Hyperventilation is the term applied to breathing more than is necessary to keep
the body’s carbon dioxide tensions at proper level. Hyperventilation (whether
voluntary or involuntary) has little effect on the body’s oxygen levels, but abnormally
lowers the partial pressure of carbon dioxide in the blood and delays the
normal urge to breathe. If the carbon dioxide stores are ventilated below the stimulus
level, there will be little urge to breathe until late in the breathhold. The
oxygen partial pressure falls progressively as oxygen is consumed continuously.
Exertion causes oxygen to be consumed faster, and decreases sensitivity of the
carbon dioxide breakpoint mechanism. This permits the oxygen level to go lower
than it would otherwise. When the diver ascends, the drop in oxygen partial pressure
in the lungs may be sufficient to stop further uptake of oxygen completely. At
the same time, the partial pressure of carbon dioxide in the lungs also drops,
giving the diver the false impression that he need not breathe. Low levels of
oxygen do not cause a powerful demand to resume breathing; thus, the level of
oxygen in the blood may reach the point at which the diver loses consciousness
before he feels a demand to breathe.
WARNING Hyperventilation is dangerous and can lead to unconsciousness and
death.
Unintentional hyperventilation can be triggered
by fear experienced during stressful situations. It can be partly initiated by the
slight “smothering sensation” that accompanies an increase in dead space,
abnormal static loading, and increased breathing resistance. Cold water exposure
can add to the sensation of needing to breathe faster and deeper. Divers using
scuba equipment for the first few times are likely to hyperventilate to some extent
because of anxiety.
Voluntary hyperventilation (taking a number of deep
breaths in a short period of time) can produce symptoms of abnormally low carbon
dioxide tension (hypocapnia). Under these circumstances, one may develop a
lightheadedness and tingling sensations. Hyperventilating over a long period,
produces additional symptoms such as weakness, headaches, numbness, faintness,
and blurring of vision. The anxiety caused by the sensation of suffocation that
often initiates hyperventilation and continues in spite of adequate ventilation, may
lead to a further increase in breathing and a vicious cycle develops. Severe hypocapnia
with muscular spasms, loss of consciousness and shock may be the end
result. The diver must pay attention to his breathing rate and, in the event of fearinduced
hyperventilation, take steps to remain calm and control his breathing.
