Indicator dilution lung water and vascular permeability in humans. Effects of pulmonary vascular pressure

Dynamic CT Measurement of Pulmonary Enhancement in Piglets with Experimental Acute Respiratory Distress Syndrome

PURPOSE

To investigate whether analysis of a washout curve of contrast material obtained with serial computed tomography (CT) enables differentiation between hydrostatic pulmonary edema and pulmonary edema caused by increased capillary permeability.

MATERIALS AND METHODS

The institutional committee on animal experiments approved this study, which was performed in accordance with designated guidelines. Chest CT was performed in 12 piglets after induction of anesthesia and start of mechanical ventilation. Dynamic CT was performed before and after induction of hydrostatic edema (n = 5) or oleic acid-induced increased vascular permeability edema (n = 7). Scans were obtained over 240 seconds during inspiratory breath holding at a single representative subcarinal level in the lungs. This anatomic level was kept constant and included areas of normal ventilation before and after induction of pulmonary edema and areas of ground-glass opacity and consolidation after induction of pulmonary edema. Measured lung attenuation in the regions of interest was normalized to that before contrast material injection and plotted as a function of time. Statistical analysis was performed by using two-way analysis of variance with repeated measures.

RESULTS

In general, before induction of pulmonary edema, attenuation of normally aerated lung areas did not increase after the initial peak of enhancement during the first pass of contrast material. In animals with hydrostatic edema, no attenuation changes in areas of ground-glass opacity were observed after the initial peak. Conversely, lung attenuation increased continuously in animals with oleic acid-induced high-permeability pulmonary edema (P = .002). After induction of lung edema, pulmonary enhancement measured in lung regions with normal ventilation or consolidation did not change in either group. Pulmonary fluid accumulation 90 minutes after induction of edema did not significantly differ between groups.

CONCLUSION

Dynamic contrast-material enhanced CT can help differentiate between permeability and hydrostatic lung edema in an animal model.

Effective attenuation of endotoxin-induced acute lung injury by 2,3-diacetyloxybenzoic acid in two independent animal models

The pathology of acute lung injury (ALI) is often modeled in animal studies by the administration of lipopolysaccharide (LPS), which results in an endotoxemia with sequelae similar to that seen in acute respiratory distress syndrome (ARDS). Here we report the results of two studies designed to examine the efficacy of a novel agent, 2,3-diacetyloxybenzoic acid (2,3-DABA), in the treatment of LPS-induced ALI. In two separate animal models, 2,3-DABA was effective in significantly reducing lung microvascular permeability, a condition commonly seen in ARDS, which results in pulmonary edema and respiratory insufficiency. In each model, it is demonstrated that the mechanism by which 2,3-DABA exerts this effect occurs subsequent to the recruitment of neutrophils to the site of inflammation. Lung permeability was significantly decreased in both models by treatment with 2,3-DABA, suggesting that this agent, either alone or in combination therapy, may be useful in the treatment of ALI associated with ARDS.

Continuous blood density measurement for hemodynamic monitoring: an analysis of its accuracy and sensitivity

Continuous measurement of arterial blood density after bolus injection of fluids of different density into the right atrium has been used to measure cardiac output and mean transit time through the central circulation. The transit time distribution for density, however, differs from that for plasma-phase tracers such as indocyanine green. This difference may yield important information about red cell transit times through the microcirculation. We analyzed the potential of the density technique to resolve small changes in transit time distributions. Rayleigh's Method was used to calculate the relationship between density distribution within the U-tube and frequency of oscillation. Fourier integral transformation of a functional representation of indocyanine green dye curves provided an estimate of amplitude versus frequency for likely input density signals. We found that the ability of the densitometer to accurately follow blood density changes depends upon physiologic parameters associated with the experimental animal and upon the physical characteristics of the densitometer itself. Even for small animals, such as a rabbit, the densitometer theoretically has the ability to accurately follow rapid density changes over time.

Lung oxidant changes after zymosan peritonitis: relationship between physiologic and biochemical changes

Our purpose was to determine the effect of non-bacteria-dependent systemic inflammation on the degree and time course of lung oxidant activity and antioxidant defenses, comparing these changes with lung, physiologic, and histologic alterations. Adult male rats were given intraperitoneal zymosan (0.7 mg/g body weight) and were fluid resuscitated. Oxidant changes were measured as lung tissue oxidized glutathione (GSSG) and malondialdehyde (MDA) content, antioxidant defenses as tissue reduced glutathione (GSH), and catalase. Animals were killed at 4, 12, and 24 h, and at 5, 10, and 30 days. Lung data were compared with that found in liver. We noted a 45% mortality in the first 18 to 36 h with all remaining animals surviving. In the first 24 h, we noted a doubling of lung MDA and an 80% conversion of tissue GSH to GSSG compared with less than 5% in control animals, indicating a severe oxidant stress. These findings corresponded with marked increase in lung neutrophils. Arterial pressure (PaO2) was significantly decreased from a control of 95 +/- 4 mm Hg to 80 +/- 5 mm Hg and 75 +/- 4 mm Hg at Days 5 and 10, respectively, but returned toward control by 30 days. Lung GSSG and MDA remained significantly increased for the 30-day period, whereas amounts of the antioxidants, catalase, and GSH returned to control after 24 h. The ongoing oxidant stress corresponded with marked mononuclear cell infiltration and interstitial thickening, which persisted over the 30-day period even after peritonitis had completely resolved.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of pulmonary vascular injury

The assessment of pulmonary injury in experimental and clinical situations remains a challenge. A method of quantifying pulmonary vascular aberrations in animal models and human clinical situations is described. A multiple-indicator dilution technique is employed to assess changes in lung capillary permeability--surface area product, extravascular lung water, and cardiac output. A mixture of 51Cr-RBC, 125I-albumin, tritiated water, and [14C]urea is injected into a central vein. Samples of the subject's blood are collected at timed intervals and counted for beta and gamma activity. Time concentration curves for each isotope are constructed. The capillary permeability--surface area product is calculated from the extraction pattern for [14C]urea. Extravascular lung water is calculated from the extraction pattern of tritiated water and cardiac output is calculated from the inverse of the area under the 51Cr curve. Normal reference curves are constructed for all subject groups. Significant changes occurred in capillary-permeability surface area product and extravascular lung water in various experimental models producing injury, in the patient population manifesting adult respiratory distress syndrome, and in those patients who have received cardiopulmonary transplants. The multiple-indicator dilution technique represents a sensitive tool for evaluating pulmonary vascular changes.

The quantitative evaluation of acute lung injury

The lung represents a complex barrier between air and blood. Subtle changes in the permeability of this barrier can be brought about by injury and only later do they become clinically and radiologically detectable. Techniques using radioactive traces offer a way of quantifying the degree of lung injury and so will aid the development of new forms of therapy.

The use of crystalloidal and colloidal solutions for volume replacement in hypovolemic shock

A wide variety of colloidal and crystalloidal fluids, as well as blood and blood products, are available to the clinician for treatment of the hypovolemic patient. These fluids vary with respect to the size, shape, and concentrations of electrolytes, colloidal molecules, and/or cellular components, duration of volume-expanding effects, incidence of allergic reactions, and effect on the coagulation system. When these fluids are administered intravenously, their distribution in the vascular, interstitial, and cellular compartments can be predicted from fundamental physiological principles as well as from the results of laboratory and clinical research. It is thus recognized that colloidal fluids and blood provide more rapid expansion of the intravascular space when compared with crystalloidal fluids. Similar volumes of crystalloidal fluids more rapidly expand the interstitial and intracellular spaces. These principles guide therapy in hypovolemic shock. A logical decision regarding intravenous fluid therapy may be based on the nature of the volume deficit (blood, plasma, or selective protein loss, loss of free water and/or electrolytes) and the predicted changes in cellular and extracellular compartments.

Determinants of diagnostic accuracy in pulmonary scintigraphy for pulmonary capillary protein leak associated with adult respiratory distress syndrome (ARDS): a technical note

Radionuclide assessment of pulmonary capillary protein leak using [99mTc] human serum albumin (99mTc-HSA) was first reported from our laboratory. In this study we investigated the impact of 1) sampling time post tracer injection, and 2) lung region assignment, on diagnostic accuracy between 2 groups (control n = 20 and ARDS n = 20). Each patient received 370 MBq 99mTc-HSA i.v. and was imaged for 45 min. The slope index (SI) [change in lung: heart activity ratio/min] was calculated from 11 computer assigned lung regions for intervals of 5-15 (early [E]) and 15-45 (late [L]) min. The diagnostic accuracy of E vs L SI calculations for the 11 regions was evaluated by stepwise logistic regression. E SI data and L SI data from the lower 1/3 of the lung did not achieve significance for inclusion in the discriminant model (P less than 0.05). In the nine remaining regions L SI was significant. Optimal discrimination was achieved from L SI data obtained from a region confined to the lateral half of the mid 3rd of the lung field (sensitivity 81%, specificity 85%, accuracy 83%). The results confirm that: 1) a late (15-45 min) sampling period and 2) proper region assignment are necessary to maximize accuracy of this technique.

Solute permeability of the alveolar capillary barrier

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Changes in lung vascular permeability after heart-lung transplantation

We have employed multiple indicator dilution techniques (MID) in six patients after heart-lung transplantation to assess changes in the lung vascular permeability-surface area product for urea (PS). Serial PS values for the patients when normalized to the predicted total lung capacity (TLC) in liters, ranged between 1.04 and 6.27 ml/sec/TLC (patient 1), 0 and 2.76 ml/sec/TLC (patient 2), 0.59 and 2.88 ml/sec/TLC (patient 3), 0.13 and 1.23 ml/sec/TLC (patient 4). The elevated values for PS in patient 1 exceed the lethal range described by K.L. Brigham et al. (J. Clin. Invest. 72:339, 1983) for severe ARDS. This strongly suggests a severely increased lung microvascular permeability in this patient possibly secondary to rejection as indicated by endomyocardial biopsy. PS values for surviving patients 2-6 fell well below the corresponding lethal value for ARDS patients. We conclude that PS urea derived from MID provides an indicator of the status of lung microvascular integrity in heart-lung transplant recipients.

Lung vascular transport at controlled pressures with reduced coronary flow in sheep

This study was performed to measure the effects of sustained coronary flow reduction on lung lymph flow and protein clearance at normal and elevated lung microvascular pressures. Eleven halothane-anesthetized sheep were provided with lung lymph and carotid-to-left-anterior-descending coronary artery cannulas. Six sheep (ischemic group) were observed in a protocol of five periods, each of 2 hr duration: baseline, left atrial pressure (PLA) increased by mitral valve obstruction, return to baseline, reduced coronary flow, and reduced coronary flow plus increased PLA. Five sheep (control group) were studied in an identical protocol except that coronary flow was not reduced. PLAS were equal in the second and fifth periods. Lung lymph flow QL and protein clearance (QL times the lymph-to-plasma protein concentration ratio) normalized to second baseline were greater during ischemia than in the comparable control period, and clearance was also greater during the second increased-pressure period. We conclude that reduced coronary flow is related to sustained, significant increases in lung vascular transport at elevated as well as at normal vascular pressures.

Thermal dye measurements of extravascular lung water in critically ill patients. Intravascular Starling forces and extravascular lung water in the adult respiratory distress syndrome

To assess the concurrent influence on extravascular lung water (EVLW) content of the intravascular Starling forces, the pulmonary capillary wedge pressure (PCWP), and the colloid osmotic pressure (COP), we measured EVLW by the thermal green dye technique in 174 patients with and without radiographically defined pulmonary edema; in the former group, patients with cardiac (CPE) and noncardiac (NCPE) causes of pulmonary edema were compared (study A). In 119 patients, EVLW was again measured one to three days later (study B). Patients with CPE demonstrated a significantly lower EVLW (9.3 +/- 3.9 ml/kg) (mean +/- SD) than patients with NCPE (14.5 +/- 4.9 ml/kg; p less than 0.05), despite a higher mean PCWP in the former group (20 +/- 7 mm Hg) than in the latter (12 +/- 6 mm Hg; p less than 0.05). In patients potentially with only a hydrostatic cause of pulmonary edema in study A, regression analysis demonstrated the following: EVLW = 3.2 + 0.30 PCWP (r2 = 0.38; p less than 0.005); and in patients with NCPE, EVLW = 10.9 + 0.304 PCWP (r2 = 0.17; p less than 0.01). In study B the change (delta) in EVLW between the two studies was described as follows: delta EVLW = 0.25 + 0.173 delta PCWP (p less than 0.01) + 0.663 group NCPE (p, not significant) + 0.236 group NCPE X delta PCWP (p less than 0.01). This latter equation indicated that the EVLW content manifested a greater change with concurrent alterations in the PCWP in patients with NCPE than was found in patients with only a hydrostatic influence to EVLW formation. Therefore, NCPE is characterized by a greater measurable thermal green dye EVLW than is observed in CPE at any given PCWP, and the PCWP synergistically influences EVLW accumulation in both CPE and NCPE.

Colloids vs. crystalloids--a continuing controversy

The crystalloid vs. colloid controversy is based on a disagreement as to the most effective, safest, and most economical method of maintaining an effective plasma volume in shock patients. This review discusses Starling's law of fluid movement, with a definition of each term in the normal physiological state, and presents examples of how each component of Starling's law differs in the two major types of pulmonary edema: (1) cardiogenic and (2) noncardiogenic. The colloid-crystalloid literature is reviewed briefly with an emphasis on the major studies that support each side, and the deficiencies in each study. The arguments supporting each side of the crystalloid-colloid debate are then listed, with a summary that demonstrates the areas of agreement between the two schools of thought on fluid resuscitation. Each major colloid (albumin, dextran, hetastarch) and a representative crystalloid (lactated Ringer's) are discussed in terms of their chemistry; pharmacology and indications; and precautions, adverse reactions, and side effects. A table is included that summarizes the available products' data regarding composition, volume expansion, duration of expansion, half-life, metabolism, elimination, precautions, adverse reactions, and dose.

Changes in lung function after routine exposure manipulations during thoracotomy

The effect of manual retraction and bronchial occlusion upon right lung function during a 2-hr thoracotomy was evaluated in sheep. Group 1 (seven sheep) underwent manual lung retraction. Group 2 (seven sheep) underwent right bronchial occlusion. Group 3 (seven sheep) served as controls. Radioisotopic indicators (51Cr-RBC, 125I-albumin, [14C]urea, 3H2O) were used to assess changes in capillary permeability-surface area product (PS-urea), extravascular lung water (VE), and intravascular blood volume (Vv). Lung water was further quantified by gravimetric technique. Pulmonary vascular resistance increased following thoracotomy in both groups (34% Group 1, 66% Group 2) and compliance decreased (16% Group 1, 33% Group 2). Mean right lung shunt increased in Group 1 from 17 to 37% (P less than 0.05) and for Group 2 from 18 to 36% (P less than 0.02). A reduction (greater than 25%) in both groups for PS-urea and VE occurred (P less than 0.05). The fall in PS-urea and VE and the increase in PVR indicate a reduction in the right lung perfusion for both groups. It is concluded that a similar marked reduction in ventilation, perfusion, and V/Q occurred after reexpansion whether the lung was retracted or the bronchus occluded.

Correlation of oxygenation with vascular permeability-surface area but not with lung water in humans with acute respiratory failure and pulmonary edema

We used a single-pass multiple tracer technique to measure cardiac output, extravascular lung water (EVLW) and lung vascular [14C]urea permeability-surface area (PSu) in 14 patients with acute respiratory failure and pulmonary edema. All patients had increased EVLW, but EVLW in the 10 surviving patients (0.26 +/- 0.06 SE ml/ml total lung capacity [TLC]) was not significantly different from that in the five patients who died (0.22 +/- 0.05). EVLW did not correlate with intravascular pressures or with alveolar-arterial oxygen pressure difference (A-aDO2). PSu was lower in surviving patients (0.50 +/- 0.16 SE ml/s X liter TLC) than in patients who died (3.44 +/- 0.36; P less than 0.05) and also lower than in previously reported data in patients with normal PSu. PSu correlated significantly with A-aDO2. Serial studies showed that PSu returned from a low value toward normal in a patient who survived but remained high in a patient who died. We conclude that the amount of edema in the lungs measured by indicator methods was not the principal determinant of either the magnitude of oxygenation defect or survival in the patients studied. We interpret the low PSu in surviving patients as decreased surface area and infer that the ability of the lung circulation to reduce perfusion of damaged and edematous areas was important in preserving oxygenation. A high PSu, presumably reflecting perfusion of areas with increased permeability, was a sign of especially poor prognosis. Multiple tracer techniques for measuring lung vascular PSu may help to define the pathogenesis and to evaluate therapies of acute lung injury in humans. Such measurements may be a more useful clinical tool than measurements of lung water in patients with acute respiratory failure and pulmonary edema.

Radionuclide evaluation of lung trauma

Nuclear medicine imaging procedures can play a significant role in evaluating the pulmonary complications that are seen in trauma patients. A quantitative method for measuring increased pulmonary capillary permeability that uses Tc-99m HSA allows early diagnosis of acute respiratory distress syndrome (ARDS) and accurately differentiates this condition from pneumonia or cardiogenic pulmonary edema. This technique may be of great value in following the response to therapy. The use of 133Xe to diagnose inhalation injury remains an important diagnostic tool, particularly at hospitals with specialized burn units. Regional decreases in ventilation-perfusion images reliably localize aspirated foreign bodies. Radionuclide techniques that are used to demonstrate gastropulmonary aspiration remain controversial and require further clinical evaluation. Pulmonary perfusion imaging, although nonspecific, may provide the earliest clue for correct diagnosis of fat embolism, air embolism, contusion, or laceration. Furthermore, the possibility of perfusion abnormality due to these uncommon conditions must be remembered whenever trauma patients are evaluated for pulmonary thromboembolism with scintigraphy. Occasionally, liver or spleen scintigraphy may be the most appropriate procedure when penetrating chest trauma also involves these subdiaphragmatic organs.

Single-tracer technique to evaluate pulmonary edema and its application to detect the effect of hexamethylene diisocyanate trimer aerosol exposures

Two hours after a four-hour exposure to hexamethylene diisocyanate trimer (HDIt) aerosol between 2.5 and 39 mg/m3, mice were injected iv with 51Cr-EDTA (chromium ethylenediaminetetraacetate). Ten minutes later the lung was lavaged. A larger amount of 51Cr-EDTA was detected in the lung lavage of HDIt mice than of controls in a concentration-related fashion. The concentration-response curve was shifted to the left compared with that constructed using lung weight increase as response. Kinetic studies of the plasma level of 51Cr-EDTA revealed a three-exponential profile in normal mice, and similar plasma levels were obtained with mice exposed to 18-24 mg/m3 HDIt. However, both the amount of 51Cr-EDTA in the alveolar space and concentration in the pulmonary extravascular compartment were higher in HDIt-exposed mice than in controls. The data of 51Cr-EDTA distribution in the lung were fitted with a three-compartment model. According to the model, HDIt exposures increase the permeability constants of 51Cr-EDTA transport into the alveolar space from blood which accounts for the larger amount of 51Cr-EDTA in lung lavage of HDIt-exposed mice. This 51Cr-EDTA injection and lung lavage technique is a sensitive method for detecting pulmonary edema.

Clinical studies of measuring extravascular lung water by the thermal dye technique in critically ill patients

We measured extravascular lung water (EVLW) by the thermal-dye technique in a broad group of critically ill patients who had either acute cardiac or noncardiac illnesses. A portable AP supine chest roentgenogram, reviewed blindly, was used to classify patients as to the presence or absence of pulmonary edema; by clinical history we categorized patients into either a cardiac or noncardiac (ie, ARDS) group. With a normal chest roentgenogram, the mean EVLW was 5.6 +/- 1.8 ml/kg, and the pulmonary capillary wedge pressure (PCWP) was 11.3 +/- 5.3 mm Hg (mean +/- SD). In contrast, patients with pulmonary edema on a cardiac basis had a mean EVLW of 10.2 +/- 3.1 ml/kg (mean PCWP, 20.5 +/- 8.2 mm Hg), while patients with clinically defined noncardiac pulmonary edema and a normal PCWP (11.6 +/- 5.7 mm Hg) had a mean EVLW of 15.8 +/- 4.6 ml/kg, significantly higher than in the cardiac group (p less than 0.001). On a severity system of 014, the EVLW increased in parallel to the severity of the chest radiologic appearance of edema in both the cardiac (r2 = .44; p less than 0.001) and noncardiac (r2 = .59; p less than 0.001) patients. This study defined a normal range of thermal-dye EVLW in critically ill patients without radiologic evidence of pulmonary edema. We further demonstrated the increased pulmonary microvascular permeability of noncardiac pulmonary edema compared with cardiac edema by the greater EVLW at normal microvascular hydrostatic pressures in the former group.

Concepts in the pharmacologic and nonpharmacologic support of cardiovascular function in critically ill surgical patients

The critically ill surgical patient requires close clinical, biochemical, and hemodynamic monitoring to define the right timing as well as the proper type of therapeutic intervention. Although many factors are available for monitoring, O2 delivery and extraction are two of the most important, since the enhanced metabolic demands of the stressed patient dictate a need to maintain greater than normal values to ensure survival. In other situations, primary therapy of the blood pressure, the PCWP, or other indices may take temporary precedence in the choice of therapeutic agents. Regardless of the means used to optimize O2 delivery, scrutiny of the consequences of therapy is equally important. Above all, any therapeutic intervention does not negate the need to treat the primary underlying process expeditiously.

Effects of red cell exchange on calculated sheep lung vascular permeability to 14C-urea and 14C-thiourea

We performed fourteen experiments on sheep to determine whether or not erythrocytes tracer transport alters the calculated value of capillary tracer permeability surface area. In each set of experiments 14C-urea or 14C-thiourea was equilibrated with: (1) a whole blood sample; (2) saline alone, and (3) packed erythrocytes alone. Aliquots of each of these samples were injected separately into the superior vena cava of sheep and multiple indicator data collected from the aorta. Lung urea or thiourea microvascular permeability surface area (PS) was calculated for each set of data using the integral extraction method. These results were compared to the predictions of a detailed theory of microvascular transport which included red cell effects. As predicted by the theory, only small differences were found between urea PS calculations based on pre-equilibrated blood or plasma injectates. When 14C-urea in the injectate was confined to red cells, the average PS calculation was approximately 60% of the average plasma-equilibrated value (also predicted by theory). This ratio was substantially lower (25%) when 14C-thiourea was used as an indicator, suggesting that the red cell membrane, rather than the microvascular barrier, limits thiourea exchange. We conclude that a finite red cel-plasma urea exchange rate does not significantly influence the calculation of lung vascular PS when the injected blood is equilibrated with urea prior to its introduction into the vascular system.

Role of longitudinal diffusion in the extravascular pulmonary space on parameter estimates derived from data of multiple indicator dilution

A mathematical model of transcapillary exchange has been developed that considers in detail the role of axial diffusion in the extravascular tissue region on estimates of such physiological parameters as lung water (VE) and pulmonary capillary permeability-surface area products (PS), obtained from multiple indicator dilution studies. The experimental cases considered correspond to two animal models of pulmonary oedema in which the integrity of the pulmonary capillary membrane is disrupted and the effects of extravascular axial diffusion may be important. A novel feature of the computational scheme is the use of an Array Processor in the solution of the governing equations, initial and boundary conditions. Computer time is reduced to 2-3 min for parameter identification, thereby allowing a wide range of values for extravascular axial diffusion coefficients (D'/L2) to be studied at little computational expense. The results indicate that diffusion in the extravascular region does not influence parameter estimates for PS to urea. A statistical correlation is suggested between values for VE, PS to water, and D'/L2.

The exchange of small molecules as a measure of normal and abnormal lung microvascular function

Evidence exists for the utility of measures of small-molecule exchange in assessing the normal and abnormal transport status of the lung vasculature. The evidence for the usefulness of PS for 14C-urea is: 1. PSu compares to other small molecules as would be expected from free-diffusion coefficients. 2. The extraction of 14C-urea decreases with increase flow as would be expected of a diffusion-limited indicator. 3. PSu is unaffected by moderate pressure increase, it increases when lymph protein flow indicated permeability increase, and it decreases when surface area is reduced. 4. Lung injuries such as E. coli endotoxemia in sheep and ARDS in patients can both reduce PSu, presumably through surface area reduction, and increase PSu, through increased permeability. Two events that accompany clinically important vascular injury complicate the interpretation of lung MT curves. These events are surface area loss and heterogeneity of flow and transport properties in the lung. Additional work is needed to precisely measure these variables and assess their importance.

Release of angiotensin converting enzyme by the lung after Pseudomonas bacteremia in sheep

We studied release of angiotensin-converting enzyme (ACE) by the lung after acute injury associated with an increase in pulmonary vascular permeability. In eight adult sheep with chronic lung lymph fistulas, we measured lymph flow (QL), and both ACE activity and total protein content in lymph and plasma under base-line conditions and during 24 h after an infusion of live pseudomonas organism. Under base-line conditions, ACE activity in plasma was 4.93 +/- 0.43 U/ml (mean +/- SEM). The [lymph]/[plasma] ([L]/[P]) ratio for ACE was 0.93 +/- 0.18, compared with a ratio of 0.79 +/- 0.08 for albumin (mean +/- SD). We estimated the molecular weight of ovine ACE to be 145,000 by gel chromatography. Predicted [L]/[P] ratio for a molecule this size is 0.51. Thus, a substantial fraction of ACE activity detected lung lymph under base-line conditions (11.1 +/- 6.2 U/h; mean +/- SD) originated in the lung, and did not diffuse passively from plasma. After pseudomonas infusion, endothelial injury was demonstrated by a rise in pulmonary vascular clearance for total protein (Crp = QL X [L]/[P]). Crp = 3.1 +/- 0.6 ml/h before pseudomonas bacteremia, and rose to 6.7 +/- 1.2 ml/h by 2 h after onset of the infusion (means +/- SEM, p less than 0.05). Crp remained significantly elevated for at least 10 h after the infusion. Release of ACE into lung lymph doubled after acute lung injury and equaled 22.3 +/- 13.8 U/h at 4 h after onset of the infusion. ACE secretion into lung lymph had returned to baseline levels by 24 h after bacteremia. We did not observe a significant rise in plasma ACE activity after acute lung injury. Pseudomonas bacteremia in sheep results in acute, reversible lung injury associated with increased pulmonary vascular permeability, and increased release of ACE by the lung. Failure to detect a rise in plasma ACE content might result from dilution in the large vascular pool or rapid catabolism of the enzyme at some site distant from the lung.

Noninvasive measurement of pulmonary transvascular protein flux in normal man

Onset of lung edema is usually associated with increase in the pulmonary transvascular flux of water and proteins. Clinical measurement of these parameters may aid in early diagnosis of pulmonary edema, and allow differentiation between "cardiogenic" and "noncardiogenic" types base on the magnitude of the detected changes. We have previously described a noninvasive method for estimating transvascular protein flux in lung (Gorin, A. B., W. J. Weidner, R. H. Demling, and N. C. Staub, 1978. Noninvasive measurement of pulmonary transvascular protein flux in sheep. J. Appl. Physiol. 45: 225-233). Using this method we measured the net transvascular flux of [113mIn]transferrin (mol wt, 76,000 in lungs of nine normal human volunteers. Plasma clearance of [113In]transferrin occurred with a T1/2 = 7.0 +/- 2.6 h (mean +/- SD). The pulmonary transvascular flux coefficient, alpha, was 2.9 +/- 1.4 X 10(-3) ml/s (mean +/- SD) in man, slightly greater than that previously measured in sheep (2.7 +/- 0.7 X 10(-3) ml/s; mean +/- SD). The pulmonary transcapillary escape rate is twofold greater than the transcapillary escape rate for the vascular bed as a whole, indicating a greater "porosity" of exchanging vessels in the lung than exists for the "average" microvessel in the body. Time taken to reach half-equilibrium concentration of tracer protein in the lung interstitium was quite short, 52 +/- 13 min (mean +/- SD). We have shown that measurement of pulmonary transvascular protein flux in man is practical. The coefficient of variation of measurements of alpha (between subjects) was 0.48, and of measurements of pulmonary transcapillary escape rates was 0.39. In animals, endothelial injury commonly results in a two- to threefold increase in transvascular protein flux. Thus, external radioflux detection should be a suitable means of quantitating lung vascular injury in human disease states.