title: Relative prolongation of inspiratory time predicts high versus low resistance categorization of hypopneas.
abstract: OBJECTIVE
  Sleep disordered breathing events conceptually separate into "obstructive" and "central" events. Esophageal manometry is the definitive but invasive means of classifying hypopneas. The purpose of this project was to identify noninvasive markers for discriminating high vs. low resistance hypopneas.
  
  
  METHODS
  Forty subjects with obstructive or central sleep apnea underwent diagnostic polysomnography with nasal cannula airflow and esophageal manometry; 200% resistance relative to reference breaths was used to define "high" resistance. Noninvasive parameters from 292 randomly selected hypopneas in 20 subjects were analyzed and correlated to resistance. The best parameter and cutoff for predicting high relative resistance was determined and tested prospectively in 2 test sets in the 20 remaining subjects. Test Set A: 15 randomly selected hypopneas in each subject; Test Set B: all hypopneas in 7 subjects.
  
  
  RESULTS
  In the development set, prolongation of inspiratory time during the 2 smallest breaths of a hypopnea (T(i)) relative to baseline had the best correlation to high relative resistance. In the Test Set A, relative T(i) > 110% classified obstructive events with sensitivity = 72%, specificity = 77%, PPV = 64%, NPV = 83%. Similar numbers were obtained for classification of hypopneas based on presence of flow limitation (FL) alone. When either relative T(i) or presence of FL were used to define high resistance, sensitivity = 84%, specificity = 74%, PPV = 65%, NPV = 89%. Similar results were obtained for Test Set B.
  
  
  CONCLUSIONS
  Relative prolongation of T(i) is a good noninvasive predictor of high/low resistance in a dataset with both FL and NFL hypopneas. Combination of FL and relative T(i) improves this classification. The use of T(i) to separate obstructive and central hypopneas needs to be further tested for clinical utility (outcomes and treatment effects).
authors.affiliation: Division of Pulmonary, Critical Care, and Sleep Medicine, NYU School of Medicine, New York, NY 10016, USA. anne.mooney@nyu.edu
authors.forename: Anne M
authors.initials: AM
authors.lastname: Mooney
authors.forename: Khader K
authors.initials: KK
authors.lastname: Abounasr
authors.forename: David M
authors.initials: DM
authors.lastname: Rapoport
authors.forename: Indu
authors.initials: I
authors.lastname: Ayappa
mesh_terms: D000403:Airway Resistance / Q000502:physiology; D005260:Female; D006801:Humans; D001239:Inhalation / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D017286:Polysomnography; D011237:Predictive Value of Tests; D012372:ROC Curve; D012680:Sensitivity and Specificity; D012891:Sleep Apnea Syndromes / Q000145:classification / Q000175:diagnosis* / Q000503:physiopathology; D020182:Sleep Apnea, Central / Q000175:diagnosis* / Q000503:physiopathology; D020181:Sleep Apnea, Obstructive / Q000175:diagnosis / Q000503:physiopathology; D013997:Time Factors