Contractile properties of intralobar pulmonary arteries and veins in the fetal lamb model of congenital diaphragmatic hernia

BACKGROUND/PURPOSE: Pulmonary hypertension plays a significant role in the pathophysiology of congenital diaphragmatic hernia (CDH). Although there has been an intensive research effort directed at mediators that may cause pulmonary vasoconstriction, no single agent has been identified. The authors hypothesize that there may be an alteration in the cGMP-nitric oxide (NO) pathway of vasodilatation contributing to the pulmonary hypertension observed in CDH. The purpose of these studies is to begin to elucidate vasoactive properties of pulmonary vessels with particular attention to the cGMP-NO pathway of vasodilatation in fetal lambs with CDH. METHODS: Fourth-generation pulmonary arteries and pulmonary veins were dissected from both right and left lungs of eight, 139-day gestational fetuses with surgically created CDH. Vessels were studied with standard isolated tissue bath techniques. Experiments examined basal release of NO in endothelium-intact PVs and PAs of both right and left lungs by measuring the contractile force of vessels constricted with norepinephrine (NE) in the presence and absence of the nitric oxide synthase (NOS) inhibitor N(omega)-nitro-L-arginine (L-NA). Concentration-response curves to the vasodilating agents zaprinast and A23187 were also obtained in vessels contracted by NE. RESULTS: Left and right pulmonary artery responses to NE are enhanced over those of historic controls. Pretreatment of left pulmonary arteries with L-NA enhances the vasoconstrictor response to NE, whereas right PAs show no increased response. Relaxation responses to A23187 and zaprinast, in both left and right pulmonary arteries were not different from control lambs. Relaxation responses of both left and right pulmonary veins to A23187 and zaprinast are blunted compared with controls. This blunting is significantly more in left pulmonary veins than right. Further, right but not left pulmonary veins display enhanced vasoconstrictive response to NE after L-NA pretreatment. CONCLUSIONS: The NO-cGMP pathway of vasodilatation is abnormal in the near term, fetal lamb with CDH. These abnormalities were most apparent in pulmonary veins and may reflect abnormal NOS activity or content between left and right lungs of the fetal lamb with CDH. Pulmonary arteries from CDH lambs have basal and stimulated NO release equal to that of historic controls but appear to be hypersensitive to exogenous vasoconstrictors.     

Intrauterine tracheal obstruction, a new treatment for congenital diaphragmatic hernia, decreases amniotic fluid sodium and chloride concentrations in the fetal lamb

The chemoattractant N-formyl-methionyl-leucyl-phenylalanine (fMLP) interacts with neutrophils, generating signals that induce activation of the superoxide anion/hydrogen peroxide-producing NADPH-oxidase. Low temperature binding of fMLP to its neutrophil surface receptors is associated with a desensitization of the cells with respect to activation of the oxidase. Other stimuli can still activate the oxidase (in fact even induce a primed response), indicating that the observed phenomenon is stimulus specific and could not be accounted for by an effect on the oxidase itself. Furthermore, no desensitization is obtained in the presence of cytochalasin B, suggesting that the cytoskeleton is involved in the process leading to desensitization. Okadaic acid is a toxin produced by dinoflagellates and exerts its effects by an inhibition of cellular phosphatases. To investigate the role of phosphorylation/dephosphorylation events in the desensitization process we used okadaic acid as a scientific tool. We show that neutrophils treated with okadaic acid are primed with respect to the fMLP-induced production of superoxide anion, and that no desensitization is obtained in toxin-treated cells. Because the recovery of ligand-receptor complexes in a Triton X-100-insoluble fraction is very low in the cells treated with okadaic acid, we suggest that protein dephosphorylation is required to obtain binding to the cytoskeleton of occupied fMLP receptors; binding of the occupied receptors to the cell cytoskeleton being the mechanism behind desensitization.     

Patterns of fetal perinasal fluid flow in cases of congenital diaphragmatic hernia

OBJECTIVE(S): Our purpose was to expand the previous reported series of observations of fetal perinasal fluid flow in cases of antenatally diagnosed congenital diaphragmatic hernia, characterize the timing parameters of the fetal breath cycle, and define the relationship of fetal perinasal fluid flow and the diaphragmatic component of fetal breathing movements. Our hypothesis was that characteristics of diaphragm-related and nondiaphragm-related perinasal fluid flow and other breath cycle characteristics differ in cases of congenital diaphragmatic hernia compared with controls. STUDY DESIGN: Fetal perinasal fluid flow velocity and fetal chest wall movements were studied in 24 cases of uncomplicated pregnancy, and flow was studied in 24 cases of antenatally diagnosed congenital diaphragmatic hernia at gestational ages ranging from 30 to 41 weeks. The examination of fetal perinasal fluid flow velocity was performed with use of an ultrasonography system applying color flow and spectral Doppler analysis. Breath-to-breath interval, time of inspiration, time of expiration, and peak inspiratory and expiratory velocities were determined for each type of perinasal flow. RESULTS: The study revealed that the time of expiration in cases of congenital diaphragmatic hernia at 30 to 36 and 37 to 41 weeks of gestation was significantly shorter than in cases of uncomplicated pregnancy. The ratio of time of inspiration and breath-to-breath interval in cases of diaphragmatic hernia was approximately 30% higher (p = 0.001) at 30 to 36 weeks of gestation than in cases of uncomplicated pregnancy. The study also showed that in cases of congenital diaphragmatic hernia the expiratory peak velocity ratio at 30 to 36 weeks of gestation was significantly lower than in cases of uncomplicated pregnancy. CONCLUSIONS: We conclude that by Doppler ultrasonography measurements of fetal perinasal fluid flow, in cases of congenital diaphragmatic hernia, we can evaluate the timing parameters of fetal diaphragm-related breath cycles, the relationship of intraalveolar and intraamniotic pressures, and fetal upper respiratory tract resistance. Fetuses with diaphragmatic hernia spent significantly more time with diaphragm-nonrelated perinasal flow than did fetuses in cases of uncomplicated pregnancy, which can cause the increased loss of lung liquid and consequently be associated with pulmonary insufficiency in the early neonatal period.     

Experimental fetal tracheal ligation reverses the structural and physiological effects of pulmonary hypoplasia in congenital diaphragmatic hernia

Infants with congenital diaphragmatic hernia (DH) and profound pulmonary hypoplasia are currently unsalvageable. The authors previously demonstrated that tracheal ligation (TL) accelerates fetal lung growth and reverses the pulmonary hypoplasia of fetal nephrectomy. The purpose of this study was to determine if the pulmonary hypoplasia of experimental DH could be similarly reversed and, if so, whether the resulting lungs would show better function than those of their DH counterparts. Eighteen fetal lambs were divided into three experimental groups of six animals each. In group 1, DH was created at 90 days' gestation. In group 2, DH was created at 90 days' gestation and TL performed during the same operation. Group 3 consisted of sham-operated controls. These animals were delivered near full-term, and their lungs analyzed by standard morphometric techniques. Ten additional fetal lambs were divided into two experimental groups of five animals each. In group 4, DH was created at 90 days' gestation. In group 5, DH was created at 90 days' gestation and TL performed 20 days later, at 110 days' gestation. These animals were pressure-ventilated via tracheostomy over a 2-hour period in which PaO2, PaCO2, and compliance were measured. Intratracheal pressure (ITP) was measured at the time of delivery in all groups. Upon retrieval, DH animals had abdominal viscera in the chest and small lungs; in contrast, DH/TL animals had the herniated viscera reduced from the chest by enlarged lungs. DH/TL lungs showed markedly increased growth, with significant increases in lung volume:body weight ratio (LV:BW; P = .0001), alveolar surface area (ALV.SA; P = .0001), and alveolar number (ALV#) (P = .0001) when compared with those of the DH or control group. This growth was associated with a normal maturation pattern based on histological appearance, normal airspace fraction, and normal alveolar numerical density. ITP in the DH/TL group was increased when compared with that of DH and control animals (P = .0001). Total lung DNA and protein were both elevated in the DH/TL animals (P = .0001). However, the DNA:protein ratio remained normal, suggesting lung growth had occurred through cell proliferation, not by hypertrophy. When ventilated over a range of settings, DH/TL lungs were more compliant (P = .0001) and achieved higher PaO2s (P < .003) and lower PaCO2s (P = .0001) than their DH counterparts. From these data, the authors conclude: (1) Experimental fetal DH produces hypoplastic lungs that are not capable of adequate gas exchange with conventional ventilation.(ABSTRACT TRUNCATED AT 400 WORDS)     

Pulmonary artery structural changes in pulmonary hypertension complicating congenital diaphragmatic hernia

Primary pulmonary hypertension is characterized by the presence of smooth muscle cells in nonmuscular compartments or segments of the vessel and the abnormal deposition of collagen in both the small muscular arteries and arterioles and the large elastic arteries. Victorian blue van Gieson staining and Immunostaining with anti-alpha smooth muscle actin (ASMA) were performed on lung tissues obtained during autopsy from 21 patients who had congenital diaphragmatic hernia (CDH) complicated by persistent pulmonary hypertension (PPH) and 10 control patients who died of sudden infant death syndrome (SIDS). The degree of medial thickening and adventitial thickening was measured in pulmonary arteries by image analysis and compared statistically. There was a significant increase in adventitial as well as medial thickness in arteries of all sizes in CDH patients compared with control patients (P < .001). The most striking increase occurred in arteries with an external diameter (ED) of less than 75 microns. Calculation of the areas of the various components in the wall of each vessel showed that for smaller vessels (< 75 microns ED), the area of the lumen was smaller and the area of the media and adventitia was larger in CDH patients compared with control patients (P < < .001). In vessels greater than 75 microns ED, the areas of media in CDH was the same as in controls and the area of adventitia in CDH was significantly larger than controls (P < .001). The present study provides evidence that an increase in adventitial thickness and adventitial area occurs in pulmonary arteries in CDH patients complicated by PPH. The structural changes in the adventitia of the pulmonary arteries may be an important factor in the development of PPH in patients with CDH.     

Tissue blood flow distribution and the effect of chronic vascular catheterization in the hind limb of the fetal lamb

In six chronically instrumented fetal lambs, hind-limb skin, bone, and muscle comprised 22.5 +/- 1.3, 35.3 +/- 1.6, and 42.3 +/- 1.1% of total limb weight, respectively. As estimated using radionuclide-labeled microspheres, blood flow to these tissues averaged 30.4 +/- 4.9, 30.1 +/- 3.3, and 14.0 +/- 3.1 mL.min-1.100 g-1, respectively, and they received 29.5 +/- 3.3, 45.3 +/- 3.6, and 25.2 +/- 4.5% of total limb blood flow. Thus, muscle has a lower blood flow in relation to its weight in comparison with the other tissues, while bone receives the largest fraction of hind-limb blood flow. The higher perfusion rate to bone may by due to a high rate of hematopoiesis in late gestation, whereas muscle flow may be lower than that reported immediately after birth because of limited limb movement and lack of shivering thermogenesis. There were no significant differences in tissue weights between the limb in which femoral arterial and lateral tarsal venous catheters were implanted (nonstudy limb) and the leg that had smaller diameter catheters placed in the pudendoepigastric artery and vein (study limb). However, nonstudy limb blood flow was 13.4 +/- 1.8% less than in the study limb, although the flow distribution to hind-limb tissues was not different between the two limbs. This suggests that the longer, larger diameter catheters inserted into the nonstudy limb had an adverse effect on hind-limb blood flow but not on overall limb growth or blood flow distribution. More attention should be paid to the effects of chronic fetal vascular catheterization on the tissues or organs normally perfused by the catheterized vessel.     

Active collagen synthesis by pulmonary arteries in pulmonary hypertension complicated by congenital diaphragmatic hernia

BACKGROUND: Patients with spinal cord injury (SCI) have an increased prevalence of gallstones. AIMS: To study prospectively the incidence of gallstones and gall bladder contractility in patients with SCI. PATIENTS AND METHODS: Thirty six consecutive patients with SCI were studied: 18 patients with SCI above thoracic 10 neuronal segment (> T10) and 18 patients with SCI below T10 (< T10). An equal number each of disease controls (multiple fractures) and healthy controls were also studied. All patients and controls underwent serial ultrasonography to detect development of gallstones and ultrasonographic measurement of gall bladder contractility. RESULTS: A significantly higher number (9/18) of patients with SCI > T10 developed biliary sludge compared with patients with SCI < T10 (2/18), disease controls (2/18), and healthy controls (1/18) (p < 0.05). No patient developed gallstones. The gall bladder fasting volume was significantly decreased in patients with SCI > T10 (20.56 ml; 95% confidence intervals (CI) 19.74 to 21.38) compared with that in patients with SCI < T10 (27.33 ml, 95% CI 26.17 to 28.49; p < 0.05), disease controls (27.92 ml, 95% CI 26.69 to 29.15; p < 0.05), and healthy controls (28.35 ml, 95% CI 27.25 to 29.45; p < 0.05). Gall bladder contractility was normal in patients with SCI as shown by normal gall bladder residual volume and emptying time. CONCLUSIONS: Patients with SCI above T10 have an increased incidence of biliary sludge and a decreased gall bladder fasting volume. Gall bladder contractility is, however, normal.     

Hypoxic pulmonary vasoconstriction is impaired in rats with nitrofen-induced congenital diaphragmatic hernia

The aim of this study was to determine the efficacy and toxicity of topotecan administered as a 21-day continuous intravenous infusion in patients with advanced or metastatic adenocarcinoma of the pancreas. 26 previously untreated patients with advanced or metastatic pancreatic adenocarcinoma received topotecan at a dose of 0.5 mg/m2/day or 0.6 mg/m2/day as a continuous intravenous infusion for 21 days. Courses were repeated every 28 days. 26 patients were assessable for response and toxicity on an intent-to-treat basis. The initial 8 patients at a starting dose of 0.6 mg/m2/day experienced unacceptable myelosuppression and dose delays. The subsequent 18 patients, therefore began therapy at a dose of 0.5 mg/m2/day. The major toxicity of topotecan at this dose and schedule was myelosuppression, which was reversible and non-cumulative. There were no complete responses and two partial responses for a total response rate of 8% (95% confidence interval, 1-25%). Response durations were 17 and 45 weeks. Stable disease was seen in 3 patients. The median time to progression for all patients was 8 weeks and the median survival was 20 weeks. Topotecan given as a 21-day continuous intravenous infusion has a similar response rate and median survival to our previously reported study of the 5-day short infusion regimen in pancreatic carcinoma.     

Prediction of outcome in congenital diaphragmatic hernia

The case records of 59 patients with congenital diaphragmatic hernia (CDH) who presented between 1984 and 1997 were studied retrospectively. Included in the study were infants born with CDH who required respiratory support within the first 6 h of life. Twenty-three were excluded from the study for various reasons; 36 were enrolled in the study; the male-to-female ratio was 18:18. Twenty-nine hernias were left-sided and 7 were right-sided. All patients were ventilated using conventional techniques. Arterial blood gases were measured on average 1.76 h following admission and the initial period of resuscitation (range 1-4 h). Three formulae were applied in an attempt to predict outcome: ventilation index against PCO2, alveolar-arterial oxygen gradient, and a newly derived formula from this institution (Red Cross formula) that comprises respiratory rate x PCO2 x FiO2 x mean airway pressure/PaO2 x 6000. Seventeen patients (47.2%) survived and 19 died (52.8%); 21 became stable enough to undergo surgery. The average time from presentation until surgery was 1.98 days (range 6 h to 4 days). The Red Cross formula, with a 100% predictive value for mortality, 85% predictive value for survival, and an overall predictive value of 91.6%, appeared to be superior to the other formulae studied. The availability of a highly accurate predictive formula may facilitate management of this frequently lethal disease.     

Contemporary controversies in the management of congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) has remained the most frustrating of the major birth defects to manage successfully. Despite the earlier detection of severe diaphragmatic defects by prenatal ultrasound, and the early recognition of CDH as a cause for respiratory distress presenting at birth, current mortality has improved little from the original series presented in 1940 by Ladd and Gross. This article discusses the difficulty in defining population with congenital diaphragmatic hernia, current controversies in the medical and surgical management of these patients, appropriate timing and usage of ECMO, a review of current, experimental therapies, and short-term and long-term outcomes of these patients.     

Sequential increases and decreases in blood flow stimulates progressive intimal thickening

Exfoliative toxins of approximately 30 kDa produced by Staphylococcus hyicus strains NCTC 10350, 1289D-88 and 842A-88 were purified and specific polyclonal antisera were raised against each of the toxins. It was shown by immunoblot analysis and ELISA that three exfoliative toxins from S. hyicus were antigenically distinct. The three toxins were designated ExhA, ExhB and ExhC. From 60 diseased pigs, each representing an outbreak of exudative epidermitis, a total of 584 isolates of S. hyicus were phage typed and tested for production of exfoliative toxin. ExhA-, ExhB- and ExhC-producing S. hyicus isolates were found in 12 (20%), 20 (33%) and 11 (18%), respectively, of the 60 pig herds investigated. Production of the different types of exfoliative toxin was predominantly associated with certain phage groups. However, toxin production was found in all of the six phage groups defined by the phage typing system. Some changes in the distribution of isolates between phage groups were observed when the results of this study were compared to previous investigations. In this study two new antigenically distinct exfoliative toxins were isolated and tools for in vitro detection of toxin producing S. hyicus isolates and for further studies on the exfoliative toxins from S. hyicus have been provided.     

Ultrasound diagnosis of fetal diaphragmatic hernia and complex congenital heart disease at 12 weeks' gestation--a case report

Congenital diaphragmatic hernia is commonly associated with congenital heart disease. Their coexistence indicates a poor prognosis. Prenatal diagnosis of these conditions in early pregnancy allows the option of pregnancy termination. We present a case of left-sided fetal diaphragmatic hernia and complex congenital heart disease diagnosed by ultrasound examination at 12 weeks' gestation.     

Two cases of the congenital posterolateral diaphragmatic hernia were reported

Case 1, a 9-year-old woman, was admitted to our hospital because of nausea, vomiting, and epigastralgia. Diagnosis of Bochdalek hernia was made by the unusual course of naso-gastric tube. At surgery through the left posterorateral thoracotomy, the herniation of the stomach, small intestine, and colon to the thoracic cavity through the dorsolateral defect of the diaphragm were revealed. Case 2, a 35-year-old man, was admitted to our hospital because of dyspnea. Similar diagnosis was made by the examination of upper G1 series and barium enema, which demonstrated the presence of multiple loops of the small intestine and colon in the left thoracic cavity. Their postoperative courses were uneventful. Most of Bochdalek hernia is observed in infancy, and adolescent or adult case is is rarely reported (approximately 10% of all cases). Since this often misdiagnosed as pleuritis or pulmonary tuberculosis, a cautious examination is necessary for the establishment of the correct diagnosis.     

Endothelin receptor blockade prevents the rise in pulmonary vascular resistance after cardiopulmonary bypass in lambs with increased pulmonary blood flow

BACKGROUND: Children with increased pulmonary blood flow may experience morbidity as the result of increased pulmonary vascular resistance after operations in which cardiopulmonary bypass is used. Plasma levels of endothelin-1, a potent vasoactive substance implicated in pulmonary hypertension, are increased after cardiopulmonary bypass. OBJECTIVES: In a lamb model of increased pulmonary blood flow after in utero placement of an aortopulmonary shunt, we characterized the changes in pulmonary vascular resistance induced by hypothermic cardiopulmonary bypass and investigated the role of endothelin-1 and endothelin-A receptor activation in postbypass pulmonary hypertension. METHODS: In eleven 1-month-old lambs, the shunt was closed, and vascular pressures and blood flows were monitored. An infusion of a selective endothelin-A receptor blocker (PD 156707; 1.0 mg/kg/h) or drug vehicle (saline solution) was then begun 30 minutes before cardiopulmonary bypass and continued for 4 hours after bypass. The hemodynamic variables were monitored, and plasma endothelin-1 concentrations were determined before, during, and for 6 hours after cardiopulmonary bypass. RESULTS: After 90 minutes of hypothermic cardiopulmonary bypass, both pulmonary arterial pressure and pulmonary vascular resistance increased significantly in saline-treated lambs during the 6-hour study period (P <.05). In lambs pretreated with PD 156707, pulmonary arterial pressure and pulmonary vascular resistance decreased (P <. 05). After bypass, plasma endothelin-1 concentrations increased in all lambs; there was a positive correlation between postbypass pulmonary vascular resistance and plasma endothelin-1 concentrations (P <.05). CONCLUSIONS: This study suggests that endothelin-A receptor-induced pulmonary vasoconstriction mediates, in part, the rise in pulmonary vascular resistance after cardiopulmonary bypass. Endothelin-A receptor antagonists may decrease morbidity in children at risk for postbypass pulmonary hypertension. This potential therapy warrants further investigation.     

Use of an automated fluorescent microsphere method to measure regional blood flow in the fetal lamb

OBJECTIVE: To investigate the source of the expanded blood CD8+ subsets during an acute primary simian immunodeficiency virus (SIV) infection of macaques and the potential role of these cells in disease progression. DESIGN AND METHODS: The primary CD8+ lymphocytosis, which occurs at 1-2 weeks following infection with SIVsmm/PBj-14, was examined in rhesus and cynomolgus macaques. Extensive subset analysis of the expanded blood CD8+ cell pool in a rhesus macaque was compared phenotypically with those in thymus, lymph nodes, spleen, ileum and lung washouts obtained at necropsy during blood lymphocytosis. The influence of the primary CD8+ cells expansion on disease progression was assessed at days 175-679 post-infection in long-term PBj-14 survivors staged according to immunological, virological and histopathological changes in their lymphoid organs. RESULT: The very rapid and transient blood lymphocytosis following infection consisted of two distinct CD45RA(low), CD8+ and CD28-, lymphocyte function-associated antigen (LFA)-1(high), CD45RA(high), CD8+ populations. These populations were present in low levels in thymus, lymph and spleen but were highly represented in mucosal tissues, such as long washout, in which CD28- LFA-1(high) CD45RA(high) CD8+ cells comprised 86% of CD8+ cells, and gut, which was predominantly CD45RA(low) CD28- CD8+ cells. A comparison of progressor and non-progressor PBj-14-infected rhesus and cynomolgus macaques also indicated that the existence or magnitude of a blood CD8+ lymphocytosis during the acute phase of infection did not by itself appear to influence or be predictive of disease progression. CONCLUSION: The marked blood CD8+ lymphocytosis observed during acute SIV infection did not result from expansion of virus-specific precursors in peripheral lymph node and did not appear to influence the rate of disease progression. The findings provide a novel explanation for the primary CD8+ cell lymphocytosis and invoke a mechanism whereby virus-induced cytokine/chemokine production in mucosal sites initiate the transient migration of a pre-existing CD8+ population into the blood from compartments such as lung and gut. Such results suggest that the magnitude of lymphocytosis may depend on the level of viral replication in mucosal tissues and the presence of other infections, for example, cytomegalovirus.     

Tracheal ligation: the dark side of in utero congenital diaphragmatic hernia treatment

This retrospective study investigates the clinical characteristics of gestational diabetes mellitus (GDM) (time of diagnosis, different treatment, metabolic parameters, etc.) in relation to prepregnancy body mass index (BMI) and the influence of BMI on neonatal outcome. 93 GDM women and 110 control subjects were divided into three groups in relation to their prepregnancy BMI: normalweight (Nw), overweight (Ow) and obese (Ob). GDM was diagnosed significantly (p < 0.01) earlier in Ow and Ob than in Nw. Preterm deliveries and cesarean sections resulted significantly (p < 0.01) increased in all BMI categories of GDM respect to matched controls. Prevalence of neonatal macrosomia was higher in GDM patients (44.6%) compared with normal controls (15.4%) and correlated (p < 0.01) with prepregnancy BMI in both groups. Nevertheless in each BMI category the prevalence of macrosomia was significantly higher in GDM patients. The body weight increase during pregnancy was not associated with neonatal macrosomia. This study shows that prepregnancy BMI is an important risk factor for GDM and is predictive for macrosomia specially in women suffering from GDM.     

Near fatal pulmonary hypertension after surgical repair of congenital diaphragmatic hernia. Successful use of inhaled nitric oxide

The addition of 10-20 parts per million nitric oxide to the inspired gas was successful in controlling near fatal pulmonary hypertension after surgical repair of a congenital diaphragmatic hernia in a neonate. A preceding prostacyclin infusion was unable to prevent the failure of pulmonary perfusion. No side effect of nitric oxide therapy was observed, and ventilatory support could be substantially reduced as a result of the treatment. On the basis of the striking and lifesaving effects of nitric oxide therapy demonstrated in this child, we believe that nitric oxide treatment will prove to be a major contribution to the management of postoperative pulmonary hypertensive crises.     

Evaluation of pulmonary vascular anatomy and blood flow by magnetic resonance

Rapidly evolving magnetic resonance (MR) imaging techniques provide noninvasive approaches to evaluating morphology and quantitative physiologic information about blood flow in the pulmonary circulation. Important clinical applications currently include the preoperative and postoperative evaluation of congenital abnormalities, assessment of vascular involvement by extrinsic and intrinsic tumors, identification of central thromboemboli, and diagnosis of vascular lung lesions. Ongoing refinements in pulmonary MR angiography may make it possible to use the technique for the noninvasive detection of acute pulmonary emboli in the near future. Quantitative measurements based upon MR flow-encoding sequences are promising for the evaluation of patients with abnormal degrees or distributions of pulmonary blood flow, for example, those with unilateral lung transplants or pulmonary arterial stenoses. MR contrast agents currently under development also show promise for quantitative measurements of regional pulmonary ventilation and perfusion. The coupling of high-resolution anatomic and functional images renders MR a uniquely attractive and powerful method for evaluating the pulmonary vasculature.