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Is the transition from day to night activity a risk factor for the development of CNS oxygen toxicity during hyperbaric oxygen exposure?

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Title: Is the transition from day to night activity a risk factor for the development of CNS oxygen toxicity during hyperbaric oxygen exposure?


1
Is the transition from day to night activity a
risk factor for the development of CNS oxygen
toxicity during hyperbaric oxygen exposure?
  • Mirit Eynan, Michael Mullokandov, Yoav Yanir and
    Yehuda Arieli, Israel Naval Medical Institute

2
Introduction
  • Professional and combat divers use closed-circuit
    oxygen apparatus. The greatest risk involved in
    diving with this apparatus is the development of
    CNS oxygen toxicity.
  • Several cases of CNS oxygen toxicity have
    occurred, including fatality.
  • Many of these incidents occurred at a time when
    the divers were active during the late night
    hours. It is well known that night activity, such
    as shift work, results in deterioration of
    performance.

3
Introduction (cont)
  • Melatonin is the primary circadian pacemaker. Its
    role is to synchronize the individuals internal
    hormonal environment with the light-dark cycle of
    the external environment.
  • Melatonin is also an antioxidant, playing an
    important role in antioxidant defense and
    regulating antioxidant enzyme activity and
    production.

4
Introduction (cont)
  • Illumination of the surrounding environment
    during the night hours causes a reduction in
    melatonin levels, which exposes the organism to
    oxidative stress.

5
Objectives
  • 1. To investigate in the fat sand rat (Psammomys
    obesus) whether a switch from day to night
    activity, is a risk factor for the development of
    CNS oxygen toxicity.
  • 2. To search for a possible correlation between
    any reduction in latency to CNS oxygen toxicity
    at night and a concomitant reduction in melatonin
    levels, by assessing urinary 6-SMT excretion.

6
Fat sand rat (Psammomys obesus)
  • Occupying the arid areas of Israel.
  • Unlike many other rodents as rat and mouse,
  • the fat sand rat is diurnal.

7
Methods
  • Each Sand-Rat was exposed to HBO at 5 ATA at day
    and night (or vice versa). Latency to CNS-OT was
    measured from the time the oxygen level reached
    95 until the appearance of the first
    convulsions.
  • In the control phase, exposure to oxygen was
    during daylight hours.
  • During the experimental phase, the animals were
    kept awake and active between the hours of 2100
    and 0300, 5 days a week for 3 weeks.

8
Methods (Cont)
  • Melatonin levels were determined by measuring
    urinary 6-SMT excretion.
  • Urine was collected at the end of the control
    phase, and at the end of the experimental phase,
    before HBO exposure. The collection was for 24
    hours at 4 hours intervals.

9
Results
10
Results
11
Methods
  • To investigate the effect of melatonin we
    administered 50 mg/kg or ethanol water only, to
    animals from both groups, 20 minuets prior to HBO
    exposure.

12
Results
13
Summary
  • Activity during the night hours resulted in a
    shortening of the latency to oxygen toxicity.
  • These changes were associated with deterioration
    of the circadian rhythm of melatonin. Acute
    melatonin administration however, has no effect
    on any of the experimental groups.

14
Conclusion
  • We conclude that a significant phase of night
    activity might play an additional risk factor for
    the development of CNS-OT.

15
What comes next?
  • 1. Means of treatment
  • Investigate whether bright light therapy in
    the morning will prolong latency to CNS-oxygen
    toxicity in the fat sand rat following prolonged
    night activity.
  • 2. Correlation of the findings in the fat sand
    rat with similar parameters in oxygen divers
  • Investigate changes in the biochemical
    parameters of circadian rhythm and oxidative
    stress in combat divers.
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