Thar she beats! The challenge of measuring a blue whale's pulse
A researcher channels his inner Ahab to attach a heart monitor to the world's largest animal
A team of researchers in the US has managed to measure the heart rate of a blue whale for the very first time, and they were amazed by the extremes they saw.
David Cade and his team found the whale's pulse dipped to as low as two beats per minute when the whale was diving and foraging underwater. When it surfaced to breathe, it rose to as high as 37 beats per minute as it re-oxygenated its blood.
That would be the equivalent of a human's pulse dipping to 20 beats per minute and then rising to 400 beats per minute, and either extreme would not be survivable.
The blue whale's low heart rate while diving is an adaptation to help it conserve oxygen during the 12 to 16 minutes it spends underwater during a foraging dive, Cade explained.
The team designed a special heart rate monitor that incorporated an electrocardiogram or ECG into a standard package of sensors that can be attached to the whale with suction cups.
Attaching the heart rate monitor to the whale was a tricky task. The team took a small boat out into the ocean off the coast of Monterey, California, and had to find a whale that behaved predictably and surfaced slowly enough for them to attach the heart rate instrument near its heart.
Cade described the experience as intense and involving a lot of coordination. He was on a platform at the front of their small boat holding a pole with a tag at the end to attach to the whale's body. He only had a few seconds to drop the instrument onto the whale when it surfaced. Luckily, everything worked out on their first try and they obtained two days worth of data from the device when it released from the whale and they recovered it.
Cade said a heart rate of 37 beats per minute is likely as high as the whale can possibly manage since it takes nearly two seconds to pump the 220 litres of blood it circulates with every beat.
And this may be why no larger cetacean than the blue whale exists. The heart of a bigger creature couldn't possibly beat fast enough at the surface to recover the oxygen they've lost by beating slowly at depth.