At 09:20 AM 3/25/98 +1000, you wrote:
>As I recall, these penguins, like whales, are able to collapse their rib
>cage and lungs to a certain extent. This would have a number of purposes.
>I can think of three.
Its not that they are able to collapse their rib cage but more that the
water pressure at depth forces the collapse of the thorax.
>1. Reduces physical damage due to increase water pressure during deep dive.
>2. Reduced volume per mass would aid overcoming bouyancy for diving.
Not a problem. Even most land mammals have neutral bouyancy. But true, at
depth they would become more negatively bouyant.
>3. I'm trying to decide if the reduced gas volume in the 'collapsed' lungs
>would help with reducing the partial pressure of CO2.
No the reduced gas volume would not help reduce the partial pressure of
CO2. CO2 constantly being produced by the body stimulates breathing needs
to be released from the blood stream into the airways. Reduced airway
volume is not ideal for this.
>I'll try to explain
>it in human terms. When free diving for a long period or deep depth (ie
>snorkelling), rather than trying to hold your breath you should exhale as
>you get to your breath holding limit. This action removes the (more than
>usual) CO2 concentrated air in your lungs. It is not lack of oxygen that
>causes the inhale response that gives you a lung-ful of water, but the buld
>up of CO2 in the bloodstream. By *exhaling* this CO2 imbalance is partially
>alleviated, which buys you a little more time. I can only hazard that the
>same technique would be used by deep/long diving mammals and birds.
Very well explained. If your body can tolerate CO2 then you can hold your
breath for longer.... up until a point when the oxygen levels in your blood
decrease and cause sudden unconsciousness.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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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