title: Polysomnographic determinants of nocturnal hypercapnia in patients with sleep apnea.
abstract: OBJECTIVE
  Identify polysomnographic and demographic factors associated with elevation of nocturnal end-tidal CO2 in patients with obstructive sleep apnea.
  
  
  METHODS
  Forty-four adult patients with obstructive sleep apnea were selected such that the maximal nocturnal end-tidal CO2 was below 45 mm Hg in 15 studies, between 45 and 50 mm Hg in 14, and above 50 mm Hg in 15. Measurements included mean event (i.e., apneas or hypopneas) and mean inter-event duration, ratio of mean post- to mean pre-event amplitude, and percentage of total sleep time spent at an end-tidal CO2 < 45, 45-50, and > 50 mm Hg. An integrated nocturnal CO2 was calculated as the sum of the products of average end-tidal CO2 at each time interval by percent of total sleep time spent at the corresponding time interval.
  
  
  RESULTS
  The integrated nocturnal CO2 was inversely correlated with mean post-apnea duration, with lesser contributions from mean apnea duration and age (R (2) = 0.56), but did not correlate with the apnea-hypopnea index, or the body mass index. Mean post-event to mean pre-event amplitude correlated with mean post-apnea duration (r = 0.88, p < 0.001). Mean apnea duration did not correlate with mean post-apnea duration.
  
  
  CONCLUSIONS
  Nocturnal capnometry reflects pathophysiologic features of sleep apnea, such as the balance of apnea and post-apnea duration, which are not captured by the apnea-hypopnea index. This study expands the indications of capnometry beyond apnea detection and quantification of hypoventilation syndromes.
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Department of Medicine, Chulalongkorn University, Bangkok, Thailand.
authors.forename: Nattapong
authors.initials: N
authors.lastname: Jaimchariyatam
authors.forename: Raed A
authors.initials: RA
authors.lastname: Dweik
authors.forename: Roop
authors.initials: R
authors.lastname: Kaw
authors.forename: Loutfi S
authors.initials: LS
authors.lastname: Aboussouan
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001785:Blood Gas Monitoring, Transcutaneous; D015992:Body Mass Index; D005260:Female; D006801:Humans; D006935:Hypercapnia / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D010092:Oximetry; D017286:Polysomnography; D012143:Respiratory Physiological Phenomena; D012189:Retrospective Studies; D020181:Sleep Apnea, Obstructive / Q000503:physiopathology*; D055815:Young Adult
keywords: Obstructive sleep apnea; body mass index; capnography; hypercapnia; obesity hypoventilation syndrome