title: Inspiratory flow limitation in a normal population of adults in São Paulo, Brazil.
abstract: OBJECTIVE
  Inspiratory flow limitation (IFL) during sleep occurs when airflow remains constant despite an increase in respiratory effort. This respiratory event has been recognized as an important parameter for identifying sleep breathing disorders. The purpose of this study was to investigate how much IFL normal individuals can present during sleep.
  
  
  METHODS
  Cross-sectional study derived from a general population sample.
  
  
  METHODS
  A "normal" asymptomatic sample derived from the epidemiological cohort of São Paulo.
  
  
  METHODS
  This study was derived from a general population study involving questionnaires and nocturnal polysomnography of 1,042 individuals. A subgroup defined as a nonsymptomatic healthy group was used as the normal group.
  
  
  METHODS
  N/A.
  
  
  RESULTS
  All participants answered several questionnaires and underwent full nocturnal polysomnography. IFL was manually scored, and the percentage of IFL of total sleep time was considered for final analysis. The distribution of the percentage of IFL was analyzed, and associated factors (age, sex, and body mass index) were calculated. There were 95% of normal individuals who exhibited IFL during less than 30% of the total sleep time. Body mass index was positively associated with IFL.
  
  
  CONCLUSIONS
  Inspiratory flow limitation can be observed in the polysomnography of normal individuals, with an influence of body weight on percentage of inspiratory flow limitation. However, only 5% of asymptomatic individuals will have more than 30% of total sleep time with inspiratory flow limitation. This suggests that only levels of inspiratory flow limitation > 30% be considered in the process of diagnosing obstructive sleep apnea in the absence of an apnea-hypopnea index > 5 and that < 30% of inspiratory flow limitation may be a normal finding in many patients.
authors.affiliation: Disciplina de Medicina e Biologia do Sono, Departamento de Psicobiologia, Universidade Federal de São Paulo, Brazil.
authors.forename: Luciana O
authors.initials: LO
authors.lastname: Palombini
authors.forename: Sergio
authors.initials: S
authors.lastname: Tufik
authors.forename: David M
authors.initials: DM
authors.lastname: Rapoport
authors.forename: Indu A
authors.initials: IA
authors.lastname: Ayappa
authors.forename: Christian
authors.initials: C
authors.lastname: Guilleminault
authors.forename: Luciana B M
authors.initials: LB
authors.lastname: de Godoy
authors.forename: Laura S
authors.initials: LS
authors.lastname: Castro
authors.forename: Lia
authors.initials: L
authors.lastname: Bittencourt
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000402:Airway Obstruction / Q000453:epidemiology*; D000403:Airway Resistance; D015992:Body Mass Index; D001938:Brazil / Q000453:epidemiology; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D001239:Inhalation; D008297:Male; D008875:Middle Aged; D017286:Polysomnography; D012307:Risk Factors; D012891:Sleep Apnea Syndromes / Q000453:epidemiology / Q000503:physiopathology; D055815:Young Adult
keywords: Flow limitation; nasal pressure cannula; sleep; upper airway resistance; weight