AD 2017 Q3

RESEARCH, EDUCATION & MEDICINE
FROM THE MEDICAL LINE
Inert Gas Washout
DAN MEDICS AND RESEARCHERS
ANSWER YOUR QUESTIONS
ABOUT DIVE MEDICINE.
Q:
My students asked what happens to
the nitrogen bubbles in untreated
decompression sickness (DCS). My
guess was that they eventually get reabsorbed or
offgassed via the lungs. What is the best answer?
A:
Divers accumulate nitrogen (and/or other
inert gases in their breathing mix) while
diving. The deeper and longer the dive,
the more gas accumulates. In cases of DCS, the inert
gas load exceeds the tissues’ capacity, so bubbles form.
Gas enters the body through the lungs, moves into the
circulatory system and then into other tissues. Offgassing
occurs by the same mechanism in reverse: Inert gas
moves from the body’s tissues into the bloodstream and
then into the lungs, where it is exhaled. A diver offgasses
when in shallow water after having been in deeper water
(during ascent and while performing a decompression
stop or safety stop, for example). Offgassing continues
after the diver exits the water. The human body has no
means by which to indefinitely retain gas or bubbles.
The vast majority of the inert gas is offgassed within
a few hours, and almost all of it leaves recreational
divers’ bodies within about 24 hours. This is why
symptoms of DCS usually appear in the first hours
following a dive and why onset of symptoms more than
24 hours after a dive generally does not represent DCS
(except in special circumstances such as saturation
diving or subsequent altitude exposure, for example).
Bubbles cause inflammation and local tissue injuries.
The larger the bubble load, the more severe the injury
and the faster the onset. Hyperbaric chamber treatment
within the first 24 hours can eliminate gas and bubbles
while the injury is still occurring. After about 24 hours,
the injury has already occurred. Bubbles are no longer
present, but the injury persists. Hyperbaric treatment
after the first day can still be very helpful by promoting
healing and recovery.
Although leaving DCS untreated is not
recommended, its general progression is improvement
over time. Some divers who do not get treated recover
completely, but others have persistent problems that
range from mild to severe.
For more information about inert gas, DCS and
hyperbaric chamber treatment, visit DAN.org or
call the DAN Medical Information Line at +1 (919)
684-2948.
— Frances Smith, MS, EMT-P, DMT
Q:
What is “oxygen ear”?
A:
Also
known as middle-ear oxygen absorption
syndrome, oxygen ear describes a gas volume
imbalance in the middle ear after diving with
breathing gas that has a higher oxygen fraction than
air. The phenomenon is commonly associated with
open-circuit diving using nitrox and closed-circuit
rebreather diving. The high-oxygen-content gas fills the
STEPHEN FRINK STEPHEN FRINK
56 | SUMMER 2017