These factors also explain the gases' major involvement with lower rather than upper airways. The acid affects peripheral airways, bronchioles, and alveoli, causing extensive tissue damage and formation of methemoglobin. Persons dying from asphyxiation due to pulmonary edema display intra-alveolar edema and exudation and thickening of alveolar walls with lymphocytic cellular infiltrates. Diagnosis Patients in the acute stages of silo filler's disease will present with moderate to severe respiratory distress. Systemic hypotension and evidence of severe hemoconcentration may be present, as may methemoglobinemia and severe metabolic acidosis.
Leukocytosis is typical.
Pulmonary function tests show a reduced vital capacity, increased airways resistance, impaired gas transfer, and hypoxemia. Because the initial illness may be mild, patients may present to a physician for the first time during a relapse, two to six weeks after exposure to NOx. At this time, cough, tachypnea, dyspnea, fever, tachycardia, cyanosis, or other symptoms of respiratory distress are due to bronchiolitis obliterans. Small, discrete nodules, with or without confluence, will be evident on the chest radiograph. A detailed medical and occupational history is crucial to correct diagnosis.