Noninvasive measurement of pulmonary transvascular protein flux in normal man

Pulmonary perfusion imaging and delayed imaging to measure pulmonary capillary permeability in pulmonary contusion

PURPOSE

Explore the application value of pulmonary perfusion imaging and delayed imaging for evaluating pulmonary capillary permeability.

MATERIALS AND METHODS

After establishing a rat model of pulmonary contusion, changes in the metabolic index of technetium-99m macroaggregated albumin (99mTC-MAA) in the lungs of model rats were evaluated for two consecutive days. 99mTC-MAA metabolic indices of rat lungs with pulmonary contusion of varying severity (mild, moderate, and severe) were correlated with lung wet/dry weight ratio (W/D) and Evans blue extravasation. Finally, the method was validated in patients with pulmonary contusion and one healthy volunteer.

RESULTS

The 99mTC-MAA metabolic index was 23.56% ± 2.44% in healthy control (HC) rat lung, 8.56% ± 3.42% immediately after lung contusion (d0), 8.35% ± 3.20% after 1 day (d1), and 17.45% ± 6.44% after 2 days (d2); indices at d0 and d1 were significantly higher than those at HC (P < 0.05). The metabolic index of 99mTC-MAA in lung had significant negative correlations with W/D (r = -0.8025; P = 0.0092) and Evans blue extravasation (r = -0.9356; P = 0.0002). Metabolic and oxygenation indices of 99mTC-MAA exhibited a significant positive linear correlation in patients with pulmonary contusion (r = 0.8925; P = 0.0416).

CONCLUSION

Pulmonary perfusion and delayed imaging of 99mTC-MAA have potential value for evaluating pulmonary capillary permeability.

The lung permeability index: a feasible measurement of pulmonary capillary permeability

BACKGROUND

We performed this study to determine the pulmonary capillary permeability (PCP) measuring radiolabeled human serum albumin leakage into the lung. The objective was to use PCP to differentiate between cardiogenic and non-cardiogenic pulmonary edema etiologies.

METHODS

We conducted this study in 10 patients admitted to the intensive care unit who had recently developed bilateral pulmonary infiltrates and required hemodynamic monitoring. In these patients we determined the association among the lung permeability index, cardiac output, pulmonary capillary wedge pressure, myocardial performance index, and the protein content of the bronchoalveolar lavage as expressed by bronchoalveolar lavage (BAL) total protein and BAL-to-serum protein ratio. Twenty mCi of technetium-labeled albumin was injected and measure in the heart and the lung at 10 and 180 min post-injection. Lung and heart uptake ratios as well as the lung permeability index were calculated.

RESULTS

We found a good correlation between the lung permeability index and both the myocardial performance index (cardiac output/pulmonary capillary wedge pressure) and the total protein content of the bronchoalveolar lavage fluid.

CONCLUSION

The lung permeability index is a feasible, noninvasive estimation of the pulmonary capillary permeability.

Simple vs complex radionuclide methods of assessing capillary protein permeability for diagnosing acute respiratory distress syndrome

PURPOSE

Using injection of gallium Ga 67 transferrin, technetium Tc 99m red cells, probes over the lungs, and blood samples, a pulmonary leak index (PLI) and pulmonary transcapillary escape rate (PTCER) for transferrin can be measured. This may help differentiating between cardiogenic pulmonary edema (CPE) and permeability (noncardiogenic) pulmonary edema of the acute respiratory distress syndrome (ARDS). The purpose of the study was to evaluate the relative importance of red cell labeling, blood sampling, and probe measurements in this assessment.

MATERIALS AND METHODS

Analysis of radionuclide data obtained in consecutive patients with radiographic evidence for pulmonary edema, classified as ARDS (n = 13), CPE (n = 8), or mixed (n = 5), was performed. The latter patients met ARDS criteria except for a high pulmonary capillary wedge pressure.

RESULTS

The PLI, PTCER, and the (67)Ga-lung/blood radioactivity increase (without (99m)Tc-red cell data) were specific and sensitive indices to differentiate ARDS/mixed from CPE. The blood transcapillary escape rate (TER) of (67)Ga-transferrin was about 2- to 6-fold higher in ARDS and mixed than in CPE. The TER had similar diagnostic value as the PLI, PTCER, and the (67)Ga-lung/blood radioactivity ratio increase.

CONCLUSIONS

The diagnostic value of the simple blood TER of (67)Ga-transferrin is similar to that of complex methods, using (99m)Tc-red cells and probe measurements over the lungs, because the complex methods largely depend on the blood TER. Simplification of the method without red cell labeling and probes may facilitate bedside use to diagnose permeability edema of ARDS, particularly in the absence of a pulmonary artery catheter.

Usefulness of pulmonary vascular leakiness assessment in interstitial pneumonitis

STUDY OBJECTIVE

Pulmonary vascular leakiness of (67)Ga-circulating transferrin in interstitial pneumonitis (IP) was estimated by our previously described method, and its ability to evaluate disease activity was compared with conventional (67)Ga scintigraphy.

DESIGN

Using 30-min dynamic scanning data after IV injection of (67)Ga citrate, the exponential equilibration coefficient of (67)Ga between the intravascular and pulmonary interstitial compartments was calculated and defined as the leak index (LI). Pulmonary (67)Ga uptake was assessed by gallium index, determined by conventional static images taken 48 h after (67)Ga citrate injection.

SETTING

Hospitalized patients.

PARTICIPANTS

The study population consisted of 17 control patients and 20 patients with IP.

RESULTS

The mean LI in patients with IP was significantly higher than in the control group (p < 0.0001), whereas no significant increase in gallium index was noted between the IP group and the control group. No significant correlation was found between gallium index and LI among all study participants. Mean LI in patients with active IP was significantly higher than in patients with stable IP (p = 0.0024).

CONCLUSIONS

An increase in pulmonary vascular leakiness was found in patients with IP. LI may be useful to assess the disease activity.

High-altitude pulmonary edema is initially caused by an increase in capillary pressure

BACKGROUND

High-altitude pulmonary edema (HAPE) is characterized by severe pulmonary hypertension and bronchoalveolar lavage fluid changes indicative of inflammation. It is not known, however, whether the primary event is an increase in pressure or an increase in permeability of the pulmonary capillaries.

METHODS AND RESULTS

We studied pulmonary hemodynamics, including capillary pressure determined by the occlusion method, and capillary permeability evaluated by the pulmonary transvascular escape of 67Ga-labeled transferrin, in 16 subjects with a previous HAPE and in 14 control subjects, first at low altitude (490 m) and then within the first 48 hours of ascent to a high-altitude laboratory (4559 m). The HAPE-susceptible subjects, compared with the control subjects, had an enhanced pulmonary vasoreactivity to inspiratory hypoxia at low altitude and higher mean pulmonary artery pressures (37 +/- 2 versus 26 +/- 1 mmHg, P<0.001) and pulmonary capillary pressures (19 +/- 1 versus 13 +/- 1 mmHg, P < 0.001) at high altitude. Nine of the susceptible subjects developed HAPE. All of them had a pulmonary capillary pressure >19 mm Hg (range 20 to 26 mmHg), whereas all 7 susceptible subjects without HAPE had a pulmonary capillary pressure < 19 mm Hg (range 14 to 18 mm Hg). The pulmonary transcapillary escape of radiolabeled transferrin increased slightly from low to high altitude in the HAPE-susceptible subjects but remained within the limits of normal and did not differ significantly from the control subjects.

CONCLUSIONS

HAPE is initially caused by an increase in pulmonary capillary pressure.

Pulmonary endothelial permeability and circulating neutrophil-endothelial markers in patients undergoing esophagogastrectomy

OBJECTIVE

Esophagogastrectomy is an established surgical treatment for esophageal malignancy. The postoperative period may be complicated by the development of acute lung injury syndromes and thus, may provide a useful model in which to study the early pathogenic mechanisms of inflammatory lung injury.

DESIGN

Open, prospective study.

SETTING

High dependency and intensive therapy units.

PATIENTS

Eight healthy male volunteers and 20 patients in the early postoperative period

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The lung protein accumulation index (PAI) of radiolabeled transferrin was determined by using a portable, double-isotope system. The following circulating inflammatory markers-thought to reflect neutrophil-endothelial activation and injury including circulating neutrophil elastase-soluble L-, E-, and P-selectins and thrombomodulin and von Willebrand factor antigen were assayed from venous blood samples The PAI for healthy volunteers was median -0.5 (range, -1.73 to 0.27) x 10(-3)/min and for patients undergoing esophagogastrectomy -0.005 (range, -1.53 to 2.28) x 10(-3)/min. There was no statistical difference between the two groups. In the postesophagogastrectomy group, a significant elevation in circulating levels of neutrophil elastase, soluble P- and E-selectin, thrombomodulin, and von Willebrand factor antigen were observed relative to the control group but only circulating plasma elastase demonstrated a significant correlation with the PAI (r2 = .23, p =.03).

CONCLUSIONS

The data suggest patients undergoing esophagogastrectomy develop a inflammatory response but this is not a surrogate of permeability and other factors are likely to determine persistent injury to the alveolar-capillary barrier function in this patient group.

In vivo measurement of lung capillary-alveolar macromolecule permeability by saturation bronchoalveolar lavage

OBJECTIVE

Measurement of capillary-alveolar permeability to fluorescein isothiocyanate-dextran (FITC-D) (molecular mass, 71,300 daltons) by a sequential bronchoalveolar lavage (BAL) technique.

DESIGN

Animal research.

SETTING

The Department of Physiology at a scientific and medical university.

SUBJECTS

Nine anesthetized and mechanically ventilated dogs.

INTERVENTIONS

Two separate experiments were performed in each subject-an initial control experiment followed by an oleic acid-induced lung injury. The indicator was administered at constant blood concentration before serial BAL including eight fluid instillation-recovery cycles.

MEASUREMENTS

Plasma to BAL solute clearance at saturation (capillary-alveolar clearance at saturation, mL/min) was calculated and normalized to lavage fluid volume (measured by 1251 serum albumin dilution) to obtain a transport rate (TR) constant.

MAIN RESULTS

TR for FITC-D70 was 4.0+/-0.8 and 46.1+/-18.1 x 10(-5) x min(-1) in control and injured lung, respectively (p < .02). Capillary-alveolar clearance of FITC-D70 was not affected by the lavage procedure itself. TR reflected essentially epithelial permeability in normal lung and combined epithelial and endothelial permeability in injured lung. A significant correlation was found between cardiac output and TR in injured lung.

CONCLUSIONS

Saturation BAL allowed us to estimate capillary-alveolar macromolecule permeability in vivo in dogs. Further study may allow bedside evaluation of lung injury by BAL in patients.

Positron emission tomography measurements of pulmonary vascular permeability with Ga-68 transferrin or C-11 methylalbumin

OBJECTIVE

To compare estimates of pulmonary endothelial barrier integrity obtained using two different tracer proteins.

DESIGN

Measure the pulmonary transcapillary escape rate with gallium (Ga)-68 labeled transferrin (PTCER(tf)) and positron emission tomography (PET) imaging and compare the results to similar measurements obtained with C-11 labeled methylalbumin (PTCER(alb)).

SETTING

Laboratory investigation.

SUBJECTS

Mongrel dogs.

INTERVENTIONS

No intervention in one group of dogs (n = 3); oleic-acid induced lung injury in another set (n = 4).

MEASUREMENTS AND MAIN RESULTS

Although PTCER(tf) was consistently higher than PTCER(alb) (mean difference: 50 x 10(-4)/min), the overall correlation between the two methods, after normalizing for differences in regression slope and intercept among the individual dogs, was excellent (r2 = .67).

CONCLUSION

The data support the continued use of PET and Ga-68 transferrin as an appropriate means of evaluating and quantifying lung injury.

Radionuclide assessment of pulmonary microvascular permeability

The literature has been reviewed to evaluate the technique and clinical value of radionuclide measurements of microvascular permeability and oedema formation in the lungs. Methodology, modelling and interpretation vary widely among studies. Nevertheless, most studies agree on the fact that the measurement of permeability via pulmonary radioactivity measurements of intravenously injected radiolabelled proteins versus that in the blood pool, the so-called pulmonary protein transport rate (PTR), can assist the clinician in discriminating between permeability oedema of the lungs associated with the adult respiratory distress syndrome (ARDS) and oedema caused by an increased filtration pressure, for instance in the course of cardiac disease, i.e. pressure-induced pulmonary oedema. Some of the techniques used to measure PTR are also able to detect subclinical forms of lung microvascular injury not yet complicated by permeability oedema. This may occur after cardiopulmonary bypass and major vascular surgery, for instance. By paralleling the clinical severity and course of the ARDS, the PTR method may also serve as a tool to evaluate new therapies for the syndrome. Taken together, the currently available radionuclide methods, which are applicable at the bedside in the intensive care unit, may provide a gold standard for detecting minor and major forms of acute microvascular lung injury, and for evaluating the severity, course and response to treatment.

The effect of cardiopulmonary bypass on intestinal and pulmonary endothelial permeability

STUDY OBJECTIVE

To quantify simultaneously the pulmonary and gastrointestinal (GI) damage that occurs during uncomplicated surgery requiring cardiopulmonary bypass (CPB), and to examine the relationships between markers of such damage.

DESIGN

Prospective, open.

SETTING

Adult ICU of a national referral hospital.

PATIENTS

Twenty patients undergoing elective CPB surgery.

MEASUREMENTS AND RESULTS

Pulmonary vascular injury was assessed using the protein accumulation index (PAI), a double isotope technique specific for high permeability pulmonary edema. The relationships of the PAI with percent neutrophils in bronchoalveolar lavage (BAL), serum, and BAL myeloperoxidase (MPO), and bypass time were examined. Splanchnic vascular injury was assessed using tonometry to measure intramucosal pH (pHi) and the ratio of absorbed lactulose to L-rhamnose (L/R ratio) to determine gut mucosal permeability. Positive correlations were observed between bypass time and PAI (r = 0.64, p < 0.01), percent neutrophils in the postoperative BAL and PAI (r = 0.51, p < 0.05), and postoperative serum MPO and PAI (r = 0.77, p < 0.001). The L/R ratio rose significantly following CPB from 0.04 +/- 0.01 in controls to 0.48 +/- 0.05 (p < 0.0001). The L/R ratio in patients who developed a low pHi was 0.59 +/- 0.06 compared with 0.32 +/- 0.07 in those whose pHi remained normal (p < 0.05). No significant correlation between bypass time and pHi (r = -0.3, p = 0.33), bypass time and L/R ratio (r = 0.27, p = 0.26), PAI and L/R ratio (r = 0.2, p = 0.42), PAI and pHi (r = -0.34, p = 0.16), postoperative serum MPO and L/R ratio (r = 0.03, p = 0.90), or postoperative serum MPO and pHi (r = -0.10, p = 0.67) could be demonstrated.

CONCLUSIONS

Pulmonary and GI injury are detectable following uncomplicated CPB. The absence of any relationship between the respective markers of dysfunction suggests that differing pathologic processes are responsible.

Pulmonary endothelial permeability in patients with severe lung injury. Clinical correlates and natural history

STUDY OBJECTIVE

To establish the natural history of lung injury in adult respiratory distress syndrome (ARDS) in terms of increased pulmonary vascular permeability. Secondly, to relate such changes to the number of neutrophils in bronchoalveolar lavage (BAL) and a clinical score of the severity of lung injury.

DESIGN

Prospective, open.

SETTING

Adult intensive care unit of a tertiary (national) referral hospital.

PATIENTS

Fourteen patients meeting accepted diagnostic criteria for ARDS.

INTERVENTIONS

Mechanical ventilatory support. Conventional intensive care and support for other failed organ systems as appropriate.

MEASUREMENTS AND RESULTS

Pulmonary vascular permeability was estimated using a dual isotope technique (protein accumulation index [PAI]), neutrophil numbers by BAL and the severity of ARDS by the lung injury score (LIS). The PAI and LIS were measured simultaneously on three occasions as far apart as possible during the course of the illness. A single BAL was performed immediately after one of the three PAI/LIS measurements, the precise timing being dictated by the clinical stability of each patient. Fourteen patients (8 male; age range, 19 to 69 years) were studied, 1.40 +/- 0.16, 11.36 +/- 1.79, and 20.90 +/- 2.30 days after the onset of ARDS (mean +/- SEM). Six patients died. The PAI (normal range, 0 to 1.0 x 10(-3)) was 2.81 +/- 0.39, 2.94 +/- 0.48, and 2.80 +/- 0.87; and LIS (severe injury > or = 2.5) was 2.18 +/- 0.25, 2.48 +/- 0.14, and 2.06 +/- 0.27, respectively. The BAL neutrophil content was 54.09 +/- 8.89. There were significant positive correlations between PAI and LIS (r = 0.73, p < 0.001) and PAI and BAL neutrophil content (r = 0.81, p < 0.001).

CONCLUSIONS

These data suggest that increased pulmonary vascular permeability persists throughout the course of ARDS and is related to a clinical score of injury severity and BAL neutrophil content.

Effect of varying the molecular weight of the MR contrast agent Gd-DTPA-polylysine on blood pharmacokinetics and enhancement patterns

The effects of varying the molecular weight of gadolinium-DTPA (diethylenetriaminepentaacetic acid)-polylysine, a macromolecular magnetic resonance (MR) imaging contrast agent, on blood pharmacokinetics and dynamic tissue MR imaging signal enhancement characteristics were studied in normal rats. Blood elimination half-life, total blood clearance, volume of the central compartment (Vcc) and the steady-state distribution volume (Vssd) were calculated for four Gd-DTPA-polylysine polymers with average molecular weights of 36, 43.9, 139, and 480 kd and compared with corresponding values for Gd-DTPA (0.57 kd) and Gd-DTPA-albumin (92 kd). Blood elimination half-life increased seven-fold with an increase in molecular weight from 36 to 480 kd. The Vcc values for all polylysine polymers did not differ significantly from the Vcc value for Gd-DTPA-albumin but were significantly smaller than the Vcc value for Gd-DTPA. The Vssd value for Gd-DTPA did not differ significantly from the Vssd value for the 36- and 43.9-kd polymers but was significantly larger than the Vssd values for the 139- and 480-kd polymers and for Gd-DTPA-albumin. On T1-weighted coronal spin-echo MR images, dynamic signal enhancement profiles in liver and kidney for the 36-, 43.9-, and 480-kd Gd-DTPA-polylysine chelates corresponded to the blood pharmacokinetic data. Increasing molecular weight of Gd-DTPA-polylysine formulations substantially slows blood clearance and produces a prolonged, almost constant tissue signal enhancement for the 60-minute observation period.

First-pass studies of acute lung injury

Mild hydrochloric acid was introduced to a caudal lung section in each of eight dogs to induce injury. Transits of 99mTc-labeled red blood cells (RBC) and [123I]iodoantipyrine (IAP) injected intravenously were recorded by a scintillation camera. Lungs and blood samples were analyzed post-mortem. Peak-to-equilibrium ratios (P/E) of RBC time-activity curves were computed to be 3.83 +/- 0.54 for the control lung, 2.58 +/- 0.55 for the injured lung and 2.23 +/- 0.58 for the injured caudal section. For IAP, the respective results were 3.78 +/- 0.29, 2.02 +/- 0.18 and 1.77 +/- 0.17. The decrease of P/E in injured areas was attributed to reduced blood flow. Using mean transit times of the tracers, we computed extravascular lung water per unit blood volume to be 0.35 +/- 0.18 for the control lungs and an increased value of 0.68 +/- 0.24 for the injured lungs. These results displayed sensitivity to injury, but were gross underestimates relative to the corresponding values of 2.04 +/- 0.54 and 4.56 +/- 1.85 in post-mortem analyses.

Measurement of capillary permeability to macromolecules by dynamic magnetic resonance imaging: a quantitative noninvasive technique

A simple, linear kinetic model has been developed for the noninvasive assessment of capillary permeability to macromolecules in the rat by dynamic magnetic resonance imaging using albumin-Gd-DTPA. Data required by the model are signal intensity responses from a target tissue and a venous structure such as inferior vena cava before and after bolus intravenous injection of albumin-Gd-DTPA. Additional requirements include an early temporal resolution of approximately one image/min and a blood sample for hematocrit. The model does not require measurement of albumin-Gd-DTPA concentration in either arterial or venous blood. Pilot experiments suggest that this technique is adequate for estimation of the fractional leak rate of macromolecules from plasma to interstitial water as well as tissue plasma volume, the product of which yields a measure of the permeability surface area product of the tissue if the extraction fraction is modest (< 0.2). The technique may be generally applicable to the study of abnormal capillary permeability in humans as well as animals.

Pulmonary granulocyte accumulation is reduced by nebulized corticosteroid in septic pigs

Nebulized beclomethasone dipropionate was administered to 14 anesthetized and artificially ventilated pigs at 6-hourly intervals after infusion of live S. aureus (BDP group). Changes in pulmonary activity from autologous granulocytes labeled with In-111 was detected externally for 12 (n = 8) to 44 h (n = 6). The changes were compared with those in ten pigs (12 h n = 7, 44 h n = 3) subjected to the same insults but given no corticosteroid (placebo group). Serial measurements of blood radioactivity, and cardiac output were performed in animals observed for 12 h. Corticosteroid-treated pigs showed a gradual decline in decay-corrected pulmonary In-111 activity. The placebo group displayed a more varied reaction, but most animals had an increased activity compared to the corticosteroid group. The difference between the groups was significant at 8 h (BDP-group 92% (88-98), placebo-group 107% (97-121), median (lower-upper quartiles), baseline = 100%. P < 0.01, U-test). Blood radioactivity and cardiac output did not differ significantly between the two groups. Nebulized corticosteroid thus diminished pulmonary granulocyte accumulation, which may be of value in the treatment of septic respiratory distress.

Pulmonary endothelial permeability following lung transplantation

During lung transplantation, a number of factors may cause endothelial injury to the donor organ, including ischemia, inadequate preservation, cardiopulmonary bypass, high potassium concentrations, and reperfusion. In this study, protein accumulation index (PAI) was used to assess pulmonary endothelial permeability (PEP) in ten patients immediately after lung transplantation. Six were studied sequentially every other day for ten days postoperatively. The PAI was also measured using the same technique in a group of 11 normal volunteers. Mean PAI x 10(-3)/min +/- (SEM) for ten patients measured within 36 h of transplantation was 1.27 (0.56) compared with 0.45 (0.08) for the normal group (p = 0.09). No correlation was found between preservation time and PAI following reperfusion. Three episodes of lung rejection were observed in two patients during the first ten postoperative days, during which PAI rose to 2.26 (0.26) compared with 0.73 (0.11) for all other studies in the group (p less than 0.01). We conclude that no increase in PEP could be demonstrated after graft reperfusion following lung transplantation as assessed by PAI in this small group of patients. However, further studies may show the technique to be useful in the detection of subsequent episodes of graft rejection.

Pulmonary nuclear medicine

This article reviews the contribution made by nuclear imaging to the assessment, diagnosis and monitoring of patients with respiratory disease. It focuses on several specific areas including the diagnosis of pulmonary embolism, the investigation of intrapulmonary infection and neoplasm and the role of positron emission tomography (PET) scanning.

Changes in pulmonary microvascular permeability accompanying re-expansion oedema: evidence from dual isotope scintigraphy

The pathophysiological mechanism of pulmonary oedema following rapid re-expansion of a collapsed lung is poorly understood. It has been suggested that the period of collapse or subsequent reinflation produces an increase in pulmonary microvascular permeability. To investigate this, the pulmonary accumulation of the plasma protein transferrin was measured by radiolabelling it in vivo with indium-113m. Plasma protein accumulation was calculated after correcting the accumulation of transferrin for changes in intrathoracic blood distribution by simultaneously monitoring technetium-99m labelled red blood cells. Functional images of plasma protein accumulation were constructed for the lung fields on a pixel by pixel basis. Investigations were performed on 14 subjects after drainage of a pleural effusion (n = 9) or evacuation of a pneumothorax (n = 5), and on 11 control subjects. Plasma protein accumulation was greater over the regions of lung re-expansion (-0.1-9.6, mean 2.9 x 10(-3)/min) than over the corresponding region of the contralateral lung (-1.2-0.8, mean 0.01 x 10(-3)/min; p less than 0.001). Patients who had undergone re-expansion procedures also had significantly greater plasma protein accumulation than normal controls. Nine of the 14 patients in the re-expansion group had clearly identifiable areas of increased plasma protein accumulation that corresponded to the part of the lung that had been re-expanded; no regional abnormalities were recorded in the control group. These results suggest that the reinflated lung displays abnormal microvascular permeability.

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.

Acute lung injury monitored with radiolabeled transferrin and lung volume measurements

Anesthetized pigs (n = 12) were given oleic acid (OA) to induce acute lung injury. Three additional pigs were used as uninjured controls. Six of the animals were pretreated with terbutaline before OA infusion. 113mIn-labeled transferrin and 99mTc-labeled erythrocytes were used for tracing of extravascular plasma leakage. A computerized gamma camera supplied image analysis of the radioactivities over the heart and lungs. A lung transferrin index (LTI), which describes the net accumulation of plasma equivalents in the lung, was calculated. OA caused an immediate increase in LTI and concurrent, correlated decreases in functional residual capacity, lung thorax compliance and arterial PO2. LTI was also correlated to the content of plasma equivalents in lung tissue samples and also to the wet weight/dry weight-ratios of the same tissue samples. Finally, LTI was correlated to the calculated plasma loss from the circulation. Changes in all these parameters were correlated to the dose of OA. We conclude that this noninvasive double radioisotope technique can detect plasma protein leakage in lung injury of different degrees. We found no significant anti-edema effect of terbutaline.

The adult respiratory distress syndrome

The adult respiratory distress syndrome is a condition of life-threatening organ failure triggered by blood-borne factors and challenges which arrive via the airways. Vascular damage is a necessary, but often not sufficient criterion for ARDS, which is observed in an acute and chronic form. There is a consensus that neutrophils and their products contribute to the pathogenesis of the syndrome, and that lung vascular tone regulation and endothelial and epithelial cell permeability are affected in ARDS. Whereas the precise roles of individual mediators for the development of ARDS are still ill-defined, a synergism between lipid mediators and other injurious principles is recognized. Chronic ARDS is a proliferative disorder which may require different treatment strategies than acute ARDS. Specific treatment modalities which inhibit the interaction between activated neutrophils and the lung endothelium, and surfactant replacement might have a future as early therapy approaches.

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.

Reduced venous compliance and increased transcapillary escape of protein in insulin-dependent diabetic patients

Lower limb venous compliance and transcapillary escape rate of transferrin were measured in eight normotensive, insulin-dependent male diabetic patients and eight control subjects using a dual isotope technique. Technetium-99m labelled autologous erythrocytes were used to measure venous compliance and to correct for local changes in blood volume, whilst Indium-113m labelled transferrin was used to measure transcapillary escape of protein. The diabetic patients were found to have reduced venous compliance 1.5 (0.7 to 3.4) x 10(-2) mmHg-1 compared with controls 3.2 (2.4 to 4.1) x 10(-2) mmHg-1 (p less than 0.01). The diabetic patients were also found to have greater transcapillary escape of transferrin -2.7 (-1.5 to -5.3) x 10(-3), compared with control subjects -5.2 (-4.1 to -8.1) x 10(-3) (p less than 0.02) in response to increasing hydrostatic pressure. These results show reduced venous compliance in patients with a mean duration of diabetes of 15 years and with only at most, early complications of diabetes, and confirm previous observations showing increased transcapillary escape of protein.

Synthesis of 11C-methylated inulin as a radiopharmaceutical for imaging brain edema and pulmonary edema

11C-methylated inulin, supposedly useful for imaging of brain edema and pulmonary edema, was prepared using cyclotron produced 11CO2. The synthesis consists of the production of 11C-methyl iodide and its coupling with inulin alkoxide sodium in dimethylsulfoxide as solvent. 11C labeled inulin was purified by alcohol precipitation. The radiochemical yield of pure 11C-inulin was 34% of 11CO2 30 min after the end of bombardment. The blood clearance and body distribution of 11C was observed in rabbits after i.v. injection of 11C-inulin. The blood clearance curve was composed of a sum of three exponential functions. The gamma camera image showed that the 11C activity in blood moved quickly to kidneys and urine and a small dose of radioactivity remained persistently in edematous tissues, i.e. the edematous lung tissues produced by oleic acid treatment.

Pulmonary vascular permeability to transferrin in the pulmonary oedema of renal failure

Thirteen patients with renal failure and pulmonary oedema were assessed for evidence of increased pulmonary vascular permeability to protein by a double isotope technique. Comparison was made with 10 patients with cardiogenic pulmonary oedema, 11 healthy volunteers, and 10 patients with the adult respiratory distress syndrome. There was no significant difference in the accumulation of a radiolabelled plasma protein (transferrin) in patients with renal or cardiogenic pulmonary oedema and normal volunteers. Patients with adult respiratory distress syndrome showed significantly greater protein permeability (p less than 0.001). In pulmonary oedema associated with renal failure managed by current regimens there was no evidence of increased permeability to transferrin.

Effects of pH on the stability of the indium-113m blood protein complex and the selective binding of indium-113m to transferrin

Indium-113m (t1/2 = 100 min; gamma-emission of 393 keV) in trace amounts was injected i.v. in rats. Blood was collected by heart puncture 15 min after the injection, and blood plasma was separated by centrifugation. Gel filtration of plasma on Sephadex G-25M equilibrated with glycine/HCl (pH 2.2-3.6), NaHCO3/CO2 (pH 4.0-11.0) glycine/NaOH (pH 8.6-10.6) or sodium acetate/acetic acid (pH 3.0-5.0) was used to separate free indium from indium bound to macromolecular proteins. Determination of radioactivity in eluted fractions showed that more than 85% of the plasma indium was bound to macromolecules at pH values between 5.0 and pH 10.6. However, dissociation of the indium plasma protein complexes occurred at pH values below 5.5, and more than 90% of the indium radioactivity was found in the low molecular weight fraction at pH 2.2. Affinity chromatography using immobilized antibodies to rat transferrin was used to isolate transferrin at pH 7.4 and 5.5. Immunodiffusion and electrophoresis were used to identify the proteins in fractions obtained by affinity chromatography. It was found that the indium-113m activity was correlated with the content of transferrin and that 80%-90% of this activity was found in fractions that had affinity to antitransferrin. These fractions contained transferrin exclusively at pH 7.4, but additional protein fractions of albumin and alpha1-globulin mobility at pH 5.5. At pH 7.4 and 5.5, 10%-20% of the indium activity was detected in molecular fractions that had no affinity to antitransferrin. Immunologic analyses showed that these fractions contained transferrin.(ABSTRACT TRUNCATED AT 250 WORDS)

Solute permeability of the alveolar capillary barrier

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Protein permeability in the adult respiratory distress syndrome. Loss of size selectivity of the alveolar epithelium

Small amounts of plasma protein normally reach the alveolar epithelial surface by a size-selective process that restricts the passage of very large molecules. Size selectivity may be compromised in the lungs of patients with the adult respiratory distress syndrome (ARDS). To assess this question, bronchoalveolar lavage fluid (BALF) from normal volunteers (n = 11), cardiac edema patients (n = 3), and ARDS patients (n = 8) was compared. Mean total protein in ARDS BALF was greater than 12 times the levels in normals or cardiac edema patients. BALF/plasma total protein ratios and measurements of epithelial lining fluid protein also separated the patients groups. The large proteins IgM and alpha 2-macroglobulin were found in ARDS BALF at greater than 90 times the concentrations of normal or cardiac edema fluid. The relationship of distribution coefficient vs. log molecular weight for seven proteins (54,000-900,000 mol wt) hyperbolically increased in normals but was flat in ARDS patients. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a paucity of high molecular weight proteins in normal and cardiac edema BALF, but demonstrated the full spectrum of plasma proteins in ARDS BALF. We conclude that normal size selectivity is preserved in cardiac edema but is destroyed by the alveolar-capillary injury of ARDS.

Beta-2-adrenoceptor agonists as inhibitors of lung vascular permeability to radiolabelled transferrin in the adult respiratory distress syndrome in man

Increased lung vascular permeability leading to increased plasma protein extravasation and accumulation (PPA) is a characteristic feature of acute lung injury. Using a previously described technique, PPA was monitored in the lungs of patients with the adult respiratory distress syndrome (ARDS)--an extreme example of acute lung injury in man. An external radiation probe detector was used to monitor the pulmonary accumulation of the plasma protein transferrin radiolabelled in-vivo with 113mIn. Ten patients with ARDS exhibiting increased PPA indices (greater than 1.0 x 10(-3)/min) were given an intravenous infusion of terbutaline (7 micrograms/kg) over 30 min. Of the four patients in whom the post-drug PPA indices remained within the ARDS range, none survived, whilst five of the six patients in whom the post-drug PPA indices were reduced to below 1.0 x 10(-3)/min survived. PPA indices prior to the administration of terbutaline were not significantly different between the survivor (n = 5) and non-survivor (n = 5) groups. There was a significant decrease in the PPA indices following terbutaline in survivors (p less than 0.01) but not in non-survivors. Thus beta-2-agonists in therapeutic doses can inhibit increased lung vascular permeability in man. These findings may have prognostic and therapeutic implications for beta-2-agonists in ARDS.

Measurement of pulmonary epithelial permeability with 99mTc-DTPA aerosol

The rate at which inhaled aerosol of 99mTc-diethylenetriamine pentaacetate (DTPA) leaves the lung by diffusion into the vascular space can be measured with a gamma camera or simple probe. In normal humans, 99mTc-DTPA clears from the lung with a half time of about 80 minutes. Many acute and chronic conditions that alter the integrity of the pulmonary epithelium cause an increased clearance rate. Thus cigarette smoking, alveolitis from a variety of causes, adult respiratory distress syndrome (ARDS), and hyaline membrane disease (HMD) in the infant have all been shown to be associated with rapid pulmonary clearance of 99mTc-DTPA. Rapid clearance is also promoted by increased lung volume and decreased surfactant activity. Although the mechanism of increased clearance in pathological states is not known, the 99mTc-DTPA lung-clearance technique has great potential clinically, particularly in patients at risk from ARDS and HMD and in the diagnosis and follow-up of alveolitis.

Extravascular lung water measurement in septic sheep

Sheep were prepared with a chronic lung lymph fistula and studied unanesthetized following septicemia by infusion of live Escherichia coli 10(9) ml/kg bw or injection of oleic acid 0.05 ml/kg bw. Extravascular lung water (EVTV) was measured with thermal-dye technique and compared to gravimetrically measured lung water (EVWV). Septic sheep had increased pulmonary artery pressure, reduced mean arterial blood pressure and reduced cardiac output. In control animals there was a correlation between EVTV-EVWV of r = 0.70. In animals given oleic acid lungs were macroscopically edematous and the correlation was r = 0.93. In septic sheep, however, no correlation could be found between EVTV and EVWV (r = -0.25). The thermal-dye technique was found to give erroneously high values. This finding could probably be due to erythrostasis and leukocyte plugging with uneven perfusion and prolonged transit times due to reduced cardiac output.

Regional lung function: physiology and clinical applications

The current status of tests of regional lung function has been reviewed from the physiological and clinical standpoint. Recent technical innovations include the use of single photon and positron emission computerized tomography (SPECT and PET). For PET work, neon-19 (t 1/2 17 sec) has been introduced as a ventilation tracer, and fluorine-18 deoxyglucose as a marker of glucose metabolism. Indium-111 labelled neutrophils have been studied. Physiological measurements of the distribution of blood flow and ventilation are concentrating on non-gravitational influences such as the pattern of force generation by the respiratory muscles and vasomotor tone. Ventilation and perfusion imaging of the lung with the gamma camera has established itself as an essential screening test for the diagnosis of pulmonary embolic disease. Inhalation of a radio-labelled aerosol of small particle size (1 micron) may be an acceptable substitute for a radioactive gas ventilation scan. Mucociliary clearance has been investigated with radionuclide techniques. Measurements of regional lung water have been replaced by tracers sensitive to alterations of epithelial (inhaled 99Tcm-DTPA) or endothelial (i.v. 113Inm-transferrin) permeability. New techniques using positron emission tomography, such as measurements of extravascular lung density, regional ventilation (19Ne) and regional glucose metabolism (18F-deoxyglucose) have been discussed briefly.

The measurement of lung water content

It is clear that lung water content or things related to lung water content can be measured. The major question is whether useful information will be obtained to make development worthwhile. In my experimental laboratory we have used, then abandoned, the measurement of lung water content in life by various techniques. We have special needs, of course, for very sensitive methods which will detect minimal injury and very small changes in lung water content. In the clinic, however, this may not be so serious a limitation, although one is always endeavoring to achieve diagnosis of minimal injury and minimal edema. Although static methods for measuring lung water content are available in profusion, none has been proven to be more useful than the chest roentgenogram. Kinetic methods are being developed which have the potential of being sensitive to minimal lung injury, such as leads to edema.

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.