Pinched nostrils, otherwise known as stenotic nares, occur when the nostrils of certain breeds of dogs are smaller than normal, resulting in a smaller passageway to the lungs with a markedly increased resistance to airflow. Though it can theoretically affect any breed, dogs with short, wide heads such as bulldogs, pekingnese, and pugs are far and away the most frequent sufferers.
In addition to the obvious problems presented by this disease, it should also be known that pinched nostrils are very often accompanied by other abnormalities such as an overlong soft palate, and a tendency for the larynx to collapse due to strain.
The disease is diagnosed based on appearance. In other words, one can simply look at the nostrils of the affected animal and plainly see that they are pinched shut and afford a much smaller opening than would be common for the breed. The severity of the disease, however, must be determined by somewhat more extensive testing, including radiographs of the chest cavity and listening to the sound of the dog's breathing through a stethoscope.
Pinched nostrils are a congenital disease, caused by an improper formation of nose cartilage long before the dog is ever born. Though the defect is apparent at birth, it usually doesn't cause any severe problems for several years. When it does become a problem, it's because the increased resistance to airflow has forced the animal to exert much more effort than normal in order to take a simple, full breath of air. Over an extended period of time, this overexertion weakens the larynx which will eventually collapse altogether. At such a point, the affected animal will quickly turn blue and then die due to suffocation.
If your animal suffers from pinched nostrils, pay special attention to him or her and look out for signs of an imminent larynx collapse such as labored or noisy breathing, and an intolerance to exercise. If you observe signs such as dark blue gums or if your animal faints, consider it an emergency and get him or her veterinary attention as soon as possible.
There's no real cure for the disease, but its severity can be managed by several different approaches. First and foremost, keeping the animal's weight in the proper range is very important. An obese dog already has to work harder for breath than a dog of normal weight, so this issue would only compound the problems already present. The use of neck collars should be avoided as they can easily become too tight and constrict the dog's ability to breathe. While this would just be a minor temporary discomfort for most dogs, it could be disastrous for one already suffering from pinched nostrils. There is a type of surgery possible that can widen the nostrils and airways, but usually it's more successful the earlier in the dog's life it's performed.
Because pinched nostrils is a congenital disease, it's impossible to do anything to prevent it. The degree to which it is passed on in a hereditary fashion is still unknown, so use caution when breeding an animal with this disease.