Decompression comparison of helium and hydrogen in rats.
Lillo, R. S., Parker, E. C. and Porter, W. R.
Diving and Environmental Physiology Department, Naval Medical
Research Institute, Bethesda, Maryland 20889-5607
APStracts 3:0517A, 1996.
The hypothesis that there are differences in decompression risk
between helium (He) and hydrogen (H2) was examined in 1607
unanesthetized male albino rats subjected to dives on 2% O2/balance
He or 2% O2/balance H2 (depths = 50 ATA, bottom times = 60 min).
Animals were decompressed to 10.8 ATA using profiles varying from
rapid to slow with up to 4 decompression stops of up to 60 min each.
Maximum likelihood analysis was used to estimate relative
decompression risk on a per unit pressure basis (termed
"potency") and rate of gas uptake and elimination, both
factors affecting the DCS risk from a specific dive profile. Hydrogen
potency for causing decompression sickness was found to be up to 35%
greater than He. Uptake rates were unresolvable between the 2 gases
with the time constant (TC) estimated at 2-3 min, leading to
saturation in both cases in < 15 min. Washout of both gases
was significantly slower than uptake, with He washout (TC1.5 - 3 h)
substantially slower than H2 washout (TC0.5 h). It is unknown whether
the decompression advantage of H2's faster washout or the
disadvantage of its increased potency, observed in the rat, would be
important for human diving.
Received 26 June 1996; accepted in final form 5 November 1996.
APS Manuscript Number A602-6.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996