Two Beats a Minute Underwater: A Lesson in Blue Whale Cardio!

During their feeding dives, blue whales will repeatedly engulf their prey. These engulfing manoeuvres are very costly in terms of energy and in turn oxygen. Normally, such energy needs would cause the heart to accelerate significantly. However, for the blue whale, these increases in heart rate are very minor compared to the resting heart rate (see Figure 2). How is this possible? One of the theories is that the physical properties of the aorta might allow for a sort of extension of the blood pulse between heartbeats. This would somewhat compensate for the low heart rate, even during the whales’ energy-intensive engulfing tactics. And, because they are minor, these increases in heart rate likely conserve oxygen in the blood. The blue whale would thus be able to stay underwater longer without breathing while engaging in energy-demanding manoeuvres. At the surface, the animal’s heart rate increases, which optimizes gas exchange with the outside and oxygenation of the blood.

In black, the heart rate in beats per minute (the solid line with a value of 15 beats/minute represents a blue whale’s heart rate when at rest). In blue, water depth.

A number of other peculiarities in blue whales explain their ability to lower their heart rate so slightly and to optimize their organs’ use of blood oxygen reserves. Blue whales can build up fairly good oxygen reserves in their muscles and many of their vital organs such as the brain. As a result, they would not have to excessively draw from their blood oxygen reserves during their dives. Further, they are believed to have the ability to greatly reduce blood circulation in their peripheral organs, which would concentrate the blood for supplying the animal’s vital organs.

The morphological and physiological adaptations that cetaceans have undergone for diving continue to impress!