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Exposure to Hyperbaric Oxygen During Long‐duration, Repeated Exercise Dives Does Not Alter Cortisol Regulation
Author(s) -
Conaty Betsy,
Shykoff Barbara,
Florian John
Publication year - 2015
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.29.1_supplement.678.7
Subject(s) - oxygen , cycle ergometer , heart rate , medicine , breathing gas , repeated measures design , anesthesia , zoology , breathing , chemistry , blood pressure , biology , statistics , mathematics , organic chemistry
Cortisol influences numerous body systems and functions, and thus any abnormal changes in cortisol levels could be associated with an increased risk for divers. This study investigated the effects of repeated bouts of in‐water exercise (simulating shallow water tactical swimming) during pure oxygen breathing on cortisol levels in experienced military divers. Twenty‐three Navy divers (31±7 [20‐44] yrs; mean±SD [minimum‐maximum]) were exposed to one of two thermoneutral experimental conditions at a pressure of 1.35 atmospheres absolute (ATA) for six hours on five consecutive days: (1) breathing air (n=13) or (2) breathing 100% oxygen (n=10). Throughout each dive they performed repeated bouts of 30 minutes of prone cycle ergometer exercise (target heart rate of 95±5 beats/min) and 30 minutes of seated rest. Serum cortisol concentrations were measured approximately one hour before and after each dive. The change in cortisol (ug/dL) after diving did not differ between air (6.01±6.21) and oxygen (4.69±6.72) phases (p>0.05). There were no differences in pre‐ or post‐dive cortisol concentrations across dive days for either of the experimental conditions (average values for air ‐ pre‐dive 16.13±6.85; post‐dive air 10.12±3.24; oxygen ‐ pre‐dive oxygen 14.64±6.11; post‐dive oxygen 8.99±4.19). This study provides evidence that repeated long‐duration hyperbaric oxygen exposures at 1.35 ATA combined with physical activity, per se, do not abnormally alter post‐dive cortisol concentrations. The observed changes likely represent the natural circadian rhythm of cortisol. Support: ONR and NAVSEA DSBDP