Acute exposure to diesel exhaust under normal city conditions leads to a worsening of symptoms of asthma, with reduction in lung function in asthmatic nonsmoking adults, dependent on the exposure dose and on the background severity of asthma.

The worsening asthma is accompanied by increased oxidative stress and inflammation in the lungs.

The investigators will recruit 60 nonsmoking asthmatics of mild and of moderate severity. They will be exposed to Oxford St. or to Hyde Park for 2 hours each, at a walking pace. Real time exposure to PM2.5, carbon monoxide and nitrogen dioxide will be made each time. Health outcome measurements will be made before and after exposure to each street. Statistical analyses will be made to examine the effect of diesel exposure on changes in health outcome measures.

Inclusion Criteria:

Subjects will be selected according to the current severity of their asthma; thirty from Steps 1 and 2 and thirty from Step 3 of the World Health Organization (WHO) Global Initiative for Asthma (GINA) asthma guidelines. These will include mild and moderate asthmatic states. Depending on baseline FEV1, subjects will undergo either a methacholine bronchial hyperresponsiveness assessment or airways reversibility testing. Subjects with normal FEV1 (>80% predicted) or normal FEV1/FVC ratio will undergo methacholine challenge. Subjects with FEV1 <80% predicted will undergo airways reversibility testing. Subjects must have either a PC20 of less than 8mg/ml methacholine, or improvement in FEV1 of 12% or more, following inhalation of short acting β-agonist (salbutamol 200μg from metered dose inhaler [MDI]). Skin prick testing will be conducted for common allergens (house dust mite, grass pollen, aspergillus fumigatus and cat hair). The results will only be for descriptive purposes, not as subject inclusion/exclusion criteria. Subjects may be atopic or non-atopic (according to history and allergy testing).

2 hours