Chico

 Often I’ve tried to touch my cats to hear congestion in their chests, or to feel how strong a heartbeat they have. The problem is, especially with my Chico, the moment my hand lands on them, they start to purr and when I say purr, I mean nothing short of a dull roar! At this point, I can’t hear anything but the purr and I’m sure you’ve noticed, cats don’t just stop purring because you tell them to. 

I’ve often wondered about purring and on occasion, I’ve briefly googled it to find out about it but have never really studied the phenomenon until now.

Join me then while we explore Why Cats Purr. Sources of my research are listed as well as links to websites that contain more information.

Why Do Cats Purr?

Have you ever wondered?

The phenomenon of purring has fascinated humans for ages. A lot of research has been conducted to figure out this feline mystique, but no one knows for certain why cats purr, though it is believed to be a voluntary act initiated by the central nervous system. In other words, cats purr on purpose, not just as an instinctive response.

Scientists report that cats produce purring sounds by using the diaphragm to push air back and forth across vibrating nerves in the larynx. Purring occurs in a frequency range between 25 and 150 hertz. At the lower end of the range, that rumbling sound can resemble an idling diesel engine, which has a similar velocity.

All domestic cats and most wild felids are are born with the ability to purr. Cats, from young kittens to senior citizens, purr when they are happy, such as when they are being petted, anticipating dinner, or snuggling on a warm, cozy bed. Mother cats purr when nursing their kittens, and kittens purr when nursing.

But many cats also purr when they are afraid or in pain. That helps explain why females may purr during labor and why some cats purr when they are being examined at a veterinary clinic or when they are recovering from an injury. The purring might serve to reassure or comfort the frightened cat, and some studies suggest that the low-level vibrations of purring physically stimulate feline muscles and bones to keep them healthy and actually hasten the healing process.

Excerpted from: Cat Behavior Answer Book by Arden Moore

Solving The Cat’s Purr Mystery using Accelerometers

Elizabeth von Muggenthaler and Bill Wright

Ever since the Egyptians started worshipping the cat, philosophers, scientists and cat lovers worldwide have wondered why cats purr. Fauna Communications and ENDEVCO initiated a novel research study that recorded the purrs of five species of cats – cheetah, puma, serval, ocelot and the domestic cat. This research has contributed valuable information that may solve the mystery behind the cat’s purr.

It is commonly believed that cats purr when content. However, cats also purr when they are severely injured, frightened or giving birth. So if cats were purring solely out of happiness they would not purr when injured, especially as the generation of the purr requires energy, and an injured animal will generally not expend precious energy needed for healing on an activity not directly connected with their survival.

Since the purr has lasted through hundreds of generations of cats, there must be a survival mechanism behind its continued existence. Suggesting that the purr evolved to function solely as a vocalisation of self-contentment goes directly against the basic tenets of evolutionary psychology and natural selection. Could the purr in any way link to the fact that vibrational stimulation not only relieves suffering in 82% of persons suffering from acute and chronic pain but also generates new tissue growth, augments wound tissue strength, improves local circulation and oxygenation, reduces swelling and/or inhibits bacterial growth?

Survival of the Fittest

Throughout history, the cat has been the most worshipped and the most persecuted domestic animal. Perhaps the most popular cat saying is that they have “nine lives”. This type of old wives’ tale usually has a grain of truth behind it, especially since there is also an old veterinary school adage that states “If you put a cat and a sack of broken bones in the same room the bones will heal”.

Most veterinary orthopedic surgeons have observed how relatively easy it is to mend broken cat bones, as compared with dogs. In a study of “High Rise Syndrome” found in the Journal of the American Veterinary Medical Association, Drs. Whitney and Mehlhaff documented 132 cases of cats plummeting from high-rise apartments, the average fall being 5.5 storeys, or 55 feet. The record height for survival was 45 storeys. Ninety percent of the 132 cats studied survived even though some had severe injuries. There is also literature that suggests that domestic cats are in general less prone to postoperative complications following elective surgeries.

Cats do not have near the prevalence of orthopedic disease or ligament and muscle traumas as dogs have, and non-union of fractures in cats is rare. Researchers believe that self-healing is the survival mechanism behind the purr. There is extensive documentation that suggests that low frequencies, at low intensity, are therapeutic. These frequencies can aid bone growth, fracture healing, pain relief, tendon and muscle strength and repair, joint mobility, the reduction of swelling, and the relief of dyspnea, or breathlessness.

In order to measure the domestic cat’s purrs and how purr vibration is spread throughout its body ENDEVCO Model 22 accelerometers were used. Weighing a mere 0.14 gram, this is the world’s smallest accelerometer. It mounts adhesively, requires no external power and is ground isolated. It is typically used on such small objects as scaled models, circuit boards and disk drives.

During tests, the cats relaxed on blankets, and were encouraged to purr by occasionally stroking them. The small, lightweight Model 22 accelerometers were placed directly on the skin of the cats and stabilised using washable make-up glue and medical tape. Each recording session lasted between 6 and 10 minutes. Data was recorded on DAT recorders and analysed.

Results indicated that despite size and different genetics, all of the individual cats have strong purr frequencies that fall within the range of a multitude of therapeutic frequencies and particular decibel levels, see Fig. 3. Frequencies of 25 and 50 Hz are the best, and 100 Hz and 200 Hz the second best frequencies for promoting bone strength. Exposure to these signals elevates bone strength by approximately 30%, and increases the speed at which the fractures heal.

Purring the Pain Away

All the cats had purr frequencies between 20 Hz and 200 Hz. With the exception of the cheetah, which had frequencies ± 2 Hz from the rest, all the species had frequencies, notably 25 Hz, 50 Hz, 100 Hz, 125 Hz, and 150 Hz, that correspond exactly with the best frequencies determined by the most recent research for bone growth, fracture healing, pain relief, relief of breathlessness, and inflammation. All of the cats’ purrs, including the cheetah, had frequencies ±4 Hz from the entire repertoire of low frequencies known to be therapeutic for all of the ailments.

That fact that the cats in this study produced frequencies that have been proven to improve healing time, strength and mobility could explain the purr’s natural selection. After a day or night of hunting, purring could be likened to an internal vibrational therapeutic system, a sort of “kitty massage” that would keep muscles and ligaments in prime condition and less prone to injury. Additionally, the purr could strengthen bone, and prevent osteodiseases. Following injury, the purr vibrations would help heal the wound or bone associated with the injury, reduce swelling, and provide a measure of pain relief during the healing process.

Taken from a cached file at: Brüel & Kjær is a world leading manufacturer and supplier of sound and vibration solutions.

Purring Is Not Always a Good Sign

My Own Experience

One time when hubby and I were travelling with our cat Rex in the interior of BC, we had parked the car outside of a forested area to stop in to see a friend. We left Rex in the car as this was the first time we’d been here and didn’t know if our friend would welcome a cat visitor.

Feral Cat

While standing outside of the car, a very large black and white cat came out of the woods and jumped up on the car. Being stupid in my younger days, I started talking to him friendly like and he jumped down off the car and began rubbing against my legs back and forth, purring very loudly with his tail straight up and vibrating. All signs of trouble but that was something I didn’t know then. I assume since he was purring that he he liked my attention, that he wanted me to pet him and be friendly.  Because cats just like me, you know?

Well, before I knew what hit me, this cat was attached to my right arm and attacking it like it wanted to kill me. Both of us were screaming and then I stupidly tried to shake the cat off me. He finally let go and ran off into the woods but my arm felt like it was on fire and I’ve never felt such pain before.  And that compared not at all to the pain I endured later that night while trying to sleep and the next day when we had to drive a marathon no stop run back to Edmonton because Ken was sick with asthma and had forgotten his inhaler. Horrible trip.

But I learned an extremely valuable lesson that day that I pass on here.  Not all purring cats want to be petted and loved. Purring doesn’t always mean that a cat is friendly so before reaching out to pet a cat you don’t know, think about it. Sometimes it’s better to just leave it be.

Now my feelings after having done this research and written this article are a little more uneasy than they were before.  Just because my cats are purring, doesn’t make it a given that they are healthy and happy.  So I’m more aware now that my cats may in fact be in pain and trying to heal when they’re purring but then knowledge is power, isn’t it?

Cher