title: Optic nerve sheath diameter is not related to high altitude headache: a randomized controlled trial.
abstract: The mechanism of high altitude headache (HAH) remains unknown. The aim of this study was to determine experimentally whether optic nerve sheath diameter (ONSD), as an indicator of intracranial pressure, is related to HAH. Following sea level measurements at 3 and 12 hours (SL), 23 subjects were passively transported to high altitude (3777 m, HA) via cable car. HAH, ONSD, arterial oxygen saturation (Spo(2)), and fluid balance were determined at 3, 12, 24, and 36 hours. After 12 hours exposure to HA, subjects were classified by visual analogue scale (VAS) as either HAH positive (HAH+) or HAH negative (HAH-). Acetazolamide (250 mg) or placebo was then randomly prescribed at 15, 20, and 28 hours. Outcome means were compared via analysis of variance, and relationships between variables were analyzed by longitudinal regression. Acetazolamide had no statistically significant effect on HAH (p=0.63) or ONSD (p=0.98), but produced a negative fluid balance (p<0.01) (and also increased Spo(2) in exploratory analyses). Spo(2) was lower in HAH+ than HAH- [85 (3)% versus 88 (2)%, p=0.03). Nevertheless, ONSD increased similarly in HAH+ and HAH- (interaction p=0.90). ONSD also remained significantly elevated above SL values for the entire HA period [SL, 5.2 (0.5) versus HA, 5.6 (0.5) mm, p<0.01], despite headache resolving with acclimatization [VAS: SL, 1/100 (3) mm versus HA 3 h, 9/100 (13); 12 h, 10/100 (14); 24 h, 8/100 (12); 36 h, 1/100 (4) mm, p<0.01]. Furthermore, HAH was significantly correlated with Spo(2) (β=-1.39, p<0.01) but not with ONSD (β=0.59, p=0.57). These data do not support that intracranial pressure is associated with the development or amelioration of mild HAH. Clinical trial registration NCT01288781.
authors.affiliation: School of Sport, Health and Exercise Sciences, Bangor University, Gwynedd, United Kingdom.
authors.forename: Justin Stevan
authors.initials: JS
authors.lastname: Lawley
authors.forename: Samuel James
authors.initials: SJ
authors.lastname: Oliver
authors.forename: Paul
authors.initials: P
authors.lastname: Mullins
authors.forename: Daniel
authors.initials: D
authors.lastname: Morris
authors.forename: Naushad Ali
authors.initials: NA
authors.lastname: Junglee
authors.forename: Charlotte
authors.initials: C
authors.lastname: Jelleyman
authors.forename: Jamie Hugo
authors.initials: JH
authors.lastname: Macdonald
mesh_terms: D000064:Acclimatization; D000086:Acetazolamide / Q000494:pharmacology / Q000627:therapeutic use*; D000328:Adult; D000531:Altitude; D000704:Analysis of Variance; D004232:Diuretics / Q000494:pharmacology / Q000627:therapeutic use*; D004311:Double-Blind Method; D005260:Female; D006261:Headache / Q000188:drug therapy* / Q000503:physiopathology*; D006801:Humans; D007427:Intracranial Pressure; D008297:Male; D009900:Optic Nerve / Q000187:drug effects / Q000473:pathology*; D009929:Organ Size / Q000187:drug effects; D010100:Oxygen / Q000097:blood; D010147:Pain Measurement; D014882:Water-Electrolyte Balance / Q000187:drug effects; D055815:Young Adult
chemical_list: D004232:Diuretics; D000086:Acetazolamide; D010100:Oxygen