ABSTRACT
Traditionally asthma control has been monitored by symptoms and lung function measurements, particularly peak expiratory flow. Airway inflammation underlies asthma symptoms but is difficult to measure directly as this involves invasive procedures, such as bronchial biopsy and bronchoalveolar lavage. More recently, the less invasive procedure of sputum induction has been introduced (1). This is more acceptable to patients, but some patients find it unacceptable, and it is not possible to obtain adequate samples from other patients. It is also difficult to apply in young children. The procedure of sputum induction with hypertonic saline itself induces airway inflammation, so cannot be repeated frequently (2,3). This has led to a search for less invasive ways to measure airway inflammation in order to assess adequate control with anti-inflammatory treatments, to predict loss of asthma control, and to assess the response to novel anti-inflammatory treatments. Several markers in exhaled breath have now been explored (4), including:
1. Exhaled gases Nitric oxide Carbon monoxide Hydrocarbons (ethane and pentane)
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2. Exhaled breath condensate Reactive oxygen and nitrogen species Inflammatory mediators Cytokines
This chapter discusses how these markers in exhaled breath have been used to assess airway inflammation and its control in asthma. This is a rapidly advancing field with the potential for enormous clinical impact. It provides new opportunities to explore the underlying inflammatory process in asthma, particularly in severe disease and in young children in whom it has been difficult to evaluate airway inflammation using traditional techniques. Noninvasive monitoring also allows repeated measurements to be made, thus allowing detailed studies of the kinetic effects of anti-inflammatory drugs.
