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Inspiratory flow limitation in normal and UARS patients in a general population sample


Inspiratory flow limitation (IFL) is defined as a “flattened shape” of inspiratory airflow contour detected by nasal cannula pressure during sleep and can indicate increased upper airway resistance especially in mild Sleep Related Breathing Disorders (SRBD). It is commonly caused by narrowing of a hypotonic upper airway in response to the negative intrathoracic pressure developed during inspiration. However IFL cut-off value for SRBD is not established yet.


The objective of the study was to determine the cut-off value of IFL in potential Upper Airway Resistance Syndrome (UARS) subjects considering clinical outcomes in a general population sample.


The baseline sample was derived from a prospective population-based study designed to assess the prevalence of sleep disorders in Sao Paulo, Brazil. A total of 1,042 subjects completed all the study assessments in 2007 and, from July 2015 to April 2016, 712 from these participants were reassessed and underwent a second examination. Full night polysomnography (PSG) at both baseline and follow-up was performed. IFL was scored based on nasal cannula recording if there were at least four consecutive breaths with flattening of the airflow curve in a 30 second epoch. We manually scored each participant and calculated their total sleep time (TST) spent in IFL during sleep. Clinical outcomes (excessive daytime sleepiness, fatigue, mood and quality of sleep) of no OSAS subjects (normal individuals and potential UARS patients) were analyzed at baseline and after 8 years.


From the 712 participants evaluated, 242 subjects without OSAS (normal individuals and potential UARS patients) were clinically evaluated at baseline and after 8 years. When an IFL cut-off value of equal to or greater than 5% of TST was considered for UARS diagnosis, there was not any statistical significant difference in clinical outcomes though 8 years. Otherwise, when an IFL cut-off value of equal to or greater than 15% of TST was considered for UARS diagnosis, normal subjects in 2007 that had potential UARS in 2016 and patients with potential UARS in 2007 that maintain their diagnosis in 2016 had more severity of depressive symptoms than normal subjects in 2007/2016.


In a general population sample, we suggest a cut-off value of IFL in normal subjects and in potential UARS patients of equal or greater than 15% of TST when clinical outcomes are considered.


flow limitation, upper airway resistance


Área Clínica


Luciana Palombini, Luciana B. M. Godoy, Monica L. Andersen, Dalva Poyares, Sergio Tufik