THE ANATOMY OF UPPER AIRWAY SYNDROME
by Magda Chiarella
Many thanks to Magda Chiarella – NTCA Health Chair – for her permission to publish this article on my website.
Since the publication of my translation of the Swiss studies on Upper Airway Syndrome (UAS), I have received numerous calls and e-mails from owners of Norwich Terriers with breathing difficulties. The most common questions are where to go to have the Norwich properly diagnosed, and what a dog’s specific symptoms indicate. The answer is two-fold. You are best served by having your dog examined under anaesthesia, with a probing endoscope, by a veterinary respiratory specialist who has experience with our breed. You should also learn as much as you can about UAS beforehand, so that you can participate with the veterinary specialist in deciding about the best course of action for your dog. It is as much about choosing the best specialist as it is about understanding the syndrome well, and making informed decisions together. Time and time again, I hear from distressed Norwich owners who wish they had been more outspoken in insisting that their dog have laser than scalpel surgery. Thus, the goal of this article is to help Norwich owners understand the anatomy of UAS. I am presenting here the information I have compiled from talking to more than twenty specialists who have diagnosed various degrees of UAS in Norwich across the country, and who have performed corrective surgeries. The information also includes conversations I have had with owners of affected dogs. Hopefully, we can learn from this collective experience and make fewer mistakes in the future.
I will start by outlining what Upper Airway Syndrome is. As the name indicates, there is a chronic airway obstruction in some place or, typically, in more than one place—hence the syndrome part of the name (a cluster of clinically recognizable features). The term “syndrome” comes from Greek and literally means “run together”. It indicates that the presence of one feature is linked to another. UAS is not a static problem, but rather a condition that can worsen in time, as one anatomic abnormality causes deformation elsewhere. I find the dynamic nature of the condition crucial to understanding UAS, but regrettably, this is the most ignored fact of the UAS. Diagnosing a dog as “mildly affected” at the age of two, for example, does not mean that he will stay that way for life. His condition will most likely worsen in time, although it could improve as well, for example, by bringing the dog’s weight down. Air can meet obstruction anywhere as it journeys towards the lungs; once it does, it creates air friction further down on its way to the lungs, causing more damage. So, please think of UAS as a chronic condition. No matter how successful a particular corrective surgery might be, it is never a permanent fix.
Dogs’ lungs expand and suck in the air. Like all mammals, dogs breathe through the process of pulling the air in, not pumping it, as amphibians do. Have you ever seen a bottom of a frog’s mouth bubbling in and out? The floor of its mouth is acting like a pump, pushing the air into the lungs. Mammals expand their chest and lungs and thus create a negative pressure. Air rushes in to fill the vacuum created by that expansion of the thoracic (chest) cavity to equalize the pressure between the lungs and the outside air. What that means is a very high air pressure going down the respiratory tract. A good way to visualize the difference between pulling and pushing the air into the lungs is your own experience with drinking straws. If you blow into the straw you will not affect it as much as when you suck in the air. You can collapse a straw with a good pull.
As air rushes through the nose at high pressure, it might already meet some resistance. The nostrils are never pinched in our breed, but the posterior nasal passages are sometimes too narrow and, therefore, afford less passage than needed. The condition is referred to as stenotic posterior nares. That nasal constrictions creates higher air pressure going down the respiratory tract and can cause problems in the laryngeal area. Dogs with narrowed posterior nasal passages are not good candidates for surgery. Many specialists do not even bother diagnosing stenotic nares in Norwich Terriers because the condition is not correctable. It is, however, helpful to know if the dog has stenoric nares because the condition has implications in developing other aspects of UAS. For example, it is helpful in predicting whether surgery to remove everted laryngeal saccules needs a follow-up in a couple of years, as saccules will most likely evert again as a result of air pressure stemming from stenotic posterior nares. The most precise method of diagnosing stenotic nares is rhinomanometry (described in detail in my Spring 2008 News article on UAS). Rhinomanometry is not easily available, so it helps to know what to look for as a symptom of stenotic posterior nares. A dog that is often breathing through the mouth is most likely compensating for having stenotic nares. When not running, barking or exercising, is your dog’s mouth often slightly open? Look through some casual photographs of your dog lying around, resting, sitting. Photos tend to show objectively any patterns.
Within a dog’s mouth, there could be deformities as well. The most common deformity in Norwich Terriers is an elongated soft palate. If you were to run your tongue along the roof of your mouth, starting from the upper teeth and moving it as far back as you can, you would feel that the roof of your mouth turns to a soft area towards the throat. That part of the anatomy is called a soft palate. If the flap of skin in that anatomic part of the mouth is too long, it will partially obstruct breathing. The longer the flap, the more obstruction. Interestingly, a too-short soft palate is not a good thing either. That too may cause air turbulence.
The most recognizable symptoms of an elongated soft palate are “sloppy” drinking of water, grass stuck in the dog’s nose, and panting with a “k” sound. “Sloppy” drinking, especially gagging when drinking, is easy to relate to an extra flap of flesh at the back of the dog’s mouth. Getting grass stuck in the dog’s nose might appear to have a less obvious connection, but it is one of the most common symptoms of an elongated soft palate. Grass gets into the dog’s nose not from being sniffed in, but being chewed on. Then, instead of being swallowed, the grass gets trapped behind that extra flap of flesh and, from there, is sucked up the nose. If your Norwich has recurrent episodes of grass stuck up in the nose, consider having this palate checked for possible excessive elongation. Panting with what I call a hard “k” sound (as in “Kate”) is another sign of an elongated soft palate. Make the hard “k” sound over and over again. Does it sound like your dog panting? If yes, chances are that his soft palate is hitting the tongue when panting because it’s elongated.
At the very end of the oral cavity there is an ingenious piece of flesh and cartilage responsible for closing the air passage when we swallow so that food does not get into the lungs. This is called epiglottis. That little flap may be malformed too, but epiglottis malformation is much less common in the breed than an elongated soft palate. I know of three Norwich Terriers diagnosed with that condition. Again, gagging when eating or drinking can be a symptom of epiglottis malformation, especially when followed by coughing.
Stenotic nares, elongated soft palate, or both these respiratory abnormalities, cause an ongoing stress on the walls of a dog’s larynx, in effect sucking the walls inward. The first part of the larynx that would take the brunt of such chronic high air turbulence and sucking in of the laryngeal walls are the laryngeal saccules. These little pockets of thin membrane lining the larynx are located just above the vocal cords. Their role is thought to be increasing the resonance of the vocal cords. In other words, they are the acoustical concert hall for our dog’s barking and wining. Chronic airway obstruction everts (pulls inwards) these little membrane sacs. Instead of being little pockets by the vocal cords, they are now little “inside-out pockets”, pulled into the glottis and further clogging the already compromised airway. Everted laryngeal saccules not only result from chronic airway obstruction; they also aggravate the problem.
Further damage, which higher turbulent air pressure cause, is inflamed tonsils. Everted laryngeal saccules often accompanied by enlarged tonsils, are considered the first stage of laryngeal collapse. In more severe cases, the remaining parts of compromised laryngeal walls, which are constantly exposed to the pulling of air, can be pulled much further inward. Remember that collapsed straw? This process is called laryngeal collapse, as the dog’s laryngeal walls collapse inwards towards the air passage. Increased vibrations in the airway result in swelling and irritation of the laryngeal membranes, further worsening the situation.
When we talk of “heavy breathers” we refer to those Norwich that have obstruction somewhere in their larynx. More often than not, the obstruction comes from everted laryngeal saccules. Dogs that breathe noisily, that do not tolerate heat well and have exercise intolerance, simply have trouble breathing. In more severe cases, the oxygen deprivation might be so severe that a dog can go into respiratory distress and cyanosis, a life-threatening condition characterized by a blue tinge to the dog’s gums and tongue indicative of serious oxygen deprivation (deoxygenating of haemoglobin)
The most severe and sad possibility within UAS is tracheal collapse, but luckily this condition is also the least common manifestation of UAS in our breed. The trachea (windpipe) is a tube composed of tracheal membrane connecting a number of cartilage rings. Contrary to common belief, the cartilage rings are not full circles. Their form is that of a C shape, with the open end of the C facing towards the dog’s spine. The trachea in affected dogs may be hypoplastic (underdeveloped) and may present still another obstacle in breathing. Needless to say, a narrow (stenotic) trachea would only contribute to overall respiratory resistance and the breathing problems already mentioned. Unfortunately, a dog may be born with a normal trachea and have it collapse as a result of chronic air turbulence stemming from upper airway abnormalities. Referred to as acquired tracheal collapse to distinguish it from a congenital condition (present at birth), this is the most common form of tracheal collapse in our breed. A characteristic symptom of tracheal collapse is a “honking” barking sound. More severe collapse is accompanied by chronic coughing, a wheezing sound on inhale and soft “honking” on exhale, and heat and exercise intolerance.
Dogs suffering from any number of UAS problems show noisy respiratory effort (especially during exercise or stress) and heat intolerance. They may snort, snore, or gag while eating of drinking; pant noisily; wheeze; reverse-sneeze. The sound of their barking is often affected, especially when either an epiglottis or laryngeal saccules are involved because of their proximity to vocal cords. The dog’s chest may “rattle” or his breathing may sound “wet”. These are only symptoms, but the real danger lies in the possibility of hypoxia (shortage of oxygen) and even death from suffocation.
There are a number of anatomic respiratory malformations that can result in UAS, some more dangerous than others. Regardless of the severity, UAS means oxygen deprivation and is a serious condition. Corrective surgeries deal with excess soft tissue, laser is the instrument of choice because it leaves less scares and less post-surgical inflammation.
Surgery is not the only option. In many cases when the degree of UAS is mild, it can be managed with much less invasive means. The single most important thing Norwich owners can do to alleviate UAS symptoms is to keep their dog’s weight down. Excessive weight in a dog affected with UAS is an inexcusable negligence on the owner’s part. I have witnessed dogs that could not exercise in warm weather become quiet breathers, eager to run and romp around, after losing just a few pounds. Let us remember that our terriers are supposed to weigh between 10 and 12 lbs. Before investing in an expensive and invasive endoscopy, please invest in a scale to weigh your dog and help him become a properly-sized Norwich, not exceeding 12 lbs.
Along with weight loss, management of UAS is another important part of minimizing the problem. Dogs with respiratory problems should not be allowed to bark excessively and they should not exercise in hot weather. With this common-sense approach of keeping a dog in good shape, relaxed, and exercised away from the worst heat of the day, the condition may be manageable in many cases. When it is not, seeking a skilled specialist and thoroughly examining the dog’s entire respiratory tract via endoscopy would give you the fullest picture of the degree of UAS affliction at that particular time in the dog’s life. For dogs that have already undergone corrective surgery, it is important to watch out for any signs of the condition worsening. And lastly, talking to other Norwich owners and sharing our collective knowledge is the only way we can become more knowledgeable about all aspects of UAS.