Introduction
The nature and management of the noisy breathing infant and preschool child is always a challenge for the paediatrician and general physician. In clinical practice the evaluation of respiratory sounds is based on parental history, describing noises heard at a distance and on doctors’ physical qualification of auscultatory findings. Although different lung sounds are well defined1, the evaluation by parents and even by physicians can be problematic. Parents and caregivers use a variety of rather descriptive terms to report respiratory sounds that could often be misleading. They use a variety of terms for the same sound and the same terms for different sounds.2-4Parental misinterpreting is well known especially in infants and young children with overuse of the term “wheeze”, describing many different respiratory sounds.3,5,6 An observational study by Elphick et al. demonstrated that “rattle” in infants younger than 18 months is often labelled by parents as “wheeze”.6
Respiratory noises can be considered as clinical features of certain conditions with underlying aetiologies consisting of pathologically distinct processes and different treatment options. Therefore, confusion in terminology must be avoided, and accurate and correct description of breath sounds is important. While early wheeze has become a predictor of subsequent persistent asthma7-9, other lung sounds could be a marker for different disease entities, not related to asthma. While the “wheezy infant” is seen as a distinct clinical entity, the “rattling infant” is not, perhaps wrongly. Infants who mainly “rattle”, were less likely to wheeze at older age and more likely to outgrow their noisy breathing.5,10
Rattles are believed to be caused by excessive airway secretions, often in combination with a viral infection, which move during normal airflow within the central airways. On occasion rattling disappears after coughing and clearing of airway secretions.11 Clinical guidelines on the treatment of rattling infants and young children are lacking and only few studies focus on this topic. The need for treatment should depend on the presence of subjective discomfort to avoid needless medication. Wheezes on the other hand, are most commonly associated with airway obstruction due to various mechanisms, e.g., bronchoconstriction, airway wall oedema, intraluminal obstruction (e.g., foreign body or mass), external compression, or dynamic airway collapse.11
Differentiating the heterogeneous group of noisy breathing infants is important to further delineate the most appropriate approach, given that they have different aetiologies, natural histories and different responses to therapy.5 An early differential diagnosis by the use of non-invasive or minimally invasive techniques is of high importance for a “precision medicine” approach preventing under- and overtreatment. Exhaled breath analysis has potential to improve noisy breathing diagnosis. Volatile organic compounds (VOCs) in exhaled breath can be valuable biomarkers that reflect metabolic processes. This study aims to investigate the clinical potential of exhaled volatile biomarkers in the differentiation of noisy breathing infants. The current manuscript examined whether the severity of rattling could be estimated from the exhaled breath profile.