The Mystery of the Cat Purr

This blog post is by David Aguilar, front desk counselor

We all love when our kitties purr with delight. People have been puzzled for centuries on how and why they do it. Cats purr when they are content, but also when injured, under distress or in labor. Cats can purr uninterrupted while inhaling and exhaling. This can be contrasted to humans, who can only talk while we’re in the process of exhaling. Unless you want to sound like something from a horror movie! A cat’s meow works under the same exhalation process as humans.  This involves air going through the larynx, which creates a pressure drop. When the pressure gets low enough, the vocal folds (or more commonly known as vocal cords) start to oscillate. This creates the sound of meows and human speech.

Recent studies have shown that the cat purr doesn’t involve the vocal folds at all. In cases where cats and humans have a tracheotomy tube (a tube in the throat used for breathing when the patient can’t breathe through the mouth), they cannot meow or talk. The reason why cats and people can’t talk is because the larynx is bypassed, and the vocal folds are compromised. Even with a tracheotomy tube, a cat can still purr. The best theory explains that cat purrs involve rapid vibrations between the larynx and diaphragm, rather than oscillating vocal folds. Both the larynx and diaphragm take turns vibrating 30 times per second. That explains why, when your cats purr, you can sometimes feel its whole body vibrate.

Now that we know how cats purr, why do they do it? After all, it takes precious energy to produce all that purring. Even though your beloved kitty doesn’t have to worry about its next meal, it’s all about energy conservation in the wild. Where meals could sometimes be days apart, every bit of energy expended affects how long they survive. With this in mind, wild kitties, like the cheetah and the bobcat, still purr. So why do they go out of their way to purr?
There are several theories that try to explain this. The first theory is that purring actually has healing properties. The frequency of a cat purr can range from 50 to 150 hertz. Strangely enough, frequencies between 25-50 hertz (most effective) and 100-150 hertz (next effective) actually promote bone, muscle, and tendon healing/growth. This might explain why the percentage of arthritis and lameness in cats is much lower than in dogs. This can also explain why cats purr so much when injured. The second theory posits that cats purr to help fight atrophy, a condition where the body starts deteriorating. One of the many ways atrophy can occur is with lack of blood circulation and activity. Because cats sleep at least 18 hours a day, purring could explain why they can maintain healthy bodies with very little exercise.

There has been little research done on how the cat purr affects people. Although I can say when I broke my arm my cat wouldn’t leave my side and would purr continuously. Was she trying to “heal” me, was she trying to comfort me? Another theory has shown that purring can lower blood pressure, reduce swelling and can even provide pain relief within cats. Was my cat trying to give me pain relief through purrs?

Cats also purr to get your attention. Researchers have found that cats can alter the frequency of their purr and meow to match the cry of a human baby. Human brains are  programmed to find that frequency very unsettling and we’ll do anything to make it stop. Cats have caught on to this. They use it to get our attention. So what do you think? Are cats’ purring abilities a bunch of baloney or have you seen them firsthand?

Thanks for reading!