The penguins are indeed the champions with respect to holding their breath.
The Emperor Penguin can remain submerged in water for 18 minutes and is
capable of diving over 260 metres. The Pekin Duck can remain submerged for
15 minutes.
The physiological responses of diving birds (and mammals)when submerged are
quite straight forward:
1. A large tidal volume (TV) in the lungs and air-sacs. The TV is the
volume of air exchanged in the lungs and air-sacs during respiration. Thus,
a large volume of oxygen is breathed in and a large volume of carbon dioxide
is breathed out during a single respiratory cycle.
2. Constriction of blood vessels in subcutaneous and posterior parts of the
body so that oxygen-carrying blood is diverted largely to essential organs
such as the heart and brain.
3. Much reduced metabolic rate (the combined rate at which all the body
organs work) and heart rate. A duck in a prolonged dive can reduce its
metabolic rate by 90% and heart rate to 5-8% of the pre-dive rate. This
response is known as bradycardia.
4. Higher concentrations of haemoglobin in the blood compared with
non-diving birds. Haemoglobin is the molecule that binds with oxygen in the
blood and carries it to the body's tissues.
5. An ability to tolerate an oxygen debt in muscles and the ability to rely
on glycolysis for fueling the muscles. Glycolysis is the biochemical
breakdown of glucose and glycogen (energy stores) in tissue in the absence
of oxygen.
6. A relative insensitivity of the respiratory centre of the brain (the
mesencephalon) to the build up of carbon dioxide and lactic acid (waste
products of the body's metabolism).
These responses are almost instantaneous once a diving bird is submerged in
water. If a non-diving animal (e.g. a human) is submerged, the heart and
metabolic rates will be reduced, but the effects are not as great and they
take up to 30 seconds to come into effect.
I remember studying the diving responses of a whole range of animals when I
was an undergraduate student at the University of Western Australia. The
diving response in human subjects was induced by immersing their face
(rather than the whole body) in a bowl of cold water! Brrrrrr ...!!!!
Kind regards,
Stephen
Dr Stephen Ambrose
Research Manager
Birds Australia (Royal Australasian Ornithologists Union)
Australian Bird Research Centre
415 Riversdale Road,
Hawthorn East,
VIC 3123.
Tel: +61 3 9882 2622
Fax: +61 3 9882 2677
Email: S.Ambrose <> (at work)
<> (at home)
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