Cited Passage
Diving Physiology 3-27
pass directly through blood vessel walls. They may redis-
solve for passage through vessel walls then reform into
bubbles, but they do not drain into vessels intact. Although bubbles are a good explanation for many
decompression problems, they may not be the sole pre-
cursor of decompression problems. Pressure may have
direct effects of its own on blood cells and other body
areas (Bookspan 1995. It is not easy to detect bubbles in tissue, but they can
be detected in circulating blood because they are moving. This is done with a device called a Doppler ultrasonic bub-
ble detector. Ultrasonic sound waves at too high a frequen-
cy to be heard are used in various ways in medical
diagnosis. Using Doppler electronics, only waves reflected
from moving objects are detected. Bubbles can be “heard”
moving through the circulation on the way to the lungs. Doppler bubble detectors have shown that normal and oth-
erwise benign dives may create a few circulating bubbles in
some divers. These are called “silent bubbles” because they
do not cause overt symptoms. In fact, the bubbles detected
in the venous blood are “on their way out” and are not
likely to be involved in decompression sickness. Doppler
bubble detection in venous blood has not proven to be use-
ful for predicting DCS in a given diver, but dive profiles
that cause a lot of bubbles also tend to cause a substantial
number of DCS cases. Major determinants of risk of DCS are depth, time at
depth, ascent rate, and multiple dives. Individual variation
is also a factor. The same depth and time profile, or
“dose” of nitrogen, varies in effect on different people, just
as the same dose of medication can vary in effect. Individ-
ual factors have been explored but are not well under-
stood, leaving these variables open to sometimes wild
conjecture. Other factors that may predispose to DCS
include fatigue, dehydration, smoking, alcohol consump-
tion, and carbon dioxide retention. Environmental factors
include chilling at the end of a dive, heavy work, and the
use of heated suits. WARNING
DECOMPRESSION SICKNESS MAY OCCUR EVEN IF
DECOMPRESSION TABLES OR COMPUTERS ARE
PROPERLY USED. ALTHOUGH IT IS UNCOMMON
FOR DCS TO OCCUR ON NO-DECOMPRESSION
DIVES, IT CAN HAPPEN. There was early speculation, now dismissed, that birth
control pills or menstruation might increase risk for
women. Given the dearth of comparative DCS studies,
there is no substantive evidence that gender plays a role in
DCS (Bookspan 1995). Most medical experts today agree
that decompression sickness is the result of complex indi-
vidual, not sex specific, factors. However, we still do not
have definitive answers and additional research is needed. WARNING
THE MAJOR DETERMINANTS OF THE RISK OF
DECOMPRESSION SICKNESS ARE DEPTH, TIME AT
DEPTH, ASCENT RATE, AND MULTIPLE DIVES. Decompression sickness was formerly divided into Type
I, Type II, and Type III. Type I DCS included skin itching or
marbling; brief, mild pain called “niggles,’’ which resolved
typically within ten minutes; joint pain; and lymphatic
swelling. Extreme fatigue was sometimes grouped into Type
I. Type II DCS was considered to be respiratory symptoms,
hypo-volemic shock, cardiopulmonary problems, and central
or peripheral nervous system involvement. Type III grouped
DCS and arterial gas embolism together, also called decom-
pression illness (DCI). Arterial gas embolism is covered in
Section 3.3.2.4. It is now more common to categorize decom-
pression sickness by area involved and severity of symptom. Limb Bends .
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