Pulmonary vascular remodeling distal to pulmonary artery ligation is accompanied by upregulation of endothelin receptors and nitric oxide synthase.

There is increasing evidence that the pathogenesis and progression of many forms of pulmonary vasculopathy are related to abnormalities in endothelial mediators, including endothelin-1 (ET-1) and nitric oxide (NO). Using a rat model of chronic unilateral pulmonary artery ligation, we investigated the role of ET-1 and NO in postobstructive pulmonary vasculopathy (POPV). Eight months after a left thoracotomy with either left main pulmonary artery ligation (ligated group) or no ligation (sham group), rat lungs, including those contralateral to the ligation (hyperperfused group), were fixed and mounted for histologic sectioning. Morphometric measurements were carried out by computer-assisted image analysis and immunohistochemical staining was performed using specific antibodies against ET-1, ETA, and EBB receptors, and endothelial NO synthase (eNOS). Compared to sham lungs, the ligated lungs showed (1) an increase in muscular, adventitial, and intimal thickness of pulmonary artery; (2) increase in external diameter of the bronchial artery (39.8 +/- 2.2 microns vs. 16.8 +/- 0.9 microns in sham group; P < .005) and number of bronchial arteries per bronchiole (3.21 +/- mu 0.26 vs. 1.86 +/- mu 0.21 in sham group; P < .001); and (3) increase in the intensity of eNOS and ETA, B receptor immunoreactivity. No morphometric or immunohistochemical differences were observed between the hyperperfused and sham lungs. These findings suggest that increased synthesis of endothelial NO may serve as a compensatory mediator in ET-1-mediated vascular remodeling.

Reperfusion lung injury after unilateral pulmonary artery occlusion.

OBJECTIVE: To test the hypothesis that reperfusion of the canine lung after 1 week of vascular occlusion results in acute injury of the reperfused lung with concurrent impairment in gas exchange. METHODOLOGY: In 11 conditioned dogs, the left pulmonary artery was completely occluded by a vascular clip placed at thoracotomy. One week later, at repeat thoracotomy, the clip was removed in six animals (reperfused group) but left in place in five (sham group). Bronchoalveolar lavage fluid (BAL) components, gas exchange, haemodynamics and histological alterations were examined. RESULTS: During occlusion, the mean pulmonary artery pressure and pulmonary vascular resistance increased significantly, and after 6 days there was a significant increase in ventilation to high ventilation perfusion ratio (V/Q) areas. With reperfusion, the previously occluded lung demonstrated, in comparison to the contralateral lung, a significant increase in BAL cellularity and neutrophil fraction, gross and histological evidence of oedema, and impaired surfactant activity. Shunt fraction, measured by the inert gas technique, also increased only after reperfusion, although mild hypoxaemia occurred in both groups. Endothelial abnormalities and perivascular oedema were noted in both groups, but were more marked in the reperfused lungs. CONCLUSION: Reperfusion of the canine lung after 1 week of complete occlusion resulted in evidence of mild acute lung injury. The aetiology of this injury was multifactorial.

Endothelin mediates pulmonary vascular remodelling in a canine model of chronic embolic pulmonary hypertension.

It is well known that endothelin (ET)-1 mediates vascular remodelling in various kinds of clinical and experimental pulmonary hypertension. The aim of this study was to investigate whether ET-1 is associated with the development of pulmonary vascular remodelling in a canine model of chronic embolic pulmonary hypertension. Pulmonary hypertension was induced in 10 mongrel dogs by repeated embolization with ceramic beads. In five of the dogs, bosentan, a nonselective ET receptor antagonist, was administered throughout the study. Haemodynamic measurements and plasma ET-1 assays were performed every 2 months. Eight months after initial embolization, computer-assisted morphometry and immunohistochemistry were performed on the lung tissue including that from three control dogs. Pulmonary arterial pressure and pulmonary vascular resistance were increased in all embolized dogs, compared to baseline. In nontreated embolized dogs, plasma ET-1 concentration and pulmonary arterial wall thickness were increased compared to control animals, and ET-1 immunoreactivity was detected in thickened pulmonary arteries. In bosentan treated dogs, pulmonary arterial walls were not significantly thickened. Pulmonary vascular remodelling, associated with elevated plasma endothelin-1 levels and positive endothelin-1 immunoreactivity in lung tissue is attenuated by the endothelin receptor antagonist, bosentan. These findings suggest that endothelin mediates pulmonary vascular remodelling in a canine model of chronic embolic pulmonary hypertension.

Percutaneous pulmonary endoarterial biopsy in an experimental model of pulmonary hypertension.

STUDY OBJECTIVES: The aims of this study were: to evaluate the performance of a novel arterial biopsy catheter in obtaining pulmonary endovascular samples in hypertensive dogs; to compare the results of pulmonary endoarterial biopsy in hypertensive vs normotensive dogs; and to assess the histologic changes in the hypertensive model. DESIGN AND INTERVENTIONS: Thirty-four dogs (27 with normal pulmonary arterial pressures and seven with pulmonary hypertension) were catheterized through an external jugular vein to obtain endovascular biopsy samples from distal pulmonary arteries 2 to 3 mm in luminal diameter. To induce pulmonary hypertension, seven dogs were given repeated infusions of 0.6- to 0.9-mm ceramic microspheres into the superior vena cava. Endoarterial samples were obtained at pulmonary systolic arterial pressures ranging from 10 to 110 mm Hg. MEASUREMENTS AND RESULTS: Sixty-two biopsy catheterization procedures were performed in the 34 dogs. After 12 initial procedures of technique refinement, endoarterial samples were obtained in each of the last 50 procedures (21 in normotensive dogs and 29 in hypertensive dogs). The average number of endovascular biopsy samples retrieved was 7.1 (range, 2 to 12) from a mean of 8.6 (range, 2 to 15) biopsy attempts per catheterization (success rate=83%). The average biopsy piece measured 1.13 mm in length, 0.33 mm in depth, and up to 1.0 mm in width. The biopsy success rates and endoarterial sample sizes were similar in normotensive and hypertensive dogs. Smooth muscle cells and endothelial cells were grown from the biopsy samples. There were no significant procedural complications, except for one self-limited hemorrhage. Histologically, samples obtained from dogs with pulmonary hypertension showed characteristic changes when compared with biopsies from normotensive dogs. CONCLUSION: This new endoarterial biopsy catheter was safe and effective when used to obtain pulmonary endoarterial samples in dogs with normal and experimentally elevated pulmonary arterial pressures. The quality and quantity of the biopsy samples allowed identification of pathologic changes.

A comparison of thoracoscopic talc insufflation, slurry, and mechanical abrasion pleurodesis.

The purpose of this study was to compare the anatomic and histopathologic results of four different methods of pleurodesis in 10 dogs. Each animal was randomly assigned to receive two of the following methods of pleurodesis: thoracoscopic talc insufflation (poudrage), talc slurry administration, focal gauze abrasion by limited thoracotomy, and mechanical abrasion by thoracoscopy using a commercially available pleural abrader. Animals were killed 30 days after pleurodesis. At autopsy, the efficacy of pleurodesis was graded by evaluating the gross appearance of each pleural cavity and lung (pleurodesis score), and by determining the extent of adhesion formation (obliteration grade). Pleural and lung biopsy specimens were obtained from the areas most representative of adhesion formation for histopathologic evaluation. Pleurodesis scores (on a scale of 0 to 4) were 3.0 +/- 0.7 for talc poudrage (p < 0.05 when compared with talc slurry), 2.2 +/- 1.7 for thoracotomy, and 1.6 +/- 1.1 for talc slurry. Adhesions produced by gauze abrasion during thoracotomy were mostly peri-incisional. Thoracoscopic pleural abrasion using the pleural abrader was uniformly unsatisfactory. Granulation tissue formation was greatest in both talc models. The degree of parietal pleural thickening was greatest in the talc slurry model, but fibrosis and inflammation occurred mostly in gravity-dependent areas within the pleural cavity. Although differences were not statistically significant, thoracoscopic talc insufflation consistently produced the most widespread, firm fibrotic adhesions as evidenced by higher obliteration grades.

Magnetic resonance detection of acute pulmonary emboli in a canine model with pathologic correlation.

RATIONALE AND OBJECTIVES: The authors evaluated the accuracy of magnetic resonance (MR) imaging in depicting acute pulmonary emboli at the lobar, segmental, and subsegmental levels. METHODS: The authors induced 29 autologous emboli in five dogs and confirmed their location with angiography and anatomic dissection. MR images obtained with four sequences were independently evaluated by two radiologists to detect emboli in each vascular segment. Sensitivities, specificities, and accuracies were calculated at segmental and lobar levels. RESULTS: The fast short-tau inversion-recovery images provided the greatest conspicuity and highest overall accuracy (reader 1 = 74.3%, reader 2 = 80%). Accuracy of two-dimensional fast multiplanar spoiled gradient-recalled-echo images was limited by spatial resolution (reader 1 = 71.4%, reader 2 = 74.3%). The fast spin-echo T2-weighted and spin-echo T1-weighted sequences were intermediate in their depiction of acute emboli. Similar results were seen at the lobar level. CONCLUSION: MR images depict acute pulmonary embolism at the segmental and lobar levels with reasonable accuracy. Fast short-tau inversion-recovery sequences provided the greatest sensitivity and accuracy.

Transvenous procurement of pulmonary artery smooth muscle and endothelial cells using a novel endoarterial biopsy catheter in a canine model.

OBJECTIVES: The aim of this study was to evaluate the performance of a new arterial biopsy catheter in obtaining pulmonary endovascular samples in a canine model. BACKGROUND: Percutaneous endomyocardial biopsy is a widely used and valuable procedure in the management of posttransplant rejection and selected cardiomyopathies. A similar method of obtaining endoarterial biopsy samples would aid in the study, diagnosis and management of arterial diseases. METHODS: Catheterization was performed in 19 dogs, each weighing 20 to 30 kg, through an 8F sheath in the external jugular vein to obtain pulmonary endoarterial samples. The catheter consists of two sliding tubes: an inner one with a beveled opening that accommodates endoarterial tissue by means of a vacuum and an outer tube with a sharp distal edge that cuts the tissue when activated. RESULTS: Overall, a total of 266 separate biopsy attempts were performed, and 161 tissue samples were obtained (success rate 61%). With modifications in technique in the last nine dogs, 54 (93%) of 58 attempts were successful. There were no deaths, extravasation of contrast material on angiography or thrombi. Of 20 vessels with prebiopsy and postbiopsy angiograms, 1 developed transient spasm (5%). On microscopic examination of cross sections of 50 separate pulmonary endoarterial biopsy samples, all had smooth muscle cells and 30 contained endothelial cells (60%). The arteries of origin showed small intimal and medial tears and mild perivascular hemorrhage. Angiographic and pathologic examination of previously biopsied arterial segments 2 weeks (two dogs) and 8 weeks (two dogs) after the procedure showed patent vessels and no thrombi. Histologically, the biopsy sites revealed mild neointimal and medial proliferation. CONCLUSIONS: This new endoarterial biopsy catheter is safe and effective in obtaining pulmonary artery samples in normotensive dogs.

Suppression of thrombolysis in a canine model of pulmonary embolism.

BACKGROUND: The brisk fibrinolytic response of canines has impaired efforts to develop a canine model of chronic thromboembolic pulmonary hypertension. Difficulties in retaining chronic embolic residuals were partially overcome by administration of tranexamic acid (TXA) (Circulation. 1991;83:1272-1279.). In this study, we used type 1 plasminogen activator inhibitor (PAI-1), a major inhibitor of the endogenous fibrinolytic system, to determine its efficacy in the suppression of thrombolysis in canines. METHODS AND RESULTS: Thrombus was induced in the inferior vena cava of anesthetized mongrel dogs with thrombin and a special double-balloon catheter; 2 hours later, the thrombus was embolized. In one group of dogs, activated type 1 plasminogen activator inhibitor (PAI-1) (130 micrograms) was delivered directly into the forming thrombus; in another, TXA (110 mg/kg) was given intravenously before thrombus formation; in controls, thrombus was induced without inhibitors. Cross-linked fibrin degradation product (D-dimer) appeared in the blood of control animals within 1 hour of thrombus induction (176 +/- 62.5 versus 1.02 +/- 0.39 ng/mL baseline; mean +/- SEM), was maximal by 4 hours (413 +/- 110 ng/mL) and remained elevated at 24 hours (90.8 +/- 19.5 ng/mL). Compared with controls, PAI-1 and TXA suppressed D-dimer release by 80% and 85%, respectively, over the first 24 hours. One week later, animals were killed, and residual emboli were harvested. Perfusion scan defects persisted in all animals at this time, but there were no scan defect differences among groups. However, emboli recovered from animals receiving PAI-1 still harbored immunoreactive PAI-1 and were, on average, more than twofold greater in mass (393 +/- 56 mg) than emboli recovered from either controls (183 +/- 76 mg) or animals receiving TXA (180 +/- 80 mg). CONCLUSIONS: Intravenous TXA and intrathrombus PAI-1 effectively suppress thrombolysis for 24 hours in canines. Thromboemboli enriched with PAI-1 appear to resist lysis for longer periods of time (up to 1 week). These findings are consistent with the hypothesis that PAI-1 remains associated with the embolus, where it continues to inhibit lysis, whereas TXA eventually diffuses out of the embolus, allowing lysis to ensue.

Factors contributing to increased vascular fibrinolytic activity in mongrel dogs.

BACKGROUND: Numerous investigators have observed that pulmonary emboli are rapidly lysed in a canine model system. This study was undertaken to delineate the unique mechanism that accounts for the rapid dissolution of pulmonary emboli in mongrel dogs. METHODS AND RESULTS: Canine plasminogen activator (PA) activity (2.6 +/- 1.1 IU/mL acidified platelet-poor plasma [PPP], < 0.3 IU/mL acidified whole blood serum [WBS], mean +/- SD; n = 6) and PA inhibitor activity (6.1 +/- 2.6 U/mL PPP, 35.4 +/- 7.8 U/mL WBS; n = 6) were determined in standard plasminogen-based chromogenic assays. Analysis of canine PPP, WBS, platelet lysates, and primary canine endothelial cell (EC) cultures by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fibrin autography revealed a plasminogen-dependent lytic zone at 45-kd relative molecular mass that was shown to be related to urokinase-type PA (u-PA) by its selective inhibition through amiloride. Analysis of canine platelets on standard 125I fibrin plate assays revealed a net fibrinolytic activity. In a clot lysis assay system, canine platelets were able to stimulate fibrinolysis when layered on the outside of fibrin clots containing autologous PPP. Moreover, net fibrinolytic activity of primary canine pulmonary artery endothelial cells was higher than the activities expressed by canine aortic or carotid artery endothelial cells. CONCLUSIONS: Rapid lysis of pulmonary emboli in mongrel dogs appears to be a result of 1) the high u-PA activity in canine PPP and 2) the predominant association of u-PA activity with canine platelets and canine pulmonary artery endothelial cells.

Effect of heparin, tissue plasminogen activator, and increased intracaval pressure on the acute morbidity of Greenfield filter insertion.

The effects of anticoagulation, thrombolytic therapy, and augmented intracaval pressure on the risks of acute caval hemorrhage from Greenfield filter insertion have not been rigorously investigated. To examine these risk factors, the device was placed in three groups of five dogs. Group 1 served as controls, with filter placement only. Groups 2 and 3 received anticoagulants before surgery. Group 3 was additionally given a continuous infusion of tissue plasminogen activator begun immediately after filter insertion. Animals were killed after a 6-hour period of observation and measurement. A second phase was carried out at autopsy in group 3: intracaval pressure was augmented and its effects on caval integrity noted. During the period of observation there were no significant decrements in central venous pressure or hematocrit. At autopsy, no evidence of caval hemorrhage and no caval perforations were found. Increased intracaval pressure did not alter these findings. These results support the clinical experience with the device, and suggest that the risk of acute hemorrhage from a properly seated filter is minimal, even with concurrent use of heparin and thrombolytic agents or high caval pressures.

The in vivo behavior of granulocytes labeled with indium-111 in a canine model of pneumococcal pneumonia.

Use of [111In]granulocytes in the study of pulmonary inflammation requires study of their in vivo behavior. To study the pulmonary deposition of these cells and their ability to migrate from the capillary to the alveolus, we injected [111In]granulocytes into dogs 24 h after the induction of a right lower lobe pneumococcal pneumonia. Using external imaging, we found rapid clearance of [111In]granulocytes from the uninvolved lung (with a residual radioactivity of 24.5 +/- 4.2% at 4 h). In contrast, 83 +/- 12.4% of the initial radioactivity was present in inflamed lung at 4 h. Bronchoalveolar lavage fluid from the inflamed lung was more cellular than that from control lung, contained a greater fraction of polymorphonuclear leukocytes (82 +/- 4.1% versus 20 +/- 6.2%), and much greater cell-associated radioactivity (ratio of 423:1, inflamed to control). Autoradiography disclosed that this radioactivity was localized to consolidated alveoli and was not prominently distributed in arterioles or venules or in airways larger than 0.6 mm. We conclude that [111In]granulocytes are biologically active in the setting of acute lung inflammation.

Hemodynamics and gas exchange during angioscopy in the dog.

We have previously developed a technique for the in vivo visualization of the pulmonary arteries in the experimental animal with a fiberoptic instrument (angioscope). To assess the potential hemodynamic and gas exchange effects of angioscopy, we studied five dogs before and after pulmonary embolization. Sequential observations were made of arterial blood gases, mean arterial pressure, pulmonary artery pressure, heart rate, cardiac output, and the electrocardiogram. The most common arrhythmias were ventricular premature contractions which were comparable to those seen with right heart catheterization. Statistically significant, but clinically minor, effects were found on cardiac output, mean arterial pressure, and heart rate in dogs when angioscopy was performed after pulmonary embolization. We conclude that fiberoptic angioscopy does not induce deleterious effects on hemodynamics or gas exchange in the experimental animal, prior to or after embolization.

Effect of histamine and propranolol on extravascular lung water.

The ability of an intravenous infusion of 21 micrograms X kg-1 X min-1 histamine diphosphate to cause pulmonary edema was studied in dogs in which beta-blockade either was or was not in effect, since current evidence suggests that beta-blockade can prevent catecholamines from antagonizing the vascular permeability effect of histamine in the systemic circulation. Mixed venous histamine levels ranging from 140 to 580 ng/ml were achieved; norepinephrine and epinephrine levels increased significantly, although in animals receiving propranolol, heart rate remained depressed. Neither lung wet weight-to dry weight ratio nor extravascular lung water increased in animals receiving histamine or histamine and propranolol. We conclude that the inability of histamine to produce substantial pulmonary edema cannot be explained on the basis of catecholamine stimulation of beta-adrenergic receptors within the lung.

Diaphragmatic function during immersion.

Diaphragmatic function during immersion to midneck level was studied in upright mongrel dogs, using constant electrophrenic stimulation. Effectiveness of diaphragmatic contraction was analyzed in terms of inspired volume (VT) (with airways open), and change in intrathoracic pressure (Pmus) (with the respiratory system occluded). Hydrostatic compression of the immersed body decreased functional residual capacity (FRC) to 55% base-line value (FRCO), resulting in a 2.8-fold increase in Pmus. In spite of this Pmus increase, VT often decreased during immersion, averaging only 83% VTO (base-line value in air). Hence, immersion was associated with a marked stiffening of the respiratory system. The Pmus increase during immersion persisted after restoration of FRC to FRCO, and was related to diaphragmatic length being greater in water than in air under condition of iso-lung volume. In all, there were three factors affecting diaphragmatic function during immersion: FRC reduction, change in thoracic configuration, and stiffening of the respiratory system.

Stability in lobar ventilation distribution during change in thoracic configuration.

Stability in lobar ventilation was examined in dogs during bilateral electrophrenic respiration (BEPR) and positive pressure-assisted ventilation (PPAV). Bilateral prior ligation of the lower and middle lobe pulmonary arteries monitoring of upper lobe ventilation as alveolar minute ventilation (VA), middle and lower lobe ventilation as dead space (VD), and VD/VT ratio, both calculated by the Bohr equation. As documented by chest films, transverse and anteroposterior thoracic diameters during BEPR decreased below FRC values whereas thoracic cephalocaudal dimension greatly increased. During PPAV, all thoracic dimensions increased. Despite these dissimilar regional chest movements, VA, VD, and VD/VT ratio were comparable between PPAV and BEPR under conditions of matched tidal volume and respiratory frequency. Stability in upper lobe ventilation during BEPR was maintained by caudal displacement despite the compression of the rib cage, as documented by tantalum bronchography. Lobar-interdependence appears to be the mechanism transmitting negative pleural pressure developed by the diaphragm to the upper lobes via lower and middle lobe inflation.