The purpose of this study is to evaluate the association of signals recorded and analysed with Ventica® Lung Function Testing System (LFTS) in infants and pre-schoolers during the whole night sleep with the gold standard for sleep recording events, polysomnography, in order to better understand the confounding factors for momentary changes in the impedance pneumography-derived tidal breathing flow-volume (TBFV) curves.

Group 1: (children referred to sleep study for clinical reasons) Inclusion criteria:

• Age 1-7 years, both sexes
• Referred to polysomnography
• Signed informed consent

Group 2: (healthy children) Inclusion criteria:

• 2-7 years, both sexes
• Healthy at the time of inclusion based on history and clinical examination according to the investigator judgement
• Lung function in the reference range
• Signed informed consent

Exclusion Criteria:

• Preterm birth with chronic respiratory disorder of prematurity
• Significant nasal congestion or adenotonsillar hypertrophy with signs and symptoms of sleep apnea or sleep disordered breathing
• Chronic rhinosinusitis, synonasal polyposis
• Personal or family history or clinical evidence of asthma, atopy or other chronic respiratory disorders (high risk for asthma and allergy)
• Use of asthma rescue or maintenance medication within 4 weeks prior to inclusion
• Recurrent bronchitis or recurrent hospitalizations because of a respiratory illness (recurrent pneumonia)
• Hospital-treated for bronchiolitis with residual symptoms
• Acute respiratory infection or hospitalization because of an acute illness within 4 weeks prior to inclusion
• Other cardiorespiratory or neurological chronic diseases or states that may significantly alter the overnight breathing pattern
• Implanted or external active medical devices
• Long lasting respiratory events during the polysomnography study like continuous upper airway limitation

Subjects referred to sleep laboratory at the investigational site or healthy volunteers from Zagreb and surroundings