Altitude or great marine depths create physiological models that allow scientists to see how different organisms in extreme environments respond. The interesting thing to study how there are animals that can live more than 100 meters deep or 5,000 meters of altitude is that different pathologies share characteristics of the extreme physiology that occurs in these environments.
If to the ability of some animals to be able to live in uninhabitable places for the human being, we add their extraordinary physiognomy, we are faced with cases such as the blue whale. It is difficult to imagine how there can be a heart that weighs more than 300 kg and pumps blood to a body of 70,000 kg over more than 20 meters long. The heart of these whales can pump almost 80 liters of blood in a single beat.
Recently, a study has been published in PNAS (Goldbogen et al., 2019) in which they have managed to measure for the first time the heart rate of a blue whale in its natural habitat, the sea. During its long dives, the activity of the heart of the whales is reduced (and with it its heart rate), which makes both its tissues and its organs - among them the heart itself - also decrease its oxygen consumption so as not to put in risk your survival. They slow down their energy consumption until their physiological limit.
But while they are in the depths, there is a time when they need to increase their energy production: when they eat. The whales feed in such a way that when they go to fish banks they open their mouths ingesting both their prey and a very large amount of water. The energy they use to eat and expel that water then is up to 50 times greater than when they are at rest, so it is to assume that their heart rate has to increase to respond to that demand. This can be critical, since the simple act of eating makes them need much more energy in the depths, which causes faster exhaustion of oxygen reserves in the blood. And, in addition, the blue whale has very low oxygen reserves compared to other species of whales such as puppets or whales of Greenland, which can store up to 5 times more oxygen because they have a greater concentration of myoglobin , Protein responsible for storing and transporting oxygen in the muscle. This causes blue whales to be less time under water than for example the puppets.
To respond to what the heart rate of these animals is when they go down to the depths to eat, a research team has monitored the heart of a blue whale in the Monterrey Bay, in California, using a suction cup that joined the body of The whale and that had an electrocardiogram with which the activity of its heart was recorded for 8 and a half hours.
The records saw that this whale made dives in search of food of up to 16 minutes, reaching a depth of 184 meters. The electrocardiogram showed that in the depths it had a heart rate around 4 pulsations (becoming 2 beats per minute), while at the time of eating it rose to 8 pulsations, to go down again to 4 at the time of Water filtering. That is, more than 180 meters deep, his heart beats 1 time every 15 ''. Already on the surface, the heart rate reaches its maximum, where the whale breathes and restores its oxygen levels.
Figure 1 . Illustration that shows how the heart rate of the blue whale slows down and accelerates when it is immersed at great depths and feeds. Credit: Alex Boersma
One of the mechanisms that compensates for this low heart rate could be in its aortic arch . The aorta (the artery responsible for carrying the oxygenated blood from the heart to all our tissues) seems to be very flexible in the blue whales, so that it is capable of storing a large amount of blood and thus ensure a continuous flow between beats without need to raise its heart rate much more, which would raise oxygen spending. This sculpted compensatory mechanism over thousands of years of evolution is the one that allows these living beings to make long dives in search of food. The structure of its cardiovascular system is closely linked to its function .
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The researchers think that the heart of the blue whale works near its limit, which could explain why no animal has a larger size, since the energy needs of a larger body would exceed what the heart could sustain. Nature hides evolutionary wonders. A 70,000 kg animal with a heart of more than 300, can pump at 180 meters deep only 4 times per minute.
The regular arrival of blood and oxygen to most of our tissues is a principle of homeostasis. On the other hand, the alteration of blood flow is the origin of many pathologies. Therefore, knowing how animals in extreme pressure conditions manage to sustain energy production even having low concentrations of myoglobin, could help us understand the processes so that tissues adapt to heterogeneous oxygen voltage processes.
Reference:
Goldbogen, Ja, Cade, de, Calambokidis, J., Czapanskiy, MF, Fahlbusch, J., Friedlaender, As, ... Ponganis, PJ (2019). Extreme Bradycardia and Tachycardia in the World's Largan Animal. Proceedings of the National Academy of Sciences, 116 (50), 25329 LP - 25332. https://doi.org/10.1073/pnas.1914273116