Role of mesenchymal cell death in lung remodeling after injury.

Repair after acute lung injury requires elimination of granulation tissue from the alveolar airspace. We hypothesized that during lung repair, signals capable of inducing the death of the two principal cellular elements of granulation tissue, fibroblasts and endothelial cells, would be present at the air-lung interface. Bronchoalveolar lavage fluid obtained from patients during lung repair induced both fibroblast and endothelial cell death, while fluid obtained at the time of injury or from patient controls did not. The mode of cell death for endothelial cells was apoptosis. Fibroblast death, while morphologically distinct from necrosis, also differed from typical apoptosis. Only proliferating cells were susceptible to the bioactivities in lavage fluid, which were trypsin sensitive and lipid insoluble. Histological examination of lung tissue from patients after lung injury revealed evidence of apoptotic cells within airspace granulation tissue. Our results suggest that cell death induced by peptide(s) present at the air-lung interface may participate in the remodeling process that accompanies tissue repair after injury.

The critical early proinflammatory events associated with idiopathic pneumonia syndrome in irradiated murine allogeneic recipients are due to donor T cell infusion and potentiated by cyclophosphamide.

We have hypothesized that lung damage occurring in the peri-bone marrow transplant (BMT) period is critical for the subsequent generation of idiopathic pneumonia syndrome (IPS), a major complication following human BMT. The proinflammatory events induced by a common pre-BMT conditioning regimen, cyclophosphamide (Cytoxan(R)) (Cy) and total body irradiation, were analyzed in a murine BMT model. Electron microscopy indicated that Cy exacerbated irradiation-induced epithelial cell injury as early as day 3 after BMT. Allogenicity was an important contributing factor to lung injury as measured by lung wet and dry weights and decreased specific lung compliance. The most significant pulmonary dysfunction was seen in mice receiving both allogeneic T cells and Cy conditioning. IPS was associated with an influx of T cells, macrophages, and neutrophils early post-BMT. Hydroxyproline levels were not increased, indicating that the injury was not fibrotic early post-BMT. As early as 2 h after chemoradiation, host macrophages increased in number in the lung parenchyma. Continued increases in macrophages occurred if splenic T cells were administered with the donor graft. The expression of costimulatory B7 molecules correlated with macrophage numbers. Frequencies of cells expressing mRNA for the inflammatory proteins TNF-alpha, IL-1beta, and TGFbeta were increased. Cy accelerated the upregulation of TGFbeta and increase in host macrophages. The exacerbation of macrophage activation and severity of IPS was dependent on allogeneic T cells, implicating immune-mediated mechanisms as critical to the outcome of IPS. This demonstration of early injury after BMT indicates the need for very early therapeutic intervention before lung damage becomes profound and irreversible.

The effect of food deprivation of the peripheral metabolism of thyroxine in rats.

Starvation depresses thyroid gland function. In addition, the peripheral turnover of thyroxine (T4) is reduced, in part due to decreased fecal elimination of T4. The present studies were performed to determine if starvation also affects the deiodinative pathway for T4 degradation. Rats were isotopically equilibrated with daily injections of exogenous [131-I]T4 while endogenous thyroidal T4 secretion and concentration of iodide were blocked with KCl04. Following a period of equilibration, either complete or 50% food deprivation was imposed on half the animals. Within 48 h of starvation, the serum T4 concentration of the fully starved rats doubled and remained high throughout. A marked decrease in fecal excretion of T4 was partially responsible for the increase. In spite of variability in the quantity of urinary 131-I excreted, the dieodinative clearance was consistently reduced. These effects were readily reversible upon resumption of normal feeding. Similar though less severe changes were observed in the half-fed rats. In both fully and partially-starved animals, the decreased dieodinative clearance in the face of increased serum T4 levels indicates a significant impairment of peripheral deiodination by some as yet unknown mechanism. In contrast, normal rats equilibrated with doses of T4 sufficient to increase serum T4 levels exhibit increased urinary clearance of iodide derived from T4. Thus the increased serum T4 levels are a consequence of impairment of the deiodinative pathway by starvation as well as decreased fecal T4 excretion. Clearly, voluntary alterations in food consumption must be controlled for differences between groups during experimental studies of T4 utilization.

Polarized distribution of Na+,K+-ATPase in giant cells elicited in vivo and in vitro.

Giant cell formation was analyzed to determine whether it results in the high level of Na+,K+-ATPase expression that characterizes multinucleated cells such as osteoclasts. Giant cells and fusing alveolar macrophages were subjected to morphological, immunological, and biochemical studies. Both subunits of the Na+,K+-ATPase were found to be present on the plasma membrane of giant cells. Their localization was restricted to the non-adherent domain of the cell surface. Dynamic studies of giant cell differentiation demonstrated that on culture and/or multinucleation, an increase in sodium pump alpha-subunit synthesis occurred and led to a high level of expression of Na pumps. Conversely, the adherent plasma membrane of giant cells was enriched in a lysosomal membrane antigen. This study demonstrates that culture and/or multinucleation induces a significant increase in the expression of sodium pumps. The polarized distribution of these pumps and of a lysosomal component suggests that fusing macrophages undergo biochemical and morphological alterations which prepare them for a new and specialized function in chronic inflammatory reactions. Giant cells may offer a suitable model system to study the differentiation of other related multinucleated cells, such as osteoclasts.

Oxidant effects on epithelial Na,K-ATPase gene expression and promoter function.

The lung epithelium resorbs alveolar fluid through combined action of sodium channels and the sodium pump, Na,K-ATPase. The lung often is exposed to hyperoxia in disease states and hyperoxia generates a mixture of reactive oxygen species. In vivo and in vitro exposure of rat lung and alveolar type II cells, respectively, increases gene expression of both alpha-1 and beta-1 subunits of the sodium pump. In contrast to the primary type II cells, several type II cell lines did not increase sodium pump gene expression with hyperoxia, but the renal tubular epithelial MDCK cell line did. Using promoter-receptor constructs transfected into MDCK cells, hyperoxia did not markedly increase transcription of the alpha-1 subunit but doubled transcription of the beta-1 subunit gene. Using 5'-deletion constructs, the region required for the beta-1 increase was localized to a 40-base pair region from -44/-84. The hyperoxic responsiveness of this region was confirmed using constructs with one or two copies of this region placed in minimal promoter-luciferase reporters. This 5' promoter region contains a consensus binding sequence for SP-1, a basal transcription factor but not for binding of other known transcription factors. Thus, hyperoxia induces Na,K-ATPase beta-1 promoter transcription, likely acting through a novel mechanism.

A universal precautions monitoring system adaptable to any health care department.

The Occupational Safety and Health Administration has proposed monitoring employee compliance with universal precautions, as recommended by the Centers for Disease Control. Our respiratory care department, following a four-step system development plan, has developed and implemented a universal precautions monitoring system that is easy to adapt to any health care department. The results from monitoring can be used for educational planning, quality assurance purposes, and employee performance reviews.

Invited review: lung edema clearance: role of Na(+)-K(+)-ATPase.

Acute hypoxemic respiratory failure is a consequence of edema accumulation due to elevation of pulmonary capillary pressures and/or increases in permeability of the alveolocapillary barrier. It has been recognized that lung edema clearance is distinct from edema accumulation and is largely effected by active Na(+) transport out of the alveoli rather than reversal of the Starling forces, which control liquid flux from the pulmonary circulation into the alveolus. The alveolar epithelial Na(+)-K(+)-ATPase has an important role in regulating cell integrity and homeostasis. In the last 15 yr, Na(+)-K(+)-ATPase has been localized to the alveolar epithelium and its contribution to lung edema clearance has been appreciated. The importance of the alveolar epithelial Na(+)-K(+)-ATPase function is reflected in the changes in the lung's ability to clear edema when the Na(+)-K(+)-ATPase is inhibited or increased. An important focus of the ongoing research is the study of the mechanisms of Na(+)-K(+)-ATPase regulation in the alveolar epithelium during lung injury and how to accelerate lung edema clearance by modulating Na(+)-K(+)-ATPase activity.

Terbutaline stimulates alveolar fluid resorption in hyperoxic lung injury.

Alveolar fluid resorption occurs by active epithelial sodium transport and is accelerated by terbutaline in healthy lungs. We investigated the effect of terbutaline on the rate of alveolar fluid resorption from rat lungs injured by hyperoxia. Rats exposed to > 95% O2 for 60 h, sufficient to increase wet-to-dry lung weight and cause alveolar edema, were compared with air-breathing control rats. After anesthesia, the animals breathed 100% O2 for 10 min through a tracheostomy. Ringer solution was instilled into the alveoli, and the steady-state rate of volume resorbed at 6 cmH2O pressure was measured via a pipette attached to the tracheostomy tubing. Ringer solution in some animals contained terbutaline (10(-3) M), ouabain (10(-3) M), or both. Normoxic animals resorbed 49 +/- 6 microliters.kg-1.min-1; ouabain reduced this by 39%, whereas terbutaline increased the rate by 75%. The effect of terbutaline was blocked by ouabain. Hyperoxic animals absorbed 78 +/- 9 microliters.kg-1.min-1; ouabain reduced this by 44%. Terbutaline increased the rate by a mean of 39 microliters.kg-1.min-1, similar to the absolute effect seen in the normoxic group, and this was blocked by ouabain. Terbutaline accelerates fluid resorption from both normal and injured rat lungs via its effects on active sodium transport.

Perfusion technique determines alveolar fluid resorption rate in the isolated perfused rat lung.

The isolated perfused lung (IPL) preparation is a well-established model for the study of alveolar epithelial sodium transport. We noted that preparations of normal fluid-filled rat lungs with recirculated perfusate reproducibly lost weight, whereas preparations in which the perfusate was discarded after a single pass through the lungs had a variable and lesser weight change. To confirm this, we performed IPL experiments by using male Sprague-Dawley specific-pathogen-free rats (175-225 g). In 10 IPLs, perfusate initially was discarded after passing through the lungs and then was recirculated continuously. During the single-pass period, the rate of weight change was +0.7 +/- 2.0 mg/min compared with -9.0 +/- 1.3 mg/min for the recirculating period. Adenosine 3',5'-cyclic monophosphate (cAMP) accumulated during recirculation. The weight loss induced by recirculation was reproduced by perfusion with 8-bromoadenosine 3',5'-cyclic monophosphate or terbutaline in single-pass fashion and blocked when the kinase inhibitor H-8 or phosphodiesterase was present in the recirculating perfusate. In summary, perfusate recirculation in the IPL stimulates fluid resorption at least partially via cAMP. This should be factored into the design and interpretation of IPL experiments.

Mechanisms of repair and remodeling following acute lung injury.

At present, we largely lack the ability to correlate the clinical course of ARDS patients with potential factors involved in the biochemical and cellular basis of lung repair. This requires very large patient databases with measurement of many biochemical parameters. Important mechanistic determinants during the repair phase can be sought by correlation with late outcomes, but a large-scale cooperative effort among multiple centers with sharing of follow-up data and patient specimens is essential. We also lack detailed human histologic material from many phases of ARDS and, particularly, know little of the long-term morphologic impact of ARDS in survivors. Establishment of a national registry that follows ARDS survivors and that would seek their cooperation in advance in obtaining autopsy specimens when they die of other causes would be very valuable. Correlating the pathology with their pulmonary function during recovery would give important insights into the reasons for the different patterns of abnormal pulmonary functions. The factors that determine the success of repair are of critical importance in testing new ARDS treatment strategies. Would accelerating the resolution of alveolar edema alter the course of subsequent fibrosis and inflammation? Does surfactant replacement therapy--a costly proposition in adults with ARDS--lead to better long-term outcomes in survivors? How much should we worry about the use of high levels of oxygen for support of arterial partial pressure of oxygen? Is it better to accept hyperoxia to avoid pressure or volume trauma induced by mechanical ventilation with higher minute ventilations? These major management issues all may affect the success of the late repair and recovery process. Intervention trials need to examine the long-term physiologic and functional outcomes.

Diagnosis and management of acute lung injury.

Severe acute lung injury, also known as the adult respiratory distress syndrome (ARDS), is a dynamic and explosive clinical syndrome which exacts a mortality of approximately 50%. The criteria for the diagnosis of severe acute lung injury include five principal elements: hypoxemia despite high concentrations of supplemental oxygen, diffuse pulmonary infiltrates on chest radiographs, decreased lung compliance, appropriate antecedent history, and the absence of congestive heart failure. Identifying an appropriate antecedent history requires consideration of a diverse group of etiologies which may injure alveolar structures via either the air-lung or blood-lung interface. The management of patients with acute lung injury should be approached with four principal goals: (1) cardiopulmonary resuscitation and stabilization; (2) rapid identification and elimination of the cause of lung injury; (3) achieving adequate tissue oxygen delivery and support of other end-organs; and (4) prevention, recognition, and aggressive treatment of any complications that develop during the course of therapy. Recent observations have suggested that conventional methods of positive-pressure ventilation may indirectly injure alveolar tissue, thereby perpetuating lung injury. Furthermore, the optimal use of fluid and hemodynamic support remains controversial. Thus, controlled clinical trials are necessary to develop oxygenation, ventilatory, and hemodynamic support strategies which optimize recovery and minimize further injury and to define the role of newer pharmacologic agents in the prevention and treatment of acute lung injury.

Massive hemoptysis. Assessment and management.

The first priorities in treating the patient with massive hemoptysis are to maintain the airway, optimize oxygenation, and stabilize the hemodynamic status. The major question to be answered is whether or not the patient should be intubated for better gas exchange, suctioning, and protection from sudden cardiorespiratory arrest. If the bleeding site is known, the patient should be placed with the bleeding lung in the dependent position. Once stabilization is accomplished, diagnostic and therapeutic interventions should be promptly performed because recurrent bleeding occurs unpredictably. Early bronchoscopy, preferably during active bleeding, should be performed with three goals in mind: to lateralize the bleeding side, localize the specific site, and identify the cause of the bleeding. In those patients with lateralized or localized persistent bleeding, immediate control of the airway may be obtained during the procedure with topical therapy, endobronchial tamponade, or unilateral intubation of the nonbleeding lung. If bleeding continues but the side of origin is uncertain, lung isolation or use of a double-lumen tube is reasonable, provided that the staff is skilled in this procedure. If the bleeding cannot be localized because the rate of hemorrhage makes it impossible to visualize the airway, emergent rigid bronchoscopy or emergent arteriography is indicated. Arteriography and embolization should be used emergently for both diagnosis and therapy in those patients who continue to bleed despite endobronchial therapy. Emergent surgical intervention should be considered in operative candidates with unilateral bleeding when embolization is not available or not feasible, when bleeding continues despite embolization, or when bleeding is associated with persistent hemodynamic and respiratory compromise. For patients in whom bleeding has ceased or is decreased, emergent intervention may not be necessary. If the bleeding site has been localized or lateralized with early bronchoscopy, recurrent bleeding can be managed more confidently and rapidly. The cause of bleeding can be determined at bronchoscopy in patients with endobronchial adenomas, carcinomas, foreign bodies, or broncholiths. If no diagnosis is obtained at bronchoscopy, elective angiography of the bronchial and, if necessary, the pulmonary vasculature is reasonable. The precise timing and nature of the further evaluation are dictated by the suspected underlying pathologic process and the clinical condition of the patient. Surgery is the most definitive form of therapy for patients with hemoptysis because it removes the source of bleeding. Whether to proceed with elective surgery in patients with a major bleed that stops or one that is controlled angiographically is a difficult decision. Little data are available to assist in this decision, even for specific diseases, such as bronchiectasis. Similarly, the long-term course of patients treated with endobronchial tamponade or topical therapy is unknown. For patients with inoperable disease, limited reserve, or bilateral progressive disease, embolization frequently controls bleeding for prolonged periods.(ABSTRACT TRUNCATED AT 400 WORDS)

Acute respiratory failure.

Respiratory failure is a common problem in the patient with cancer. Many of these patients require intubation and treatment in an intensive care unit. Expeditiously determining the cause of the respiratory failure and treating it appropriately is mandatory. In addition, understanding the reason for respiratory failure permits rational determination of the aggressiveness of therapy.

Pulmonary sequelae and lung repair in survivors of the adult respiratory distress syndrome.

The high in-hospital mortality of ARDS has not diminished over the past 10 years, despite improvements in supportive intensive care. Much of the mortality arises from infections, particularly sepsis and pneumonia, and from organ failure, especially kidney failure. The rapid advances in understanding the interlocking pathophysiologic mechanisms of ARDS have not yet been translated into therapeutic trials of new methods for diminishing the injury or for stimulating normal repair. In part, this is because it is difficult to predict which high-risk patients will develop ARDS and then intervene early in the injury process. Patients in whom the risk for ARDS is extremely high have a very high mortality even without ARDS, thereby making efficacy of an early or prophylactic therapy quite difficult to prove. In spite of severe pathologic abnormalities, including fibrosis, early in the course of ARDS, most survivors return to almost normal pulmonary function. The few cases that have been studied with serial biopsies demonstrate resolution of fibrosis. This amazing recovery poses many fascinating questions about how the lung repairs itself. Given the heterogeneous causes of ARDS and the large number of structural, cellular, and biochemical abnormalities described, one can postulate that any one of numerous factors is important in normal repair. Most promising of these are the degree of basement membrane damage, the control of type II cell proliferation and differentiation, the control of collagen synthesis, the anatomic localization of fibrosis, and the control of collagenase action. These interactions of epithelial and mesenchymal tissues probably recreate the process of lung development in the injured adult lung. At a clinical level, the role of oxygen toxicity remains a significant issue. Oxygen acting as an oxidant may be partially responsible for the small airways disease seen in approximately one quarter to one third of survivors. The mortality data stress the need for better ways of preventing and diagnosing lung infections. Better definition of the clinical factors that put survivors at risk for persistent loss of lung function is also needed, and could define a subgroup in which trials of agents designed to improve repair would be most worthwhile. More information about the long-term pathologic course, though difficult to obtain, would also be very important. Perhaps some registry of ARDS survivors would permit closer follow-up and make available more late autopsy pathology when these people die of other causes. The rapid time course of ARDS provides an ideal testing ground for agents designed to either decrease lung injury or stimulate repair.(ABSTRACT TRUNCATED AT 400 WORDS)