title: Control of upper airway muscle activity in younger versus older men during sleep onset.
abstract: Pharyngeal dilator muscles are clearly important in the pathophysiology of obstructive sleep apnoea syndrome (OSA). We have previously shown that the activity of both the genioglossus (GGEMG) and tensor palatini (TPEMG) are decreased at sleep onset, and that this decrement in muscle activity is greater in the apnoea patient than in healthy controls. We have also previously shown this decrement to be greater in older men when compared with younger ones. In order to explore the mechanisms responsible for this decrement in muscle activity nasal continuous positive airway pressure (CPAP) was applied to reduce negative pressure mediated muscle activation. We then investigated the effect of sleep onset (transition from predominantly alpha to predominantly theta EEG activity) on ventilation, upper airway muscle activation and upper airway resistance (UAR) in middle-aged and younger healthy men. We found that both GGEMG and TPEMG were reduced by the application of nasal CPAP during wakefulness, but that CPAP did not alter the decrement in activity in either muscle seen in the first two breaths following an alpha to theta transition. However, CPAP prevented both the rise in UAR at sleep onset that occurred on the control night, and the recruitment in GGEMG seen in the third to fifth breaths following the alpha to theta transition. Further, GGEMG was higher in the middle-aged men than in the younger men during wakefulness and was decreased more in the middle-aged men with the application of nasal CPAP. No differences were seen in TPEMG between the two age groups. These data suggest that the initial sleep onset reduction in upper airway muscle activity is due to loss of a 'wakefulness' stimulus, rather than to loss of responsiveness to negative pressure. In addition, it suggests that in older men, higher wakeful muscle activity is due to an anatomically more collapsible upper airway with more negative pressure driven muscle activation. Sleep onset per se does not appear to have a greater effect on upper airway muscle activity as one ages.
authors.affiliation: Harvard Medical School and Division of Sleep Medicine, Brigham and Women's Hospital, 221 Longwood Avenue, Boston, MA 02115, USA. rfogel@partners.org
authors.forename: Robert B
authors.initials: RB
authors.lastname: Fogel
authors.forename: David P
authors.initials: DP
authors.lastname: White
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Pierce
authors.forename: Atul
authors.initials: A
authors.lastname: Malhotra
authors.forename: Jill K
authors.initials: JK
authors.lastname: Edwards
authors.forename: Judy
authors.initials: J
authors.lastname: Dunai
authors.forename: Darci
authors.initials: D
authors.lastname: Kleverlaan
authors.forename: John
authors.initials: J
authors.lastname: Trinder
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000403:Airway Resistance / Q000502:physiology; D045422:Continuous Positive Airway Pressure; D004569:Electroencephalography; D004576:Electromyography; D006801:Humans; D008297:Male; D008875:Middle Aged; D010156:Palatal Muscles / Q000502:physiology; D010609:Pharyngeal Muscles / Q000502:physiology*; D011312:Pressure; D012123:Pulmonary Ventilation / Q000502:physiology; D015656:Respiratory Mechanics / Q000502:physiology; D012132:Respiratory Muscles / Q000502:physiology; D012890:Sleep / Q000502:physiology; D012894:Sleep Stages / Q000502:physiology*; D014851:Wakefulness / Q000502:physiology