Clearance of different-sized proteins from the alveolar space in humans and rabbits.

Investigation of the clearance of proteins from the air spaces is important for an understanding of the resolution of pulmonary edema and also because of current interest in delivery of therapeutic peptides via the distal air spaces. Few experimental studies have examined the size dependence for alveolar clearance of large macromolecules; there have been no human studies. In anesthetized rabbits, we measured clearance of cyanocobalamin and different-sized human proteins instilled into the air spaces. After 8 h, the amounts of instilled tracer recovered in the lungs were [57Co]cyanocobalamin, 19.4 +/- 3.0% (Stokes radius 0.65 nm); 125I-labeled insulin, 64.6 +/- 3.9% (1.2 nm); 131I-labeled albumin, 87.0 +/- 4.0% (3.5 nm); and 125I-labeled immunoglobulin G, 91.8 +/- 3.3% (5.5 nm) (P < 0.05). Sieving of different-sized proteins occurred across the alveolar epithelial barrier because tracer concentrations in air space lavage fluid after 8 h were decreased more for the smaller tracers than the larger ones. Size selectivity for alveolar protein clearance in humans with resolving alveolar edema was investigated by measuring the changes in albumin and total protein concentration. The fraction of total protein concentration made up of albumin was greater in the edema fluid than in the plasma initially. The albumin fraction decreased with time in 9 of 10 patients with resolving edema, from 0.62 +/- 0.2 to 0.58 +/- 0.10 (P < 0.05) after 10 +/- 5 h. Thus both rabbit studies and human studies provide evidence for size-dependent clearance of protein from the air spaces of the lung.(ABSTRACT TRUNCATED AT 250 WORDS)     

Adaptation of the inert gas FRC technique for use in heavy exercise

We automated the inert gas rebreathe technique for measurement of end-expiratory lung volume (EELV) during heavy exercise. We also assessed the use of two gas tracers (He and N2) vs. a single gas tracer (He) for measurement of this lung volume and compared the two-tracer EELV to changes in the inspiratory capacity (defined with transpulmonary pressure) and shifts in the end-expiratory pressure from rest through heavy exercise. A computer program switched a pneumatic valve when flow crossed zero at end expiration and defined points in the He and N2 traces for calculation of EELV. An inherent delay of the rebreathing valve (50 ms) caused virtually no error at rest and during light exercise and an error of 74 +/- 9 ml in the EELV at peak inspiratory flow rates of 4 l/s. The measurement of EELV by the two gas tracers was closely correlated to the single-gas tracer measurement (r = 0.97) but was consistently higher (120 +/- 10 ml) than when He was used alone. This difference was accentuated with increased work rates (2-5% error in the EELV, rest to heavy exercise) and as rebreathe time increased (2-7% error in the EELV with rebreathe times of 5-20 s for all work loads combined). The double-gas tracer measurement of EELV agreed quite well with the thoracic gas volume at rest (P greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of three tracers for detecting lung epithelial injury in anesthetized sheep

We compared the ability of three aerosolized tracers to discriminate among control, lung inflation with a positive end expired pressure of 10 cmH2O, lung vascular hypertension and edema without lung injury, and lung edema with lung injury due to intravenous oleic acid. The tracers were 99mTc-diethylenetriaminepentaacetate (99mTc-DTPA, mol wt 492), 99mTc-human serum albumin (99mTc-ALB, mol wt 69,000), and 99mTc-aggregated albumin (99mTc-AGG ALB, mol wt 383,000). 99mTc-DTPA clearance measurements were not able to discriminate lung injury from lung inflation. The 99mTc-AGG ALB clearance rate was unchanged by lung inflation and increased slightly with lung injury. The 99mTc-ALB clearance rate (0.06 +/- 0.02%/min) was unchanged by lung inflation (0.09 +/- 0.02%/min, P greater than 0.05) or 4 h of hypertension without injury (0.09 +/- 0.04%/min, P greater than 0.05). Deposition of 99mTc-ALB within 15 min of the administration of the oleic acid increased the clearance rate to 0.19 +/- 0.06%/min, which correlated well with the postmortem lung water volume (r = 0.92, P less than 0.01). This did not occur when there was a 60-min delay in the deposition of 99mTc-ALB. We conclude that 99mTc-ALB is the best indicator for studying the effects of lung epithelial injury on protein and fluid transport into and out of the air spaces of the lungs in a minimally invasive manner.     

Measurement of lung fluid volumes and albumin exclusion in sheep

A radioactive tracer technique was used to determine interstitial diethylenetriaminepentaacetic acid (DTPA) and albumin distribution volume in sheep lungs. 125I- and/or 131I-labeled albumin were injected intravenously and allowed to equilibrate for 24 h. 99mTc-labeled DTPA and 51Cr-labeled erythrocytes were injected and allowed to equilibrate (2 h and 15 min, respectively) before a lethal dose of thiamylal sodium. Two biopsies (1-3 g) were taken from each lung and the remaining tissue was homogenized for wet-to-dry lung weight and volume calculations. Estimates of distribution volumes from whole lung homogenized samples were statistically smaller than biopsy samples for extravascular water, interstitial 99mTc-DTPA, and interstitial albumin. The mean fraction of the interstitium (Fe), which excludes albumin, was 0.68 +/- 0.04 for whole lung samples compared with 0.62 +/- 0.03 for biopsy samples. Hematocrit may explain the consistent difference. To make the Fe for biopsy samples match that for homogenized samples, a mean hematocrit, which was 82% of large vessel hematocrit, was required. Excluded volume fraction for exogenous sheep albumin was compared with that of exogenous human albumin in two sheep, and no difference was found at 24 h.     

Influence of flow on pulmonary vascular surface area inferred from blue dextran efflux data.

Blue dextran (BD), which binds to proteins on the pulmonary endothelial surface and to plasma albumin, was used in isolated perfused dog lung lobe experiments to address the question: do changes in perfusate flow rate cause changes in perfused vascular surface area? When BD was added to a protein-free perfusate under zone 3 conditions at a high flow rate (15.8 +/- 0.7 ml/s), it was adsorbed by the endothelial surface. Then by changing the perfusate entering the lobe to an albumin-containing perfusate, the BD was eluted from the perfused surface by competitive binding to the perfusate albumin. The amount of BD eluted was measured in three experiments. In experiment 1, elution of the BD by the perfusate albumin was initiated after a balloon had been inflated within the lobar arterial tree to occlude a portion of the lobar vascular bed containing BD. Then the balloon was deflated, permitting albumin perfusate to perfuse the previously occluded part of the lobe. In experiment 2, BD elution began at a flow rate of 3 +/- 0.1 ml/s under zone 3 conditions and continued after the high-flow zone 3 conditions were reestablished. In experiment 3, the BD elution began at a flow rate of 4.2 +/- 0.7 ml/s under zone 2 conditions and continued after the high-flow zone 3 conditions were reestablished. Balloon inflation reduced the amount of BD recovered by 43%, demonstrating that a decrease in perfused vascular surface area could decrease BD recovery.(ABSTRACT TRUNCATED AT 250 WORDS)     

Use of norepinephrine uptake to measure lung capillary recruitment with exercise

We used the multiple indicator-dilution technique with norepinephrine, a vascular endothelium surface marker, to study the pulmonary vascular changes in awake exercising dogs. The vascular space tracers, labeled erythrocytes and albumin, and a water space tracer, 1,8-octanediol, were injected with the norepinephrine, and right atrium-aortic root dilution curves were obtained in nine dogs, at rest and at two increasing levels of exercise. Extravascular lung water multiple tracer dilutional estimates increased with flow and rapidly approached a maximal asymptotic value representing 75% of the postmortem lung weight. The ratio of the extravascular lung water measured in this way to that measured gravimetrically also increased, to reach an asymptotic proportion of close to 100%. The transit time-defined central vascular space increased linearly with flow; the ratio of lung tissue space to lung vascular space, therefore, decreased with increasing flow. The mean tracer upslope norepinephrine extractions at rest and at the two levels of exercise were 17 +/- 1.2, 14 +/- 0.8, and 15 +/- 0.8% (SE). With the use of the Crone approximation, we computed permeability-surface area products for norepinephrine; these increased linearly with flow. If permeability does not change, the increase in the permeability-surface area product with flow can be attributed to capillary recruitment. We conclude that when all lung tissue has become accessible to 1,8-octanediol delivered via the perfused vascular space, there is nevertheless further recruitment, with increase in flow, of vascular surface that can extract norepinephrine.     

Regional lung hematocrit in humans using positron emission tomography

Regional lung hematocrit ratio (R) was measured in five normal subjects and five patients (2 with pneumonia, 2 with nephrotic syndrome with anemia, and 1 with pancreatitis) using positron emission tomography, a red cell marker 11CO, and a plasma marker [methyl-11C]albumin). The measurements were made in a transaxial thoracic section at midheart level with the subject in supine posture and with a spatial resolution of 1.7 cm. The normal regional hematocrit ratio (means +/- SE) calculated for the lung was 0.90 +/- 0.014, 0.94 +/- 0.023 for the thoracic wall, and 1.00 +/- 0.003 for the heart chambers. The regional lung hematocrit ratio in the patients ranged between 0.81 and 0.86. No correlation was found among the regional lung hematocrit ratio and regional blood volume, lung extravascular density, and the peripheral hematocrit (obtained from venous blood samples). To the extent that 70% of the pulmonary blood in the field of view is in larger vessels with normal hematocrit, the hematocrit in the capillary bed is approximately two-thirds that of the peripheral venous value. Blood volume measurements on the basis of single vascular tracers need to take account of these results.     

Measurement of lung water in dog lobes using inhaled C15O2 and injected H215O

Indicator-dilution analysis was used in a recirculation-free isolated dog lobe preparation to compare an inhaled water tracer (C15O2) and an injected water tracer (H215O) with direct weighing as a measure of total lung water. Residue detection (counting over the lung) was compared with outflow detection (counting over the venous effluent). With outflow detection, inhaled C15O2 measured 74% and injected H215O 90% of the gravimetric lung water. In hemodynamic edema, the increase in lung water measured by residue detection of both tracers correlated well with increases in weight (r = 0.92, slope = 1.03). However, outflow detection of both tracers underestimated the lung water increase by 53% in edema (r = 0.88, slope = 0.47). Thus, in edema, equilibration of both tracers within the lung water volume is rapid, but clearance from the lung is delayed because slowly clearing water pools develop. The errors caused by inhomogeneity of perfusion distribution were investigated after pulmonary arterial injection of 34-, 50-, and 175-micrometers spheres. For the same lung weight, C15O2 transit was delayed and H215O transit accelerated greatly by the 175-micrometers spheres and slightly by the 50-micrometers spheres.     

Estimation of lung liquid production in fetal sheep with blue dye dextran and radioiodinated serum albumin.

Lung liquid production and reabsorption rates and lung volumes were measured in 99 fetal sheep (119-148 days of gestation) by indicator-dilution methods with the simultaneous use of blue dye dextran (BDD) and radioiodinated serum albumin (RISA). There were no significant differences between rates of lung liquid production or reabsorption by the two methods (n = 71 pairs; paired t-test; Wilcoxon test; ANOVA); this was equally true for rates in milliliters per hour or milliliters per kilogram body weight per hour and was independent of age. Volumes measured by both methods showed a close linear relationship (r = 0.97; for slope P < 0.0001; n = 99), whether expressed as milliliters or milliliters per kilogram body weight. Either method could give the higher volume. Values differed by only approximately 4%, independent of age or parameter (ml or ml/kg body wt; volumes regressed to original volume, or as measured in untreated control hours). However, this small difference was significant by paired t-test or Wilcoxon test when all data were combined irrespective of age; it was not significant after allowance for gestational age (two-way ANOVA). Both indicators showed the same increase in lung volume toward birth and the same fall when related to body weight (slopes significant P = 0.0003-0.0004; r = 0.93). Two-way ANOVA showed that the declines were significant (P = 0.003). The data suggest that 1) there was no significant difference in production or reabsorption rates measured by BDD or RISA, 2) differences in volumes measured by the two indicators were only significant if gestational age was ignored and were too small to have physiological importance, and 3) although BDD and RISA each may have methodological weaknesses, for purposes of measuring lung liquid volumes both are sufficiently accurate and reproducible to obtain meaningful physiological results.     

Changes in versican and chondroitin sulfate proteoglycans during structural development of the lung

We have examined whether changes in versican levels, or in the sulfation pattern of its chondroitin sulfate (CS) side chains, are associated with the reduction in perialveolar tissue volumes that characterize lung maturation in late-gestation fetal sheep. Lung tissue was collected from fetuses [90-142 days gestational age (GA)] and lambs (2 wk after term birth). The level and distribution of versican and CS glycosaminoglycans (GAG) were determined using immunohistochemistry, whereas fluorophore-assisted carbohydrate electrophoresis was used to determine changes in CS sulfation patterns. Versican was the predominant CS-containing proteoglycan in the lung and decreased from 19.9 +/- 2.7 arbitrary units at 90 days GA to 6.0 +/- 0.5 arbitrary units at 142 days GA, in close association (P < 0.05) with the reduction in tissue volumes (from 66.0 +/- 4.6 to 25.3 +/- 1.5% at 142 days); similar reductions occurred for both chondroitin-6-sulfate and chondroitin-4-sulfate CS side chains. Hyaluronic acid levels decreased from 3,168 +/- 641 pmol/microg GAG at 90 days GA to 126 +/- 9 pmol/microg GAG at 142 days GA, and the predominant sulfated disaccharide changed from Delta-di-6S at 90 days GA to Delta-di-4S at term. These data indicate that structural development of the lung is closely associated with marked changes in versican levels and the microstructure of CS side chains in perisaccular/alveolar lung tissue.     

Pulmonary transvascular flux of transferrin

We compared the pulmonary transvascular fluxes of transferrin and albumin in the intact sheep lung. Anesthetized sheep were prepared with lung lymph fistulas. The vascular blood pool was marked with 99mTc-erythrocytes, autologous transferrin was labeled with 113mIn, and albumin was labeled with 125I. Samples of blood, plasma, lymph, and lung were obtained up to 180 min after tracer infusion. Lymph tissue radioactivities were corrected for the intravascular component and expressed as extravascular-to-plasma concentration ratios. Clearance of transferrin and albumin from the plasma space followed a two-compartment model. The clearance rate constant was 2.1 +/- 0.1 x 10(-3) min for albumin and 2.4 +/- 0.1 x 10(-3) min for transferrin (P less than 0.05). Lymph-to-plasma ratios for albumin and transferrin were not different. However, the extravascular-to-plasma ratio for albumin was greater than transferrin (P less than 0.05). The lymph and lung data were deconvoluted for the plasma input function and fit to a two-compartment model. The results indicate that albumin and transferrin have similar permeabilities across the vascular barrier but have different pulmonary circulation to lymph kinetics because the extravascular volume of distribution of albumin is greater than transferrin.     

Impact of microvascular circulation on peripheral lung stability

The involvement of pulmonary circulation in the mechanical properties was studied in isolated rat lungs. Pulmonary input impedance (ZL) was measured at a mean transpulmonary pressure (Ptpmean) of 2 cmH2O before and after physiological perfusion with either blood or albumin. In these lungs and in a group of unperfused lungs, ZL was also measured at Ptpmean values between 1 and 8 cmH2O. Airway resistance (Raw) and parenchymal damping (G) and elastance (H) were estimated from ZL. End-expiratory lung volume (EELV) was measured by immersion before and after blood perfusion. The orientation of the elastin fibers relative to the basal membrane was assessed in additional unperfused and blood-perfused lungs. Pressurization of the pulmonary capillaries significantly decreased H by 31.5 +/- 3.7% and 18.7 +/- 2.7% for blood and albumin, respectively. Perfusion had no effect on Raw but markedly altered the Ptpmean dependences of G and H < 4 cmH2O, with significantly lower values than in the unperfused lungs. At a Ptpmean of 2 cmH2O, EELV increased by 31 +/- 11% (P = 0.01) following pressurization of the capillaries, and the elastin fibers became more parallel to the basal membrane. Because the organization of elastin fibers results in smaller H values of the individual alveolus, the higher H in the unperfused lungs is probably due to a partial alveolar collapse leading to a loss in lung volume. We conclude that the physiological pressure in the pulmonary capillaries is an important mechanical factor in the maintenance of the stability of the alveolar architecture.     

Early fluid and protein shifts in men during water immersion

High precision blood and plasma densitometry was used to measure transvascular fluid shifts during water immersion to the neck. Six men (28-49 years) undertook 30 min of standing immersion in water at 35.0 +/- 0.2 degrees C; immersion was preceded by 30 min control standing in air at 28 +/- 1 degrees C. Blood was sampled from an antecubital catheter for determination of blood density (BD), plasma density (PD), haematocrit (Ht), total plasma protein concentration (PPC), and plasma albumin concentration (PAC). Compared to control, significant decreases (p less than 0.01) in all these measures were observed after 20 min immersion. At 30 min, plasma volume had increased by 11.0 +/- 2.8%; the average density of the fluid shifted from extravascular fluid into the vascular compartment was 1006.3 g.l-1; albumin moved with the fluid and its albumin concentration was about one-third of the plasma protein concentration during early immersion. These calculations are based on the assumption that the F-cell ratio remained unchanged. No changes in erythrocyte water content during immersion were found. Thus, immersion-induced haemodilution is probably accompanied by protein (mainly albumin) augmentation which accompanies the intravascular fluid shift.     

Calcium diffusion in transient and steady states in muscle.

Rates of diffusion through the extracellular space of thin sheets of myocardium from the right ventricular outflow tract of kittens were estimated at 23 degrees C for 45Ca2+ and an inert reference tracer, [14C]sucrose. The myocardial sheets were mounted in an Ussing chamber and equilibrated with Tyrode solution with varied calcium concentrations, Cao. The tracers were added to one side and their concentrations on the other side measured at 5-15-min intervals for 6 h. The apparent tracer diffusion coefficient for sucrose was 1.11 +/- 0.06 X 10(-6) cm2s-1 (mean +/- SEM, n = 74), 22% of the free diffusion coefficient; the lag time before reaching a steady state provided estimates of the intratissue volume of distribution or diffusion space of 0.41 +/- 0.15 ml/ml tissue (n = 74), a value compatible with expectations for extracellular fluid space. Over the range of Cao from 0.02 to 9.0 mM, the intratissue apparent diffusion coefficient for Ca, DCa, averaged 1.65 +/- 0.10 X 10(-6) cm2s-1, n = 74, which is 21% of the free DoCa, and was not influenced by Cao. Because transsarcolemmal Ca permeation is slow, DCa is the diffusion coefficient in the extracellular region. The paired ratios DCa/Ds averaged 1.32 +/- 0.05 (n = 67) for all levels of Cao but at physiologic or higher Cao averaged 1.45 +/- 0.07 (n = 39), close to the ratio of free diffusion coefficients, 1.53. Equations distinguishing transient from steady state diffusion were fitted to the data, showing that the apparent distribution volume of "binding sites" external to the diffusion pathway diminished at higher Cao in a fashion suggesting that a least two different Ca2+ binding sites were present.     

Microvascular albumin permeability in isolated perfused lung: effects of EDTA

We examined the effects of decreases in perfusate concentrations of calcium and magnesium on the pulmonary vascular permeability in the isolated perfused rabbit lung. The albumin permeability-surface area product (PS) and the albumin reflection coefficient (sigma) were determined in the same lung using 125I- and 131I-labeled albumin tracers. Decreases in vascular Ca2+ and Mg2+ concentrations were induced by adding ethylenediaminetetraacetic acid (EDTA) to the perfusate. Decreases in the concentration of these cations resulted in an increase in the PS from a control value of 1.18 +/- 0.13 X 10(-3) to 7.69 +/- 0.75 X 10(-3) cm3 X min-1 X g wet lung wt-1 and a decrease in the sigma from 0.96 +/- 0.01 to 0.74 +/- 0.02. The decrease in sigma suggests an increase in the calculated equivalent pore radius from 44 to 63 A. The results indicate that Ca2+ and Mg2+ play a role in the maintenance of normal pulmonary vascular permeability to proteins.     

A new method to evaluate extravascular albumin and blood cell accumulation in the lung

A method was developed to evaluate blood volume, accumulation of extravascular albumin (ALBev), and platelet (PL) or polymorphonuclear neutrophil (PMN) sequestration in lungs after challenge with inflammatory agents. Erythrocytes (RBC), albumin, and PL or PMN, labeled with 99mTc, 131I, and 111In,-respectively, were injected intravenously into anesthetized and ventilated guinea pigs. The different parameters were calculated from in vivo lung and blood radioactivity values. When N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP) was injected intravenously at 10 micrograms.kg-1, lung RBC content dropped by 14.7 +/- 1.8% (SE; n = 10), indicating a reduced lung blood volume, ALBev rose to 15.0 +/- 3.2% of the initial albumin vascular content, and the circulating PMN were sequestered by 9.2 +/- 1.7%. A transient PL sequestration was also observed 1 min after the injection of fMLP (13.1 +/- 2.0%, n = 7). During the infusion of 1-O-hexadecyl-2-acetyl-sn-glycero-3-phosphorylcholine, the lung PL content rose dose dependently from 10.1 +/- 2.2% of the circulating pool with 3 ng.kg-1.min-1 to 54.9 +/- 20.1% with 44 ng.kg-1.min-1, the lung RBC content decreased by greater than 10%, and the ALBev increased beyond 16%. Our method allows the study of the correlations between cell entrapment and the variations of the albumin exchanges in the lung and may lead to a better understanding of the correlations between cell activation and edema.     

Oxidation of glutamine by the splanchnic bed in humans

[1,2-(13)C(2)]glutamine and [ring-(2)H(5)]phenylalanine were infused for 7 h into five postabsorptive healthy subjects on two occasions. On one occasion, the tracers were infused intravenously for 3.5 h and then by a nasogastric tube for 3.5 h. The order of infusion was reversed on the other occasion. From the plasma tracer enrichment measurements at plateau during the intravenous and nasogastric infusion periods, we determined that 27 +/- 2% of the enterally delivered phenylalanine and 64 +/- 2% of the glutamine were removed on the first pass by the splanchnic bed. Glutamine flux was 303 +/- 8 micromol. kg(-1). h(-1). Of the enterally delivered [(13)C]glutamine tracer, 73 +/- 2% was recovered as exhaled CO(2) compared with 58 +/- 1% of the intravenously infused tracer. The fraction of the enterally delivered tracer that was oxidized specifically on the first pass by the splanchnic bed was 53 +/- 2%, comprising 83% of the total tracer extracted. From the appearance of (13)C in plasma glucose, we estimated that 7 and 10% of the intravenously and nasogastrically infused glutamine tracers, respectively, were converted to glucose. The results for glutamine flux and first-pass extraction were similar to our previously reported values when a [2-(15)N]glutamine tracer [Matthews DE, Morano MA, and Campbell RG, Am J Physiol Endocrinol Metab 264: E848-E854, 1993] was used. The results of [(13)C]glutamine tracer disposal demonstrate that the major fate of enteral glutamine extraction is for oxidation and that only a minor portion is used for gluconeogenesis.     

Estimation of equivalent pore radii in pulmonary microvasculature after lung lymph fistula preparation

The effect of lung lymph fistula preparation on pulmonary microvascular permeability was investigated in sheep. Acutely prepared animals (n = 9) were compared with animals with a chronic lung lymph fistula (n = 5). The osmotic reflection coefficients (sigma) for total protein, albumin, immunoglobins (Ig) G and M, and the equivalent pore dimensions were calculated. Data were achieved at maximal possible lymph flows (QL) following elevation of left atrial pressure. In sheep with a chronic lung lymph fistula sigma's for total protein, albumin, IgG, and IgM at maximal lymph flows were 0.76 +/- 0.01, 0.65 +/- 0.09, 0.79 +/- 0.03, and 0.91 +/- 0.01, respectively. In the acutely prepared group the minimum lymph-to-plasma protein concentration for total protein was 0.39 +/- 0.06, corresponding to a sigma of 0.61 +/- 0.01. The sigma for albumin, IgG, and IgM were 0.48 +/- 0.04, 0.64 +/- 0.02, and 0.87 +/- 0.01, respectively. The equivalent pore radii in the chronic group were determined to be 54 and 190 A with 29% of the filtration accounted for by large pores. In the acute group the small pores were 56 A and the large pores 175 A with 53% of total volume flow at maximum lymph flows occurring through the large pores. Assuming a constant small-pore population the large pore number increased 4.5 times after surgery. For total protein, IgG, and IgM, sigma's in the acutely prepared group were significantly lower than in the control group. These results thus indicate that surgical preparation of a lung lymph fistula in sheep may cause acute increases in pulmonary microvascular permeability.     

Lung liquid secretion, flow and volume in response to moderate asphyxia in fetal sheep

The effects of moderate fetal asphyxia, induced by constriction of the maternal common internal iliac artery, on lung liquid secretion, tracheal fluid efflux and lung liquid volume have been investigated in unanaesthetized fetal sheep (111-142 days) in utero. During periods of fetal asphyxia the percent oxygen saturation, PO2, pH, and PCO2 of fetal carotid arterial blood changed from 57.2 +/- 1.3% (mean +/- SEM), 22.9 +/- 0.6 mmHg, 7.35 +/- 0.01 and 45.6 +/- 1.0 mmHg to 26.3 +/- 0.5% (P less than 0.001), 14.7 +/- 0.2 mmHg (P less than 0.001), 7.28 +/- 0.02, (P less than 0.001) and 47.8 +/- 0.4 mmHg (P less than 0.02), respectively. Fetal asphyxia, over 6 h, decreased the efflux of tracheal fluid from 7.07 +/- 0.47 ml/h to 3.97 +/- 0.36 ml/h (P less than 0.01) and, over 4 h, decreased the rate of lung liquid secretion from 9.42 +/- 1.76 ml/h to 4.91 +/- 1.54 ml/h (P less than 0.005), whereas it had no significant effect on lung liquid volume. The incidence of fetal breathing movements decreased from 52.9 +/- 2.5% to 22.6 +/- 3.5% during 6-h periods of fetal asphyxia. Thus, although fetal asphyxia decreased the net production of lung liquid, lung liquid volume was maintained probably, because the net efflux of fluid from the lungs via the trachea decreased to a similar extent.     

Alveolar epithelial barrier functions in ventilated perfused rabbit lungs

We employed ultrasonic nebulization for homogeneous alveolar tracer deposition into ventilated perfused rabbit lungs. (22)Na and (125)I-albumin transit kinetics were monitored on-line with gamma detectors placed around the lung and the perfusate reservoir. [(3)H]mannitol was measured by repetitive counting of perfusion fluid samples. Volume of the alveolar epithelial lining fluid was estimated with bronchoalveolar lavage with sodium-free isosmolar mannitol solutions. Sodium clearance rate was -2.2 +/- 0.3%/min. This rate was significantly reduced by preadministration of ouabain/amiloride and enhanced by pretreatment with aerosolized terbutaline. The (125)I-albumin clearance rate was -0.40 +/- 0.05%/min. The appearance of [(3)H]mannitol in the perfusate was not influenced by ouabain/amiloride or terbutaline but was markedly enhanced by pretreatment with aerosolized protamine. An epithelial lining fluid volume of 1.22 +/- 0.21 ml was calculated in control lungs. Fluid absorption rate was 1.23 microl x g lung weight(-1) x min(-1), which was blunted after pretreatment with ouabain/amiloride. We conclude that alveolar tracer loading by aerosolization is a feasible technique to assess alveolar epithelial barrier properties in aerated lungs. Data on active and passive sodium flux, paracellular solute transit, and net fluid absorption correspond well to those in previous studies in fluid-filled lungs; however, albumin clearance rates were markedly higher in the currently investigated aerated lungs.