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Chapter 3 The Physiology of Diving and Nitrox 37
LEARNING GOALS
Comprehension Objectives
Learn about the physiological effects of nitrogen
and diving.
Understand basic information about nitrogen
narcosis and decompression sickness.
Learn about the physiological effects of low
oxygen levels.
Learn about the physiological effects of high
oxygen levels.
Explain the signs and symptoms of oxygen
toxicity.
Explain limits of hyperbaric oxygen exposure.
When we dive, we subject ourselves to external physical
forces that are beyond our everyday experience. Our
body does its best to keep its functions balanced and
within safe ranges (homeostasis), but past some point,
short- and long-term exposure to the hyperbaric diving
environment may affect us in ways that range from
mildly impeding to life threatening. In this course we are
concerned with the physiological effects of the gas we
will be breathing – oxygen enriched air. The dictionary
defines physiology as “the study of the organic processes
and phenomena of an organism or any of its parts or
of a particular bodily process.” A basic knowledge of
the physiology of nitrogen and oxygen will help you to
understand their effects in diving, and you will be able to
use that knowledge to plan safe dives and avoid possible
undesirable effects.
This chapter discusses possible harmful things that
can result from nitrogen and oxygen overexposure, their
prevention, and first aid procedures for breathing-gasrelated
problems. Earlier chapters introduced you to the
importance of the nitrogen and oxygen in your everyday
life as well as when diving. This chapter will review this
information and take your understanding a step further.
The information presented here is still only an
introduction, and it is primarily focused on practical
information as it applies to diving with oxygen-enriched
air. If you want to explore these subjects in greater depth,
the NAUI Master Scuba Diver course or courses in
aspects of technical diving offer opportunities for you to
do so.
NITROGEN: NARCOSIS AND
DECOMPRESSION SICKNESS
In our normal lives above water, nitrogen just dilutes
the concentration of oxygen in the air. Remember that
our bodies do not need or use nitrogen in metabolism.
The problem develops when, under increased pressure,
as in diving, higher concentrations of nitrogen become
dissolved in our bodies.
Nitrogen Narcosis
You were introduced to nitrogen narcosis in your
entry-level scuba course as well as in the discussion of
the composition of air in Chapter 2. Nitrogen narcosis
is produced by increased nitrogen partial pressure. It
is a state of near-unconsciousness or insensibility; a
condition characterized by impaired mental and physical
performance and changes in mood and behavior.
Although there is marked variation in individual
susceptibility and effect, narcosis places a depth limit on
safe diving using compressed air. Nitrogen narcosis was
called “rapture of the deep” by Jacques Cousteau and is
often referred to by divers as being “narked.”
Reasoning and judgment, recent memory, and ability
to concentrate are the first to be affected by narcosis.
Perceptual narrowing and careless behavior can also
be symptoms. The diver may feel a pleasant euphoria–
especially in warm, comfortable, tropical waters–but,
on the other hand, may experience feelings of dread
or foreboding. An early study called it “semi-loss of
consciousness” and noted that divers at depths of 60
meters (200 feet) would neglect to perform assigned tasks
and would not remember events of the dive after they
returned to the surface. Divers have reported that it feels
“darker,” that they feel closed in, or that they have to
concentrate more intently on what they are doing.
The mechanisms of nitrogen narcosis are imperfectly
understood, but they are thought to be similar to that of
gases used in general anesthesia for surgical procedures.
Narcotic effects are not limited to nitrogen. Any inert
Figure 3-1 A basic knowledge of the physiology
of nitrogen and oxygen will help you to
understand their effects in diving.