Exhaled Hydrogen Sulphide as a Biomarker of Airways Disease in Asthma

Objectives: 1. Perform a cross-sectional study in non-asthmatic subjects and asthmatic subjects of varying severities of the levels of Hydrogen Sulphide in exhaled breath in relation to the severity and control of asthma 2. Compare the levels of exhaled Hydrogen Sulphide with exhaled Nitric Oxide. We will recruit 30 health volunteers and 90 patients with a range of severity of asthma. Particpants will attend for either 2 or 4 visits. At these visits the following measurements will be taken: 1. Exhaled Hydrogen Sulphide 2. Serum Hydrogen Sulphide 2\. Exhaled Nitric Oxide 3. Spirometry 4. Asthma Symptom Score (ACQ) The investigators will use a Hydrogen Sulphide UV fluorescent machine Model T101 (0-50 ppb to 0-20 ppm) (Cal-Bay Control Inc, USA) to measure directly on line exhaled breath Hydrogen Sulphide. This method has been used previously in normal people, but we will first determine whether there is an exhaled flow-dependence on the measurement of H2S levels. The investigators will use a hand-held Nitric Oxide machine (NO Breath) to measure Nitric Oxide in exhaled breath. Subjects must have asthma according to one or more of the following criteria documented in the last 12 months: 1. Improvement in FEV1 (forced expiratory volume at one second) ≥ 12% and 200ml predicted after inhalation of 400 mcg salbutamol 2. Airway hyper-responsiveness (PC20 \<8mg/ml) 3. Diurnal variation in PEF (peak expiratory flow): amplitude % mean of twice daily PEF \> 8% 4. Decrease in pre-bronchodilator FEV1 \>12% and \>200mls within 4 weeks after tapering treatment with one or more of the following drugs: inhaled corticosteroids, oral corticosteroids, long-acting beta-agonists, long-acting beta-agonists and short-acting beta-agonists. PLUS A history of wheeze occurring spontaneously or on exertion