Postevent ventilation as a function of CO(2) load during respiratory events in obstructive sleep apnea.
Maintenance of eucapnia during sleep in obstructive sleep apnea (OSA) requires a balance between CO(2) loading during apnea and CO(2) elimination. This study examines individual respiratory events and relates magnitude of postevent ventilation to CO(2) load during the preceding respiratory event in 14 patients with OSA (arterial PCO(2) 42-56 Torr). Ventilation and expiratory CO(2) and O(2) fractions were measured on a breath-by-breath basis during daytime sleep. Calculations included CO(2) load during each event (metabolic CO(2) production - exhaled CO(2)) and postevent ventilation in the 10 s after an event. In 12 of 14 patients, a direct relationship existed between postevent ventilation and CO(2) load during the preceding event (P < 0.05); the slope of this relationship varied across subjects. Thus the postevent ventilation is tightly linked to CO(2) loading during each respiratory event and may be an important mechanism that defends against development of acute hypercapnia in OSA. An inverse relationship was noted between this postevent ventilatory response slope and the chronic awake arterial PCO(2) (r = 0.90, P < 0.001), suggesting that this mechanism is impaired in patients with chronic hypercapnia. The link between development of acute hypercapnia during respiratory events asleep and maintenance of chronic awake hypercapnia in OSA remains to be further investigated.
Division of Pulmonary and Critical Care Medicine and Bellevue Hospital Chest Service, Department of Medicine, New York University School of Medicine, New York, New York 10016, USA. kenneth.berger@med.nyu.edu
Kenneth I
KI
Berger
Indu
I
Ayappa
I Barry
IB
Sorkin
Robert G
RG
Norman
David M
DM
Rapoport
Roberta M
RM
Goldring
D000328:Adult; D001158:Arteries; D002245:Carbon Dioxide / Q000097:blood; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008297:Male; D008875:Middle Aged; D010100:Oxygen; D010313:Partial Pressure; D012119:Respiration; D012890:Sleep / Q000502:physiology; D012891:Sleep Apnea Syndromes / Q000503:physiopathology*; D014797:Vital Capacity; D014851:Wakefulness / Q000502:physiology
D002245:Carbon Dioxide; D010100:Oxygen