Chapter 3 - The Physiology of Diving and Nitrox
The Physiology of Diving and Nitrox
35
To plan dives, we use dive tables or dive computers.
Because we reduce the rate of nitrogen uptake
when we breathe oxygen-enriched air, special nitrox
dive tables or computers are used for nitrox diving. We
can also use a calculated “equivalent air depth” with
standard air tables. These tools are discussed later in
their own chapter.
As a responsible diver, you should be mindful of
other predisposing factors that are likely to increase
susceptibility to DCS. Dehydration, which reduces the
efficiency of your circulation, is now believed to be a
major contributor to the development of DCS. Divers
are well advised to drink plenty of fluids and avoid
excessive amounts of diuretic drinks, such as coffee, caffeinated
soft drinks, and alcohol, which can contribute
to dehydration instead of preventing it. During diving,
heavy exercise will increase circulation to the exercised
parts and speed up ingassing. After diving, exercise can
increase likelihood of bubble formation, while resting
and relaxing will give the body better opportunity to
offgas properly. General physical fitness is also beneficial
because it promotes more efficient muscle use and blood
flow. A person’s general circulation becomes less efficient
with increasing age, and therefore older divers are
advised to dive more conservatively.
OXYGEN: THE GOOD AND THE BAD
In your beginning scuba course, your instructor
probably said: “At extreme depths, even the oxygen in
the air you breathe can become toxic, but this only
happens at depths far greater than recreational limits,
so don’t worry about it.” End of subject. Now you are
learning to dive with oxygen-enriched air, and oxygen
toxicity and oxygen safety are very real concerns.
Oxygen is vital to our being. It is our essential
life-support element. If we are deprived of oxygen, our
survival time is measured in just minutes. Still, our bodies
operate well only within a rather narrow range of oxygen
partial pressures. Too high an oxygen level can be just as
harmful as too low.
Moreover, because oxygen is so highly reactive,
supporting combustion and combining aggressively
with many substances, special care and precautions are
USES AND PHYSIOLOGY OF OXYGEN
OXYGEN
PARTIAL
PRESSURE
3.0 ATA EAN50 used in 6 ata (50 msw/165 fsw)
recompression chamber treatment.
2.8 ATA 100% oxygen used in 2.8 ata (18 msw/60 fsw)
recompression chamber treatment.
2.4 ATA EAN40 used in 6 ata (50 msw/165 fsw)
recompression chamber treatment.
2.2 ATA
100% oxygen used in commercial/military
on-site “surface decompression” chambers at
2.2 ata (12 msw/40 fsw).
1.6 ATA NOAA maximum oxygen partial pressure limit
for a working scientific diver.
1.4 ATA NAUI recommended maximum oxygen partial
pressure for recreational diving.
0.5 ATA Threshold for long-term exposure pulmonary
oxygen toxicity effects.
0.35-0.4
ATA
Normal oxygen partial pressure limit for
commercial “saturation divers.”
0.21 ATA Normal oxygen level in the atmosphere at sea
level.
0.14-0.16
ATA Initial signs and symptoms of hypoxia appear.
0.09-0.10
ATA Serious signs and symptoms of hypoxia.
0.08-0.10
ATA Most persons lose consciousness.
0.08 ATA Coma and death.
FIGURE 3-4: USES AND PHYSIOLOGICAL EFFECTS OF DIFFERENT
LEVELS OF OXYGEN
required when handling pure oxygen or gas mixtures
that are high in oxygen concentration. A later chapter of
this book is devoted to oxygen handling and equipment
considerations.