Fibrinogen and the prediction of residual obstruction manifested after pulmonary embolism treatment.

Residual pulmonary vascular obstruction (RPVO) and chronic thromboembolic pulmonary hypertension (CTEPH) are both long-term complications of acute pulmonary embolism, but it is unknown whether RPVO can be predicted by variants of fibrinogen associated with CTEPH.We used the Akaike information criterion to select the best predictive models for RPVO in two prospectively followed cohorts of acute pulmonary embolism patients, using as candidate variables the extent of the initial obstruction, clinical characteristics and fibrinogen-related data. We measured the selected models' goodness of fit by analysis of deviance and compared models using the Chi-squared test.RPVO occurred in 29 (28.4%) out of 102 subjects in the first cohort and 46 (25.3%) out of 182 subjects in the second. The best-fit predictive model derived in the first cohort (p=0.0002) and validated in the second cohort (p=0.0005) implicated fibrinogen Bß-chain monosialylation in the development of RPVO. When the derivation procedure excluded clinical characteristics, fibrinogen Bß-chain monosialylation remained a predictor of RPVO in the best-fit predictive model (p=0.00003). Excluding fibrinogen characteristics worsened the predictive model (p=0.03).Fibrinogen Bß-chain monosialylation, a common structural attribute of fibrin, helped predict RPVO after acute pulmonary embolism. Fibrin structure may contribute to the risk of developing RPVO.

Structural insights into fibrinogen dynamics using amide hydrogen/deuterium exchange mass spectrometry.

We determined the amide hydrogen/deuterium exchange profile of native human fibrinogen under physiologic conditions. After optimization of the quench and proteolysis conditions, more than 1,200 peptides were identified by mass spectrometry, spanning more than 90% of the constituent Aα, Bß, and γ chain amino acid sequences. The compact central and distal globular regions of fibrinogen were well protected from deuterium exchange, with the exception of the unfolded amino-terminal segments of the Aα and Bß chains extending from the central region, and the short γ chain "tail" extending from each distal globular region. The triple-helical coiled-coil regions, which bridge the central region to each distal region, were also well protected with the exception of a moderately fast-exchanging area in the middle of each coiled-coil adjacent to the γ chain carbohydrate attachment site. These dynamic regions appear to provide flexibility to the fibrinogen molecule. The γ chain "out loop" contained within each coiled-coil also exchanged rapidly. The αC domain (Aα 392-610) exchanged rapidly, with the exception of a short segment sandwiched between a conserved disulfide linkage in the N-terminal αC subdomain. This latter finding is consistent with a mostly disordered structure for the αC domain in native fibrinogen. Analysis of the dysfibrinogen Bß 235 Pro/Leu, which exhibits abnormal fibrin structure, revealed enhanced deuterium exchange surrounding the Pro/Leu substitution site as well as in the vicinity of the high affinity calcium binding site and the A knob polymerization pocket within the γC domain. The implication of these changes with respect to fibrin structure is discussed.

Pilot study comparing SPECT perfusion scintigraphy with CT pulmonary angiography in chronic thromboembolic pulmonary hypertension.

BACKGROUND AND OBJECTIVE: The management of chronic thromboembolic pulmonary hypertension (CTEPH) is dependent on the extent of pulmonary artery obstruction, which is usually evaluated by planar perfusion scanning and CT pulmonary angiography (CTPA). We previously reported that SPECT perfusion scanning is more sensitive than planar scanning for detecting vascular obstruction in CTEPH. The purpose of this study is to compare SPECT with CTPA for detecting segmental pulmonary artery obstruction in CTEPH. METHODS: SPECT and CTPA were carried out before pulmonary endarterectomy in 12 CTEPH patients. Field experts documented the anatomical distribution of perfusion defects disclosed by SPECT, the anatomical distribution of pulmonary arterial filling defects disclosed by CTPA and the segmental anatomy of the vascular obstructions based on a review of clinical and pathology records, without knowledge of scan results. RESULTS: Clinical/pathological evaluation disclosed 140 obstructed (15.5 ± 2.5 per patient) and 40 unobstructed lung segments. SPECT scanning identified 87/140 (62%) of the obstructed and 29/40 (72%) of the unobstructed segments. By comparison, CTPA identified 67/140 (47.8%) of the obstructed and 32/40 (80%) of the unobstructed segments. Sensitivity for detecting obstructed segments was significantly higher for SPECT compared with CTPA (62 ± 4.1% vs 47.8 ± 2.9%, respectively; P = 0.03). CONCLUSIONS: SPECT is more sensitive than CTPA for identifying obstructed segments in this small sample of CTEPH patients. However, even SPECT under-represents the extent of vascular obstruction from this disease.

High prevalence of dysfibrinogenemia among patients with chronic thromboembolic pulmonary hypertension.

The mechanism by which chronic thromboembolic pulmonary hypertension (CTEPH) develops after acute pulmonary thromboembolism is unknown. We previously reported that fibrin from CTEPH patients is relatively resistant to fibrinolysis in vitro. In the present study, we performed proteomic, genomic, and functional studies on fibrin(ogen) to investigate whether abnormal fibrin(ogen) might contribute to the pathogenesis of CTEPH. Reduced and denatured fibrinogen from 33 CTEPH patients was subjected to liquid chromatography-mass spectrometry analysis. Fibrinogen from 21 healthy controls was used to distinguish atypical from commonly occurring mass peaks. Atypical peaks were further investigated by targeted genomic DNA sequencing. Five fibrinogen variants with corresponding heterozygous gene mutations (dysfibrinogenemias) were observed in 5 of 33 CTEPH patients: Bbeta P235L/gamma R375W, Bbeta P235L/gamma Y114H, Bbeta P235L, Aalpha L69H, and Aalpha R554H (fibrinogens(San Diego I-V)). Bbeta P235L was found in 3 unrelated CTEPH patients. Functional analysis disclosed abnormalities in fibrin polymer structure and/or lysis with all CTEPH-associated mutations. These results suggest that, in some patients, differences in the molecular structure of fibrin may be implicated in the development of CTEPH after acute thromboembolism.

Single photon emission computed tomography in chronic thromboembolic pulmonary hypertension.

BACKGROUND AND OBJECTIVE: The management of chronic thromboembolic pulmonary hypertension (CTEPH) is largely dependent on the extent of obstruction in the pulmonary arteries. Planar perfusion scans are commonly used to quantify perfusion defects in CTEPH patients. However, planar scans typically under-represent the extent of vascular obstruction in CTEPH. We conducted this study to test the hypothesis that SPECT lung perfusion scans are more accurate than planar scans for determining the location and extent of perfusion defects in patients with CTEPH. METHODS: Planar ventilation scans, planar and SPECT perfusion scans were performed preoperatively in patients undergoing pulmonary thromboendarterectomy for treatment of CTEPH. Two clinical experts independently documented the segmental anatomy of the vascular obstructions by reviewing clinical records, pulmonary and CT angiograms, and surgical specimens. A nuclear medicine expert documented the segmental anatomy of the perfusion defects observed by planar and SPECT scans independently. RESULTS: Clinical/pathological evaluation disclosed 241 obstructed and 99 unobstructed lung segments in 17 patients. Sensitivity for detecting obstructed segments was significantly higher for SPECT than for planar scanning (63.5 ± 3.1% vs. 42.7 ± 3.2%, respectively; P < 0.01). Specificities of SPECT and planar scanning were not significantly different (62.6 ± 4.8% vs. 76.8 ± 4.2%, respectively; P = 0.092). CONCLUSIONS: The SPECT is more sensitive than planar perfusion scanning for identifying obstructed segments in CTEPH. However, even SPECT under-represents the true extent of the vascular occlusions in CTEPH.

Risk of SARS-CoV-2 Transmission During Flexible Laryngoscopy: A Systematic Review.

IMPORTANCE: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) reportedly infected otolaryngologists disproportionately in the early parts of the coronavirus disease 2019 pandemic. Recommendations from national and international health organizations suggest minimizing the use of flexible laryngoscopy as a result. OBJECTIVE: To review evidence on the risks of aerosolization and transmission of SARS-CoV-2 from patients to health care personnel during endoscopy of the upper aerodigestive tract. EVIDENCE REVIEW: A comprehensive review of literature was performed on April 19, 2020, using the PubMed/MEDLINE (1966-April 2020), Embase (1975-April 2020), and Web of Science (1900-April 2020) databases. All English-language primary research studies were included if they assessed the transmission of SARS-CoV-2 or SARS-CoV-1 during procedures in the upper aerodigestive tract. The primary outcome measure was disease transmission among health care workers. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were used for accuracy of reporting. FINDINGS: The queries for SARS-CoV-2 and SARS-CoV-1 identified 6 articles for systematic review. No studies included in this review provided data for SARS-CoV-2 transmission during flexible laryngoscopy. A total of 204 of 1264 health care workers (16.1%) had procedure-specific infections of SARS-CoV-1 or SARS-CoV-2. Among those, 53 of 221 (24.0%) were exposed during intubation, 1 of 15 (6.7%) during bronchoscopy, and 1 of 1 (100%) during endoscopy-assisted intubation. CONCLUSIONS AND RELEVANCE: A substantial lack of research precludes formal conclusions about the safety of flexible laryngoscopy and transmission of SARS-CoV-2 from patients to health care workers. The use of appropriate precautionary measures and personal protective equipment appears to reduce the risk of transmission. Given the uncertainty in transmission and the known benefits of safety precautions, upper airway endoscopy may be reasonable to perform if precautionary steps are taken.

Pharmacokinetics of UH and LMWH are similar with respect to antithrombin activity.

BACKGROUND: The ability to administer low molecular weight heparins (LMWH) subcutaneously without laboratory monitoring contributes to their popularity for the treatment of thrombotic disorders. Subcutaneous unfractionated heparin, although less expensive, is deemed to require routine laboratory monitoring on the basis of more variability in drug effect compared to LMWH. However, the more predictable pharmacokinetic profiles of low molecular weight heparins are largely based on anti-Xa activity, while antithrombin activity may be at least as important to their mechanisms of action. METHODS: We performed a clinical pharmacokinetic trial to compare the variability in peak antithrombin effect between subcutaneous unfractionated heparin and various LMWHs, all given in recommended weight-adjusted treatment doses. Sixty-one patients enrolled in a warfarin clinic were randomized to receive one of four different weight-adjusted subcutaneous heparin doses: unfractionated heparin, 250 units/kg (n=15); tinzaparin, 175 units/kg (n=15); dalteparin, 200 units/kg (n=15); or enoxaparin, 1 mg/kg (n=16). The areas under the curves of antithrombin levels during the first 3 h after administration were determined for each patient, and the coefficients of variation (CV) and 95% confidence intervals of the AUCs were compared among the treatment groups. RESULTS: There was no statistically significant difference in the coefficients of variation of antithrombin effect between unfractionated heparin (52.8, 95% CI: 32.6-72.9) and enoxaparin (56.5, 95% CI: 35.7-77.4) or dalteparin (43.5, 95% CI 25.4-61.6). Tinzaparin had statistically significant decrease in coefficients of variation (21.6, 95% CI: 12.2-30.9) relative to unfractionated heparin, dalteparin and enoxaparin. CONCLUSIONS: LMWHs, as a class of drugs, are no more predictable in antithrombin effect after subcutaneous injection than unfractionated heparin. There were considerable differences among LMWHs in the observed variability of antithrombin effects, with tinzaparin being somewhat more predictable than the other drugs tested.

Surfactant from diving aquatic mammals.

Diving mammals that descend to depths of 50-70 m or greater fully collapse the gas exchanging portions of their lungs and then reexpand these areas with ascent. To investigate whether these animals may have evolved a uniquely developed surfactant system to facilitate repetitive alveolar collapse and expansion, we have analyzed surfactant in bronchoalveolar lavage fluid (BAL) obtained from nine pinnipeds and from pigs and humans. In contrast to BAL from terrestrial mammals, BAL from pinnipeds has a higher concentration of phospholipid and relatively more fluidic phosphatidylcholine molecular species, perhaps to facilitate rapid spreading during alveolar reexpansion. Normalized concentrations of hydrophobic surfactant proteins B and C were not significantly different among pinnipeds and terrestrial mammals by immunologic assay, but separation of proteins by gel electrophoresis indicated a greater content of surfactant protein B in elephant seal surfactant than in human surfactant. Remarkably, surfactant from the deepest diving pinnipeds produced moderately elevated in vitro minimum surface tension measurements, a finding not explained by the presence of protein or neutral lipid inhibitors. Further study of the composition and function of pinniped surfactants may contribute to the design of optimized therapeutic surfactants.

Urine and plasma levels of fibrinopeptide B in patients with deep vein thrombosis and pulmonary embolism.

BACKGROUND: Many patients with pulmonary thromboembolism remain undiagnosed, possibly because of the difficulty clinicians have in determining which patients merit work-up with accurate (but expensive) imaging techniques. OBJECTIVES: We present the first prospective clinical study of pulmonary embolism (PE) and deep venous thrombosis (DVT) detection using the FPBtot assay, which measures fibrinopeptide B and its first derivative, des-arginine fibrinopeptide B. METHODS: Twenty three patients with signs or symptoms of PE or DVT were enrolled in the study prior to the performance of definitive testing. Using a novel immunoassay, FPBtot levels were measured in urine and plasma samples from patients as well as from healthy controls. Urine and plasma FPBtot levels were compared to the diagnostic results, as blindly adjudicated by one of the investigators. Patients were excluded if they withdrew (n =1), had inconclusive diagnostic testing (n = 7), or did not give samples (n = 2 for urine, n = 3 for plasma). RESULTS: The mean FPBtot concentration in the urine of the 'DVT/PE positive' group was 78.4 +/- 35.2 ng/ml and 2.7 +/- 1.9 ng/ml in the 'DVT/PE negative' group (p = 0.03). The urine FPB(tot) concentrations in the 'DVT/PE negative' group were not significantly different from those in the healthy control group (2.2 +/- 0.4 ng/ml, p = 0.40). The area under the ROC curve for urine FPB(tot) concentrations was 97.3 +/- 3.8%, suggesting a high degree of diagnostic accuracy. Plasma FPB(tot) concentrations were not significantly different between groups. CONCLUSIONS: Urine FPBtot levels may help detect patients with PE and DVT.

Improved imaging of deep venous thrombi during anticoagulation using radiolabelled anti-D-dimer antibodies.

OBJECTIVES: Radiolabelled anti-fibrin antibodies have not yet enabled reliable and practical diagnosis of venous thromboembolism. However, previous unsuccessful clinical trials were performed with anti-fibrin beta-chain antibodies that do not optimally bind to thrombi during anticoagulation. The current experiments were performed to determine if radiolabelled anti-D-dimer antibodies more reliably allowed nuclear medicine imaging of deep venous thrombi during anticoagulation than anti-beta-chain antibodies. METHODS: Dogs with pre-existing unilateral femoral vein thrombi were anticoagulated with heparin (300 units.kg (-1) bolus followed by 90 units.kg(-1).h(-1) continuous infusion). They were then allocated to receive one of three (111)In labelled antibodies: anti-D-dimer, anti-beta or a non-specific control antibody. Gamma scans of the legs were performed at regular intervals for 24 h. Scans were interpreted in a blinded fashion and the number of gamma counts from the femoral area on the thrombosed side was compared to the contralateral side. Clot/blood isotope density ratios were determined post-mortem. RESULTS: Leg thrombi were 100% detectable in the anti-D-dimer group, but only 60% detectable in the anti-beta group. Mean +/- SD relative counts in the thrombosed femoral area was 137 +/- 10% compared to the contralateral side in the anti-D-dimer group, but only 116 +/- 20% in the anti-beta group. The clot/blood ratio was 24.5 +/- 2.8 in the anti-D-dimer group, but only 7.8 +/- 2.0 in the anti-beta group. CONCLUSIONS: In labelled anti-D-dimer provides superior nuclear medicine images of thrombi during intensive anticoagulation compared to anti-beta. Clinical results with radiolabelled anti-D-dimer may be more promising than those previously observed with other anti-fibrin antibodies.

Chronic thromboembolic pulmonary hypertension-associated dysfibrinogenemias exhibit disorganized fibrin structure.

INTRODUCTION: Mechanisms contributing to the pathogenesis of chronic thromboembolic pulmonary hypertension (CTEPH) are poorly understood. This disorder is characterized by incomplete resolution of pulmonary perfusion defects resulting from acute venous thromboembolism. We previously identified several dysfibrinogenemias in some patients with CTEPH. The purpose of this study was to determine whether fibrin clot architecture might be implicated in the thrombolytic resistance in patients with these CTEPH-associated dysfibrinogenemias. MATERIALS AND METHODS: Purified fibrinogen from patients and healthy controls was clotted with thrombin in the presence of calcium. Clot turbidity, porosity, and susceptibility to fibrinolysis were evaluated by spectrophotometric and permeation analyses. Fibrin network structure was assessed by laser-scanning confocal microscopy. RESULTS: Compared to normal fibrinogen, CTEPH-associated dysfibrinogenemias exhibited low clot turbidity, decreased porosity, and fibrinolytic resistance. In addition, the dysfibrinogenemias exhibited a more disorganized fibrin network structure characterized by thinner fibers, greater network dispersal and more extensive fiber branching. CONCLUSIONS: Abnormal clot architecture and fibrinolytic resistance may contribute to incomplete clot resolution following acute venous thromboembolism in patients with CTEPH-associated dyfibrinogenemia.

Efficacy of methylprednisolone in preventing lung injury following pulmonary thromboendarterectomy.

BACKGROUND: We sought to determine the efficacy and safety of perioperative treatment with methylprednisolone on the development of lung injury after pulmonary thromboendarterectomy. METHODS: This was a randomized, prospective, double-blind, placebo-controlled study of 98 adult patients with chronic thromboembolic pulmonary hypertension who were undergoing pulmonary thromboendarterectomy at a single institution. The patients received either placebo (n = 47) or methylprednisolone (n = 51) (30 mg/kg in the cardiopulmonary bypass prime, 500 mg IV bolus following the final circulatory arrest, and 250 mg IV bolus 36 h after surgery). The primary end point was the presence of lung injury as determined by two independent, blinded physicians using prospectively defined criteria. The secondary end points included ventilator-free, ICU-free, and hospital-free days and selected levels of cytokines in the blood and in BAL fluid. RESULTS: The incidence of lung injury was similar in both treatment groups (45% placebo, 41% steroid; P = .72). There were no statistical differences in the secondary clinical end points between treatment groups. Treatment with methylprednisolone, compared with placebo, was associated with a statistically significant reduction in plasma IL-6 and IL-8, a significant increase in plasma IL-10, and a significant reduction in postoperative IL-1ra and IL-6, but not IL-8 in BAL fluid obtained 1 day after surgery. CONCLUSIONS: Perioperative methylprednisolone does not reduce the incidence of lung injury following pulmonary thromboendarterectomy surgery despite having an antiinflammatory effect on plasma and lavage cytokine levels.

Chronic exposure to fibrin and fibrinogen differentially regulates intracellular Ca2+ in human pulmonary arterial smooth muscle and endothelial cells.

Acute pulmonary embolism occurs in more than half a million people a year in the United States. Chronic thromboembolic pulmonary hypertension (CTEPH) develops in approximately 4% of these patients due to unresolved thromboemboli. CTEPH is thus a relatively common, progressive, and potentially fatal disease. One currently proposed theory for the poor resolution advocates that modification of fibrinogen in CTEPH patients causes resistance of emboli to fibrinolysis. The current study investigated the regulation of cytosolic Ca(2+) ([Ca(2+)](cyt)), central to the control of cell migration, proliferation, and contraction, by chronic exposure of pulmonary artery smooth muscle (PASMC) and endothelial (PAEC) cells to fibrinogen and fibrin. Basal [Ca(2+)](cyt) was substantially elevated in PAEC after culture on fibrinogen, fibrin, and thrombin and in PASMC on fibrinogen and fibrin. In PAEC, fibrinogen significantly decreased the peak [Ca(2+)](cyt) transient (P <0.001) without a change in the transient peak width (at 50% of the peak height). This response was independent of effects on the proteinase-activated receptor (PAR) 1. Furthermore, chronic exposure to thrombin, an activator of PAR, significantly reduced the peak agonist-induced Ca(2+) release in PAEC, but increased it in PASMC. The recovery rate of the agonist-induced [Ca(2+)](cyt) transients decelerated in PASMC chronically exposed to fibrin; a small increase of the peak Ca(2+) was also observed. Substantial augmentation of PASMC (but not PAEC) proliferation was observed in response to chronic fibrin exposure. In conclusion, chronic exposure to fibrinogen, fibrin, and thrombin caused differential changes in [Ca(2+)](cyt) in PAEC and PASMC. Such changes in [Ca(2+)](cyt) may contribute to vascular changes in patients who have CTEPH where the pulmonary vasculature is persistently exposed to thromboemboli.

Fibrin derived from patients with chronic thromboembolic pulmonary hypertension is resistant to lysis.

RATIONALE: Although acute pulmonary embolism is epidemiologically associated with chronic thromboembolic pulmonary hypertension, the factors responsible for resistance to thrombolysis and a shift toward vascular remodeling within the pulmonary arteries of patients with chronic thromboembolic pulmonary hypertension are unknown. OBJECTIVE: Determine whether fibrin from patients is more resistant to plasmin-mediated lysis than fibrin from healthy control subjects. METHODS: Fibrinogen purified from patients and control subjects was used to prepare fibrin clots, which were subsequently digested with plasmin for various periods of time. The degradation of the alpha-, beta-, and gamma-chains of fibrin and the appearance of peptide fragments over time were assessed by polyacrylamide gel electrophoresis and Western blotting. MEASUREMENTS AND MAIN RESULTS: Densitometry of Coomassie-stained gels revealed significantly slower cleavage of all three polypeptide chains of fibrin from patients compared with control subjects (p < 0.05). In particular, release of N-terminal fragments from the beta-chain of fibrin, which promote cell signaling, cell migration, and angiogenesis, was retarded in patients compared with control subjects (p < 0.01). CONCLUSIONS: The relative resistance of patient fibrin to plasmin-mediated lysis may be due to alterations in fibrin(ogen) structure affecting accessibility to plasmin cleavage sites. The persistence of structural motifs of fibrin, such as the beta-chain N-terminus, within the pulmonary vasculature could promote the transition from acute thromboemboli into chronic obstructive vascular scars.

Effect of CTP:phosphocholine cytidylyltransferase overexpression on the mouse lung surfactant system.

CTP:phosphocholine cytidylyltransferase (CT) is the rate-limiting enzyme in the biosynthesis by type II pneumocytes of phosphatidylcholine (PC), the predominant phospholipid in lung surfactant. Augmentation of endogenous CT activity might therefore result in enhanced surfactant PC production. To test this hypothesis, transgenic mice were created in which rat CT (rCT) was expressed under control of the human surfactant protein C (SP-C) promoter. Transgenic mice were identified by tail-clip PCR analysis and studies of four founder lines were initiated. Lung CT gene expression was enhanced in two transgenic founder lines relative to wild-type controls. These two transgenic lines also exhibited significantly higher levels of immunoreactive CT protein and CT activity in whole-lung homogenates and in cultured type II cell extracts. Disaturated PC (DSPC) content in whole-lung homogenates and the rate of DSPC synthesis in cultured type II cells were significantly increased in one transgenic line. However, neither the incorporation of radiolabeled precursors (choline and palmitate) into DSPC in vivo nor the cellular metabolism of DSPC differed significantly between transgenic and control mice. This transgenic model provides opportunity for further study of factors controlling surfactant phospholipid production in vivo.

Embolization itself stimulates thrombus propagation in pulmonary embolism.

The role of active thrombosis in the pathophysiology of pulmonary embolism is unclear. We tested the hypothesis that venous thrombi significantly increase their thrombotic activity once they embolize into the high-flow circulation of the pulmonary arteries. Thrombotic activity was measured using an immunoassay that measures both fibrinopeptide B (FPB) as well as its most abundant metabolite des-arginine FPB. Thrombi were formed in the femoral veins of adult dogs. In one group, the thrombi were embolized without anticoagulation. In the second group, heparin (300 U/kg bolus, then 90 U x kg(-1) x h(-1) infusion) was administered before embolization to prevent subsequent thrombotic activity. Plasma FPB concentrations were significantly suppressed in the heparinized group relative to the nonheparinized group for 1 h postembolization (P = 0.038). We conclude that pulmonary embolization itself causes preexisting venous thrombi to greatly intensify their thrombotic activity and that embolization-associated thrombus propagation can be prevented by heparin.

Single photon emission computed tomography of pulmonary emboli and venous thrombi using anti-D-dimer.

Previous attempts to diagnose thromboemboli using radiolabeled antibodies and nuclear medicine imaging have been disappointing. We present the results of experiments with intravenous technetium-99m-labeled deimmunized antifibrin Fab' fragments to diagnose thromboemboli using single photon emission computed tomography (SPECT), a highly sensitive scintigraphic imaging technique. Pulmonary emboli (PEs) and lower extremity deep vein thrombi (DVTs) were formed in five dogs, then technetium-99m-labeled Fab' ( approximately 400 mg, approximately 260 MBq) were injected via forelimb veins. Thoracic and lower extremity SPECT scans were performed at 2-hour intervals after antibody infusion to visualize the thromboemboli. Four hours after antibody infusion, all PEs and DVTs of mass 0.4 g or greater were clearly visualized on SPECT scans as 'hot spots' within the lungs and legs, respectively. PEs (0.48 +/- 0.09 g) were intensely radiolabeled, yielding clot/blood radioactivity ratios of 22.8 +/- 5.6. DVTs (0.45 +/- 0.31 g) also had high clot/blood ratios (11.7 +/- 2.6). Infusion of these radiolabeled antibody fragments, combined with SPECT, produces clear images of PEs and DVTs within a clinically feasible time frame. The technique reliably identified even peripheral thromboemboli of relatively small size, which are difficult to diagnose with currently available imaging techniques, and may enable imaging of PEs, DVTs, or both in the same patient.

Treatment of acute respiratory distress syndrome with recombinant surfactant protein C surfactant.

We performed a phase I/II trial in North America of a recombinant surfactant protein C-based surfactant (Venticute) as treatment for the acute respiratory distress syndrome. Patients were prospectively randomized to receive either standard therapy or standard therapy plus one of two doses of exogenous surfactant given four times over 24 hours. Surfactant administration was well tolerated. No significant treatment benefit was associated with surfactant treatment. Bronchoalveolar lavage of treated patients at 48 hours reflected the presence of exogenous surfactant components, did not show evidence of improved surface tension lowering function, and had interleukin-6 concentrations that were significantly lower than control group values, consistent with an antiinflammatory treatment effect. The presence of exogenous surfactant was not detected in lavage fluid obtained at 120 hours. Future studies might rationally employ larger surfactant doses and a more prolonged dosing schedule.