The medical term for pinched nostrils is stenotic nares and it is a common problem in many of the brachycephalic or pug-nosed dogs. These breeds seem to have a huge list of respiratory problems that can develop over time due to their short head formation and the compact nature of the respiratory system. Stenotic nares in themselves may not be problematic for the dog unless there are other complications that make breathing difficult for the pet.
The most common breeds affected by stenotic nares include Pugs, Boston Terriers, Pekingese, English Bulldogs, Boxers and Shih Tzus. These dogs are born with cartilage malformations in the nose that limit or restrict the opening of the nostril, slightly to greatly reducing the airflow through the nose. Since it is a congenital malformation asking about any problems with stenotic nares in the breeding line is a good question to ask the breeder. Also be aware that dogs with mild cases of stenotic nares will quickly adjust and breathe more from their mouth than their nose. This is important to know to help avoid heat stroke and heat prostration if the dog is breathing through his or her mouth, especially when outside on hot and humid days.
Typically the condition, if it is problematic, will be noticed immediately once the puppy starts to move around and investigate his or her surroundings. As they start to move they will breathe more deeply and need to move greater volumes of air through the body. When the nostrils are too small the puppy will then start to breath through his or her mouth, resulting in a rather loud wheezing or roaring sound as they move air in and out through the mouth rather than the nose. This is not the same sound as panting and is not in an attempt to cool off, it is the actual mechanism by which the dog is breathing.
If stenotic nares are present the dog will also breathe through his or her mouth when they are sleeping, usually resulting in snoring or snorting, often with a great amount of volume for such as small puppy. If there are other respiratory problems in the dog or puppy such as problems with a collapsing trachea or malformation of the larynx or air passages the breathing will become more stressed and more problematic with coughing and wheezing increasingly noted. With this additional pressure on the system there is greater chance of a full trachea collapse or serious respiratory system damage, even resulting in fatality if the dog cannot breath.
In cases where there are no other complications besides the pinched nostrils a vet can surgically enhance or expand the open of the nostrils to provide more opportunity for air passage. With other respiratory conditions additional surgeries or drug therapies may be needed to control the coughing and prevent the build up of pressure on the trachea.