At 05:21 PM 4/2/98 +1000, you wrote:
>> Absolutely true. With a breath-hold dive you cannot absorb more than a
>> lung full of nitrogen and therefore the body tissues cannot be
>> super-saturated.
>
>This is not obvious to me. It really depends on how the nitrogen gets
>distributed. I'd guess freediving human (theoretically) following an
>Emperor Penguin's dive profile (< 10 minutes dive time, maximum depth
>500+m, fast ragged ascent) might get bubbles in some fast tissues. I'd
>want to see some maths (but maybe you've done some calculations).
>
>I'm jealous of an u/w Little Penguin sighting. I've seen a
>Little Pied Cormorant at 5m chasing fish but thats it for scuba bird
>sightings.
Its true that you cannot develop decompression sickness on just one
breath-hold dive. There is only a limited volume of nitrogen that can be
absorbed and most people cannot stay down long enough or deep enough for
any extra nitrogen to be absorbed. However as Julie Raines pointed out it
is possible to absorb extra nitrogen by doing multiple dives to deep depths
(over 2 ATA). If you free-dive to 20 m for 3 min with a lung-full of air
and don't exhale you will return to the surface with a slightly less volume
of air in your lungs. This is because at the 20 m mark the extra ambient
pressure (=3 ATA) on your body / diaphragm / lungs will force a little
extra gas into your pulmonary blood stream. By ascending quickly the
likelihood of this small volume of gas being retained in the body is
increased. Frequent dives to 20 m will gradually build up the nitrogen
concentration in the blood and body tissues. After repeated similar dives
the volume of absorbed gas is small but additive. Such a case would be
even more important for penuins with their relatively huge airsac supply
theoretically acting as a mini-internal-SCUBA unit. I tried to explain
this before but failed....
Cormorants and penguins move amazingly fast underwater don't they!.
.................. Oh and the u/w little penguin was spotted while
free-diving.
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Shane Raidal BVSc PhD MACVSc
Lecturer in Veterinary Pathology
Veterinary and Biomedical Sciences
Murdoch University phone: +61 8 9360 2418
Perth,WA, 6150 fax: +61 8 9310 4144
Australia
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