Medline ® Abstracts for References 1,41,42
of 'Reactive airways dysfunction syndrome and irritant-induced asthma'
Reactive airways dysfunction syndrome (RADS). Persistent asthma syndrome after high level irritant exposures.
Brooks SM, Weiss MA, Bernstein IL
Ten individuals developed an asthma-like illness after a single exposure to high levels of an irritating vapor, fume, or smoke. In most instances, the high level exposure was the result of an accident occurring in the workplace or a situation where there was poor ventilation and limited air exchange in the area. In all cases, symptoms developed within a few hours and often minutes after exposure. We have designated the illness as reactive airway dysfunction syndrome (RADS) because a consistent physiologic accompaniment was airways hyperreactivity. When tested, all subjects showed positive methacholine challenge tests. No documented preexisting respiratory illness was identified nor did subjects relate past respiratory complaints. In two subjects, atopy was documented, but in all others, no evidence of allergy was identified. In the majority of the cases, there was persistence of respiratory symptoms and continuation of airways hyperreactivity for more than one year and often several years after the incident. The incriminated etiologic agent varied, but all shared a common characteristic of being irritant in nature. In two cases, bronchial biopsy specimens were available, and an airways inflammatory response was noted. This investigation suggests acute high level, uncontrolled irritant exposures may cause an asthma-like syndrome in some individuals which is different from typical occupational asthma. It can lead to long-term sequelae and chronic airways disease. Nonimmunologic mechanisms seem operative in the pathogenesis of this syndrome.
Effects of dexamethasone on functional and pathological changes in rat bronchi caused by high acute exposure to chlorine.
Demnati R, Fraser R, Martin JG, Plaa G, Malo JL
Toxicol Sci. 1998;45(2):242.
We assessed the effects of dexamethasone on functional and histological changes after acute exposure to a high level of chlorine gas in an animal model of reactive airways dysfunction syndrome (RADS). Sprague-Dawley male rats were exposed to 1500 ppm of chlorine for 5 min and treated with either dexamethasone (dex; 300 micrograms/kg/day) or saline intraperitoneally for 7 days. Lung resistance (RL), airway responsiveness to inhaled methacholine (MCh), airway wall morphometric measurements, and bronchoalveolar lavage (BAL) cells were assessed over a 2-week period after exposure. Dex administration significantly attenuated both chlorine-induced increased RL and chlorine-induced increased responsiveness to methacholine compared with saline: -2.7 +/- 6.8% vs 102.3 +/- 36.6% change from baseline RL (P<0.01) and 2.5 +/- 0.6 mg/ml vs 1.2 +/- 0.7 mg/ml in the MCh concentration required to double the RL from baseline (P<0.01). There was a tendency, albeit nonsignificant, for improvement in some indices of epithelial injury. Dex significantly attenuated the postexposure neutrophilic cellular response in BAL 1 day after exposure (15.8 +/- 4.9% neutrophils in the dex group vs 49.8 +/- 2.7% neutrophils in the saline group) (P<or = 0.001). Our results show that dex administration helps maintain pulmonary function, reduces BAL inflammatory cell number, and tends to improve some morphometric airway wall structure parameters in rats exposed to chlorine.
Department of Chest Medicine, Hôpital du Sacré-Coeur, Montreal, Quebec, Canada.
Chlorine-induced injury to the airways in mice.
Martin JG, Campbell HR, Iijima H, Gautrin D, Malo JL, Eidelman DH, Hamid Q, Maghni K
Am J Respir Crit Care Med. 2003;168(5):568.
Exposure to chlorine gas (Cl2) causes occupational asthma that we hypothesized occurs through the induction of airway inflammation and airway hyperresponsiveness by oxidative damage. Respiratory mechanics and airway responsiveness to methacholine were assessed in A/J mice 24 hours after a 5-minute exposure to 100, 200, 400, or 800 ppm Cl2 and 2 and 7 days after inhalation of 400 ppm Cl2. Airway responsiveness was higher 24 hours after 400 and 800 ppm Cl2. Responsiveness after inhalation of 400 ppm Cl2 returned to normal by 2 days but was again elevated at 7 days. Airway epithelial loss, patchy alveolar damage, proteinaceous exudates, and inflammatory cells within alveolar walls were observed in animals exposed to 800 ppm Cl2. Macrophages, granulocytes, epithelial cells, and nitrate/nitrite levels increased in lung lavage fluid. Increased inducible nitric oxide synthase expression and oxidation of lung proteins were observed. Epithelial cells and alveolar macrophages from mice exposed to 800 ppm Cl2 stained for 3-nitrotyrosine residues. Inhibition of inducible nitric oxide synthase with 1400W (1 mg/kg) abrogated the Cl2-induced changes in responsiveness. We conclude that chlorine exposure causes functional and pathological changes in the airways associated with oxidative stress. Inducible nitric oxide synthase is involved in the induction of changes in responsiveness to methacholine.
Meakins-Christie Laboratories, 3626 St Urbain, Montreal, Province of Quebec, H2X 2P2 Canada. email@example.com