title: Hyperbaric nitrogen prolongs breath-holding time in humans.
abstract: Either an increase in PaCO(2) or a decrease in PaO(2), can affect respiratory stimulation through respiratory centers, thus influencing breath-holding time (BHT). This study was designed to determine whether and how hyperbaric air could influence BHT in comparison with hyperbaric oxygen in humans. We studied 36 healthy volunteers in a multiplace hyperbaric chamber. BHT, pulse oximeter, and transcutaneous carbon dioxide tension were measured at 1 and 2.8 atmosphere absolute (ATA) in two groups. Group A (n = 20) breathed air. Group O (n = 16) breathed oxygen with a face mask (5 L/min). BHTs were 108 +/- 28 s at 1.0 ATA and 230 +/- 71 s at 2.8 ATA in Group A, and 137 +/- 48 s at 1.0 ATA and 180 +/- 52 s at 2.8 ATA in Group O. Transcutaneous carbon dioxide tension in Group A (59 +/- 2 mm Hg) was higher than that in Group O (54 +/- 2 mm Hg) at the end of maximal breath-holding at 2.8 ATA. The prolongation of BHT in hyperbaric air is significantly greater than that in hyperbaric oxygen.
  
  
  CONCLUSIONS
  Breath-holding time is significantly prolonged in hyperbaric air than it is in hyperbaric oxygen. The mechanism involves the anesthetic effect of nitrogen suppressing the suffocating feeling during breath-holding.
authors.affiliation: Department of Anesthesiology, Nagasaki University School of Medicine, Japan. morooka@net.naasaki-u.ac.jp
authors.forename: H
authors.initials: H
authors.lastname: Morooka
authors.forename: Y
authors.initials: Y
authors.lastname: Wakasugi
authors.forename: H
authors.initials: H
authors.lastname: Shimamoto
authors.forename: O
authors.initials: O
authors.lastname: Shibata
authors.forename: K
authors.initials: K
authors.lastname: Sumikawa
mesh_terms: D000328:Adult; D000399:Air Pressure; D002245:Carbon Dioxide / Q000097:blood; D005260:Female; D006801:Humans; D006931:Hyperbaric Oxygenation; D008297:Male; D009584:Nitrogen / Q000494:pharmacology*; D012119:Respiration / Q000187:drug effects*
chemical_list: D002245:Carbon Dioxide; D009584:Nitrogen