Upper airway muscle responsiveness to rising PCO(2) during NREM sleep.
Although pharyngeal muscles respond robustly to increasing PCO(2) during wakefulness, the effect of hypercapnia on upper airway muscle activation during sleep has not been carefully assessed. This may be important, because it has been hypothesized that CO(2)-driven muscle activation may importantly stabilize the upper airway during stages 3 and 4 sleep. To test this hypothesis, we measured ventilation, airway resistance, genioglossus (GG) and tensor palatini (TP) electromyogram (EMG), plus end-tidal PCO(2) (PET(CO(2))) in 18 subjects during wakefulness, stage 2, and slow-wave sleep (SWS). Responses of ventilation and muscle EMG to administered CO(2) (PET(CO(2)) = 6 Torr above the eupneic level) were also assessed during SWS (n = 9) or stage 2 sleep (n = 7). PET(CO(2)) increased spontaneously by 0.8 +/- 0.1 Torr from stage 2 to SWS (from 43.3 +/- 0.6 to 44.1 +/- 0.5 Torr, P < 0.05), with no significant change in GG or TP EMG. Despite a significant increase in minute ventilation with induced hypercapnia (from 8.3 +/- 0.1 to 11.9 +/- 0.3 l/min in stage 2 and 8.6 +/- 0.4 to 12.7 +/- 0.4 l/min in SWS, P < 0.05 for both), there was no significant change in the GG or TP EMG. These data indicate that supraphysiological levels of PET(CO(2)) (50.4 +/- 1.6 Torr in stage 2, and 50.4 +/- 0.9 Torr in SWS) are not a major independent stimulus to pharyngeal dilator muscle activation during either SWS or stage 2 sleep. Thus hypercapnia-induced pharyngeal dilator muscle activation alone is unlikely to explain the paucity of sleep-disordered breathing events during SWS.
Pillar
G
G
Sleep Disorders Section, Divisions of Endocrinology and Pulmonary and Critical Care Medicine, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts, 02115, USA.
Malhotra
A
A
Fogel
R B
RB
Beauregard
J
J
Slamowitz
D I
DI
Shea
S A
SA
White
D P
DP
D000328:Adult; D002245:Carbon Dioxide / Q000494:pharmacology*; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000187:drug effects / Q000502:physiology*; D010614:Pharynx / Q000187:drug effects / Q000502:physiology*; D017286:Polysomnography; D015656:Respiratory Mechanics / Q000502:physiology*; D012894:Sleep Stages / Q000502:physiology*; D013990:Tidal Volume / Q000187:drug effects; D014851:Wakefulness / Q000502:physiology
D002245:Carbon Dioxide