At 03:28 PM 4/1/98 +0800, Shane Raidal wrote:
>So in summary I also don't buy the reduced heart rate as an indicator of
>decreased metabolism. You can explain it other ways. The cardiac output
>could still be the same or even increased if only the brain and muscles are
>receiving the bulk of the blood flow. This is the key : heart rate does
>not = cardiac output.
>Of course I could be totally wrong and don't mind being proved so.
Shane, I agree with this last point. However, it appears that diving birds
DO have a decreased cardiac output when their heart rate decreases during a
dive. I can't find any data for penguins (maybe I haven't been looking hard
enough), but Johansen & Aakhus (1963) found that blood stroke volume in
ducks remained the same during a dive, while cardiac output decreased
(Johansen 1964).
Prosser (1974) states that the Pekin Duck reduces its metabolic rate by 90%
and its heart rate to between 5-8% of its pre-dive rate during a prolonged
dive. Similar results have been found in seals (Scholander 1940), Domestic
Ducks (Scholander 1940, Andersen 1959, Pickwell 1968) and the American
Alligator (Andersen 1961).
>
>Can anyone remember how we started this discussion ???????
Phew, it HAS been a bit of a marathon, hasn't it? Didn't Mauro have
something to do with it??????
References:
Andersen, H.T. (1959). Depression of metabolism in the duck during diving.
Acta Physiol. Scand. 46: 234-9.
Andersen, H.T. (1961). Physiological adjustments to prolonged diving in the
American Alligator, Alligator mississippiensis. Acta Physiol. Scand. 53:
23-45.
Johansen, K. (1964). Regional distribution of circulating blood during
submersion asphyxia in the duck. Acta Physiol. Scand. 62: 1-9.
Johansen, K. & Aakhus, T. (1963). Central cardiovascular responses to
submersion asphyxia in the duck. Amer. J. Physiol. 205: 1167-71.
Pickwell, G.V. (1968). Energy metabolism in ducks during submersion
asphyxia: assessment by a direct method. Comp. Biochem. Physiol. 27: 455-85.
Prosser, C.L. (1975). Comparative Animal Physiology (W.B. Saunders Co.,
Philadelphia).
Scholander, P.F. (1940). Experimental investigations on the respiratory
function in diving mammals and birds. Hvalradets Skrifter Norske
Videnskaps-Akad, Oslo. 22: 1-131.
Best wishes,
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)
************************************************************
|
