Chest
Volume 118, Issue 4, October 2000, Pages 1031-1041
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Clinical Investigations
SLEEP AND BREATHING
Abbreviated Method for Assessing Upper Airway Function in Obstructive Sleep Apnea

https://doi.org/10.1378/chest.118.4.1031Get rights and content

Study objectives:

Previous studies have shownthat the level of flow through the upper airway in patients withobstructive sleep apnea (OSA) is determined by the critical closingpressure (Pcrit) and the upstream resistance (Rn). Wedeveloped a standardized protocol for delineating quasisteady-statepressure-flow relationships for the upper airway from which thesevariables could be derived. In addition, we investigated the effect of body position and sleep stage on these variables by determining Pcritand Rn, and their confidence intervals (CIs), for eachcondition.

Design:

Pressure-flow relationships wereconstructed in the supine and lateral recumbent positions (nonrapid eyemovement [NREM] sleep, n = 10) and in the supine position (rapideye movement [REM] sleep, n = 5).

Setting:

University Hospital Antwerp, Belgium.

Patients:

Tenobese patients (body mass index, 32.0 ± 5.6 kg/m2) withsevere OSA (respiratory disturbance index, 63.0 ± 14.6 events/h)were studied.

Interventions:

Pressure-flowrelationships were constructed from breaths obtained during a series of step decreases in nasal pressure (34.1 ± 6.5 runs over 3.6 ± 1.2h) in NREM sleep and during 7.8 ± 2.2 runs over 0.8 ± 0.6 h in REM sleep.

Results:

Maximal inspiratory airflowreached a steady state in the third through fifth breaths following adecrease in nasal pressure. Analysis of pressure-flow relationshipsderived from these breaths showed that Pcrit fell from 1.8 (95% CI,−0.1 to 2.7) cm H2O in the supine position to −1.1 cmH2O (95% CI, −1.8 to 0.4 cm H2O; p = 0.009)in the lateral recumbent position, whereas Rn did notchange significantly. In contrast, no significant effect of sleep stagewas found on either Pcrit or Rn.

Conclusions:

Our methods for delineating upper airwaypressure-flow relationships during sleep allow for multipledeterminations of Pcrit within a single night from which small yetsignificant differences can be discerned between studyconditions.

Section snippets

Patient Selection

Ten patients with OSA were recruited for this study from the Sleep Disorders Unit at the University Hospital Antwerp, Belgium. Theywere considered eligible if the respiratory disturbance index (RDI)during nonrapid eye movement (NREM) sleep was > 10 episodes/h. Patients with any concurrent medical illnesses except hypertension wereexcluded. The Local Review Board of the Antwerp University Hospitalapproved the protocol for which all patients gave informed consent.

Study Design

Each patient underwent baseline

Patient Characteristics

Anthropometric, pulmonary function, and PSG data at baseline are presented in Table 1. Patients included in this study were middle-aged obese men who had PSGevidence of severe OSA (NREM RDI, 61.7 ± 7.0 episodes/h). No patientwas hypoxemic (Pao2 < 65 mm Hg) orhypercapnic (Paco2 > 45 mm Hg)during wakefulness. Moreover, no significant change in BMI or neckcircumference occurred between baseline and experimental PSG. BMI was32.0 ± 5.6 kg/m2 and 32.0 ± 5.8kg/m2, respectively).

Analysis of Vimax Responses to StepDecreases in Pn

Step decreases in Pn

Discussion

In this study, we developed an abbreviated, standardized methodfor characterizing upper airway function during sleep by examiningpressure-flow relationships for the upper airway in patients with OSA. These relationships were constructed from breaths obtained afterlowering Pn abruptly from a relatively high holding pressure level. When several breaths were evaluated after step reductions in Pn, wefound that the level of Vimax fell to a relativelylow level within the first three breaths and

ACKNOWLEDGMENT

The authors thank M. Willemen for his technicalassistance and L. Allan for his help in analyzing the data andpreparing the Figures for this article.

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  • Cited by (0)

    Supported by HL 503781, HL 37379, and the Fund of Scientific ResearchFlanders (FWO), Belgium.

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