Modulation of endotoxin-induced neutrophil alveolitis by captopril and by hyperoxia.

We compared survival and the intensity of bronchoalveolar inflammation reflected by lung lavage after the intraperitoneal injection of endotoxin from Escherichia coli serotype 055B5 in rats breathing air and those breathing 60% oxygen for six days after endotoxin injection. Survival following 7.5 mg/kg of endotoxin was comparable in air-breathing rats (50%) and in oxygen-breathing rats (63%). Endotoxin caused a dose-dependent increase in the recovery of polymorphonuclear leukocytes from the lung. Oxygen breathing reduced the percentage of neutrophils recovered by lavage 24 hr after endotoxin from 17% to 9% after 2.5 mg/kg of endotoxin and from 34% to 12% after 7.5 mg/kg of endotoxin. The absolute number of neutrophils recovered was also significantly decreased in oxygen-breathing rats. The activity of pulmonary angiotensin-converting enzyme (ACE) has been reported to be affected by oxygen tension, and ACE degrades bradykinin, a proinflammatory mediator. Therefore, we questioned whether the salutary effect of increased inspired oxygen tension on the magnitude of neutrophil influx into the airspaces could be related to changes in ACE activity. We found that after 48 hr of peroral pretreatment of the rats with captopril, a specific ACE inhibitor, there was increased recovery of neutrophils by lavage 24 hr after injection of endotoxin in air-breathing rats. Captopril pretreatment also increased the chemotactic activity of bronchoalveolar lavage fluid (BALF). There was no concomitant alteration in the accumulation of 125I albumin in the lung following captopril pretreatment either in endotoxin-treated rats or in controls. Thus, breathing 60% oxygen decreased the accumulation of neotrophils in airspaces after intraperitoneal endotoxin injection and pharmacologic inhibition of ACE had the opposite effect. Alterations in the activity of pulmonary angiotensin-converting enzyme related to alveolar oxygen tension is a potential speculative mechanism for modulation of alveolar inflammation by the inspired oxygen concentration in this model.

Shift in subfractions of rat alveolar macrophages in vivo during endotoxin-induced alveolitis.

To elucidate changes in alveolar macrophages that accompany sepsis-induced lung injury, this study analyzed the subfractions of alveolar macrophages (AM) recovered by lung lavage during the onset of endotoxin-induced acute neutrophilic alveolar inflammation in the rat model. Centrifugation on continuous self-generated density gradients of Percoll was used to fractionate AM into subpopulations between density limits 1.012 and 1.130. Two-thirds of AM recovered from pathogen-free control rats (group C) were in a fraction with a density range of 1.058-1.078 ["normal" density fraction, (ND)]. Only 6% were located in a very low density (VLD) fraction 1.037-1.048. Neutrophils accounted for less than 1% of recovered cells and usually were found in the fraction with density range of 1.079-1.130. By contrast, if rats underwent lung lavage 15 hours after the administration of endotoxin (group E), only 38% of macrophages were recovered in the "normal" density fraction, whereas 26% of the AM recovered were in the VLD fraction. This shift in the relative sizes of the density based subpopulations coincided with the onset of acute bronchoalveolar inflammation as indicated by the recovery of neutrophils by bronchoalveolar lavage (PMN = 7 X 10(4) in C, vs. 9.4 X 10(5) in E, p less than .001). The macrophages on the low density subfractions showed functional impairment: they were less viable in culture and migrated poorly in response to endotoxin-activated serum compared to macrophages in the "normal" density fraction from the endotoxin-treated animals. The rapid emergence of the low density population after endotoxin could represent an influx of new cells, but more likely indicates that injury to or previous activation of resident macrophages has caused their density to decrease. We speculate that the emergence of a population of AM in airspaces with low density and impaired function could weaken pulmonary host defence following endotoxemia.

Massive hemoptysis and tension pneumothorax following pulmonary artery catheterization.

We report a case of massive hemoptysis and bilateral tension pneumothorax immediately following placement of a fiberoptic pulmonary artery catheter. We postulate air entry into a traumatic communication caused by the catheter, traversing a parenchymal artery, the contiguous airspace and the interstitial space. Dissection of air through the perivascular sheath and into tissue planes of the thorax and abdomen followed. This sequence was rapidly fatal. Tension pneumothorax should be considered if dynamic respiratory system compliance remains poor despite aggressive evacuation of blood from the trachea of a patient with a recently inserted balloon-type catheter.

Adult respiratory distress syndrome following intrapleural instillation of talc.

After intrapleural instillation of talc for sclerosis of malignant pleural effusions, dyspnea occurred in three patients, progressed gradually over 72 hours, and culminated in acute respiratory failure characterized by bilateral diffuse pulmonary infiltrates with normal pulmonary artery occlusion pressures. Two patients recovered and one died. The chronological similarity of the sequence of fever, dyspnea, and respiratory failure in the absence of documented infection or other conditions that predispose to the adult respiratory distress syndrome (ARDS) suggests that intrapleural talc may have induced the syndrome in these patients through unknown mechanisms. This experience emphasizes that other agents are preferable for initial attempts to promote pleural symphysis in the palliation of recurrent malignant effusions. When talc is used in patients who are unresponsive to tetracycline, we suggest clinical monitoring for respiratory compromise for 72 hours after the procedure.

Mechanisms and mediators of the adult respiratory distress syndrome.

In 1990, we are much less certain that we understand ARDS than we were in 1982, and we have yet to identify specific therapy. It is tempting to conclude that we have made no progress, but this conclusion would be unwarranted. In those 8 years, important advances have been made. The complement hypothesis has survived, with significant modifications. Recognition of the importance of infection in clinical outcome and of endotoxin in augmentation of neutrophil-mediated injury has evolved in concert and meshes well. A new class of peptide mediators, cytokines, has assumed a central role. Lipid mediators now appear as modulators of cytokine-induced effects by priming, amplification, and regulation of gene expression rather than as unifactorial "causes" of the physiologic manifestations of ARDS. These interdigitating mechanisms have been recognized as pansystemic, resulting in overt multiple organ dysfunction and ultimately in death if amplification mechanisms go unchecked. Technologies in molecular genetics, generally unknown to the pulmonary community in 1982, have had a significant impact. Recombinant cDNA technology has permitted identification of the existence, structure, and functions of novel cytokines; made them available in sufficient quantity for detailed study; and prompted interest in the regulation of gene expression in the evolution and resolution of inflammation. Proteins modified by genetic engineering, as well as monoclonal antibodies and receptor antagonists for specific cytokines, are promising future approaches to therapy. At present, the complexity of the redundant networks by which inflammation is regulated seems bewildering in relation to ARDS. Bewildering or not, the age of the "mediator" of ARDS, and of the corresponding therapeutic "magic bullet," is over. The complexity of the system of regulatory checks and balances must be addressed at the molecular level.

Effects of ibuprofen on endotoxin-induced alveolitis: biphasic dose response and dissociation between inflammation and hypoxemia.

Ibuprofen is a cyclo-oxygenase inhibitor that is alleged to have additional direct effects on leukocyte function. These properties suggest that Ibuprofen may be of potential therapeutic value for neutrophil (PMN)-mediated acute lung injury in humans such as that resulting from septicemia by gram-negative organisms. This study quantitated the effect of pretreatment with Ibuprofen on the intensity of acute neutrophilic alveolitis following endotoxemia. The effect of Ibuprofen on neutrophilic alveolitis was biphasic: There was suppression of inflammation at a high dose (30 mg/kg), enhancement at a low dose (3 mg/kg), and intermediate doses (10-20 mg/kg) had no effect. In contrast, both 10 and 30 mg/kg of Ibuprofen prevented early hypoxemia following endotoxemia, suggesting that early hypoxemia and inflammation by neutrophils were not causally related. The dose of Ibuprofen required to suppress neutrophil alveolitis exceeds that required to inhibit cyclooxygenase in the model. Therefore, suppression of alveolitis by 30 mg/kg of Ibuprofen may depend on other pharmacologic properties of Ibuprofen such as its direct effect on neutrophil migration.

Neutrophil-endothelial interactions: Modulation of neutrophil activation responses by endothelial cells.

There is controversy concerning whether intravascular activation of neutrophils during acute inflammation injures contiguous endothelial cells in vivo. Several physiologic defense mechanisms tend to limit such injury. In this paper we have examined evidence for one of these putative protective mechanisms: endothelial cell modulation of the activation responses of neutrophils during adherence and diapedesis. In vitro, endothelial cells co-incubated with neutrophils inhibit the release of superoxide anion when stimulated by receptor-mediated activators. The possible mechanisms include contact-linked down-regulation of neutrophil activation, the release from endothelial cells of soluble mediators which attenuate neutrophil activation responses, and the presence of free radical scavengers in endothelial cells which are active at the interface between endothelial cells and adherent neutrophils. There may be a broad spectrum of mechanisms by which intercellular interactions protect the lining cells of the vascular lumen from 'inadvertent' destruction by phagocytes which become activated while in an intravascular location.

Neutrophil-endothelial interactions: modulation of neutrophil activation responses by endothelial cells.

There is controversy concerning whether intravascular activation of neutrophils during acute inflammation injuries contiguous endothelial cells in vivo. Several physiologic defense mechanisms tend to limit such injury. In this paper we have examined evidence for one of these putative protective mechanisms: endothelial cell modulation of the activation responses of neutrophils during adherence and diapedesis. In vitro, endothelial cells co-incubated with neutrophils inhibit the release of superoxide anion when stimulated by receptor-mediated activators. The possible mechanisms include contact-linked down-regulation of neutrophil activation, the release from endothelial cells of soluble mediators which attenuate neutrophil activation responses, and the presence of free radical scavengers in endothelial cells which are active at the interface between endothelial cells and adherent neutrophils. There may be a broad spectrum of mechanisms by which intercellular interactions protect the lining cells of the vascular lumen from 'inadvertent' destruction by phagocytes which become activated while in an intravascular location.

Role of alveolar macrophages in endotoxin-induced neutrophilic alveolitis in rats.

Although bacterial endotoxins have potent effects on blood monocytes and tissue macrophages, the role of alveolar macrophages in regulating intrapulmonary neutrophil traffic following endotoxemia has not been studied previously. We have previously reported that a single intraperitoneal injection of endotoxin from Escherichia coli serotype 055B5 causes acute lung inflammation by neutrophils (PMN) in rats. The factors which influence the migration of PMN in the lung in this model are unknown. To determine whether macrophage-derived products could play a role in directing migration, we enumerated neutrophils in histologic sections and employed electron microscopy to document the location of neutrophils in the lung in vivo following endotoxin. We also cultured the alveolar macrophages recovered by lung lavage to measure the effect of their culture supernatants on neutrophil migration in vitro. In the first 6 hr following endotoxin, and also 24 hr later, there was an increase in the number of PMN enumerated in the lung parenchyma by light microscopy. Electron microscopy showed the location of the neutrophils to be exclusively intravascular at 6 hr. By contrast, neutrophils were observed in both interstitial and bronchoalveolar spaces at 24 hr, confirming that transvascular migration was active at that time. The pulmonary macrophages which were recovered by lung lavage from groups of rats sacrificed at 4 and at 15 hr following the administration of endotoxin were assayed for the release into culture media of migration-stimulatory activity for neutrophils. Macrophages from animals sacrificed 4 hr following endotoxin released less migration-stimulating activity into media than macrophages from controls. These macrophages could be stimulated to release migration-stimulating activity into culture media at levels comparable to macrophages from controls by the addition of opsonized Zymosan to the culture media. By contrast, macrophages from animals sacrificed 15 hr after endotoxin spontaneously released more migration-stimulating activity for neutrophils than did macrophages from controls. Thus, in this model, a specific increase in the synthesis or release by alveolar macrophages of factors which stimulate the migration of neutrophils in vitro coincided with a transition from intravascular to extravascular alveolar inflammation by neutrophils in vivo. These observations are consistent with the hypothesis that pulmonary alveolar macrophages may contribute to the regulation of alveolar inflammation following endotoxemia by releasing factors which influence the migration of neutrophils.

Oxygen therapy, oxygen therapy in medical patients hospitalized outside of the intensive care unit.

The administration of O2-enriched breathing mixtures to acutely ill patients is based on the premise that this form of treatment can overcome the known deleterious effects of tissue hypoxia. Therapeutic practices are founded on a knowledge of the physiology of oxygenation in normal and diseased persons and on knowledge of pulmonary O2 toxicity rather than on demonstrated alterations in disease outcome. The arterial PO2 (Pao2), when markedly diminished, indicates O2 deprivation of tissues, especially in unstable or acute states. However, th Pao2 may show little or no abnormality in states with sharply diminished generalized or regional systemic blood flow. Despite these shortcomings, the Pao2 remains a useful guide for initiating and monitoring O2 therapy in many circumstances. To minimize pulmonary O2 toxicity, the concentration of O2 chosen should be the lowest dose that will correct hypoxemia; 40% O2 is not known to be clinically toxic even after prolonged administration, but toxicity increases progressively above this value. In hypoxemic eucapnic patients, Pao2 of 60 mm Hg represents a reasonable value for treatable hypoxemia, but it is often rational to treat unstable patients with higher Pao2 values, especially if the alveolar-arterial Po2 difference is abnormally wide; 40% O2 represents a reasonable initial dose, with adjustments made on the basis of serial Pao2 measurements. When hypercapnia accompanies hypoxemia, O2 is often not given for Pao2 values greater than 50 mm Hg, and controlled low-dose O2 (24 to 30%) should be used to correct hypoxemia partially while preserving an element of hypoxemic ventilatory drive. In states of low blood flow, high O2 concentrations should be used to maximize the amount of O2 dissolved in plasma, and the duration of therapy should be as brief as possible to minimize O2 toxicity.

Deterioration of oxygenation and abnormal lung microvascular permeability during resolution of leukopenia in patients with diffuse lung injury.

To determine whether circulating leukocytes contribute to gas exchange abnormalities in diffuse lung injury, we retrospectively examined oxygenation in 6 patients who met 3 criteria: leukopenia caused by marrow aplasia from remission-inducing chemotherapy for myelogenous leukemia, the eventual resolution of leukopenia, and concurrent acute respiratory failure diagnosed clinically as increased permeability pulmonary edema. Four of the 6 patients abruptly developed overt clinical evidence of pulmonary dysfunction within the 96 h preceding the resolution of the peripheral leukopenia. In all 6 patients, the alveolar to arterial oxygen tension difference increased between leukocyte counts. The mean value for the alveolar to arterial oxygen tension difference for the group doubled during this period (148 +/- 37 mmHg 3 days prior to resolution; 290 +/- 37 mmHg 1 day after resolution; p less than 0.05). As an index of lung capillary permeability, we measured the lung permeability-surface area product for urea (PSu) for an additional patient with oxygen toxicity and drug-induced leukopenia whose hypoxemia increased immediately before the resolution of leukopenia. The PSu in this patient was high, in the range previously reported as being highly specific for increased permeability pulmonary edema with a fatal outcome. We conclude that such diffuse lung injury resembling the adult respiratory distress syndrome can occur in leukopenic patients, but the resolution of leukopenia in such patients may be associated with worsening oxygenation and with abnormally high pulmonary microvascular permeability. These observations do not prove a causal relationship but provide a clinical parallel to several leukocyte-depletion studies reported in animal models of increased permeability pulmonary edema that implicate white blood cells in the pathogenesis of hypoxemia and lung edema.

Effect of methylprednisolone and of ibuprofen, a nonsteroidal antiinflammatory agent, on bronchoalveolar inflammation following endotoxemia.

Septicemia by gram-negative organisms is a common cause of the adult respiratory distress syndrome (ARDS). The role of neutrophils in causing parenchymal lung damage in ARDS has recently been emphasized. A single intraperitoneal injection of Escherichia coli endotoxin in rats causes acute neutrophil alveolitis similar to that of ARDS. We studied the ability of pretreatment with either ibuprofen (IBU) or methylprednisolone (MP) to ablate directly the alveolar inflammatory response to endotoxin in the rat model. To compare the severity of inflammation, we quantified inflammatory cell recovery by whole lung lavage 24 hours after injection of endotoxin, the time point at which neutrophil alveolitis due to endotoxin is most intense. Pretreatment with a single dose of IBU 3.75 mg/kg prior to endotoxin injections was associated with a significant increase in the total number of inflammatory cells, and in both the percentage and the absolute number of neutrophils recovered from the lung, despite significantly decreasing the plasma level of thromboxane B2, which increased 10-fold after endotoxin. Paradoxically, IBU 30 mg/kg significantly decreased the intensity of neutrophil alveolitis. MP 30 mg/kg had no effect on recovery of inflammatory cells from the lung by bronchoalveolar lavage following endotoxin. Cyclooxygenase inhibitors such as ibuprofen may cause a dose-dependent biphasic effect on lung inflammation following endotoxin: enhancement of inflammation at a low dose and suppression of inflammation at a high dose.

Protection by deferoxamine from endothelial injury: a possible link with inhibition of intracellular xanthine oxidase.

Hydroxyl radical scavengers and xanthine oxidase inhibitors protect cultured bovine pulmonary endothelial cells (BPAEC) from lytic injury by the endotoxin lipopolysaccharide (LPS). We hypothesized that exposure of BPAEC to cytotoxic concentrations of LPS activated intracellular xanthine oxidase, and that intracellular iron-dependent hydroxyl radical formation (a Fenton reaction) ensued, resulting in cell lysis. To test this, the protective effects of deferoxamine against H2O2 and LPS-induced cytotoxicity to BPAEC was assessed by 51Cr release. Preincubation with 0.4 mM deferoxamine conferred 67 +/- 15% (mean +/- SE) protection from LPS-induced cytotoxicity but 48 h of preincubation were required to induce significant protection. Significant protection form a classical Fenton reaction model, injury by 50 microM H2O2, could be induced by a 1-h preincubation with a 0.4 mM deferoxamine. The dissociated time course suggested that deferoxamine might work by different mechanisms in these models. The effects of LPS and deferoxamine on BPAEC-associated xanthine oxidase (XO) and xanthine dehydrogenase (XD) activity were assessed using a spectrofluorophotometric measurement of the conversion of pterin to isoxanthopterin. BPAEC had 106 +/- 7 microU/mg XD+XO activity; XO activity constituted 48 +/- 1% of total XO+XD activity. LPS at a cytotoxic concentration did not alter XO, XD, or percent XO. Deferoxamine had striking proportional inhibitory effects on XO and XD in intact cells. XO+XD activity fell to 6 +/- 1% of control levels during a 48-h exposure of BPAEC to deferoxamine. Deferoxamine did not inhibit XO+XD ex vivo.(ABSTRACT TRUNCATED AT 250 WORDS)

Ischemic necrosis of both lower extremities as a result of the microembolism syndrome complicating the adult respiratory distress syndrome caused by Escherichia coli pneumonia and septicemia.

Extensive gangrene of both lower extremities necessitating bilateral above-the-knee amputations complicated the adult respiratory distress syndrome (ARDS) caused by Escherichia coli pneumonia and septicemia in a 52-yr-old man. Concurrent with the evolution of tissue necrosis, peripheral blood leukocyte and platelet counts fell, and pulmonary vascular resistance increased. Adequacy of the cardiac output was confirmed by repeated thermodilution cardiac output measurements, and major vascular occlusion was excluded surgically. Fibrin degradation products and thrombocytopenia were present, but the other usual criteria for disseminated intravascular coagulation were absent. Small vessel thrombosis by fibrin and leukocytes was observed histologically in the amputated extremities. These findings suggest that gangrene was due to the "microembolism syndrome"--diffuse small vessel occlusion by fibrin thrombi complicating ARDS. This unusual complication of ARDS may occur without abnormalities suggestive of diffuse intravascular coagulation in routine laboratory tests of blood coagulation. It should be suspected and treated promptly to avoid severe disability in survivors.

Effect of mechanical ventilator mode on tendency towards respiratory alkalosis.

The question whether assist-control ventilation (A/C) results in more frequent or more severe respiratory alkalosis than intermittent mandatory ventilation (IMV) is often raised. We prospectively compared the respiratory rates and arterial blood tensions of 18 critically ill patients with respiratory failure of diverse causes who were mechanically ventilated for 1 h with each of these ventilatory modes. Each patient served as his own control. We found that after 1 h of IMV the average pH was 7.42 +/- 0.2 (mean +/- SEM), after 1 h of A/C the pH was 7.45 +/- 0.01 (p less than 0.005), the average PaCO2 during IMV was 40.7 +/- 1.8, the average PaCO2 during A/C was 37.9 +/- 1.6 (p less than 0.001), the average respiratory rate during IMV was 21 +/- 2.0, and the average respiratory rate during A/C was 15 +/- 2.0 (p less than 0.001). One patient became alkalemic (pH 7.55) during A/C. These pH and PaCO2 changes were not associated with any adverse clinical sequelae. We conclude that the responsible physician should be guided by factors other than control of pH in choosing the mode of mechanical ventilation for most patients.

Active chloride secretion by in vitro guinea-pig seminal vesicle and its possible relation to vesicular function in vivo.

1. The guinea-pig seminal vesicle in vivo is characterized by a transmural electrical potential difference of approximately 11 mV with the lumen electrically negative with respect to the interstitial fluid. The concentrations of Na, Cl and K in the vesicular fluid are 13, 15, and 0-4 mM, respectively. 2. When mounted as a flat sheet in a short-circuit apparatus, guinea-pig seminal vesicles initially undergo a decline in the transmural electrical potential difference and short-circuit current ('low phase') followed by a spontaneous increase in these parameters ('high phase'). 3. During the low phase, net C1 movements across the tissue do not differ significantly from zero, and there is a small 'residual' current that is unaccounted for. 4. During the high phase, there is a significant active C1 secretion into the mucosal solution, not detectable net movement of Na and an unaccounted for or 'residual' current that is equal to that found in the low phase. 5. Theophylline, dibutyryl-3'-5' cyclic adenosinemonophosphate,prostaglandin E1 and prostaglandin F2alpha markedly stimulate the transmural electrical potential difference and short-circuit current during the low phase, but have no effect when added to the bathing solution during the high phase. 6. Diffusion potentials determined across in vitro seminal vesicles suggest that the spontaneous transmural electrical potential difference in vivo may be attributable to the large ionic asymmetries between the vesicular fluid and the plasma. 7. It is postulated that two phases are involved in the elaboration of seminal vesicular fluid. The initial phase, following emptying of the vesicle, is characterized by the secretion of electrolytes, organic molecules and water. Active C1 secretion presumably regulated by intracellular cyclic adenosinemonophosphate and/or prostaglandins may be the driving force for this initial secretion of electrolytes. Following this secretory phase, electrolytes and water are reabsorbed, thereby concentrating the organic components in the vesicular reservoir.