The use of bronchial challenge to diagnose asthma in preschool children.

Wheezing and respiratory symptoms are very common in preschool children, and the ability to diagnose asthma correctly is important. This review describes an approach to the diagnosis of asthma in preschool children by means of an inhalation bronchial challenge. The child is exposed to increasing doses of challenge agent until wheezing is detected at a dose below that at which normal subjects respond, thus indicating bronchial hyperreactivity. The technique was originally developed using simple stethoscope auscultation of the lungs together with recording of respiratory rate and oxygen saturation (by pulse oximetry). Extensive studies have confirmed the safety and practicability of the technique and the specificity for asthma when the challenge agent is adenosine 5'-monophosphate (AMP). Subsequently, acoustic recordings have been used to detect and analyse breath sounds and to quantify the wheeze; these show excellent correlation between the clinical detection of wheeze and the wheeze rate (duration of wheeze/duration of recording) during bronchial challenges in children. Equipment is now becoming available that can perform the acoustic quantification of wheeze automatically and facilitate bronchial challenges in young children.