Dec. 18, 2012 -- An investigation into the origin of Rudolph the Reindeer's red nose has ended the generations-old debate by uncovering an elusive but long-hypothesized scientific explanation: A snootful of red cells.
Detailed evaluation of adult reindeer's nasal microcirculation revealed similarities with human nasal microvasculature, but also striking differences. Reindeer nasal microcirculation exhibited a highly vascularized nasal mucosa, a red cell-rich nasal septal mucosa, and a microvessel density 25 percent greater than that of humans.
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The architecturally distinct nasal microvasculature confers on Rudolph a nose that "is red and well adapted to carrying out his duties in extreme temperatures," according to a new study published in the journal BMJ.
"These results highlight the intrinsic physiological properties of Rudolph's legendary luminous red nose, which help to protect it from freezing during sleigh rides and to regulate the temperature of the reindeer's brain, factors essential for flying reindeer pulling Santa Claus' sleigh under extreme temperatures," study author Can Ince of Erasmus Medical Center in Rotterdam, the Netherlands, and co-authors wrote in their study.
The findings are consistent with an inherent adaptive mechanism in reindeer vascular development to deal with the cold climate, according to a researcher who was not involved in the study.
"In colder climates and also when they are higher up in the atmosphere pulling Santa's sleigh, the increase in blood flow in the nose will help keep the surface warm," John Cullen of the University of Rochester in New York told MedPage Today.
The nasal mucosa, and its associated microcirculation, plays a major role in human health and disease. In the healthy state the nasal microcirculation facilitates the processing of inhaled air (heating, filtering, dehumidifying), control of inflammation, fluid transport for mucous formation, and oxygenation of nasal parenchyma.
The nasal mucosa also aid drug uptake and response to allergens.
Despite the physiologic importance of the nasal microvasculature, few studies have examined the microvasculature's function and morphology. To a large extent, the paucity of investigation reflected the lack of suitable instrumentation to conduct studies.
The evolution of hand-held intravital video microscopes has proved the means for direct visualization of the nasal microcirculation. Availability of the devices has afforded opportunities to study the human nasal microvasculature and to perform comparative studies.
Ince and colleagues described the use of hand-held vital video microscopy to study the microvasculature of the human nose and compare it with that of the reindeer nose. The study involved five healthy volunteers, one patient with grade 3 nasal polyposis, and two adult reindeer from Tromsø, Norway, which is located near the North Pole.
By means of the hand-held microscope, investigators obtained high-quality images of the nasal septum and inferior turbinate of the volunteers and the patient with nasal polyposis. Circularly arranged capillaries were seen throughout the nasal mucosa.
Quantification of nasal microcirculation in the volunteers demonstrated a mean perfused vessel density of 15 mm/mm2 and a microvascular flow index of 3.0 arbitrary units. In the patient with nasal polyposis, nasal microvascular was irregular, and characteristic architectural findings were absent, such as hairpin-like capillaries.
Investigators examined nasal microvasculature in one of the volunteers after a vasoconstrictor challenge with 100 mg of cocaine, which is routinely used as a local anesthetic and vasoconstrictor by ear, nose, and throat specialists, the authors noted. The challenge resulted in transient cessation of microcirculatory flow.
"We're kind of glad they didn't do the same thing with the reindeer, because the last thing we would want is reindeer on cocaine, pulling Santa around the sky," said Cullen.
After administration of medetomidine anesthesia, the investigators performed similar evaluations of the reindeer nasal mucosa. They found an abundant microcirculation carrying a heavy concentration of red cells. Mean perfused vessel density was 20, as compared with 15 in the human volunteers.
The authors also evaluated the reindeer nasal microcirculation after the animals completed a treadmill test, which showed that "they do indeed have red noses. In addition to the nose having a high microvascular density, the nasal mucosa also revealed an abundance of ring-like vascular arrangements, similar to those in humans."
The study does not completely resolve questions surrounding the origin of Rudolph's red nose, according to Cullen. Noting that many human's noses turn red during alcohol consumption, he said the role of alcohol in Rudolph's bright red nose remains to be seen.
"It would have been interesting to see if giving the reindeer alcohol would have caused their noses to be redder and increased the blood flow," said Cullen.
If alcohol does play a role in the color of Rudolph's nose, the study has implications that extend beyond well beyond a single reindeer.
"I think [the message] will be 'Don't let Santa drive drunk,' because he won't be able to deliver the presents," said Cullen.
"Seriously, a lot of people leave out quick drinks for Santa and carrots for the reindeer, so I think maybe we should stick to healthier food and drink for both Santa and the reindeer."