Over the course of evolution, purring has probably offered some selective advantage to cats. Most felid species produce a "purr-like" vocalization. In domestic cats, purring is most noticeable when an animal is nursing her kittens or when humans provide social contact via petting, stroking or feeding.
Although we assume that a cats purr is an expression of pleasure or is a means of communication with its young, perhaps the reasons for purring can be deciphered from the more stressful moments in a cats life. Cats often purr while under duress, such as during a visit to the veterinarian or when recovering from injury. Thus, not all purring cats appear to be content or pleased with their current circumstances. This riddle has lead researchers to investigate how cats purr, which is also still under debate.
Scientists have demonstrated that cats produce the purr through intermittent signaling of the laryngeal and diaphragmatic muscles. Cats purr during both inhalation and exhalation with a consistent pattern and frequency between 25 and 150 Hertz. Various investigators have shown that sound frequencies in this range can improve bone density and promote healing.
This association between the frequencies of cats' purrs and improved healing of bones and muscles may provide help for some humans. Bone density loss and muscle atrophy is a serious concern for astronauts during extended periods at zero gravity. Their musculo-skeletal systems do not experience the normal stresses of physical activity, including routine standing or sitting, which requires strength for posture control.
Because cats have adapted to conserve energy via long periods of rest and sleep, it is possible that purring is a low energy mechanism that stimulates muscles and bones without a lot of energy. The durability of the cat has facilitated the notion that cats have "nine lives" and a common veterinary legend holds that cats are able to reassemble their bones when placed in the same room with all their parts. Purring may provide a basis for this feline mythology. The domestication and breeding of fancy cats occurred relatively recently compared to other pets and domesticated species, thus cats do not display as many muscle and bone abnormalities as their more strongly selected carnivore relative, the domestic dog. Perhaps cats' purring helps alleviate the dysplasia or osteoporotic conditions that are more common in their canid cousins. Although it is tempting to state that cats purr because they are happy, it is more plausible that cat purring is a means of communication and a potential source of self-healing.
How Cats Purr
The cats can purr continuously meaning the purr while both inhaling and exhaling. It is believed that the purring sound is produced by the laryngeal muscles. These muscles open and close the glottis which separates the vocal chords and causes vibration and as a result of this vibration the purring sound is produced. It is believed that there is an endogenous neurological oscillator that drives this vibration, similar to an endogenous oscillator driving our heartbeats.
The central nervous system of an emotionally charged cat sends signals to the laryngeal muscles which causes them to tighten up to a point that when air passes through them they vibrate and the result is the purring sound. So a cat with compromised laryngeal muscles cannot purr.
How Cat Purr affects Humans
It is believed that the purr frequency of 25 and 150 hertz also acts as a healing mechanism for humans and if you are not feeling well the purr of your cat might help you in feeling better. Some studies also suggest that people with high blood pressure would feel better if a cat sits in their laps and purrs. Just like it is said that cat purr helps bone growth and healing it is also believed that it has a similar affect on humans.
