Changes in lung volume and diaphragm muscle activity at sleep onset in obese obstructive sleep apnea patients vs. healthy-weight controls

D Stadler, Ronald McEvoy, Jana Bradley, Denzil Paul, Peter Catcheside

    Research output: Contribution to journalArticlepeer-review

    25 Citations (Scopus)


    Obese obstructive sleep apnea (OSA) patients potentially defend end-expiratory lung volume (EELV) during wakefulness via increased expiratory diaphragmatic activity (eEMG dia). A reduction in eEMG dia and EELV at sleep onset could, therefore, increase upper airway collapsibility via reduced tracheal traction. The aim of this study was to establish if eEMG dia is greater in obese OSA patients vs. healthy-weight controls during wakefulness, and to compare eEMG dia and EELV changes at sleep onset between groups as a function of stable breathing, hypopnea vs. apnea events developing within the first few breaths after sleep onset. Eight obese men with OSA and eight healthy-weight men without OSA were studied in the supine position while instrumented with an intraesophageal catheter to measure eEMGdia and magnetometer coils to assess changes in EELV. While eEMG dia expressed as %maximal activity was not significantly different between groups during wakefulness, OSA patients experienced a greater fall in eEMG diafollowing sleep onset (group × breath, P < 0.001) and a greater decrease when respiratory events accompanied sleep onsets (category × breath, P < 0.001). The decrease in EELV by the third postsleep onset breath was small (OSA, 61.4 8.0 ml, P < 0.001; controls, 34.0 ± 4.2 ml, P- 0.001), with the decrease significantly greater in OSA patients over time (group × breath, P < 0.007). There was a greater decrease with more severe events (category × breath, P < 0.001), with EELV decreasing by 89.6 ± 14.2 ml (P < 0.001) at the onset of apneas in the OSA group. These data support that diaphragm tone and EELV frequently decrease following sleep onset, with greater falls at transitions accompanied by respiratory events. In addition to decrements in upper airway dilator muscle activity, decreasing lung volume potentially contributes to an increased propensity for upper airway collapse in OSA patients at sleep onset.

    Original languageEnglish
    Article numberCurrent Contents search
    Pages (from-to)1027-1036
    Number of pages10
    JournalJournal of Applied Physiology
    Issue number4
    Publication statusPublished - Oct 2010


    • Caudal traction
    • Intra-abdominal pressure
    • Wake-sleep transition


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