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Hi,

I am a new reader to the techdiver group. A couple of your readers
suggested I join in. My diving qualifications are under the BSAC
(First class diver and National Instructor) and ANDI.

Following a recent Nitrox course I began to wonder about the following
question. I would appreciate your views or comments.

When teaching on a BSAC Oxygen Administration course we tell our students
to expect a transient worsening of symptons to a casualty shortly after
starting to administer 100% O2. This is due to two reasons. Firslty, if
there is a lodged bubble some of the oxygen in solution will diffuse into
the nitrogen bubble. Secondly, the body reacts to the higher partial pressure
of O2 and reduces the blood flow due to vasoconstriction. This can be read
in the BSAC Safety and Rescue manual.

My basic question is if a diver does a dive on air and then transfers to
O2 for stops does the vasoconstriction occur? This will reduce blood flow
and hence increase the risk of DCS. 

On the other hand there are plenty of divers who use O2 for stops with no
problem and therefore this cannot be true. Which is right or is it only the
BSAC who expect this transient worsening? Or is the transient worsening only
due to increased bubble size and not vasoconstriction? Do other organisations
talk about transient worsening of symptoms (ie PADI, DAN etc)?

I look forward to your replies.

Stuart Cannon
Stuart.Cannon@Br*.ac*.uk*

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