NAUI Nitrox Diver
32 The Physiology of Diving and Nitrox
LEARNING GOALS
In this chapter, you will learn:
• The physiological effects of nitrogen in diving.
• Basic information about nitrogen narcosis and
decompression sickness.
• The physiological effects of low oxygen levels.
• The physiological effects of high oxygen levels.
• Signs and symptoms of oxygen toxicity.
• The 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
gas-related 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 stuporous 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 gas breathed under pressure can cause narcosis,
and the malady is more correctly called inert gas
narcosis. The narcotic potency of an inert gas is related