EMBARGOED FOR RELEASE UNTIL OCTOBER 10, 2006
Contact:
Christine Guilfoy
Office: (301) 634-7253
cguilfoy@the-aps.org
Seals Shiver In The Cold Air But Not During
An Icy Dive
Physiological adaptation conserves oxygen, protects brain
Virginia Beach,
Va (October 10, 2006) – Seals shiver when exposed to cold air but not
when diving in chilly water, a finding that researchers believe allows the
diving seal to conserve oxygen and minimize brain damage that could result
from long dives.
The researchers will present the study at The
American Physiological Society’s conference “Comparative Physiology
2006: Integrating Diversity,” in Virginia Beach, Va., October 8-11. The
researchers, Arnoldus Schytte Blix, Petter H. Kvadsheim and Lars P. Folkow
hail from the University of Tromsø, located above the Arctic Circle in
Tromsø, Norway.
The research provides insight into how seals allow
their bodies to cool (become hypothermic) during a dive, presumably to
better cope with a lack of oxygen (hypoxia). Research into hypothermia and
hypoxia is important because they are problems that affect people under a
variety of circumstances. Doctors often are called upon to treat people who
have suffered accidental hypothermia, for example, as a result of falling
into the ocean or becoming lost during the winter. In addition, several
hundred thousand people die or are irreversibly injured each year following
cardiac arrest, stroke or respiratory disorders which cause inadequate
oxygen supply to the brain, Folkow explained.
Folkow will present a second study on hypoxia,
involving diving birds, at the conference. The study “Neuronal hypoxic
tolerance in diving birds and mammals,” examines how diving birds and seals
preserve brain cell function in the face of oxygen deficits. The study is by
Folkow, Stian Ludvigsen and Blix, of the University of Tromsø and Jan-Marino
Ramirez of the University of Chicago.
Shivers produce warmth
Shivering is an involuntary response that consists of
muscle contractions which produce warmth. Mammals and birds are
physiologically programmed to shiver when body temperature drops below a
certain “set-point.”
While breathing air, seals shiver just like other
animals. But when they dive below the surface in frigid water, shivering is
switched off, the study found.
By shutting down the shivering response, a seal allows
its body temperature to drop and achieves the benefits of hypothermia: a
slower metabolism and lowered oxygen requirements which extends the dive
time, Folkow said.
Taking the plunge
The seal experiment took place in a tank in which the
seals took a series of experimental dives into cold water of 2-3° C. The
researchers recorded shivering, heart rate, brain temperature and rectal
temperature while the seals were on the surface and while they were diving.
The seals shivered on the surface but stopped or nearly
stopped shivering when they dove, even though their bodies continued to
cool. Their heart rates and temperatures dropped while they dove, but when
they returned to the surface they restarted their shivering nearly
immediately.
Seals have a remarkable capacity to store oxygen in
their blood and muscles – four times as much as humans – to which they add
this oxygen-conserving step of not shivering, Folkow said. By allowing body
temperatures to drop, they slow metabolism and reduce oxygen demand. In
addition, since shivering itself requires oxygen, there is an
oxygen-conserving advantage to not shivering when diving.
In addition to slowing metabolism and generally
reducing the need for oxygen, the researchers found that the seal’s brain
may cool about 3° C during the dives. The cooler brain requires less energy
and oxygen and reduces the chance of damage caused by hypoxia, Folkow
explained.
Achieved while remaining
active
Seals have this physiological adaptation available just
in case. This study found the seals can dive to more than 1,000 meters and
for more than an hour. However, they usually take dives much shorter than
their maximum capacity, and only occasionally perform very long dives. By
limiting dive duration, seals maintain aerobic metabolism, avoid lactate
buildup that occurs in the face of insufficient oxygen and require little
time to recover, Folkow explained. Seals often spend 80-90% of their time at
sea underwater, he said.
Seals in the wild occasionally dive for so long that
they use nearly all their oxygen, but they can recover with these special
adaptations. Humans cannot tolerate oxygen levels nearly so low as a seal
can.
“Somehow they tolerate hypoxia better, we don’t know
why,” Folkow said. The study of how seals handle this lack of oxygen may
someday give us knowledge that is useful in treating people who have
suffered severe hypoxia, although those advances are likely years in the
future, he added.
* * *
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