Effects of lung volume on clearance of solutes from the air spaces of lungs

Several investigators have shown that the clearance rate of aerosolized 99mTc-labeled diethylenetriamine pentaacetate (DTPA, mol wt = 492, radius = 0.6 nm) from the air spaces of the lungs of humans and experimental animals increases with lung volume. To further investigate this phenomenon we performed a compartmental analysis of the 2-h clearance of DTPA from the lungs of anesthetized sheep using a new method to more accurately correct for the effects of DTPA recirculation. This analysis showed that the DTPA clearance in eight sheep ventilated with zero end-expired pressure was best described by a one-compartment model with a clearance rate of 0.42 +/- 0.15%/min. Ventilating eight sheep with an end-expired pressure of 10 cmH2O throughout the study increased the end-expired volume 0.4 +/- 0.1 liter BTPS and created a clearance curve that was best described by a two-compartment model. In these sheep 56 +/- 16% of the DTPA cleared from the lungs at a rate of 7.9 +/- 2.9%/min. The remainder cleared at a rate similar to that measured in the sheep ventilated with zero end-expired pressure (0.35 +/- 0.18%/min). Additional control and lung inflation experiments were performed using 99mTc-labeled human serum albumin (mol wt = 66,000, radius = 3.6 nm). In six control sheep ventilated with zero end-expired pressure the albumin clearance was best described by a one-compartment model with a clearance rate of 0.06 +/- 0.02%/min. The clearance rate in six sheep with increased lung volume was slightly larger (0.09 +/- 0.02, P less than 0.05) but was well described by a one-compartment model.(ABSTRACT TRUNCATED AT 250 WORDS)     

Regional extravascular and interstitial lung water in normal dogs

We measured the regional distribution of pulmonary extravascular and interstitial water to examine the possibility that regional differences in microvascular pressure or tissue stress may cause regional differences in lung water. We placed chloralose-anesthetized dogs in an upright (n = 6) or supine (n = 7) position for 180 min. We injected 51Cr-labeled EDTA to equilibrate to the extracellular space and 125I-labeled albumin to equilibrate with plasma. At the end of the experiment, the lungs were removed, passively drained of blood, and inflated before rapid freezing. Lungs were divided into horizontal slices, and extravascular, interstitial, and plasma water, red cell volume, and dry lung weight were determined for each slice. We found that regional extravascular and interstitial water were constant throughout the lungs in both groups and that there were no significant differences between upright and supine dogs. There were no significant differences in hematocrit between slices. We conclude that gravity and body position have no measurable effect on either the total size of the extravascular and interstitial compartments or their regional distribution.     

Pulmonary lymphatic clearance of 99mTc-DTPA from air spaces during lung inflation and lung injury

A total of 22 sheep with lymphatic cannulas were used to determine if 99mTc-labeled diethylenetriaminepentaacetic acid (DTPA) clears directly from the air spaces of the lungs into the lymph vessels. Each sheep was anesthetized and ventilated with an aerosol of the DTPA for 2-5 min, and the DTPA activities in the lymph and plasma were measured every 15 min for 2 h. After the first 45 min, the average ratio of the DTPA in the lymph to that in the plasma (L/P) was 1.03 +/- 0.06 (SD) in the six control experiments and 1.11 +/- 0.05 in the six experiments in which the lungs were inflated with a positive end-expired pressure of 10 cmH2O throughout the study. Direct movement of the DTPA from the air spaces into the lymph was not necessary to account for the DTPA clearance in these experiments because the L/P ratio was not significantly different from 1.0. Eight additional sheep received intravenous infusions of air at 0.2 ml.kg-1.min-1 for 2 h to induce lung injury before depositing the DTPA. In these sheep L/P was 1.53 +/- 0.28, which was significantly higher than the value measured in the control group (P less than 0.01). We considered the possibility that the increased L/P ratio in these sheep could be due to alterations in the distribution of the blood flow to the tissue, but the L/P ratio in four sheep whose distribution of blood flow was altered by inflation of a balloon in the right pulmonary artery was 1.05 +/- 0.10, the same as the control value.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

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.     

Pulmonary neutrophil kinetics in sheep: effects of altered hemodynamics

We investigated the effect of elevated left atrial pressure and reduced cardiac output on pulmonary neutrophil kinetics in the sheep. Sheep neutrophils were isolated, labeled with 111In-oxine, and reinfused. Erythrocytes were labeled with [99mTc]pertechnetate. A gamma camera measured the lung activities of the labeled neutrophils and erythrocytes. The results indicated that 38.5% of the total injected neutrophils marginated in the lung. Pulmonary hemodynamics were altered by inflating a left atrial balloon three times in each sheep for 15-30 min to achieve 5- to 25-mmHg increments in pulmonary arterial wedge pressure. At least a 30-min recovery period was allowed between inflations. After each left atrial balloon inflation, neutrophil uptake remained unchanged from base line, despite decreased mean cardiac output to 0.67 +/- 0.24 (+/- SD) 1/min and increased pulmonary blood volume. The absence of pulmonary neutrophil uptake was confirmed by arterial-venous measurements. Increased pulmonary blood volume had little effect on lung neutrophil uptake, suggesting that most of the pulmonary neutrophils are marginated. We conclude that the lungs have a large marginated neutrophil pool compared with the circulating pool and that reduced cardiac output and elevated left atrial pressure have no effect on pulmonary neutrophil kinetics in the sheep.     

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.     

Concentration of aerosolized 99mTc-albumin in the pulmonary lymph of anesthetized sheep

We examined the lymphatic concentration of 99mTc-albumin deposited in the air spaces of anesthetized sheep to determine whether changes in the concentration reflected changes in lung epithelial function. Five control sheep were ventilated with an aerosol of 99mTc-albumin for 6 min, and the lung lymphatic concentration of the tracer was monitored for the next 2 h. During the last 45 min the lymphatic concentration stabilized at a value that was 0.03 +/- 0.01% of the estimated value in the air spaces. Pulmonary vascular hypertension, induced in seven sheep by increasing the left atrial pressure 20 cmH2O for 4 h, increased the lung lymph flow from a base-line value of 3 +/- 2 to 21 +/- 14 ml/h. This caused the concentration of the 99mTc-albumin in the lymph to double to 0.07 +/- 0.03% of the air space concentration (P less than 0.01). Lung injury induced by infusing 0.08-0.10 ml/kg oleic acid intravenously in seven other sheep increased the lymphatic concentration of the 99mTc-albumin 10-fold to 0.31 +/- 0.09% of the air space concentration (P less than 0.01). The increased tracer concentration in the sheep with pulmonary vascular hypertension could be the result of the increased lymph flow causing a diversion of tracer into the lymphatics. However, a mathematical model showed that the 10-fold increase in the lymphatic concentration in the sheep with lung injury was primarily the result of an increase in both permeability and surface area of the epithelium that participated in the transfer of the 99mTc-albumin from the air spaces into the lung tissue drained by the lymphatics.(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.     

Evaluating flux of labeled albumin into the pulmonary interstitium of sheep lungs.

A noninvasive method was used to measure the movement of 131I-labeled albumin across the pulmonary microvascular barrier of a blood-perfused in situ sheep lung lymph preparation. After injection of labeled albumin into the blood, external measurements of gamma activity were taken for 2 h. The interstitial concentrations were calculated by applying the external activities and sampled lung lymph concentrations to a mass transport model. For the external activities and lymph activities to yield the same quantitative results, two modifications were necessary. First, lymph concentrations were corrected for transport delay from the lymphatic system. Second, externally detected radioactivity had to be corrected for the contribution of unbound nuclide. Application of a mathematical model to the data indicated the extravascular distribution volume for albumin was 79% of the pulmonary blood volume, and the extravascular distribution volume for radiolabeled iodide was 4.42 times greater than the pulmonary blood volume. The permeability-surface area product for iodide in the lung was estimated to be 0.274 ml.min-1.g blood-free dry lung wt-1. The transport delay in the lymphatic system was approximately 30-45 min and represented a volume of 1.44-2.80 ml.     

Oleic acid reduces pulmonary microvascular sieving capacity in sheep

Changes in pulmonary microvascular permeability in sheep, after oleic acid injection, were studied using estimations of the osmotic reflection coefficient (sigma d) for total protein, albumin, immunoglobulins (Ig) G and M and calculation of the equivalent small and large pores of the microvessels. A chronic lung fistula was prepared in eight sheep. After a base-line period, left atrial pressure (Pla) was increased. Oleic acid (0.05 mg/kg body wt) was injected after a filtration-independent state had been obtained, and the spontaneously ventilating animals were then followed for 2 h. The sigma d for the normal lung was 0.65 +/- 0.03, 0.59 +/- 0.02, 0.72 +/- 0.04, and 0.84 +/- 0.02 for total protein, albumin, IgG, and IgM, respectively. The equivalent pore radii were 54 and 225 A. After oleic acid infusion, arterial pressure and arterial O2 tension decreased and leukocytes and platelets were consumed. At the end of the experiment, sigma d's were 0.27 +/- 0.04, 0.24 +/- 0.07, 0.33 +/- 0.06, and 0.55 +/- 0.04 for total protein, albumin, IgG, and IgM, respectively. The equivalent pore radii were 54 and 275 A, and the number of large pores was increased by 195%. The results indicate that oleic acid produces an increased vascular permeability by increasing the size and the numbers of large pores of the pulmonary microvascular walls.     

Interstitial exclusion of positively and negatively charged IgG in rat skin and muscle

Volume exclusion, i.e., the space not available for a specific probe, may be dependent on the probe charge. Therefore, interstitial exclusion was measured for positively and negatively charged immunoglobulin (IgG) in skin and muscle of rats by using a continuous infusion method (30). Steady-state concentration of (125)I-labeled IgG 1 (pI = 8.7) and (131)I- labeled IgG 4 (pI = 6.6) was maintained by infusion of tracer for 120-168 h with an implanted osmotic pump. At the end of the infusion period and before tissue sampling, the rat was anesthetized and nephrectomized, and (51)Cr-labeled EDTA was injected and allowed 4 h for equilibration to measure interstitial fluid volume (V(i)). Interstitial fluid was isolated from skin and muscle by using nylon wicks implanted post mortem. The relative IgG available space was measured as the ratio between labeled IgG and (51)Cr-labeled EDTA wick fluid equivalent spaces, and relative excluded volume fraction (V(e)/V(i)) was calculated as 1--V(a)/V(i). V(e)/V(i) in hindlimb skin averaged 0.37 +/- 0.05 (SE) and 0.65 +/- 0.06 (P < 0.01) for IgG 1 and 4, respectively, with corresponding figures of 0.24 +/- 0.05 and 0.51 +/- 0.04 (P < 0.01) in hindlimb muscle (n = 9 for both tissues). These experiments suggest that fixed negative charges, most likely glycosaminoglycans, influence distribution of macromolecules in the interstitium and therefore affect interstitial fluid balance.     

Influence of chest background on pulmonary 99mTc-DTPA clearance in interstitial lung disease.

We examined the effect of chest extracellular 99mTc-diethylenetriamine pentaacetate (DTPA) as a background in the measurement of pulmonary 99mTc-DTPA clearance in patients with interstitial lung disease (ILD). Eight healthy nonsmokers (HN) and eight patients with ILD were studied. We monitored changes in gamma counts after the inhalation of 99mTc-DTPA aerosol by using a gamma camera placed over the anterior chest. The rate constant of pulmonary 99mTc-DTPA clearance (k; %/min) was assessed by calculating the slope of the decrease in the gamma counts. The chest background, estimated by 99mTc-DTPA intravenous injection, was subtracted from the original data to obtain the corrected DTPA clearance (kc; %/min). In patients with ILD, k was significantly greater [2.19 +/- 1.03 (SD) %/min; n = 8] compared with HN (0.86 +/- 0.17%/min; n = 8; P < 0.01). In patients with ILD, kc was also greater (2.80 +/- 1.15%/min; n = 8; P < 0.01) compared with HN (1.20 +/- 0.12%/min; n = 8). There was no difference in percent underestimation of k between the two groups (29.1 +/- 8.8% for HN, 22.5 +/- 7.9% for patients with ILD). There was a significant correlation between k and kc among all subjects (r = 0.987, P < 0.01). We conclude that background causes significant underestimation of pulmonary 99mTc-DTPA clearance.     

Regional differences in interstitial fluid albumin concentration in edematous lamb lungs.

We have determined regional lung interstitial fluid albumin concentration in lambs with hydrostatic pulmonary edema and correlated it with lung lymph and plasma albumin concentrations. In anesthetized lambs, we raised left atrial pressure to 25-30 cmH2O by obstructing the aorta and volume overloading the lambs with infusions of Ringer lactate solution (group I, n = 10) or sheep's blood (group II, n = 9). We measured lung lymph flow and concentrations of total protein and albumin in plasma and lymph. With micropipettes we also collected interstitial fluid from interlobular septal pools and peribronchial, periarterial, and perivenous liquid cuffs near the hilum for measurement of albumin concentration by the gel immunoelectrophoresis method. In both groups, lung lymph flow increased with left atrial hypertension, and the ratio of lymph to plasma protein concentration fell. For group I, plasma and lymph albumin concentrations during the phase of hydrostatic edema were 1.97 +/- 0.49 and 1.15 +/- 0.36, respectively; for group II, they were 3.77 +/- 0.42 and 2.43 +/- 0.39 g/dl, respectively. Lung wet-to-dry weight ratio averaged 6.0 in both groups. Albumin concentration was always lower in interstitial fluid than in plasma. In both groups, albumin concentration was similar in periarterial and peribronchial fluid cuffs (group I 1.19 +/- 0.6 and 1.36 +/- 0.79 g/dl, respectively; group II 2.87 +/- 1.05 and 2.33 +/- 0.58 g/dl, respectively) but was always greater than that in perivenous and interlobular septal pools (group I 0.61 +/- 0.21 and 0.67 +/- 0.23 g/dl, respectively; group II 1.76 +/- 0.49 and 1.55 +/- 0.52 g/dl, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of increased hydrostatic pressure on lymphatic elimination of hyaluronan from sheep lung

The effects of increased hydrostatic pressure on the concentrations of hyaluronan (hyaluronic acid) in lung lymph and serum were investigated in awake sheep with a cannula in the efferent vessel from the caudal mediastinal lymph node. Lung lymph was sampled at base line [left atrial pressure (LAP) 6.5 +/- 1.7 mmHg] and after two increases of LAP to 25.7 +/- 2.2 mmHg (level 1) and 37.0 +/- 5.1 mmHg (level 2). The lung lymph flow increased from 1.9 +/- 0.5 at base line to 9.3 +/- 2.2 and 15.9 +/- 0.7 ml/30 min, and the lymph-to-plasma concentration ratio of total protein decreased from 0.63 +/- 0.02 to 0.32 +/- 0.04 and 0.32 +/- 0.05 at the two elevated levels of LAP, respectively. The hyaluronan concentration in lung lymph was unchanged, and there was a flow-dependent elimination of hyaluronan from the lung that increased from 23 +/- 8 to 87 +/- 19 and 137 +/- 37 micrograms/30 min, respectively. The lung concentration of hyaluronan was 167 +/- 28 micrograms/g fresh lung, and at base line it was calculated that slightly less than 2% of the lung hyaluronan was eliminated by the lymphatic route in 24 h. If extrapolated to 24 h, the elimination rate of hyaluronan seen during elevated LAP would result in lymphatic elimination of 18% of the lung hyaluronan over this time period. Since hyaluronan is responsible for part of the protein exclusion in the extracellular matrix, it is plausible that washout of interstitial hyaluronan contributes to the decrease in albumin exclusion from the interstitium that occurs after an elevation of LAP.     

Vascular and epithelial damage in the lung of the mouse after X rays or neutrons

The response of the lung was studied in CFLP mice after exposure of the whole thorax to X rays (250 kVp) or cyclotron neutrons (16 MeV deuterons on Be, mean energy 7.5 MeV). To measure blood volume and leakage of plasma proteins, 51Cr-labeled red blood cells and 125I-albumin were injected intravenously and 24 h later lungs were lavaged via the trachea. Radioactivities in lung tissue and lavage fluid were determined to estimate the accumulation of albumin in the interstitial and alveolar spaces indicating damage to blood vessels and alveolar epithelium respectively. Function of type II pneumonocytes was assessed by the amounts of surfactant (assayed as lipid phosphorous) released into the lavage fluid. During the first 6 weeks, lavage protein and surfactant were increased, the neutron relative biological effectiveness (RBE) being unity. During pneumonitis at 12-24 weeks, surfactant levels were normal, blood volume was decreased, and both interstitial and alveolar albumin were increased. Albumin levels then decreased. At late times after exposure (42-64 weeks) alveolar albumin returned to normal but interstitial albumin was still slightly elevated. Values of RBE for changes in blood volume and interstitial and alveolar albumin at 15 weeks and for changes in blood volume and interstitial albumin at 46 weeks were 1.4, comparable with that for animal survival at 180 days. The results indicate that surfactant production is not critical for animal survival. They suggest that changes in blood vessels and alveolar epithelium occur during acute pneumonitis; epithelial repair follows but some vascular damage may persist. The time course of the changes in albumin levels did not correlate with increases in collagen biosynthesis which have been observed as early as 1 month after exposure and persist for up to 1 year. Furthermore, a dose which had no effect on leakage caused a marked increase in collagen biosynthesis. Thus the present results do not support a causal relationship between exudation of vascular protein during pneumonitis and the later development of fibrosis.     

Modeling kinetics of infused 13NN-saline in acute lung injury.

A mathematical model was developed to estimate right-to-left shunt (Fs) and the volume of distribution of 13NN in alveolar gas (VA) and shunt tissue (Vs). The data obtained from this model are complementary to, and obtained simultaneously with, pulmonary functional positron emission tomography (PET). The model describes 13NN kinetics in four compartments: central mixing volume, gas-exchanging lung, shunting compartment, and systemic recirculation. To validate the model, five normal prone (NP) and six surfactant-depleted sheep in the supine (LS) and prone (LP) positions were studied under general anesthesia. A central venous bolus of 13NN-labeled saline was injected at the onset of apnea as PET imaging and arterial 13NN sampling were initiated. The model fit the tracer kinetics well (mean r2 = 0.93). Monte Carlo simulations showed that parameters could be accurately identified in the presence of expected experimental noise. Fs derived from the model correlated well with shunt estimates derived from O2 blood concentrations and from PET images. Fs was higher for LS (54 +/- 18%) than for LP (5 +/- 4%) and NP (1 +/- 1%, P < 0.01). VA, as a fraction of PET-measured lung gas volume, was lower for LS (0.18 +/- 0.09) than for LP (0.96 +/- 0.28, P < 0.01), whereas Vs, as a fraction of PET-measured lung tissue volume, was higher for LS (0.46 +/- 0.26) than for LP (0.05 +/- 0.08, P < 0.01). The main conclusions are as follows: 1) the model accurately describes measured arterial 13NN kinetics and provides estimates of Fs, and 2) in this animal model of acute lung injury, the fraction of available gas volume participating in gas exchange is reduced in the supine position.     

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.     

Removal of pleural liquid and protein by lymphatics in awake sheep

The contribution of the parietal pleural lymphatics to pleural liquid and protein removal is unclear. We asked two questions. What is the rate of removal of sterile, artificial hydrothoraxes in awake sheep? What percentage is removed through parietal pleural lymphatics? Three days after the placement of a rib capsule in 18 sheep, we instilled a 10 ml/kg 1.0 g/dl autologous protein solution with labeled albumin and erythrocytes through the capsule into the pleural space. Erythrocytes were used as a marker for lymphatic flow. We measured terminal pleural liquid volume and radioactivity at periods from 2 to 48 h. In three sheep, we obtained a third volume measurement at 6 h by the volume of dilution technique. We found that hydrothorax removal could be described by a linear function with a constant rate: 0.28 +/- 0.01 ml.kg-1.h-1 (mean +/- SE) for the grouped data, and 0.20, 0.28, and 0.31 ml.kg-1.h-1 for the individual sheep. At 24 h, erythrocyte clearance was 89 +/- 16% (mean +/- SD) that of liquid and albumin clearance. We conclude that in awake sheep with large hydrothoraxes, pleural liquid and protein are removed at a rate of 0.28 +/- 0.01 ml.kg-1.h-1 (mean +/- SE) and lymphatics are responsible for at least 89% of this removal.     

Respiratory failure after endotoxin infusion in sheep: lung mechanics and lung fluid balance

Infusion of Escherichia coli endotoxin (0.12-1.5 micrograms/kg) into unanesthetized sheep causes transient pulmonary hypertension and several hours of increased lung vascular permeability, after which sheep recover. To produce enough lung injury to result in pulmonary edema with respiratory failure, we infused larger doses of E. coli endotoxin (2.0-5.0 micrograms/kg) into 11 chronically instrumented unanesthetized sheep and continuously measured pulmonary arterial, left atrial and aortic pressures, dynamic lung compliance, lung resistance, and lung lymph flow. We intermittently measured arterial blood gas tensions and pH, made interval chest radiographs, and calculated postmortem extravascular bloodless lung water-to-dry lung weight ratio (EVLW/DLW). Of 11 sheep 8 developed respiratory failure; 7 died spontaneously 6.3 +/- 1.1 h, and one was killed 10 h after endotoxin infusion. All sheep that had a premortem room air alveolar-arterial gradient in partial pressure of O2 (PAo2-Pao2) greater than 42 Torr (58 +/- 5 (SE) Torr) died. Of eight sheep that had radiographs made, six developed radiographically evident interstitial or interstitial and alveolar edema. Pulmonary artery pressure rose from base line 22 +/- 2 to 73 +/- 3 cmH2O and remained elevated above baseline levels until death. There was an initial fourfold decrease in dynamic compliance and sixfold increase in pulmonary resistance; both variables remained abnormal until death. EVLW/DLW increased with increasing survival time after endotoxin infusion, suggesting that pulmonary edema accumulated at the same rate in all fatally injured sheep, regardless of other variables. The best predictor of death was a high PAo2-Pao2. The marked increase in pulmonary resistance and decrease in dynamic compliance occurred too early after endotoxin infusion (15-30 min) to be due to pulmonary edema. The response to high-dose endotoxin in sheep closely resembles acute respiratory failure in humans following gram-negative septicemia. Respiratory failure and death in this model were not due to pulmonary edema alone.