Bottle-nose dolphins breathe through their blowhole, which
is a specialized single nostril, located at the top of their
head. A dolphin may empty and refill its lungs in less than
a fifth of a second. As the dolphin breathes the air leaves
the blowhole at speeds of over 100 mph. Complex nerve endings
around the blowhole sense pressure changes so the dolphin
knows exactly when the blowholeis in or nearing air and can
be opened. Water in a dolphin's blowhole will actually drown
it so powerful muscles close the blowhole as it dives under
the water again.
Although dolphins may take a breath of air on the average
of 2 to 3 per minute, they can hold their breath for periods
in excess of 10 minutes. Dolphins open its blowhole and begins
to exhale just before reaching the surface of the water. At
the surface, the dolphin quickly inhales and relaxes the muscular
flap to close it.
As the dolphin exhales, seawater that has collected around
the blowhole is carried up with the respiratory gases. Seawater
and the water vapor condensing in the respiratory gases as
they expand in the cooler air form the visible blow of a dolphin.
During each respiration a dolphin exchanges 80 percent or
more of its lung air. This is much more efficient than humans,
who exchange only about 17 percent of their with each breath.
Exhaling and inhaling takes about 0.3 seconds.