Can a blue whale, the world's largest animal, actually survive with a heart rate of less than 10 beats per minute? It turns out that they can, but only during a dive phase for feeding. The lowest heart rate recorded during a dive phase is 2 bpm, with the average being between 4-8 bpm. The exact reasoning of having such a low heart rate during a dive phase is not fully understand. It would be expected that a low heart rate would decrease the rate of blood oxygen depletion allowing the whales to have a longer time period for a dive. The way whales eat is through an extremely high-cost mechanism. They engulf an amount of water that is larger than their body which is thought to limit the amount of time the whales can spend in a dive phase as this method of eating causes a rapid depletion of blood oxygen levels.
When whales start to ascend and resurface after eating they experience a rapid increase in their heart rate. While resurfacing a whales heart rate is between 25-37 bpm, which is thought to be near their maximal heart rate, meaning that whales are experiencing tachycardia while ascending. The overall heart rate of the blue whale seems to be fluctuating the majority of the time, rather than being maintained at a resting heart rate. This is the first study that has recorded data of this nature in a mammal not held in captivity and has opened up several avenues for new research.
Reference:
Goldbogen, J. A., Cade, D. E., Calambokidis, J., Czapanskiy, M. F., Falhbush, J., Friedlaender, A., S, Gough, W. T., Kahane-Rapport, S. R., Savoca, M. S., Ponganis, K. V., & Ponganis, P. J. (2019). Extreme bradycardia and tachycardia in the world's largest animal. PNAS(116), 25329-25332. http://doi.org/10.1073/pnas.1914273116
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