Confounding Factors of Impedance Pneumography

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