Captive Bubble Surfactometer Research Articles

The Role of Surfactant Proteins in DPPC Enrichment of Surface Films

A pressure-driven captive bubble surfactometer was used to determine the role of surfactant proteins in refinement of the surface film. The advantage of this apparatus is that surface films can be spread at the interface of an air bubble with a different lipid/protein composition than the subphase vesicles. Using different combinations of subphase vesicles and spread surface films a clear correlation between dipalmitoylphosphatidylcholine (DPPC) content and minimum surface tension was observed. Spread phospholipid films containing 50% DPPC over a subphase containing 50% DPPC vesicles did not form stable surface films with a low minimum surface tension. Addition of surfactant protein B (SP-B) to the surface film led to a progressive decrease in minimum surface tension toward 1 mN/m upon cycling, indicating an enrichment in DPPC. Surfactant protein C (SP-C) had no such detectable refining effect on the film. Surfactant protein A (SP-A) had a positive effect on refinement when it was present in the subphase. However, this effect was only observed when SP-A was combined with SP-B and incubated with subphase vesicles before addition to the air bubble containing sample chamber. Comparison of spread films with adsorbed films indicated that refinement induced by SP-B occurs by selective removal of non-DPPC lipids upon cycling. SP-A, combined with SP-B, induces a selective adsorption of DPPC from subphase vesicles into the surface film. This is achieved by formation of large lipid structures which might resemble tubular myelin.

Effect of budesonide and salbutamol on surfactant properties

The objective of this study was to evaluate the in vitro effect of budesonide and salbutamol on the surfactant biophysical properties. The surface-tension properties of two bovine lipid extracts [bovine lipid extract surfactant (BLES) and Survanta] and a rat lung lavage natural surfactant were evaluated in vitro by the captive bubble surfactometer. Measurements were obtained before and after the addition of a low and high concentration of budesonide and salbutamol. Whereas salbutamol had no significant effect, budesonide markedly reduced the surface-tension-lowering properties of all surfactant preparations. Surfactant adsorption (decrease in surface tension vs. time) was significantly reduced (P < 0.01) at a high budesonide concentration with BLES, both concentrations with Survanta, and a low concentration with natural surfactant. At both concentrations, budesonide reduced (P < 0.01) Survanta film stability (minimal surface vs. time at minimum bubble volume), whereas no changes were seen with BLES. The minimal surface tension obtained for all surfactant preparations was significantly higher (P < 0.01), and the percentage of film area compression required to reach minimum surface tension was significantly lower after the addition of budesonide. In conclusion, budesonide, at concentrations used therapeutically, adversely affects the surface-tension-lowering properties of surfactant. We speculate that it may have the same adverse effect on the human surfactant.

Dimeric N-Terminal Segment of Human Surfactant Protein B (dSP-B 1–25) Has Enhanced Surface Properties Compared to Monomeric SP-B 1–25

Surfactant protein B (SP-B) is a 17-kDa dimeric protein produced by alveolar type II cells. Its main function is to lower the surface tension by inserting lipids into the air/liquid interface of the lung. SP-B's function can be mimicked by a 25-amino acid peptide, SP-B 1–25, which is based on the N-terminal sequence of SP-B. We synthesized a dimeric version of this peptide, dSP-B 1–25, and the two peptides were tested for their surface activity. Both SP-B 1–25 and dSP-B 1–25 showed good lipid mixing and adsorption activities. The dimeric peptide showed activity comparable to that of native SP-B in the pressure-driven captive bubble surfactometer. Spread surface films led to stable near-zero minimum surface tensions during cycling while protein free, and films containing SP-B 1–25 lost material from the interface during compression. We propose that dimerization of the peptide is required to create a lipid reservoir attached to the monolayer from which new material can enter the surface film upon expansion of the air/liquid interface. The dimeric state of SP-B can fulfill the same function in vivo.

Alterations in pulmonary surfactant after rapid arousal from torpor in the marsupial Sminthopsis crassicaudata.

Torpor in the dunnart, Sminthopsis crassicaudata, alters surfactant lipid composition and surface activity. Here we investigated changes in surfactant composition and surface activity over 1 h after rapid arousal from torpor (15-30 degrees C at 1 degrees C/min). We measured total phospholipid (PL), disaturated PL (DSP), and cholesterol (Chol) content of surfactant lavage and surface activity (measured at both 15 and 37 degrees C in the captive bubble surfactometer). Immediately after arousal, Chol decreased (from 4.1 +/- 0.05 to 2.8 +/- 0.3 mg/g dry lung) and reached warm-active levels by 60 min after arousal. The Chol/DSP and Chol/PL ratios both decreased to warm-active levels 5 min after arousal because PL, DSP, and the DSP/PL ratio remained elevated over the 60 min after arousal. Minimal surface tension and film compressibility at 17 mN/m at 37 degrees C both decreased 5 min after arousal, correlating with rapid changes in surfactant Chol. Therefore, changes in lipids matched changes in surface activity during the postarousal period.

SULFURIC ACID AEROSOL INDUCES CHANGES IN ALVEOLAR SURFACE TENSION IN THE GUINEA PIG BUT NOT IN THE RAT

The purpose of this study was to investigate the effects of an acid aerosol, at high concentration, on the surface properties of the extracellular fluid lining the airways and alveolae. Guinea pigs and rats were exposed to 43 mg/m3 and 94 mg/m3 of sulfuric acid aerosol mass median aerodynamic diameter (MMAD) 0.9 mu m or water aerosol (control), respectively, for 4 hours in an exposure chamber. Surfactant material was extracted from bronchoalveolar lavage fluid (BAL) by centrifugation, and phospholipid, protein, and cell concentrations measured. The extract was reconstituted to 300 mu g/mL of phospholipid, and its surface properties assessed with a captive bubble surfactometer. The minimum surface tension for the acid-exposed guinea pig BAL was 12.1 +/- 8.48 (mean SD) mN/m, which was significantly higher than the control group, 2.0 +/- 0.43 (mean SD) mN/m, or the acid-exposed rats, 1.29 +/- 0.11 (mean SD). The change in film area obtained by compressing the film from equilibrium surface tension (25 mN/m) to its minimum value (gamma n) was 62.9 +/- 13.83 mi (meanSD)% for acid-exposed guinea pigs, compared to 16. 35.77 (meanSD)% for the control guinea pigs. The most sensitive index of surfactant inhibiion was found to be the maximum film compressibility (C) of the compression isotherm. This index was 119 times greater for the acid max exposed guinea pigs compared to control animals. These abnormalities were associated with an elevation of total protein (0.95 +/- 0.33 [mean SD] mg/mL compared to 0.13 +/- 0.03 [meanSD] mg/mL in controls) and polymorphonuclear leucocytes in the BAL. There was no change in total phospholipids. By contrast BAL retrieved from rats exposed to approximately twice the concentration of acid aerosol showed no cellular nor biochemical abnormalities and its surface tension properties were normal. We conclude that the abnormalities of surfactant activity in the acid- exposed guinea pigs result from the cellular and humoral responses of acute lung injury rather than a direct effect of acid.

Production of surfactant protein C in the baculovirus expression system: the information required for correct folding and palmitoylation of SP-C is contained within the mature sequence

Surfactant protein C (SP-C) is synthesized in the alveolar type II cells of the lung as a 21 kDa propeptide which is proteolytically processed to a 4.2 kDa mature active form. The main function of this extremely hydrophobic protein is to enhance lipid insertion into the air/liquid interface in the lung upon inhalation. This is necessary to maintain a relatively low surface tension at this interface during breathing. In this report we describe the production of mature human SP-C in the baculovirus expression system. The recombinant protein contains a secondary structure with a high α-helical content (73%), comparable to native SP-C, as determined by circular dichroism and attenuated total reflection Fourier transform infrared analysis. The expressed protein is a mixture of dipalmitoylated (15%) and non-palmitoylated SP-C. This suggests that the information required for palmitoylation is contained within the sequence of the mature protein. The activity of the protein to insert phospholipids into a preformed monolayer of lipids at an air/liquid interface was determined with a captive bubble surfactometer. Recombinant SP-C significantly reduced the surface tension at the air/liquid interface during dynamic expansion and compression. We conclude that correctly folded, dipalmitoylated and active SP-C can be expressed in the baculovirus expression system. Our results may facilitate investigations into the relation between structure and function of SP-C and into protein palmitoylation in general.

Hydrophobic lung surfactant proteins B and C remain associated with surface film during dynamic cyclic area changes

The biophysical activity of lung surfactant depends, to a large extent, on the presence of the hydrophobic surfactant proteins B (SP-B) and C (SP-C). The role of these proteins in lipid adsorption and lipid squeeze-out under dynamic conditions simulating breathing is not yet clear. Therefore, the aim of this study was to investigate the interaction of spread hydrophobic surfactant proteins with phospholipids in a captive-bubble surfactometer during rapid cyclic area changes (6 cycles/min). We found that SP-B and SP-C facilitated the rapid transport of lipids into the air–water interface in a concentration-dependent manner (threshold concentration ≥0.05:0.5 mol% SP-B/SP-C). Successive rapid cyclic area changes did not affect the concentration-dependent lipid adsorption process, suggesting that SP-B and SP-C remained associated with the surface film.

A Spreading Technique for Forming Film in a Captive Bubble

Mechanisms underlying the surface properties of lung surfactant are extensively studied in in vitro systems such as the captive-bubble surfactometer (CBS), the pulsating-bubble surfactometer, and the Wilhelmy balance. Among these systems, the CBS is advantageous when a leakproof system and high cycling rates are required. However, widespread application of the CBS to mechanistic studies of dynamic surfactant protein-phospholipid interactions of spread film and to comparative studies between spread and adsorbed film is hampered because spreading of film is difficult. In addition, when film is formed by adsorption, the amount of material required is fairly large. We have developed an easy spreading technique that allows routine formation of film by spreading of small amounts of surfactant components at the air-water interface of an air bubble in a CBS. The technique is reliable, precise, and accurate, and the biophysical activity of film formed by spreading is similar to that of film formed by adsorption. This method will be useful for mechanistic studies of surfactant components under dynamic conditions and for comparative studies of spread films and adsorbed films.

Alterations in the surface properties of lung surfactant in the torpid marsupial Sminthopsis crassicaudata.

Torpor changes the composition of pulmonary surfactant (PS) in the dunnart Sminthopsis crassicaudata [C. Langman, S. Orgeig, and C. B. Daniels. Am. J. Physiol. 271 (Regulatory Integrative Comp. Physiol, 40): R437-R445, 1996]. Here we investigated the surface activity of PS in vitro. Five micrograms of phospholipid per centimeter squared surface area of whole lavage (from mice or from warm-active, 4-, or 8-h torpid dunnarts) were applied dropwise onto the sub-phase of a Wilhelmy-Langmuir balance at 20 degrees C and stabilized for 20 min. After 4 h of torpor, the adsorption rate increased, and equilibrium surface tension (STeq), minimal surface tension (STmin), and the %area compression required to achieve STmin decreased, compared with the warm-active group. After 8 h of torpor, STmin decreased [from 5.2 +/- 0.3 to 4.1 +/- 0.3 (SE) mN/m]; %area compression required to achieve STmin decreased (from 43.4 +/- 1.0 to 27.4 +/- 0.8); the rate of adsorption decreased; and STeq increased (from 26.3 +/- 0.5 to 38.6 +/- 1.3 mN/m). ST-area isotherms of warm-active dunnarts and mice at 20 degrees C had a shoulder on compression and a plateau on expansion. These disappeared on the isotherms of torpid dunnarts. Samples of whole lavage (from warm-active and 8-h torpor groups) containing 100 micrograms phospholipid/ml were studied by using a captive-bubble surfactometer at 37 degrees C. After 8 h of torpor, STmin increased (from 6.4 +/- 0.3 to 9.1 +/- 0.3 mN/m) and %area compression decreased in the 2nd (from 88.6 +/- 1.7 to 82.1 +/- 2.0) and 3rd (from 89.1 +/- 0.8 to 84.9 +/- 1.8) compression-expansion cycles, compared with warm-active dunnarts. ST-area isotherms of warm-active dunnarts at 37 degrees C did not have a shoulder on compression. This shoulder appeared on the isotherms of torpid dunnarts. In conclusion, there is a strong correlation between in vitro changes in surface activity and in vivo changes in lipid composition of PS during torpor, although static lung compliance remained unchanged (see Langman et al. cited above). Surfactant from torpid animals is more active at 20 degrees C and less active at 37 degrees C than that of warm-active animals, which may represent a respiratory adaptation to low body temperatures of torpid dunnarts.

Plasmalogens effectively reduce the surface tension of surfactant-like phospholipid mixtures.

The alkenyl-acyl subclass of phosphatidylethanolamine (PtdEtn) and phosphatidylcholine (plasmalogens) are minor components of alveolar surfactant. Plasmalogens promote and stabilize hexagonal structures of phospholipids. In another study (W.R. Perkins, R.B. Dause, R.A. Parente, S.R. Michey, K.C. Neuman, S.M. Gruner, T.F. Taraschi, and A.S. Janoff. Science 273: 330-332, 1996), it was shown that polymorphic phase behavior may have an important role in the effective functioning of pulmonary surfactant. Therefore, we hypothesized that surface properties of phospholipid mixtures that contain plasmalogens are superior to plasmalogen-free mixtures. The effect of plasmalogens on surface tension of surfactant-like phospholipid mixtures (70 mol% dipalmitoyl phosphatidylcholine, 10 mol% phosphatidylglycerol, and 20 mol% PtdEtn) was measured. Using the pulsating bubble surfactometer, we show that an increasing amount of ethanolamine plasmalogens [plasmenylethanolamine (PlsEtn) results in reduction of surface tension (0 mol% PlsEtn 44.7 +/- 1.7, 2 mol% 33.5 +/- 1.7, 4 mol% 36 +/- 3.1, 6 mol% 26.2 +/- 2.9, and 8 mol% 22.2 +/- 0.3 mN/m). By means of the captive bubble surfactometer, minimal surface tension reached with 8 mol% PlsEtn was even lower (3.8 +/- 0.7 mN/m). With regard to morphological studies (B. Fringes, K. Gorgas, and A. Reith. Eur. J. Cell Biol. 46: 136-143, 1988), clofibrate treatment of rats might increase the plasmalogen content of alveolar surfactant. However, in the present study, we could not show that synthesis and secretion of plasmalogens are affected by clofibrate treatment.

In vivo determination of surface tension in the horse trachea and in vitro model studies

We measured the surface tension in the trachea of the non-anaesthetised horse from the spreading behaviour of fluid drops, using videotracheoscopy. To do this, we placed small oil drops onto the tracheal wall with a thin Teflon tubing inserted into a videocolonoscope used in humans. Either 5 ml of saline (control) or 5 ml of bovine lipid extract surfactant (BLES) at 4 mg/ml were administered. Tracheal surface tension was 31.9±0.54 mN/m (Mean±SEM, n=30) in the control experiments and 24.5±0.51 mN/m (Mean±SEM, n=21) in the entire trachea after the administration of BLES. These values were determined from calibration curves relating film surface tension to the relative diameter of test fluid droplets. In the calibration experiments, the test fluid droplets were placed onto a surfactant film at various surface tensions in either a modified Langmuir–Wilhelmy balance or a captive bubble surfactometer. The spreading behaviour of a given test fluid droplet in the model studies did not only depend on the film surface tension but also on the thickness of the aqueous layer below the surfactant film. Hence, the computed surface tensions in the trachea depend on the choice of which in vitro model is applied.

Measurement of the interfacial properties of lung surfactant

The classical methods used to investigate the surface activity of lung surfactant are the Langmuir-Wilhelmy surface balance and the pulsating bubble surfactometer. Over the past few years, it has become increasingly apparent that these methods are inadequate in many respects. These shortcomings, however, have been overcome by recent developments in lung surfactant methodologies: the captive bubble surfactometer and axisymmetric drop shape analysis.

Role of the palmitoylation of surfactant-associated protein C in surfactant film formation and stability.

The effect of palmitoylation of pulmonary surfactant-associated protein C (SP-C) on the surface activity of phospholipid mixtures of dipalmitoylphosphatidylcholine and phosphatidylglycerol was studied. Phospholipids reconstituted with palmitoylated or depalmitoylated bovine SP-C were examined at neutral and acidic pH using a captive bubble surfactometer. At low pH, effective lipid adsorption and near zero surface tensions upon compression were obtained even with protein-free samples. At physiological pH, only SP-C-containing samples achieved such properties. Lipid adsorption was decreased by prior SP-C depalmitoylation. Bubbles with palmitoylated SP-C were more mechanically stable and required less compression to reach low surface tensions. Subphase depletion experiments showed that dynamically cycled surface layers containing palmitoylated SP-C maintained their surface activity after subphase lipid depletion. In contrast, surface activity was rapidly lost where depalmitoylated SP-C or SP-B was included. Our results indicate that although SP-C palmitoylation has little effect on its ability to enhance lipid adsorption and surface tension reduction, it greatly enhances lipid respreading and film stability and is therefore important for surfactant function.

Assessment of pulmonary surfactant function using a captive-bubble surfactometer

A captive-bubble surfactometer was built to measure the surface properties of reconstituted pulmonary surfactants ( l-α-dipalmitoyl phosphatidylcholine (DPPC), Exosurf, Alveofact) and whole lung surfactants obtained from normal and injured rat lungs (silica induced Lipoproteinosis). Whole surfactants from normal or injured rats were further characterized by protein and phospholipid measurements. We used soluble test substances (ethanol, water) to ascertain the precision, reliability, and cleanliness of the captive-bubble surfactometer. We performed three types of experiments by controlling the system pressure on the air bubble: adsorption, dynamic, and quasi-static cycling. Lateral views of the bubble were continuously recorded. The bubble height and diameter were determined by image analysis and were used for the calculation of bubble tension and related parameters. Adsorption was slow with DPPC, faster with Exosurf and Alveofact, and fastest with whole lung surfactants. During the dynamic cycling experiments, DPPC immediately exhibited low bubble tension. The bubble tension for Exosurf, Alveofact, and whole lung surfactants showed both decreasing values at minimum area and increasing values at maximum area during dynamic cycling. In initial cycles of the quasi-static cycling experiments, isotherm hystereses were different for the various surfactants, and the bubble tension and compressibility were least with pure DPPC as compared to Exosurf and Alveofact. In contrast to all other surfactants, DPPC showed minimal refinement of film characteristics after repeated cycling. Whole lung surfactants exhibited surface properties comparable to those of reconstituted surfactants, albeit at only half the phospholipid concentration. Whole lung surfactant from injured rat lungs was characterized by increased lipid and protein content, whereas changes in the phospholipid composition and surface activity were only subtle compared to surfactant obtained from normal rat lungs. The characterization of the surface properties of biological substances using the captive-bubble surfactometer is feasible and discriminates between different reconstituted and whole surfactants. This method is useful for studying biological materials because it enables measurements of surface properties under dynamic non-equilibrium conditions without film leakage, which is in contrast to other methods.

Inhaled nitric oxide injures the pulmonary surfactant system of lambs in vivo.

Nitric oxide (.NO) is a free radical, and as such may damage the pulmonary surfactant system. To determine the potential toxicity of .NO in vivo, we exposed 35 newborn lambs to 0, 20, 80 or 200 ppm .NO in either 21 or 60% O2 for 6 h. At the end of the exposure, lambs had normal values of arterial Po2, Pco2, and pH; total protein concentration in the bronchoalveolar lavage was also at normal levels. There were no differences in the surface properties of surfactant among the air or 60% O2 groups. Pulmonary surfactant samples, isolated from the bronchoalveolar lavage of lambs breathing air or 20 ppm .NO and reconstituted at a lipid concentration of 3 mg/ml, reached a low minimum surface tension (Tmin < 3 mN/m) in a pulsating bubble surfactometer. On the other hand, abnormal surface properties were observed in 36 and 60% of surfactant samples isolated from lungs of lambs that breathed 80 or 200 ppm .NO, respectively. These findings were confirmed using a captive bubble surfactometer. Surfactant protein A, isolated from the lungs of lambs that breathed 200 ppm .NO, exhibited decreased ability to aggregate lipids in vitro. These data are consistent with injury to the surfactant apoproteins during inhalation of either 80 or 200 ppm .NO for 6 h.

Mechanisms of bilirubin toxicity.

Possible mechanisms of bilirubin toxicity on the brain and lung were studied in animal experiments and in vitro. The uptake of tyrosine as precursor of dopamine in rat synaptosomes was evaluated to study the role of different bilirubin concentrations on synaptic neurotransmission. The results of this study show a statistically significant correlation between bilirubin levels and tyrosine uptake, supporting the hypothesis that the effect of bilirubin on neuronal excitability is dose-dependent. Concerning bilirubin toxicity on the lung, we studied the effect of different bilirubin concentrations on surface activity of modified natural surfactant (Curosurf) and synthetic surfactant (Exosurf), both in current clinical use for treatment of neonatal respiratory distress syndrome. Surface activity of Curosurf and Exosurf was investigated with the captive bubble surfactometer. The results of this study show that bilirubin impairs, in vitro, the surface tension activity of natural surfactant in a dose dependent manner and has no effect on surface tension activity of artificial surfactant. These data suggest that bilirubin interferes with surfactant proteins SP-B and/or SP-C, thus impairing surfactant activity at the air-liquid interface. We conclude that bilirubin shows its toxic effect reacting with different biological systems in a dose-dependent fashion.

The Surface-Associated Surfactant Reservoir in the Alveolar Lining

A small atmospheric bubble was introduced into a surfactant suspension in a captive bubble surfactometer. After film formation to the equilibrium surface tension at the bubble air-liquid interface, the bulk phase surfactant was depleted by replacing the chamber contents several times with a saline-CaCl2 solution. The remaining film adsorbed at the bubble surface was then compressed stepwise in quasi-static fashion to near zero minimum surface tension. This was followed by a series of quasi-static expansion steps to surface tensions slightly above equilibrium. The surface tension of films from lipid extract surfactants and phospholipid mixtures did not increase in a manner consistent with the presence of a single surface monolayer. After the initial, rapid rise in surface tension at each expansion step, a decrease in surface tension to a new value was observed. This decrease in surface tension is likely due to the adsorption of 'surplus' material from a 'surface-associated reservoir' into the surface active film. The presence of surplus non-monolayer surfactant material in situ at the alveolar surface was also demonstrated by electron microscopy. SP-A acted as a potent promoter for the movement of excess material (equivalent to 2-3 monolayers) at the interface into the surface active film. In contrast, inhibitory serum proteins prevented the formation of a surface-associated reservoir or the adsorption of excess material into a surface active film.

Surface activity of rabbit pulmonary surfactant subfractions at different concentrations in a captive bubble.

This study investigates the surface activity of rabbit pulmonary surfactant subfractions at different concentrations in a new pressure-driven captive bubble surfactometer, which provides more rigorous testing conditions than heretofore applied to this material. Subfractions were separated by centrifugation of lavage return into a third (P3; 1,000 x average g, 20 min), a fourth (P4; 60,000 x average g, 60 min), and a fifth (P5; 100,000 x average g, 16 h) pellet. At 2.0 mg phospholipid/ml, P3 and P4 demonstrated more rapid adsorption, lower minimum surface tensions on first and subsequent compressions, and lower monolayer compressibilities than did P5. This surface activity of P3 and P4 increased with concentration between 0.1 and 2.0 mg phospholipid/ml. Adsorption rate constants were approximately 10,000 times faster than desorption constants. We conclude that, in a normal lung, components of P3 and P4 determine alveolar surface tension. We speculate that under special circumstances even the less surface active P5 could have an important influence at the air-water interface.

Comparison of captive and pulsating bubble surfactometers with use of lung surfactants

We compared surface tension measures of surfactants with various surface activities by using a pulsating bubble surfactometer (PBS) and a captive bubble surfactometer (CBS). Rabbit lung lavage surfactant (60,000 x average g for 60 min), bovine surfactant extract (Survanta), and a synthetic lipid surfactant mixture (dipalmitoylphosphatidylcholine-egg phosphatidylglycerol-palmitic acid) were studied at 1.25 mg phospholipid/ml. The PBS was used either unmodified according to manufacturer's instructions or with the sample chamber capillary kept dry and the sample adsorbing at maximum bubble size (5 min). The CBS was used in a manner that imitated the unmodified PBS. We found that all three techniques indicated low surface tension on the first cycle for 60K. For Survanta, the CBS and the modified PBS reported low surface tension on the first cycle, whereas the unmodified PBS did not achieve this within 10 cycles. For the synthetic lipid surfactant mixture, only the CBS measured low surface tension within 10 cycles. Video observations indicate that the modified PBS performs better than the unmodified PBS because keeping the capillary dry prevents surface film from occupying this large surface during cycling, thereby allowing larger area compressions.

Evaluation of pressure-driven captive bubble surfactometer

We modified the captive bubble surfactometer [S. Schürch et al. J. Appl. Physiol. 67: 2389-2396, 1989] to facilitate the measurement of surface adsorption rates and to simplify its construction. We used a range of standards and monolayers of dipalmitoylphosphatidylcholine to check the calibration of the device against measurements made in a Wilhelmy surface balance and in the captive bubble by using a cathetometer, and we found good agreement. As a further test we measured the surface properties of rabbit lavage lung surfactant (60,000 x average g for 60 min) at 1.0 mg phospholipid/ml. This material adsorbed within 1 s to near-equilibrium surface tension, reached surface tensions of < 5 mN/m on the second compression, and formed very stable films. We conclude that a captive bubble surfactometer can provide accurate information about important surface properties of lung surfactant films.