Pulmonary edema due to increased microvascular permeability to fluid and protein

Computational pulmonary edema: A microvascular model of alveolar capillary and interstitial flow

We present a microvascular model of fluid transport in the alveolar septa related to pulmonary edema. It consists of a two-dimensional capillary sheet coursing by several alveoli. The alveolar epithelial membrane runs parallel to the capillary endothelial membrane with an interstitial layer in between, making one long septal tract. A coupled system of equations uses lubrication theory for the capillary blood, Darcy flow for the porous media of the interstitium, a passive alveolus, and the Starling equation at both membranes. Case examples include normal physiology, cardiogenic pulmonary edema, acute respiratory distress syndrome (ARDS), hypoalbuminemia, and effects of PEEP. COVID-19 has dramatically increased ARDS in the world population, raising the urgency for such a model to create an analytical framework. Under normal conditions fluid exits the alveolus, crosses the interstitium, and enters the capillary. For edema, this crossflow is reversed with fluid leaving the capillary and entering the alveolus. Because both the interstitial and capillary pressures decrease downstream, the reversal can occur within a single septal tract, with edema upstream and clearance downstream. Clinically useful solution forms are provided allowing calculation of interstitial fluid pressure, crossflows, and critical capillary pressures. Overall, the interstitial pressures are found to be significantly more positive than values used in the traditional physiological literature. That creates steep gradients near the upstream and downstream end outlets, driving significant flows toward the distant lymphatics. This new physiological flow provides an explanation to the puzzle, noted since 1896, of how pulmonary lymphatics can function so far from the alveoli: the interstitium is self-clearing.

An in silico approach to understanding the interaction between cardiovascular and pulmonary lymphatic dysfunction

The lung is extremely sensitive to interstitial fluid balance, yet the role of pulmonary lymphatics in lung fluid homeostasis and its interaction with cardiovascular pressures is poorly understood. In health, there is a fine balance between fluid extravasated from the pulmonary capillaries into the interstitium and the return of fluid to the circulation via the lymphatic vessels. This balance is maintained by an extremely interdependent system governed by pressures in the fluids (air and blood) and tissue (interstitium), lung motion during breathing, and the permeability of the tissues. Chronic elevation in left atrial pressure (LAP) due to left heart disease increases the capillary blood pressure. The consequent fluid accumulation in the delicate lung tissue increases its weight, decreases its compliance, and impairs gas exchange. This interdependent system is difficult, if not impossible, to study experimentally. Computational modeling provides a unique perspective to analyze fluid movement in the cardiopulmonary vasculature in health and disease. We have developed an initial in silico model of pulmonary lymphatic function using an anatomically structured model to represent ventilation and perfusion and underlying biophysical laws governing fluid transfer at the interstitium. This novel model was tested against increased LAP and noncardiogenic effects (increased permeability). The model returned physiologically reasonable values for all applications, predicting pulmonary edema when LAP reached 25 mmHg and with increased permeability.NEW & NOTEWORTHY This model presents a novel approach to understanding the interaction between cardiac dysfunction and pulmonary lymphatic function, using anatomically structured models and biophysical equations to estimate regional variation in fluid transport from blood to interstitial and lymphatic flux. This fluid transport model brings together advanced models of ventilation, perfusion, and lung mechanics to produce a detailed model of fluid transport in health and various altered pathological conditions.

Computational pulmonary edema: A microvascular model of alveolar capillary and interstitial flow

We present a microvascular model of fluid transport in the alveolar septa related to pulmonary edema. It consists of a two-dimensional capillary sheet coursing by several alveoli. The alveolar epithelial membrane runs parallel to the capillary endothelial membrane with an interstitial layer in between, making one long septal tract. A coupled system of equations is derived using lubrication theory for the capillary blood, Darcy flow for the porous media of the interstitium, a passive alveolus, and the Starling equation at both membranes. Case examples include normal physiology, cardiogenic pulmonary edema, noncardiogenic edema Acute Respiratory Distress Syndrome (ARDS) and hypoalbuminemia, and the effects of positive end expiratory pressure. COVID-19 has dramatically increased ARDS in the world population, raising the urgency for such a model to create an analytical framework. Under normal conditions, the fluid exits the alveolus, crosses the interstitium, and enters the capillary. For edema, this crossflow is reversed with the fluid leaving the capillary and entering the alveolus. Because both the interstitial and capillary pressures decrease downstream, the reversal can occur within a single septal tract, with edema upstream and clearance downstream. Overall, the interstitial pressures are found to be significantly more positive than values used in the traditional physiological literature that creates steep gradients near the upstream and downstream end outlets, driving significant flows toward the distant lymphatics. This new physiological flow may provide a possible explanation to the puzzle, noted since 1896, of how pulmonary lymphatics can function so far from the alveoli: the interstitium can be self-clearing.

Gene Therapy for Acute Respiratory Distress Syndrome

Acute respiratory distress syndrome (ARDS) is a devastating clinical syndrome that leads to acute respiratory failure and accounts for over 70,000 deaths per year in the United States alone, even prior to the COVID-19 pandemic. While its molecular details have been teased apart and its pathophysiology largely established over the past 30 years, relatively few pharmacological advances in treatment have been made based on this knowledge. Indeed, mortality remains very close to what it was 30 years ago. As an alternative to traditional pharmacological approaches, gene therapy offers a highly controlled and targeted strategy to treat the disease at the molecular level. Although there is no single gene or combination of genes responsible for ARDS, there are a number of genes that can be targeted for upregulation or downregulation that could alleviate many of the symptoms and address the underlying mechanisms of this syndrome. This review will focus on the pathophysiology of ARDS and how gene therapy has been used for prevention and treatment. Strategies for gene delivery to the lung, such as barriers encountered during gene transfer, specific classes of genes that have been targeted, and the outcomes of these approaches on ARDS pathogenesis and resolution will be discussed.

Pravastatin attenuates sepsis-induced acute lung injury through decreasing pulmonary microvascular permeability via inhibition of Cav-1/eNOS pathway

BACKGROUND

Disruption of alveolar endothelial barrier caused by inflammation drives the progression of septic acute lung injury (ALI). Pravastatin, an inhibitor of HMG Co-A reductase, has potent anti-inflammatory effects. In the present study, we aim to explore the beneficial role of pravastatin in sepsis-induced ALI and its related mechanisms.

METHODS

A septic ALI model was established by cecal ligation and puncture (CLP) in mice. The pulmonary microvascular endothelial cells (PMVECs) were challenged with lipopolysaccharide (LPS). The pathological changes in lung tissues were examined by HE staining. The pulmonary microvascular permeability was determined by lung wet-to-dry (W/D) weight ratio and Evans blue staining. The total protein concentration in bronchoalveolar lavage fluid (BALF) was detected by BCA assay. The levels of TNF-α, IL-1β, and IL-6 were assessed by qRT-PCR and ELISA. Apoptosis was determined by flow cytometry and TUNEL. Western blotting was performed for detection of target protein levels. The expression of VE-Cadherin in lung tissues was evaluated by immunohistochemical staining.

RESULTS

Pravastatin improved survival rate, attenuated lung pathological changes and reduced pulmonary microvascular permeability in septic mice. In addition, pravastatin restrained sepsis-induced inflammatory response and apoptosis in the lung tissues and PMVECs. Moreover, pravastatin up-regulated the levels of junction proteins ZO-1, JAM-C, and VE-Cadherin. Finally, pravastatin suppressed inflammation, apoptosis and enhanced the expression of junction proteins via regulating Cav-1/eNOS signaling pathway in LPS-exposed PMVECs.

CONCLUSION

Pravastatin ameliorates sepsis-induced ALI through improving alveolar endothelial barrier disruption via modulating Cav-1/eNOS pathway, which may be an effective candidate for treating septic ALI.

Quantification of lung water in heart failure using cardiovascular magnetic resonance imaging

BACKGROUND

Pulmonary edema is a cardinal feature of heart failure but no quantitative tests are available in clinical practice. The goals of this study were to develop a simple cardiovascular magnetic resonance (CMR) approach for lung water quantification, to correlate CMR derived lung water with intra-cardiac pressures and to determine its prognostic significance.

METHODS

Lung water density (LWD, %) was measured using a widely available single-shot fast spin-echo acquisition in two study cohorts. Validation Cohort: LWD was compared to left ventricular end-diastolic pressure or pulmonary capillary wedge pressure in 19 patients with heart failure undergoing cardiac catheterization. Prospective Cohort: LWD was measured in 256 subjects, including 121 with heart failure, 82 at-risk for heart failure and 53 healthy controls. Clinical outcomes were evaluated up to 1 year.

RESULTS

Within the validation cohort, CMR LWD correlated to invasively measured left-sided filling pressures (R = 0.8, p < 0.05). In the prospective cohort, mean LWD was 16.6 ± 2.1% in controls, 17.9 ± 3.0% in patients at-risk and 19.3 ± 5.4% in patients with heart failure, p < 0.001. In patients with or at-risk for heart failure, LWD >  20.8% (mean + 2 standard deviations of healthy controls) was an independent predictor of death, hospitalization or emergency department visit within 1 year, hazard ratio 2.4 (1.1-5.1, p = 0.03).

CONCLUSIONS

In patients with heart failure, increased CMR-derived lung water is associated with increased intra-cardiac filling pressures, and predicts 1 year outcomes. LWD could be incorporated in standard CMR scans.

Pulmonary endothelial permeability and tissue fluid balance depend on the viscosity of the perfusion solution

Fluid filtration in the pulmonary microcirculation depends on the hydrostatic and oncotic pressure gradients across the endothelium and the selective permeability of the endothelial barrier. Maintaining normal fluid balance depends both on specific properties of the endothelium and of the perfusing blood. Although some of the essential properties of blood needed to prevent excessive fluid leak have been identified and characterized, our understanding of these remains incomplete. The role of perfusate viscosity in maintaining normal fluid exchange has not previously been examined. We prepared a high-viscosity perfusion solution (HVS) with a relative viscosity of 2.5, i.e., within the range displayed by blood flowing in vessels of different diameters in vivo (1.5–4.0). Perfusion of isolated murine lungs with HVS significantly reduced the rate of edema formation compared with perfusion with a standard solution (SS), which had a lower viscosity similar to plasma (relative viscosity 1.5). HVS did not alter capillary filtration pressure. Increased endothelial shear stress produced by increasing flow rates of SS, to mimic the increased shear stress produced by HVS, did not reduce edema formation. HVS significantly reduced extravasation of Evans blue-labeled albumin compared with SS, indicating that it attenuated endothelial leak. These findings demonstrate for the first time that the viscosity of the solution perfusing the pulmonary microcirculation is an important physiological property contributing to the maintenance of normal fluid exchange. This has significant implications for our understanding of fluid homeostasis in the healthy lung, edema formation in disease, and reconditioning of donor organs for transplantation.

Acute Respiratory Failure in Pregnancy

Acute respiratory failure in pregnancy has multiple etiologies, including thromboembolism, amniotic fluid embolism, venous air embolism, aspiration of gastric contents, respiratory infections, asthma, beta-adrenergic tocolytic therapy, and pneumomediastinum and pneu mothorax. Proper management of acute respiratory fail ure in pregnancy requires an understanding of the specific diseases and the normal gestational changes that occur in maternal respiration (decreased functional re sidual capacity, increased minute ventilation, mild respi ratory alkalosis) and hemodynamics (increased cardiac output, increased blood and plasma volume, unchanged central pressures). Knowledge of the determinants of oxygen delivery to fetal tissue (uterine blood flow, pla cental transfer, fetal circulation) and how they are af fected by changes in maternal hemodynamics, position, acid-base status, and medications can help sustain nor mal fetal development, whenever possible, without compromising maternal care. Diagnostic testing such as radiography, hemodynamic monitoring, and fetal moni toring are considered in terms of attendant risk to the mother or the fetus, alterations in normal values related to gestation, and indications for usage. Similarly, the risks and benefits of supportive and specific therapies for the various etiologies of acute respiratory therapy are reviewed.

A Model for Interstitial Drainage Through a Sliding Lymphatic Valve

This study investigates fluid flow and elastic deformation in tissues that are drained by the primary lymphatic system. A model is formulated based on the Rossi hypothesis that states that the primary lymphatic valves, which are formed by overlapping endothelial cells around the circumferential lining of lymphatic capillaries, open in response to swelling of the surrounding tissue. Tissue deformation and interstitial fluid flow through the tissue are treated using the Biot equations of poroelasticity and, the fluid flux (into the interstitium) across the walls of the blood capillaries, is assumed to be linearly related to the pressure difference across the walls via a constant of proportionality (the vascular permeability). The resulting model is solved in a periodic domain containing one blood capillary and one lymphatic capillary starting from a configuration in which the tissue is undeformed. On imposition of a constant pressure difference between blood and lymphatic capillaries, the solutions are found to settle to a steady state. Given that the magnitude of pressure fluctuations in the lymphatic system is much smaller than this pressure difference between blood and lymph, it is postulated that the resulting steady-state solution gives a good representation of the state of the tissue under physiological conditions. The effects of changes to the Young's modulus of the tissue, the blood-lymphatic pressure difference, vascular permeability and valve dimensions on the steady state are investigated and discussed in terms of their effects on oedema in the context of age- and pregnancy-related changes to the body.

High positive end-expiratory pressure: only a dam against oedema formation?

Introduction

Healthy piglets ventilated with no positive end-expiratory pressure (PEEP) and with tidal volume (V_T) close to inspiratory capacity (IC) develop fatal pulmonary oedema within 36 h. In contrast, those ventilated with high PEEP and low V_T, resulting in the same volume of gas inflated (close to IC), do not. If the real threat to the blood-gas barrier is lung overinflation, then a similar damage will occur with the two settings. If PEEP only hydrostatically counteracts fluid filtration, then its removal will lead to oedema formation, thus revealing the deleterious effects of overinflation.

Methods

Following baseline lung computed tomography (CT), five healthy piglets were ventilated with high PEEP (volume of gas around 75% of IC) and low V_T (25% of IC) for 36 h. PEEP was then suddenly zeroed and low V_T was maintained for 18 h. Oedema was diagnosed if final lung weight (measured on a balance following autopsy) exceeded the initial one (CT).

Results

Animals were ventilated with PEEP 18 ± 1 cmH₂O (volume of gas 875 ± 178 ml, 89 ± 7% of IC) and V_T 213 ± 10 ml (22 ± 5% of IC) for the first 36 h, and with no PEEP and V_T 213 ± 10 ml for the last 18 h. On average, final lung weight was not higher, and actually it was even lower, than the initial one (284 ± 62 vs. 347 ± 36 g; P = 0.01).

Conclusions

High PEEP (and low V_T) do not merely impede fluid extravasation but rather preserve the integrity of the blood-gas barrier in healthy lungs.

Perioperative fluid management for pulmonary resection surgery and esophagectomy

Perioperative fluid management is of significant importance during pulmonary resection surgery and esophagectomy. Excessive fluid administration has been consistently shown as a risk factor for lung injury after thoracic procedures. Probable causes of this serious complication include fluid overload, lung lymphatics and pulmonary endothelial damage. Along with new insights regarding the Starling equation and the absence of a third space, current evidence supports a restrictive fluid regimen for patients undergoing pulmonary resection surgery and esophagectomy. Multiple minimally invasive hemodyamic monitoring devices, including pulse pressure/stroke volume variation, esophageal Doppler, and extravascular lung water measurement, were evaluated for optimizing perioperative fluid therapy. Further research regarding the prevention, diagnosis, and treatment of acute lung injury after pulmonary resection and esophagectomy is required.

The lung permeability index: a feasible measurement of pulmonary capillary permeability

BACKGROUND

We performed this study to determine the pulmonary capillary permeability (PCP) measuring radiolabeled human serum albumin leakage into the lung. The objective was to use PCP to differentiate between cardiogenic and non-cardiogenic pulmonary edema etiologies.

METHODS

We conducted this study in 10 patients admitted to the intensive care unit who had recently developed bilateral pulmonary infiltrates and required hemodynamic monitoring. In these patients we determined the association among the lung permeability index, cardiac output, pulmonary capillary wedge pressure, myocardial performance index, and the protein content of the bronchoalveolar lavage as expressed by bronchoalveolar lavage (BAL) total protein and BAL-to-serum protein ratio. Twenty mCi of technetium-labeled albumin was injected and measure in the heart and the lung at 10 and 180 min post-injection. Lung and heart uptake ratios as well as the lung permeability index were calculated.

RESULTS

We found a good correlation between the lung permeability index and both the myocardial performance index (cardiac output/pulmonary capillary wedge pressure) and the total protein content of the bronchoalveolar lavage fluid.

CONCLUSION

The lung permeability index is a feasible, noninvasive estimation of the pulmonary capillary permeability.

Negative pressure pulmonary edema in the coronary care unit

A 63-year-old woman with no known cardiac history presented with pulmonary edema accompanied by electrocardiographic evidence of ischemia. Echocardiography demonstrated normal cardiac dimensions, normal wall motion and mild diastolic dysfunction. Despite repeat attempts at extubation following aggressive diuresis, the patient required ongoing ventilatory support. Although cardiac catheterization revealed normal coronary arteries, computed tomography revealed a 4 cm 9 cm multinodular goiter extending into the mediastinum and compressing the trachea. A diagnosis of negative pressure pulmonary edema should be considered in the differential diagnosis of any patient presenting with acute heart failure.

New method for evaluation of lung lymph flow rate with intact lymphatics in anaesthetized sheep

AIM

Lung lymph has commonly been studied using a lymph fistula created by tube cannulation into the efferent duct of the caudal mediastinal node in sheep. In this method, the tail region of the caudal mediastinal node is resected and the diaphragm is cauterized to exclude systemic lymph contamination, and cannulation is performed into one of the multiple efferent ducts originating from the caudal mediastinal node. Moreover, the pumping activity of lymphatics might be diminished by cannulation. Therefore, the purpose of the study was to evaluate the flow rate of lung lymph with maintenance of intact lymphatic networks around the caudal mediastinal node to the thoracic duct in sheep.

METHODS

An ultrasound transit-time flow meter was used to measure lung lymph flow. The thoracic duct was clamped just above the diaphragm and the flow probe was attached to the thoracic duct just after the last junction with an efferent duct from the caudal mediastinal node. The lung lymph flow rate was measured at baseline and under conditions of lung-oedema formation.

RESULTS

The baseline lung lymph flow rate in our model was three- to sixfold greater than values obtained with the cannulation method. With oedema-formation, the lung lymph flow rate was the same as that measured using cannulation.

CONCLUSION

The lung lymph flow was unexpectedly large under the conditions of the study, and our data suggest that the drainage effect of lymphatics is significant as a safety factor against pulmonary oedema formation.

Possible factors contributing to the postmortem lung weight in fire fatalities

The aim of the present study was to examine the factors that contribute to the postmortem lung weight in acute fire fatalities (n=149) including those with lower (<60%) and higher (>60%) blood carboxyhemoglobin (COHb) levels (n=94 and 55, respectively). The control groups consisted of acute myocardial infarction/ischemia (AMI, n=99) and mechanical asphyxiation (n=85). For all cases (n=333), the lung and heart weights were independent of the postmortem time (4.5-72 h) and charring of the body. The combined weight of both lobes of the lung showed a significant gender difference (males>females, P<0.001), negative regression with respect to age (R=0.167, P<0.01) and positive regression with respect to heart weight (R=0.316, P<0.001). The gender difference was also significant for each cause of death even after being corrected using body height measurements. When the lung-heart weight ratio was estimated to diminish the influence of possible cardiogenic factors, the gender difference was insignificant for each cause of death among the non-elderly (<60 years of age). However, for elderly fire fatalities (>60 years of age), there was a gender difference (males>females) for the lower COHb group (P<0.05) and higher COHb group (P<0.001). A significant age-dependent difference (non-elderly>elderly) in the lung-heart weight ratio was observed for fire fatalities with a lower COHb and AMI among males and for fire fatalities with a higher COHb among females. Such gender- and/or age-dependent influences were not significant for fatal mechanical asphyxiation. These findings suggest that a person's heart weight may be a possible contributory factor to an increase in the lung weight in acute death, and that gender- and/or age-dependent susceptibilities may be additional factors that contribute to fire fatalities and AMI. In addition, elderly females appear to be most susceptible among fire casualties, and extreme cardiomegaly may also be a potential fatal risk factor.

Pathophysiology of Postpneumonectomy Pulmonary Edema

Pulmonary edema is a rare, potentially fatal complica tion associated with major resection of the lung, usually pneumonectomy. Although pulmonary edema in this setting can often be attributed to a variety of causes such as cardiac failure, bacterial pneumonia, and fluid overload, the specific syndrome of postpneumonec tomy pulmonary edema (PPE) occurs in the absence of these factors. PPE remains a diagnosis of exclusion, and its pathophysiology is poorly understood. Overzealous perioperative fluid administration has traditionally been implicated in clinical cases of postpneumonectomy pulmonary edema, but there is a body of evidence suggesting several other potential mechanisms. These include increases in cardiac output secondary to cat echolamine release, interruption of mediastinal lym phatic drainage, endothelial injury secondary to release of humoral factors or stretching of intercellular junc tions, hyperinflation, and other unknown factors.

Post-pneumonectomy pulmonary edema: is anesthesia to blame?

Post-pneumonectomy pulmonary edema is a major cause of early mortality following lung resection surgery. It is not clear whether this complication is caused by excessive perioperative intravenous fluid as was previously thought. The recent demonstration of increased pulmonary capillary permeability of the lung following a pneumonectomy suggests measures to try and decrease the incidence of this highly lethal syndrome. These measures include the judicious use of intravenous crystalloids, avoidance of lung hyperinflation and efforts to minimize the pulmonary artery pressure.

Postpneumonectomy pulmonary edema: can it be predicted preoperatively?

Postpneumonectomy pulmonary edema (PPE) is a rarely reported form of acute lung injury which occurs in up to 4% of all pneumonectomies. The details of two well-documented cases of PPE are described with special emphasis paid to the preoperative lung functions. Both cases illustrated a striking disparity between preserved spirometric lung function and advanced emphysema as detected by quantitative CT emphysema scores and single-breath diffusion of carbon monoxide measurements. Though retrospective in nature, these results suggest a restricted capillary volume plays a critical role in the development of PPE.

Bacterial toxin-induced pulmonary epithelial cytotoxicity and the protective effect of dibutyryl-cAMP

Bacterial infection is the most common cause of the adult respiratory distress syndrome which, in turn is associated with endothelial capillary permeability and alveolar oedema. Previously, we have demonstrated the direct cytotoxicity of the bacterial toxins Pseudomonas aeruginosa exotoxin A (Exo A) and Salmonella enteritidis lipopolysaccharide (LPS) on pulmonary endothelial cells. The purpose of this study was to investigate the effect of Exo A and LPS on pulmonary epithelial cells in vitro. We also tested the protective effect of dibutyryl cyclic adenosine monophosphate (db-cAMP) on Exo A-induced cytotoxicity. In cultured rat alveolar epithelial cells (RAEC) Exo A caused cytotoxicity as measured by 51Cr release from these cells. LPS did not injure RAEC's. Pretreatment of RAEC with db-cAMP (1 mM) attenuated Exo A induced cytotoxicity. We conclude that (1) Exo A directly injures epithelial lung cells and may contribute to lung injury in cases of bacterial infection; (2) db-cAMP protects alveolar epithelial cells against Exo A-induced cytotoxicity and (3) alveolar epithelial cells in this model are resistant to LPS induced injury.

Pulmonary edema induced by angiotensin I in rats

This study was performed to demonstrate an experimental procedure of pulmonary edema induced by angiotensin I (AT I) in rats and to elucidate the mechanism of hemodynamic pulmonary edema. In the previous pilot study, 20 microg/kg of AT I was found to be an adequate dose for inducing pulmonary edema. To elucidate the mechanism of AT I pulmonary edema and protective measures against it, we observed the effects of captopril (CAP, 5 and 10 mg/kg), an angiotensin converting enzyme inhibitor; losartan (LOS, 10 mg/kg), an angiotensin II (AT II)-receptor antagonist; and phentolamine (PHE, 10 mg/kg), an alpha-adrenergic receptor blocker, on AT I-induced pulmonary edema in rats. Similarly, we also observed the effects of CAP (10 and 20 mg/kg) on pulmonary edema induced by 25 microg/kg of adrenaline (ADR) in rats. The development of AT I-induced pulmonary edema was significantly suppressed by CAP and LOS, but was unaffected by PHE. In contrast, the development of ADR-induced pulmonary edema was not suppressed by CAP. These results suggest that AT I-induced pulmonary edema is developed via the AT II and a specific AT II-receptor, without the indirect action of adrenaline.

Endothelial selectins in acute mountain sickness and high-altitude pulmonary edema

STUDY OBJECTIVES

Mechanical or inflammatory injury to pulmonary endothelial cells may cause impaired pulmonary gas exchange in acute mountain sickness (AMS) and noncardiogenic pulmonary edema in high-altitude pulmonary edema (HAPE). This study was designed to determine whether markers of endothelial cell activation or injury, plasma E- and P-selectin, were increased after ascent to high altitude, in AMS or in HAPE.

DESIGN

We collected clinical data and plasma specimens in control subjects at sea level and after ascent to 4,200 m, and in climbers with AMS or HAPE at 4,200 m. Data analysis was performed using standard nonparametric statistical methods, and results reported as mean+/-SD.

SETTING

National Park Service medical camp at 4,200 m on Mt. McKinley (Denali), Alaska.

PATIENTS

Blood samples and clinical data were collected from 17 healthy climbers at sea level and again after ascent to 4,200 m, and from a different group of 13 climbers with AMS and 8 climbers with HAPE at 4,200 m. Climbers with AMS were divided into normoxic (n=7) and hypoxemic (n=6) groups.

MEASUREMENTS AND RESULTS

Using an enzyme immunoassay technique, plasma E-selectin concentrations were found to be increased in the 17 control subjects after ascent to 4,200 m (17.2+/-8.2 ng/mL) as compared to sea level (12.9+/-8.2 ng/mL) (p=0.001). Plasma E-selectin concentrations were also increased in subjects with hypoxemic AMS (30.6+/-13.4 ng/mL) and HAPE (23.3+/-9.1 ng/mL) compared to control subjects at sea level (p=0.009). Increased plasma E-selectin concentration significantly correlated with hypoxemia (p=0.006). Plasma P-selectin concentrations were unchanged after ascent to 4,200 m and in subjects with AMS and HAPE.

CONCLUSION

Because E-selectin is produced only by endothelial cells, increased plasma E-selectin after ascent to high altitude and in hypoxemic climbers with AMS and HAPE provides evidence that endothelial cell activation or injury is a component of hypoxic altitude illness.

Postpneumonectomy pulmonary edema. A retrospective analysis of incidence and possible risk factors

OBJECTIVE

To analyze the incidence of postpneumonectomy pulmonary edema (PPE) and to determine potential risk factors for PPE.

MATERIAL AND METHODS

A group of 197 patients was studied retrospectively, and the incidence of PPE was recorded over a 5-year period. Preoperative, perioperative, and postoperative clinical data were collected, and preoperative and postoperative chest radiographs were reviewed. A scoring system was used to distinguish between premanifest and manifest PPE. Postpneumonectomy patients with pulmonary edema, with no clinically evident cause, were considered to have PPE.

RESULTS

The incidence of premanifest PPE was 12.2% (n = 24), and that of manifest PPE was 2.5% (n = 5). Mortality in the group of patients who developed manifest PPE was 100%. Two significant perioperative associations were found in the PPE group. One was the administration of fresh frozen plasma (FFP) transfusions (relative risk, 4.3; 95% confidence interval, 1.3 to 14.4 corrected for age and sex), while the other was higher mechanical ventilation pressures during surgery (relative risk, 3.0; 95% confidence interval, 1.2 to 7.3).

CONCLUSION

Our data suggest that FFP transfusions form an important risk factor for PPE. The mechanism may be an increased permeability of the pulmonary vessels due to an immunologic reaction after multiple FFP transfusions. The significantly higher mechanical ventilation pressures we found in the PPE group may be explained as an early sign of the development of PPE.

Treatment of surgical and non-surgical septic multiorgan failure with bicarbonate hemodialysis and sequential hemofiltration

OBJECTIVE

Hospital mortality of patients with septic multiorgan failure (MOF) is still around 95%. The present study investigates whether this high mortality could be significantly reduced by the addition of sequential hemofiltration (SH) with bicarbonate hemodialysis (HD) to the currently used life supportive measures.

DESIGN

35 (18 surgical and 17 nonsurgical) patients, with 3 or more organ failures, had daily sessions of zero balance SH, for periods ranging from 2-22 days.

MEASUREMENTS AND RESULTS

SH induced significant improvement of PaO2/100 FIO2, Apache II score, MAP, as well as blood chemistry in survivors. Dying patients had less marked improvement of blood oxygenation, non-significant changes in other variables, in addition to low MAP before and after SH, as well as marked hemodynamic unstability during the procedure. The observed hospital mortality was 38% for the surgical group, and 35.3% for the medical patients (n.s.).

CONCLUSIONS

Mortality observed in this retrospective, uncontrolled study was significantly lower than that currently observed with conventional supportive therapy, with or without the addition of other forms of blood purification, e.g. CAVH and CAVHD. This improvement in results appears to be related to the property of SH to completely clear 90% of the blood from mediators of inflammation in only one passage through the hemofilter, and to better tolerance of HD done using bicarbonate buffer. A definite evaluation of this technique will be eventually reached by a programmed, appropriate sample size study, which is out of reach for one individual ICU.

Effect of bronchodilators on lung mechanics in the acute respiratory distress syndrome (ARDS)

The acute respiratory distress syndrome (ARDS) is a disorder of diffuse lung injury secondary to a wide variety of clinical insults (eg, sepsis) and is manifested by impaired oxygenation, pulmonary edema, and decreased static and dynamic compliance. More recently, airflow resistance has been shown to be increased in humans with ARDS. We designed a prospective, randomized, placebo-controlled, crossover trial to determine the presence and reversibility of increased airflow resistance in ARDS. We studied eight mechanically ventilated patients with ARDS (criteria: PaO2 < or = 70 mm Hg with FIO2 < or = 0.4; diffuse bilateral infiltrates; and pulmonary artery wedge pressure < or = 18 mm Hg). Each was intubated with a No. 8.0 orotracheal tube. We measured dynamic compliance (Cdyn), static compliance (Cstat), airflow resistance across the lungs (RL), shunt fraction (Qs/Qt on FIO2 = 1.0), minute ventilation (VE), PaO2/PAO2, and dead space to tidal volume ratio (VD/VT). Patients were blindly assigned to receive either metaproterenol (1 mL 0.5% in 3 mL saline solution) or saline solution (4 mL) aerosolized over 15 min 6 h apart and in random order so that patients served as their own controls. Metaproterenol significantly reduced RL, peak and plateau airway pressure, and increased Cdyn. Metaproterenol tended to increase PaO2/PAO2, but had no effect on pulmonary shunt or dead space ventilation. We conclude that the increase in airflow resistance of ARDS is substantially reversed by aerosolized metaproterenol without affecting dead space. These data suggest that abnormalities of RL are at lest partially due to bronchospasm.

Acute lung injury: what have we learned from animal models?

In 1950, Carl John Wiggers, philosopher and physiologist, wrote, "Reactions to definite types of stimulation may be observed or recorded, and concealed phenomena may be revealed by the use of apparatus that transforms them into forms that are recognizable by human senses. But complete understanding of physiological reactions often necessitates extensive operative procedures and sometimes the ultimate sacrifice of life. For this reason experimentation on animals is indispensable." Acute lung injury is still a significant cause of death in the developed world, and modern pharmacology and intensive care have failed to alter the clinical course of this complex condition. In the past decade, there was an explosion in understanding of the pathophysiology of acute lung injury, and with this has come the development of a new generation of agents that may provide a tool with which to combat this disorder. Use of animal model systems led to this greater understanding and is currently at the heart of evaluating the new therapeutic agents. This review briefly addresses the contribution animal model systems have made to what appear to be a watershed in attempts to obviate the effects of this mortal condition.

Postpneumonectomy pulmonary edema

Pulmonary edema is an uncommon but serious complication associated with major resection of the lung, usually after pneumonectomy. The pathophysiology of this condition is not completely understood, but recent experimental and clinical data suggest that this condition results from a combination of increased filtration gradient across the pulmonary microcirculation together with hyperpermeability. Overzealous perioperative infusions of fluid have been implicated in clinical cases. We present the reports of 2 patients with postpneumonectomy pulmonary edema we recently encountered and a review of the literature to provide diagnostic and therapeutic guidelines in dealing with this serious complication.

Lung protein leakage in feline septic shock

The aim of the present study was to explore lung microvascular leakage of protein and water in a feline model of septic shock, using a double isotope technique with external gamma camera detection and gravimetric lung water measurements. The experiments were performed on artificially ventilated cats. One group of cats (n = 8) was given an infusion of live Escherichia coli bacteria, and another group (n = 5) served as a control group receiving saline. Plasma transferrin was radiolabeled in vivo with indium-113m-chloride, and erythrocytes were labeled with technetium-99m. The distribution of these isotopes in the lungs was continuously measured with a gamma camera. A normalized slope index (NSI) was calculated, indicative of the transferrin accumulation corrected for changes in local blood volume that reflect protein leakage. In the septic group there was a protein leakage after bacterial infusion, with a NSI of 39 x 10(-4) +/- 5 x 10(-4) min-1 (mean +/- SEM), and the PaO2 diminished from 21 +/- 1 to 9.5 +/- 1 kPa. In control cats a slight protein leakage with a NSI of 9 +/- 10(-4) +/- 2 x 10(-4) min-1 was detected, probably caused by the operative procedure, but PaO2 did not change. Wet-to-dry-weight ratios of postmortem lungs were not significantly different between the groups. It was concluded that an intravenous infusion of live E. coli bacteria induces a lung capillary protein leakage without increased lung water and a concomitantly disturbed gas exchange.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac evaluation

Over the past decade there has been a dramatic, rapid development of new imaging modalities used in the evaluation of the cardiac patient. These newer techniques are frequently complex and specialized in their application and interpretation. Nonetheless, the prevalence of cardiac disease in the United States, and the wide application of these diagnostic tests, mandate that the well-rounded clinician has a basic understanding of the utility of these diagnostic modalities. Unfortunately, the burgeoning field of cardiac imaging seems at times to overshadow our most important basic diagnostic tools, namely, the history, physical exam, chest radiograph, and electrocardiogram (ECG). This review will attempt to impart a basic understanding of the newer cardiac diagnostic tests and their utility in various disease states. Emphasis on the importance of the basic clinical exam and the precise integration of specific diagnostic tests into the cardiac evaluation will be emphasized. The article will deliver a basic review of exercise treadmill testing, echocardiography, radionuclide imaging techniques, magnetic resonance imaging, and cardiac catheterization. It is hoped that this review will impart to the noncardiologist clinician a basic understanding of the cardiovascular diagnostic techniques so that an accurate, precise, cost-effective, efficient diagnostic plan for the patient with cardiovascular disease can be developed and applied.

Improved outcome based on fluid management in critically ill patients requiring pulmonary artery catheterization

We performed a randomized, prospective trial to evaluate whether fluid management that emphasized diuresis and fluid restriction in patients with pulmonary edema could affect the development or resolution of extravascular lung water (EVLW), as well as time on mechanical ventilation and time in the intensive care unit (ICU), in critically ill patients requiring pulmonary artery catheterization (PAC). PAC was performed on 101 patients. A total of 52 patients were randomized to an EVLW management group using a protocol based on bedside indicator-dilution measurements of EVLW. The other 49 patients were randomized to a wedge pressure (WP) management group in whom fluid management decisions were guided by WP measurements. A total of 89 patients had pulmonary edema (defined as EVLW greater than 7 ml/kg ideal body weight). Except for a clinically unimportant difference in mean age, the two groups were entirely comparable at baseline. The study groups were managed differently, as evidenced by cumulative input-output of 2,239 +/- 3,695 ml (median = 1,600 ml) in the WP group versus 142 +/- 3,632 ml (median = 754 ml) in the EVLW group (p = 0.001). EVLW decreased significantly, and ventilator-days and ICU days were significantly shorter only in patients from the EVLW group. No clinically significant adverse effect occurred as a result of following the EVLW group algorithm. Thus, a lower positive fluid balance, especially in patients with pulmonary edema regardless of cause, is associated with reduced EVLW, ventilator-days, and ICU days.

Initial treatment of pulmonary edema: a physiological approach

An understanding of the physiological principles involved in lung fluid balance is useful in the initial treatment of pulmonary edema. Normally, a very small volume of fluid is filtered from the pulmonary vasculature into the interstitial space. This interstitial fluid enters the pulmonary lymphatics and is transferred to mediastinal lymphatics at an estimated rate of 20 ml/hr. Under abnormal circumstances, fluid filtration may occur at such a rapid rate that it overwhelms the lymphatics and interstitial space and results in alveolar flooding. This may occur as a result of increased pulmonary vascular pressure or increased vascular permeability. The two general goals of initial therapy are (1) to relieve hypoxemia and (2) to reduce pulmonary capillary pressure. Relieving hypoxemia may require the use of supplemental oxygen by nasal prongs or mask, continuous positive airway pressure (CPAP) mask, or even endotracheal intubation and mechanical ventilation. Measures to decrease preload and thereby reduce pulmonary capillary pressure include sitting the patient up, administering a loop diuretic or morphine intravenously, and in some circumstances using sublingual nitroglycerin. After initial treatment is underway, a search for and specific management of the underlying cause of pulmonary edema can proceed.

High permeability pulmonary oedema: pathophysiology and mechanisms of injury

Many critically ill patients are at risk for developing HPPE. Since 60% of patients develop HPPE within 24 hours of the pulmonary insult with 11% developing respiratory failure within 72 hours, it is imperative that the critical care nurse understand the pathophysiological responses (Bernard & Bradley, 1986). While the pathophysiological responses are specific, injury to the alveolar-capillary membrane, the mechanisms of injury are diffuse. Knowing the mechanisms can alert health care providers to those patients who are at risk for developing HPPE and more quickly mobilize interventions to alleviate or lessen its occurrence.

Modern approaches to the therapy of septic shock

Bacteremia from gram-negative rods is a great cause of concern for hospital physicians today. Shock-complicating gram-negative sepsis has a mortality rate of 60% and above, despite early diagnosis and treatment. Intensive research efforts have shown new pathophysiological mechanisms and mediators involved in septic shock, with changes in recommended treatment protocols. In this report, the authors review the use of corticosteroids, fibronectin, naloxone hydrochloride, and immunotherapy, with emphasis on theoretical considerations and relevant clinical experience. Although these treatment methods may have been promising initially, data from large double-blind human trials are either lacking or unencouraging. While continued research and modern therapeutic approaches should improve future survival rates from septic shock, use of the therapies reviewed should be considered experimental at this time.

Plasma volume expansion and PEEP in a canine model of acute Pseudomonas pneumonia

Four groups of anesthetized, ventilated dogs (n = 6 in each group) inoculated endotracheally with Pseudomonas aeruginosa were studied over 5 h as bilateral, hemorrhagic pneumonia developed. Groups I and II were ventilated with zero end-expiratory pressure (ZEEP) and groups III and IV with positive end-expiratory pressure (PEEP) (8 cmH2O). Hetastarch (6%) in saline was infused intravenously to maintain similar transmural pulmonary wedge pressures (Pwtm) in groups I and III (approximately 5 mmHg) and groups II and IV (approximately 10 mmHg) throughout the experiment. The effects of plasma volume expansion were analyzed by comparing groups I and III with groups II and IV and of PEEP by comparing groups I and II with groups III and IV. The number of lobes with gross consolidation was greater in groups II (4.8 +/- 1.2) and IV (5 +/- 0.9) than in groups I (2 +/- 1.1) and III (3.3 +/- 1). The mean lung wet weight/body weight ratio was greater in groups II (40 +/- 11 g/kg) and IV (48 +/- 12 g/kg) than in groups I (19 +/- 3 g/kg) and III (32 +/- 6 g/kg) and in groups III and IV than in groups I and II. Plasma volume expansion, in the absence of PEEP (group II vs. group I), dramatically increased intrapulmonary shunt (Qs/Qt 5 h after inoculation: group II, 62 +/- 13%; group I, 25 +/- 12%). However, overall gas exchange 5 h after inoculation was not significantly different between PEEP-treated groups and ZEEP-treated groups despite more extensive disease in the former. Despite maintenance of Pwtm, cardiac output fell significantly over the 5 h study period in groups III (4.3 +/- 0.7 to 3.3 +/- 1.0 L/min) and IV (7.2 +/- 1.7 to 3.8 +/- 2.4 L/min) compared to groups I (3.8 +/- 1.0 to 3.5 +/- 1.2 L/min) and II (6.9 +/- 3.2 to 7.3 +/- 2.6 L/min). We conclude that plasma volume expansion, within the normal physiological range of Pwtm, increases the extent of pneumonia. Positive end-expiratory pressure with maintenance of Pwtm also independently increases pneumonia size, possibly by increasing pulmonary capillary hydrostatic pressure, but masks this effect by maintaining arterial oxygenation through recruitment of additional lung units for gas exchange. The data also suggest that PEEP adversely affects cardiac performance in this model of acute pneumonia.

The role of airflow resistance in patients with the adult respiratory distress syndrome

Although reduced lung compliance is a hallmark of the adult respiratory distress syndrome (ARDS), the role of increased airflow resistance in this disorder has not been well studied. Because animal models of ARDS show marked increases in airflow resistance and because mediators known to participate in lung parenchymal injury have also been implicated in models of increased airway reactivity, we hypothesized that increased airflow resistance is a major contributor to altered lung mechanics in human ARDS. We studied 10 mechanically ventilated patients with ARDS (criteria: PaO2 less than or equal to 70 mm Hg breathing FIO2 greater than or equal to 0.4; bilateral pulmonary roentgenographic infiltrates; Ppaw less than or equal to 18 mm Hg) measuring dynamic (Cdyn) and static (Cstat) compliance, airflow resistance across the lungs (RL), shunt fraction (QS/QT breathing FIO2 = 1.0), minute ventilation (VE), (a/A)PO2, dead space to tidal volume ratio (VD/VT), airflow (pneumotachograph), transpulmonary pressure (intratracheal pressure minus esophageal pressure) and volume (integrated from flow) at 50 L/min peak flow rate. Airflow resistance was uniformly elevated and averaged six times normal (5.32 +/- 0.92 cm H2O/L/s versus 0.88 +/- 0.08) (p less than 0.05). Cdyn correlated directly with (a/A)PO2. RL correlated with peak pressure, but did not correlate with VE, shunt, (a/A)PO2, or VD/VT. We conclude that increased pulmonary airflow resistance contributes significantly to the altered lung mechanics in ARDS. These data are consistent with studies of animal models of ARDS and long-term survivors of ARDS and may be secondary to tissue factors, airway hyperreactivity, or airway inflammation.

Determinants of diagnostic accuracy in pulmonary scintigraphy for pulmonary capillary protein leak associated with adult respiratory distress syndrome (ARDS): a technical note

Radionuclide assessment of pulmonary capillary protein leak using [99mTc] human serum albumin (99mTc-HSA) was first reported from our laboratory. In this study we investigated the impact of 1) sampling time post tracer injection, and 2) lung region assignment, on diagnostic accuracy between 2 groups (control n = 20 and ARDS n = 20). Each patient received 370 MBq 99mTc-HSA i.v. and was imaged for 45 min. The slope index (SI) [change in lung: heart activity ratio/min] was calculated from 11 computer assigned lung regions for intervals of 5-15 (early [E]) and 15-45 (late [L]) min. The diagnostic accuracy of E vs L SI calculations for the 11 regions was evaluated by stepwise logistic regression. E SI data and L SI data from the lower 1/3 of the lung did not achieve significance for inclusion in the discriminant model (P less than 0.05). In the nine remaining regions L SI was significant. Optimal discrimination was achieved from L SI data obtained from a region confined to the lateral half of the mid 3rd of the lung field (sensitivity 81%, specificity 85%, accuracy 83%). The results confirm that: 1) a late (15-45 min) sampling period and 2) proper region assignment are necessary to maximize accuracy of this technique.

Smoke inhalation

An attempt has been made to review the characteristics of fire and smoke and the epidemiology of smoke inhalation to identify some of the many variables which interact to control the severity of the injury. An experimental model appropriate to study the pulmonary injury of smoke victims who survive to enter the health care system is described. Experiments which define how smoke damages the lung are reviewed in an effort to explain why the smoke-damaged lung is vulnerable to additional stress and why those with an injured lung and a burn have such a high mortality rate.

Hypoxia-induced increases in pulmonary transvascular protein escape in rats. Modulation by glucocorticoids

Pulmonary edema after ascent to altitude is well recognized but its pathogenesis is poorly understood. To determine whether altitude exposure increases lung vascular permeability, we exposed rats to a simulated altitude of approximately 14,500 feet (barometric pressure [Pb] 450 Torr) and measured the pulmonary transvascular escape of radiolabeled 125I-albumin corrected for lung blood content with 51Cr-tagged red blood cells (protein leak index = PLI). Exposures of 24 and 48 h caused significant increases in PLI (2.30 +/- 0.08 and 2.40 +/- 0.06) compared with normoxic controls (1.76 +/- 0.06), but brief hypoxic exposures of 1-13 h produced no increase in PLI, despite comparable increases in pulmonary artery pressure. There were associated increases in gravimetric estimates of lung water in the altitude-exposed groups and perivascular edema cuffs on histologic examination. Normobaric hypoxia (48 h; fractional inspired oxygen concentration [FIO2] = 15%) also increased lung transvascular protein escape and lung water. Dexamethasone has been used to prevent and treat altitude-induced illnesses, but its mechanism of action is unclear. Dexamethasone (0.5 or 0.05 mg/kg per 12 h) started 12 h before and continued during 48 h of altitude exposure prevented the hypoxia-induced increases in transvascular protein escape and lung water. Hemodynamic measurements (mean pulmonary artery pressure and cardiac output) were unaffected by dexamethasone, suggesting that its effect was not due to a reduction in pulmonary artery pressure or flow. The role of endogenous glucocorticoid activity was assessed in adrenalectomized rats that showed augmented hypoxia-induced increases in transvascular protein escape, which were prevented by exogenous glucocorticoid replacement. In summary, subacute hypoxic exposures increased pulmonary transvascular protein escape and lung water in rats. Dexamethasone prevented these changes independent of reductions of mean pulmonary artery pressure or flow, whereas adrenalectomy increased pulmonary vascular permeability and edema at altitude. Increases in vascular permeability in hypoxia could contribute to the development of high-altitude pulmonary edema and endogenous glucocorticoids may have an important influence on pulmonary vascular permeability in hypoxia.

Decreased density distribution of mesenteric and diaphragmatic microvascular anionic charges during murine abdominal sepsis

Pulmonary edema of sepsis is a consequence of increased transmural conductance for water and proteins at the level of lung microvessels induced by vasoactive endogenous mediators, liberated after activation of complement by bacterial endotoxins. Intermittent opening of interendothelial junctions at the level of post-capillary venules has been implicated as being the pathway for the leaking plasma proteins and water. Microvascular basement membranes and endothelial cell surfaces have fixed anionic charges (AS) which prevent the escape of plasma proteins from the circulation as well as the adhesion of blood cells to the luminal endothelium. The density distribution of these AS was substantially reduced in visceral and systemic microvessels during murine abdominal sepsis. This observation suggest that MOF secondary to sepsis is the consequence of a severe and generalized alteration of the microvascular electronegative charge, induced by liberation of inflammatory mediators.

Sulfidopeptide-leukotriene peptidases in pulmonary edema fluid from patients with the adult respiratory distress syndrome

The human pulmonary edema fluid concentrations of LTC4 and of LTD4 and LTE4, derived peptidolytically from LTC4, were assessed by radioimmunoassays of the mediators resolved by reverse-phase high-performance liquid chromatography. The mean pulmonary edema fluid concentration (+/- SD) of LTD4 of 19.2 +/- 25.6 nM for 12 patients with the adult respiratory distress syndrome and of LTE4 of 192 +/- 309 nM for 10 of the patients were significantly higher (P less than 0.005 and P less than 0.05) than those of 2.2 +/- 2.4 and 11.0 +/- 18.2 nM, respectively, for 10 patients with cardiogenic pulmonary edema, whereas the lower mean concentrations of LTC4 were not significantly different for the two groups. Pulmonary edema fluid from five patients with adult respiratory distress syndrome, one with cardiogenic pulmonary edema, and one with an indeterminate syndrome contained similar concentrations of peptidoleukotriene peptidases. The LTC4 and LTD4 peptidolytic activities in ARDS fluids were 81 and 142 kD, respectively, by gel filtration. The extents of peptidolysis of [3]LTC4 and [3]LTD4 by 100 microliter of pulmonary edema fluid attained respective mean maximum levels of 74.5 +/- 2.9% (N = 5) and 37.7 +/- 10.2% (N = 4) after 30 min at 37 degrees C and were inhibited by serine-borate and by cysteine, respectively. The predominance of LTD4 and LTE4 over LTC4 in states of altered pulmonary vascular pressure and permeability thus is attributable to two distinct peptidases.

Effects of oleic acid-, alpha-naphthylthiourea-, and phorbol myristate acetate-induced microvascular damage on indexes of pulmonary endothelial function in anesthetized dogs

To study the value of indexes of endothelial cell function in experimentally induced pulmonary microvascular injury, lung damage was produced in anesthetized dogs by intravenous injection of oleic acid (OA; n = 6), alpha-naphthylthiourea (ANTU; n = 5), or phorbol myristate acetate (PMA; n = 6). Angiotensin-converting enzyme (ACE) activity in serum and simultaneous measurements of serotonin (SER) and propranolol (PROP) pulmonary extraction along with several physiologic parameters were determined and compared with those obtained in a control group (n = 5) before and then at 2-h intervals for 8 h after administration of the toxic agent. ACE activity in serum showed a sustained and significant increase in the PMA and OA groups throughout the whole study period, whereas it decreased significantly at 4 h in the ANTU group. SER pulmonary uptake decreased significantly, but slightly, only in the PMA group at 8 h (-5%). At 6 and 8 h respectively, PROP extraction dropped significantly in the PMA (-11 and -13%) and OA (-13 and -19%) groups. This decrease in PROP extraction was likely to result from physiologic changes due to the development of pulmonary edema as suggested by the correlation between the changes in amine uptake and those affecting pulmonary artery pressure and total static respiratory compliance. The lack of effects on SER uptake by the lungs under these experimental conditions indicate that dissociation exists between metabolic dysfunction of pulmonary endothelial cells and fluid leakage.