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Abstract
Repeated exposure to increased partial pressure of oxygen (PO2) is the standard of
care for several medical conditions. The side-effects of repeated exposure to hyperbaric
oxygen (HBO), however, are not well defined. Previous studies have demonstrated that
acute exposure of rats to HBO causes hypothermia that precedes convulsions. In the
present studies, rats that were repeatedly exposed to 100% oxygen at 4 atmospheres
absolute (ATA) pressure developed convulsions earlier than naive controls. There was
also a trend toward less hypothermia in the rats repeatedly exposed to oxygen. The
purpose of this study was to test the hypothesis that repeated exposure to HBO increases
sensitivity to convulsions induced by HBO and to determine if the time to onset of
convulsions is affected by the hypothermia caused by exposure to HBO. Rats were repeatedly
exposed to 2 ATA oxygen for a total of 10 days. After 72 h, these rats were challenged
by exposure to 100% oxygen at 4 ATA pressure. Rats repeatedly exposed to HBO had convulsions
significantly earlier than the naive controls (84 +/- 8 min compared to 147 +/- 11
min), and they developed significantly less hypothermia. Control studies suggested
that the decrease in the degree of hypothermia was caused by both repeated exposure
to oxygen and adaptation to the mild restraint used during oxygen re-exposures. Adaptation
to restraint eliminated the hypothermia induced by oxygen but did not change the time
to onset of convulsions. Increased sensitivity to convulsions was present after five
exposures to 2 ATA oxygen and persisted for 10 days after the last 2 ATA oxygen re-exposure.(ABSTRACT
TRUNCATED AT 250 WORDS)