Arterial stress hormones during scuba diving with different breathing gases.
OBJECTIVE
The purpose of the study was to determine whether the conditions during scuba diving without exercise (e.g., submersion, restricted breathing) stimulate the activities of the sympathoadrenergic system and the hypothalamic-pituitary-adrenal axis. This might facilitate panic reactions in dangerous situations.


METHODS
Fifteen experienced rescue divers participated in three experiments with two submersions each in a diving tower where ambient pressure could be varied. During submersion (duration = 15 min), they were breathing either pure oxygen (ambient pressure = 1.1 bar) or air (1.1 and 5.3 bar) or Heliox21 (21% O(2) and 79% He, 1.1 and 5.3 bar). The subjects stayed upright immediately below the water surface holding one hand with a cannulated radial artery out in the air. Noradrenaline, adrenaline, and dopamine concentrations in arterial blood and heart rate (HR) variability as indicators of sympathoadrenergic activity and cortisol and adrenocorticotropic hormone concentrations as strain indicators were measured.


RESULTS
[Noradrenaline] and [adrenaline] (initial values (mean ± SE) = 1616 ± 93 and 426 ± 38 pmol·L(-1)) decreased significantly by up to 30% and 50%, respectively, after 11 min of submersion, independent of pressure and inspired gas. HR variability showed roughly corresponding changes and also indications for parasympathetic stimulation, but artifacts by interference among HR monitors reduced the number of usable measurements. The other hormone concentrations did not change significantly.


CONCLUSIONS
There was no increase of stress hormone concentrations in experienced subjects. The reduction of [noradrenaline] and [adrenaline] during scuba diving seems to be a reaction to orthostatic relief caused by external hydrostatic pressure on peripheral vasculature. The activity of the vegetative nervous system might be estimated from HR variability if interference among pulse watches can be avoided.
Department of Sports Medicine, Institute of Physiology, Campus Benjamin Franklin, Charité-University Medicine Berlin, Berlin, Germany.
Frank
F
Weist
Günther
G
Strobel
Mathias
M
Hölzl
Dieter
D
Böning
D000324:Adrenocorticotropic Hormone / Q000097:blood; D000328:Adult; D000388:Air; D004242:Diving / Q000502:physiology*; D004837:Epinephrine / Q000097:blood; D005740:Gases; D005858:Germany; D006371:Helium / Q000008:administration & dosage; D006801:Humans; D006854:Hydrocortisone / Q000097:blood; D007030:Hypothalamo-Hypophyseal System / Q000378:metabolism*; D008297:Male; D009638:Norepinephrine / Q000097:blood; D010100:Oxygen / Q000008:administration & dosage; D010913:Pituitary-Adrenal System / Q000378:metabolism*; D012119:Respiration; D013312:Stress, Physiological / Q000502:physiology*; D013564:Sympathetic Nervous System / Q000378:metabolism*
D005740:Gases; D006371:Helium; C038949:heliox; D000324:Adrenocorticotropic Hormone; D010100:Oxygen; D006854:Hydrocortisone; D009638:Norepinephrine; D004837:Epinephrine