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Published ahead of print on July 17, 2003, doi:10.1164/rccm.200211-1304OC

Am. J. Respir. Crit. Care Med., Volume 168, Number 6, September 2003, 659-663

A more recent version of this article appeared on September 15, 2003
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Submitted on November 8, 2002
Accepted on July 14, 2003

STATIC AND DYNAMIC UPPER AIRWAY OBSTRUCTION IN SLEEP APNEA.ROLE OF THE BREATHING GAS PROPERTIES

Ramon Farre1*, Jordi Rigau1, Josep M Montserrat2, Lara Buscemi1, Eugeni Ballester2, and Daniel Navajas1

1 Unitat Biofisica i Bioenginyeria, Facultat de Medicina, Universitat de Barcelona-IDIBAPS, Barcelona, Spain, 2 Institut Clinic Pneumologia i Cirurgia Toracica, Hospital Clinic Provincial-IDIBAPS, Barcelona, Spain

* To whom correspondence should be addressed. E-mail: farre{at}medicina.ub.es.

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/h) when breathing air and 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 (0.0013) lower when breathing He-O2 (8.44±1.66 cmH2O; mean±SD) than air (10.18±2.34 cmH2O). Rup was markedly lower (p=0.0001) when breathing He-O2 (9.21±3.93 cmH2O.s/L) than air (15.92±6.27 cmH2O.s/L). Pcrit was similar (p=0.039) when breathing He-O2 (4.89±2.37 cmH2O) and air (4.19±2.93 cmH2O). 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.
Key words: obstructive sleep apnea, hypopnea, flow limitation, continuous positive airway pressure, breathing gas density




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