title: The heterogeneity of obstructive sleep apnea (predominant obstructive vs pure obstructive apnea).
abstract: OBJECTIVE
  To compare the breathing instability and upper airway collapsibility between patients with pure OSA (i.e. 100% of apneas are obstructive) and patients with predominant OSA (i.e., coexisting obstructive and central apneas).
  
  
  METHODS
  A cross-sectional study with data scored by a fellow being blinded to the subjects' classification. The results were compared between the 2 groups with unpaired student t-test.
  
  
  METHODS
  Standard polysomnography technique was used to document sleep-wake state. Ventilator in pressure support mode was used to introduce hypocapnic apnea during CO(2) reserve measurement. CPAP with both positive and negative pressures was used to produce obstructive apnea during upper airway collapsibility measurement.
  
  
  METHODS
  21 patients with OSA: 12 with coexisting central/mixed apneas and hypopneas (28% ± 6% of total), and 9 had pure OSA.
  
  
  METHODS
  The upper airway collapsibility was measured by assessing the critical closing pressure (Pcrit). Breathing stability was assessed by measuring CO(2) reserve (i.e., ΔPCO(2) [eupnea-apnea threshold]) during NREM sleep.
  
  
  RESULTS
  There was no difference in Pcrit between the 2 groups (pure OSA vs. predominant OSA: 2.0 ± 0.4 vs. 2.7 ± 0.4 cm H(2)O, P = 0.27); but the CO(2) reserve was significantly smaller in predominant OSA group (1.6 ± 0.7 mm Hg) than the pure OSA group (3.8 ± 0.6 mm Hg) (P = 0.02).
  
  
  CONCLUSIONS
  The present data indicate that breathing stability rather than upper airway collapsibility distinguishes OSA patients with a combination of obstructive and central events from those with pure OSA.
authors.affiliation: Population Health Sciences, University of Wisconsin, Madison, WI, USA. axie@wisc.edu
authors.forename: Ailiang
authors.initials: A
authors.lastname: Xie
authors.forename: Ajay
authors.initials: A
authors.lastname: Bedekar
authors.forename: James B
authors.initials: JB
authors.lastname: Skatrud
authors.forename: Mihaela
authors.initials: M
authors.lastname: Teodorescu
authors.forename: Yuansheng
authors.initials: Y
authors.lastname: Gong
authors.forename: Jerome A
authors.initials: JA
authors.lastname: Dempsey
mesh_terms: D000328:Adult; D045422:Continuous Positive Airway Pressure; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017286:Polysomnography; D015656:Respiratory Mechanics / Q000502:physiology*; D020182:Sleep Apnea, Central / Q000503:physiopathology*; D020181:Sleep Apnea, Obstructive / Q000503:physiopathology*; D014109:Total Lung Capacity / Q000502:physiology