title: Worsening of central sleep apnea at high altitude--a role for cerebrovascular function.
abstract: Although periodic breathing during sleep at high altitude occurs almost universally, the likely mechanisms and independent effects of altitude and acclimatization have not been clearly reported. Data from 2005 demonstrated a significant relationship between decline in cerebral blood flow (CBF) at sleep onset and subsequent severity of central sleep apnea that night. We suspected that CBF would decline during partial acclimatization. We hypothesized therefore that reductions in CBF and its reactivity would worsen periodic breathing during sleep following partial acclimatization. Repeated measures of awake ventilatory and CBF responsiveness, arterial blood gases during wakefulness. and overnight polysomnography at sea level, upon arrival (days 2-4), and following partial acclimatization (days 12-15) to 5,050 m were made on 12 subjects. The apnea-hypopnea index (AHI) increased from to 77 ± 49 on days 2-4 to 116 ± 21 on days 12-15 (P = 0.01). The AHI upon initial arrival was associated with marked elevations in CBF (+28%, 68 ± 11 to 87 ± 17 cm/s; P < 0.05) and its reactivity to changes in PaCO2 [>90%, 2.0 ± 0.6 to 3.8 ± 1.5 cm·s(-1)·mmHg(-1) hypercapnia and 1.9 ± 0.4 to 4.1 ± 0.9 cm·s(-1)·mmHg(-1) for hypocapnia (P < 0.05)]. Over 10 days, the increases resolved and AHI worsened. During sleep at high altitude large oscillations in mean CBF velocity (CBFv) occurred, which were 35% higher initially (peak CBFv = 96 cm/s vs. peak CBFv = 71 cm/s) than at days 12-15. Our novel findings suggest that elevations in CBF and its reactivity to CO(2) upon initial ascent to high altitude may provide a protective effect on the development of periodic breathing during sleep (likely via moderating changes in central Pco2).
authors: Peninsula Sleep Laboratory, Sydney, New South Wales, Australia. kburgess@nsccahs.health.nsw.gov.au
authors: Keith R
authors: KR
authors: Burgess
authors: Samuel J E
authors: SJ
authors: Lucas
authors: Kelly
authors: K
authors: Shepherd
authors: Andrew
authors: A
authors: Dawson
authors: Marianne
authors: M
authors: Swart
authors: Kate N
authors: KN
authors: Thomas
authors: Rebekah A I
authors: RA
authors: Lucas
authors: Joseph
authors: J
authors: Donnelly
authors: Karen C
authors: KC
authors: Peebles
authors: Rishi
authors: R
authors: Basnyat
authors: Philip N
authors: PN
authors: Ainslie
mesh_terms: D000064:Acclimatization; D000328:Adult; D000531:Altitude; D001783:Blood Flow Velocity; D001784:Blood Gas Analysis; D002245:Carbon Dioxide / Q000097:blood*; D002560:Cerebrovascular Circulation; D018450:Disease Progression; D005260:Female; D006801:Humans; D006935:Hypercapnia / Q000097:blood / Q000503:physiopathology; D018496:Hyperoxia / Q000097:blood / Q000503:physiopathology; D016857:Hypocapnia / Q000097:blood / Q000503:physiopathology; D000860:Hypoxia / Q000097:blood / Q000503:physiopathology; D016014:Linear Models; D008168:Lung / Q000503:physiopathology*; D008297:Male; D010100:Oxygen / Q000097:blood; D010507:Periodicity; D017286:Polysomnography; D012119:Respiration; D012890:Sleep; D020182:Sleep Apnea, Central / Q000097:blood / Q000209:etiology* / Q000503:physiopathology; D013997:Time Factors; D055815:Young Adult
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen