute values of the DPL concentrations as determined from the L/S ratios-these results willbe reported in detail in a separate paper. The concentration of DPL necessary for BFF formation is higher than the concentration a t which the DPL foam film ruptures (Figure 4a-negative test result) by no more than 2 pg/ mL-this fact explains the high sensitivity of the method (Figure 5). At the same time the two states of the film (Figure 4, a vs. c) sharply differ in appearance as well as from a physical point of view.23 The dependence of the equilibrium thickness ( h ) of the films from AF on the electrolyte concentration and the dependence of h on the pressure applied allowed us to conclude in our previous works that the BFFs from AF are foam films of the New-
668
Langmuir 1986, 2, 668-671
ton type.25926 The concentration of phospholipids in the AF is obviously a critical parameter as to the formation of stable BFF. The fact that from a certain phospholipid concentration upward the possibility for BFF formation correlates 100% with fetal lung maturity (clinical result in Table I) suggests the idea that the Newton black film is suitable for use as a model in investigations on the alveolar surface and the alveolar stability. The correlation between the test and the clinical results for the 182 samples reported in this paper is based on only one (3.4-fold) statistically obtained and tentatively chosen dilution of the AF samples. In a separate paper we will report the reliability of the method in predicting the clinical result a t a wide range of dilutions of the AF samples (from 2- to 8-fold) and the correlation between the cutoff dilutions and the gestational age. Our preliminary results imply that a dilution other than (but near to) 3.4 may be expected which will "recognize" mature and immature samples in a better way and will, therefore, improve the reliability of the method. The advantages of the method presented here are as follows: high reliability of the prediction for both the mature and the immature samples; rapidity of determination (the test result is obtained within 30 min); ease of
determination (only a reflected light microscope is necessary); simplicity of determination (the test result is straightforward and no special qualification of the clinician is necessary); use of available reagents (NaC1and ethanol); use of small volumes of AF (0.5 mL is quite enough to obtain the test result); availability and low cost of the test. By now the BFF method has been introduced in the largest hospital in Sofia (The Research Institute of Obstetrics and Gynecology a t the Medical Academy-Sofia) and in some other larger hospitals in Bulgaria where it shows good results. It can be easily applied in small hospitals, as well. In perspective the method can be developed to indicate not only the maturity or the immaturity of the fetal lung but also to evaluate the "degree" of maturity or immaturity. The value of the maximal dilution at which single AF samples are still able to give BFF could possibly be used as a criterion. Another appropriate dilution could be found to predict fetal lung maturity in cases of pathological pregnancies (diabetes, RH isoimmunization, etc.). Sample contamination by blood and meconium might influence the test results too. Investigations aiming to elucidate these points are in progress. Registry No. DPL, 2644-64-6.
Bilayer and Multilayer Foam Films: Model for Study of the Alveolar Surface and Stability3 Dotchi Exerowa*t and Zdravko Lalchevt Institute of Physical Chemistry, Bulgarian Academy of Sciences, Sofia 1040, Bulgaria, and Department of Biochemistry, Faculty of Biology, University of Sofia, Sofia 1421, Bulgaria Received March 7, 1986. I n Final Form: June 24, 1986 A new hypothesis for the structure of the alveolar surface is proposed on the basis of model studies with Newtonian black foam films (foam bilayers) and stratificated foam films (multilayers) of amniotic fluid and of the lipid fraction of alveolar surfactant. According to this concept the continuous lipid monolayer of the alveolar surface at the airfwater interface may at some locations be in contact with underlying multilayer lamellar formations or with the membranes of the underlying epithelial cells. Furthermore, there is no free-water layer at the locations of contact or between the lamellae. An essential consequence of this structure is that the alveolar stability in respiratory activity should be considered not only in terms of nearest-neighbor lateral interactions of lipid molecules lying in a monolayer on an unordered liquid phase but also in terms of normal interactions of the monolayer with the molecules of the underlying ordered phase as is the case with foam bilayers.
Introduction The alveolar surface in contact with the air is composed of a thin liquid layer, formed by the molecules of the lung surfactant (mostly lipids and proteins). These substances, generally called alveolar surfactant (AS), play an important role in stabilizing the alveoli during the process of breathing. It is well-known that the lipid AS molecules exist as monomers and micellar structures in the space between the epithelial cell membranes and the alveolar air (i.e., in the so-called hypophase) and also as a continuous monolayer at the &/liquid interface. This is an interesting Bulgarian Academy of Sciences. University of Sofia. 8 Presented at the symposium on "Fluid-Fluid Interfaces: Foams",190th National Meeting of the American Chemical Society, Chicago, IL, Sept 8-13, 1985. +
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case of "membrane" out of the cell. AS can be studied by using (i) pulmonary washing of different animals and (ii) human amniotic fluid (AF) where AS molecules accumulate during pregnancy,'V2 so that AF "reflects" in some way the AS composition. Model experiments with AS or AF lipid and lipid-protein monolayers a t the water surface have proved effective for obtaining important information about lung mechanic^.^-^ For instance the so-called "stability index" reflecta the ability of the lung phospholipids to form a monomolecular layer with a definite sur(1)Clementa,J.; Platzker, A.; Tiemey, D.; et al. N. Engl. J.Med. 1972, 286, 1077. (2) Gluck, L.; Kulovich, M. Am. J . Obstet. Gynecol. 1971, 109, 440. (3) Colacicco, G. Biochim. Biophys. Acta 1971, 266, 313. (4) Horn, L.; Gershfeld, N. Biophys. J. 1977, 18,301. (5) Maller-Tyl, E.; Lempert, J.; Salzer, H.; et al. Geburtshilfe Frauenheilkd. 1977, 37, 718.
Q 1986 American
Chemical Society
