The Adult Respiratory Distress Syndrome: Cell Populations and Soluble Mediators in the Air Spaces of Patients at High Risk

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Abstract
In order to better understand the modulation of polymorphonuclear neutrophil influx into the lung during the development of the adult respiratory distress syndrome (ARDS), we evaluated bronchoalveolar lavage fluids from control subjects (n = 9), patients at high risk of developing ARDS (n = 12), and patients with ARDS (n = 11) for cellular and protein content and capacity to promote neutrophil adhesion to tissue culture plastic. Analysis of the lavage fluids from high risk patients and patients with ARDS showed an 8- to 10-fold increase in the total number of cells, an increase in the percentage of neutrophils present (control subjects = 1 .+-. 0.4%, high risk = 53 .+-. 8%, ARDS = 70 .+-. 7%), and a 10- to 40-fold increase in protein content. The adherence of normal neutrophils to plastic surfaces after pretreatment with either concentrated lavage fluid, ultrafiltrates of BALF, or plasma samples was determined to evaluate the neutrophil adherence-promoting activity of each. Lavage fluid from high risk patients and patients with ARDS promoted an approximate 3-fold increase in neutrophil adherence when compared with control lavage fluid. Neutrophil adhesion-promoting activity of the plasma and lavage filtrates (mw < 500 daltons) was not significantly different from that of control subjects. The adherence-promoting activity found in ARDS lavage was stable at 56.degree. C for 30 min. Higher temperatures (100.degree. C) and exposure to trypsin or rabbit antihuman-C5a reduced, but did not abolish, activity. These results indicate that neutrophil influx into the air spaces and permeability changes in patients at high risk for ARDS occur prior to development of the syndrome. Further, substances capable of enhancing neutrophil adhesion are present in the air spaces, but not in plasma, prior to the onset of ARDS. These substances share both lipid and protein characteristics.