title: Static and dynamic upper airway obstruction in sleep apnea: role of the breathing gas properties.
abstract: Increased upper airway collapsibility in the sleep apnea/hypopnea syndrome (SAHS) is usually interpreted by a collapsible resistor model characterized by a critical pressure (Pcrit) and an upstream resistance (Rup). To investigate the role played by the upstream segment of the upper airway, we tested the hypothesis that breathing different gases would modify Rup but not Pcrit. The study was performed on 10 patients with severe SAHS (apnea-hypopnea index: 59 +/- 14 events/hour) when breathing air and helium-oxygen (He-O2) during non-REM sleep. The continuous positive airway pressure that normalized flow (CPAPopt) was measured. Rup and Pcrit were determined from the linear relationship between maximal inspiratory flow VImax and nasal pressure (PN):VImax = (PN - Pcrit)/Rup. Changing the breathing gas selectively modified the severity of dynamic (CPAPopt, Rup) and static (Pcrit) obstructions. CPAPopt was significantly (p = 0.0013) lower when breathing He-O2 (8.44 +/- 1.66 cm H2O; mean +/- SD) than air (10.18 +/- 2.34 cm H2O). Rup was markedly lower (p = 0.0001) when breathing He-O2 (9.21 +/- 3.93 cm H2O x s/L) than air (15.92 +/- 6.27 cm H2O x s/L). Pcrit was similar (p = 0.039) when breathing He-O2 (4.89 +/- 2.37 cm H2O) and air (4.19 +/- 2.93 cm H2O). The data demonstrate the role played by the upstream segment of the upper airway and suggest that different mechanisms determine static (Pcrit) and dynamic (Rup) upper airway obstructions in SAHS.
authors.affiliation: Unitat de Biofísica i Bioenginyeria, Facultat de Medicina, Universitat de Barcelona, Spain. rfarre@ub.edu
authors.forename: Ramon
authors.initials: R
authors.lastname: Farré
authors.forename: Jordi
authors.initials: J
authors.lastname: Rigau
authors.forename: Josep M
authors.initials: JM
authors.lastname: Montserrat
authors.forename: Lara
authors.initials: L
authors.lastname: Buscemi
authors.forename: Eugeni
authors.initials: E
authors.lastname: Ballester
authors.forename: Daniel
authors.initials: D
authors.lastname: Navajas
mesh_terms: D000328:Adult; D000402:Airway Obstruction / Q000503:physiopathology*; D000403:Airway Resistance / Q000502:physiology*; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D017286:Polysomnography; D011446:Prospective Studies; D011659:Pulmonary Gas Exchange; D018570:Risk Assessment; D012494:Sampling Studies; D012720:Severity of Illness Index; D012891:Sleep Apnea Syndromes / Q000175:diagnosis* / Q000503:physiopathology; D012894:Sleep Stages