Month: April 2021

How the Largest Land Animal Stays Cool – And What We Can Learn From It

African Elephant raising tusk
African Elephant. Credit: Wolfgang Schlaifer

African Elephants have the largest volume to surface-area ratio of any living land mammal; it’s not a surprise then that they have to dissipate a tremendous amount of heat. You and me eat 2,500 calories a day – an adult male elephant might consume over 70,000 calories each day! This means these gigantic beasts need to remove several kilowatts of heat. So how do they do it? And can we learn anything from these biological marvels?

Physical Features

Close up of an elephant's ears. Details on blood vessels going through ear flap.
Close up of elephant’s ear, credit: Magda Ehlers

In order to combat the heat, elephants have developed several unique features. First is the large, flapping ears. Phillips and Heath have studied the heat exchange by the ears extensively, finding remarkable advantages. It may not look like it, but those ears make up 20% of an elephants surface area – this essentially transforms them into large heat sinks. But that’s not the end of their ears’ advantages. Elephants are able to regulate heat transfer through vasomotion; this is an oscillation of blood vessels that is unrelated to heart beat. Thus, elephants are able to store heat in their ears by expanding the blood vessels, then releasing this heat during the nighttime when it is more efficient. Modeling has shown that nearly 100% of heat loss requirements can be met through the movement of the ear.

Close up of African Elephant hair. The hair is not very dense and very thin.
Close up of African Elephant hair on head. Credit: Conor L. Myhrvold in the Woodland Park Zoo, Seattle, Washington.

Elephant ears aren’t the only heat-reducing mechanism. Myhrvold et al. propose that a low density of hair could also be a method to remove heat. As humans we often think of hair as a mechanism to keep us warm – this is true as it will serve as insulation against our skin. Low density hair, however, provides a larger surface area (they act as small little heat fins) that offsets any increased insulation they may cause. Researchers found the break-even point to be 0.3 million hairs/m2 – elephants only have 1500 hairs/m2.

Internal Control

A thermal image of elephants; the animals are much brighter compared to their environment.
Thermal image of elephants, credit: Endangered Wildlife Trust/LJMU

Us humans are homeotherms – this means our internal body temperature is kept stable regardless of outside temperatures. Most other mammals follow homeothermic tendencies, but there is recent evidence that elephants are actually heterotherms – their bodies are both self-regulating and adaptive to the environment. In fact, elephant body regulation is very similar to desert mammals like camels. During the day elephants will increase their body temperatures, and during the night they will lower them (this also helps for when the night is very cold and the animal wishes to conserve instead of dissipate heat). Weissenböck et al. discovered that elephants can have a body temperature range from 35.0°C – 37.5°C (95°F – 99.5°F), a range that is about twice as large compared to humans.

What We Can Learn

African Elephants present a unique natural problem: how do you cool something so large that produces so much heat? This problem is also present in our own human world from cooling down skyscrapers to making sure your computer CPU doesn’t overheat. One of the more promising developments is thermal energy storage and how it can heat, cool, and provide electricity for the modern world. Elephants’ physiological adaptations can serve as the blueprints for future innovation in heat transfer and dissipation.

Sources and Additional Readings

Polly K Phillips &James Edward Heath. “Heat exchange by the pinna of the african elephant (Loxodonta africana)”, Comparative Biochemistry and Physiology Part A: Physiology, Volume 101, Issue 4, 1992.

P.G. Wright & C.P. Luck. “Do elephants need to sweat”, South African Journal of Zoology, Volume 19, Issue 4, 1984.

Myhrvold et al. “What is the Use of Elephant Hair?” PLOS One. 2012.

Alex Fowler & Adrian Bejan. “Forced convection from a surface covered with flexible fibers”, International Journal of Heat and Mass Transfer, Volume 38, Isssue 5, 1995.

Weissenbock et al. “Taking the heat: thermoregulation in Asian elephants under different climatic conditions”, Journal of Comparative Physiology B, Issue 182, 2011.

Not Everyone Breathes While they Sleep: The Dangers of Sleep Apnea

You might think that breathing in our sleep should come naturally – if breathing and sleeping are both physiologically necessary, then we must be able to do them simultaneously right? Unfortunately, almost a quarter of middle-aged American men and nearly 10% of women suffer from sleep apnea, a chronic condition characterized by repeatedly stopping breathing while sleeping. The clinical symptoms seem rather benign – snoring, sleepiness, fatigue during the day or other issues sleeping. However, by far the most dangerous aspect of this disease is that it puts patients at increased risk of high blood pressure, stroke, coronary heart disease, as well as occupational and/or automobile accidents. Over the last several decades, a variety of therapy options have been studied to treat this condition, ranging from drugs to masks to surgery.

One of the earliest documented therapy options is using protriptyline to treat obstructive sleep apnea. Protriptyline is an anti-depressant drug that was used for its ability to clear airway obstructions during sleep; however, it did not gain significant popularity due to its adverse effects including cardiac complications and limited demographics for whom it would be an appropriate treatment.

The next treatment discussed was altering sleep positions for patients suffering from sleep apnea. A seemingly simple idea, a study determined that laying on the back significantly increased the severity of sleep apnea. Interestingly, the difference in severity between back and side sleeping positions was most noticeable in healthy, non-obese patients. The authors believe that lying on the back causes tissues of the throat to obstruct the trachea and prevent smooth airflow during breathing, as shown in the image below, which would explain why obesity can exacerbate sleep apnea.

Diagram of airflow obstruction through mouth and throat
Photo by Habib M’Henni on Wikimedia Commons.

Multiple non-invasive devices were also studied, including oral appliances, sleep posture alarms, and positive airway pressure devices. Oral appliances can either protrude the lower jaw or restrain the tongue; both aim to restructure the upper airway (mouth, trachea, etc.). Sleep posture alarms were suggested to train patients to sleep on either side, rather than on their backs. Positive airway pressure devices (Bi-PAP, CPAP) are the most commonly used treatment for sleep apnea currently; they maintain a consistent air pressure flowing into the mouth to ensure the airways do not collapse during sleep.

Man sleeping while using CPAP machine
Photo by ApneaMed

The final treatment studied was nocturnal supplemental oxygen (NSO), which involves increasing the concentration of oxygen in the air inhaled while sleeping. However, a study comparing use of a CPAP with use of NSO found that CPAP treatment was far more effective at decreasing the patients’ blood pressure and still proved effective in patients already taking blood pressure medication.

Overall, the best method for treating sleep apnea is dependent on the patient and his or her underlying conditions. Changes in sleep posture could greatly enhance the sleep quality of a moderate case of sleep apnea; CPAP would be ideal for someone who can easily tolerate the mask and does not frequently move in his or her sleep. Each of these demographics makes it difficult to define one optimal solution for treating sleep apnea, but the variety of available treatment options provides hope for those patients who suffer from this chronic illness.