Have you ever thought about how Rudolph keeps his cool? I mean he spends an entire day and night flying from roof top, to roof top all the way around the world, with the ever-so-slim Santa (no offense Mr. Claus), millions of toys, for all the girls and boys, and that pretty nifty magical sleigh. It is winter, and pretty cold, but he must be cooking under that thick insulated fur jacket of his. It is quite amazing that he doesn’t overheat, working so hard every Christmas Eve. How can he do it? Well, as it turns out I am not the only one who is pondering the magic of Rudolphs thermal regulation, Arnoldus Blix from the University of Tromso, in Norway was curious as well, and he took action.
Blix gathered two of his colleagues, Lars Folkow, also from Tromso, and Lars Walloe, from the Univeristy of Oslo, and began to train the reindeer to run on treadmills. “Reindeer are the best animals to work with; once they trust the trainer they will do anything for you,” stated Blix. So, the reindeers started out on a trot. They were going about 9km/h in a room that was about 10 to 30°C. As they were warming up their respiration rate spiked going from 7 breaths/min to 260 breaths/min. This was their first strategy of cooling off; panting with their mouths closed. With this high rate of respiration, the animals are breathing in the cool air, which is in turn evaporating water from the mucous membranes in their noses. This evaporation cools their blood in the nasal sinuses and is then transmitted back to the rest of the body, cooling them down.This form of cooling only lasts so long though.
With increased exercise, more heat is being generated under their thick coat causing them to alter thier strategy in an attempt to get more cool air in. This is where they open they mouths and being panting like a dog. This second trait is working with evaporation, just like the previous one, except it is evaporating water off their tongues. With high circulation in the tongue this leads to a more efficient way of cooling themselves down as they can now send more cool blood back into thier bodies.
Bix and his colleagues kept running the reindeer until they realized a very interesting temperature change occurring in the reindeer’s brain when it hit a high of 39°C. The reindeer began to divert the cooled off blood from their nose away from the body, up to the brain. They were selectively cooling the blood to their brain! This seemed not logical to Blix as, “only 2% of the respiratory volume went through the nose when they resorted to open mouth panting.” But because they do reside in such cold temperatures, up in the Arctic, this was just enough to keep their brains cool and functional.
So, there you have it, Rudolph and the other six reindeer pulling Santa’s sleigh, have three different traits to cool themselves off as they are vigorously flying through the air; panting through their nose, flapping their tongue around in hope of more evaporation and selectively cooling their brain!
I read this and thought, they actually cool their brain? Wouldn't that be bad for them, maybe lead to neurological consequences? Turns out, they're not the only animals that do this.
ReplyDeleteElkhawad did a study on camels, and made the claim that many desert animals have developed this adaptive mechanism of brain cooling. They do this in order to prevent heat stress to the brain, and also to allow the animals to tolerate higher temperatures, something that desert animals cant avoid. The method of action of brain cooling occurs by constricting craniofacial veins (which become cool by evaporative heat loss), enabling the incoming arteries to exchange heat with the already cool veins, ultimately leading to a cooling of the brain tissue(1). There has also been a study showing that seals engage in selective brain cooling as well(2).
Because so many animals are known to cool their brains (either because of where they live, or by extended exercise), it seems as though this physiological mechanism has been preserved throughout evolution, and has been proven to occur in humans as well(3).
This reduction in heat stress is a big reason why there is a growing trend for athletes, primarily cyclists, to put ice on the back of their neck, so as to give the impression that their brain is cooler than it actually is (something that Dr. Campisi spoke about in class), enabling them to exercise more vigorously for a longer period of time. The idea of this makes sense, but my question is, is it safe?
References:
(1) http://www.ncbi.nlm.nih.gov/pubmed/1348454
(2) http://www.ncbi.nlm.nih.gov/pubmed/20639422
(3) http://jap.physiology.org/content/110/2/569.extract
As ArronS618 suspected that cooling of the brain may “lead to neurological consequences” shows some promise, as seen in researched by Blix et al. In another study, the temperature of seals as they dive was looked at for bodily cooling (including cranial cooling) . The experiment examined the Brain, intra-aorta, latissimus dorsi muscle, and rectal temperatures of the seals as they dove with in water that was 4 degrees Celsius. Similar to Rudolph, the seals where able to consciously control cooling of their bodies since there was recorded temperature drops before diving. This means that, for the seals, temperature control falls under cortical response. During dives it was the Aortal and brain temperatures that fell significantly while lattisimus dorsal tissue remained fairly stable. This all has to do with the brachial artery of the front flipper. The blood that goes through this artery has two options when being routed through the body: 1) the blood will go through flipper capillaries to undergo vascular heat exchange to avoid heat loss to the environment or 2) the blood is carried to the heart via large superficial veins through numerous arterio-venious shunts in the skin. These shunts are holes that can open or close and give the blood an opportunity to pass from one part of the body to the next. How much the brain is cooled is determined by the ration of the carotid artery to the brachial artery blood flow. The only problem is that this actively down regulated during diving to cool the brain to as much as 2.5 C leads to a reduction in oxygen delivery to the brain as much as 25%.
ReplyDeleteAlthough Santa’s sleigh is not pulled by Harper seals the moral of the story… the fat man needs to hit 24 hour fitness or get rid of some of those presents to lighten his load, because by pushing his Reindeer to hard they could develop Cerebral Hypoxia (reduced oxygen levels of the brain). Clearly this could be catastrophic since all those little boys and girls out there may never receive their presents because Santa’s sleigh crashes. Think about it Mr. Clause, take it easy. Think about the children!
Blix AS, Walløe L, Messelt EB, Folkow LP (2010). Selective brain cooling and its vascular basis in diving seals. J Exp Biol. 1;213(Pt 15):2610-6
http://nhfonline.org/treatment.php
A.D.A.M. Medical Encyclopedia (2010). Cerebral hypoxia.