Oxygen pulse in guinea pigs in hyperbaric helium and hydrogen.
Kayar, Susan R., and Erich C. Parker.
Albert R. Behnke Diving Medicine Research Center, Naval Medical
Research Institute, 8901 Wisconsin Avenue, Bethesda, Maryland 20889
-5607
APStracts 3:0515A, 1996.
We analyzed oxygen pulse, the total volume of O2 consumed per heart
beat, in guinea pigs at pressures from 10 to 60 atm. Animals were
placed in a hyperbaric chamber and breathed 2% O2 in either helium
(heliox) or hydrogen (hydrox). Oxygen consumption rate (O2) was
measured by gas chromatographic analysis. Core temperature and heart
rate were measured using surgically implanted radiotelemeters. The O2
was modulated over a range of 4x by varying chamber temperature from
25 to 36 degrees C. There was a direct correlation between O2 and
heart rate, which was significantly different for animals in heliox
versus hydrox (P = 0.003). By multivariate regression analysis, we
identified variables that were significant to O2 pulse: body surface
area, chamber temperature, core temperature, and pressure. After
normalizing for all non-pressure variables, the residual O2 pulse was
found to decrease significantly (P = 0.02) with pressure for animals
in heliox, but did not decrease significantly (P = 0.38) with
pressure for animals in hydrox over the range of pressures studied.
This amounted to a roughly 25% lower O2 pulse for normothermic
animals in 60 atm heliox versus hydrox. These results suggest that
reduction of cardiovascular efficiency in a hyperbaric environment
can be mitigated by the choice of breathing gas.
Received 14 December 1995; accepted in final form 28 October
1996.
APS Manuscript Number A1305-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996