UPPER AIRWAY SYNDROME

 

Does Brachycephalic Airway Obstruction Syndrome Affect Brachycephalic Breeds Only?

 

             Until quite recently BAOS (Brachycephalic Airway Obstruction Syndrome), a combination of upper airway disorders, was associated with brachycephalic dogs only, the dogs with very short muzzles. We all have heard at one time or another a Bulldog or a Pug noisily puffing around the show ring, or maybe we have witnessed a Shih Tzu or a Pekingese wheezing and snorting, in the act known as reverse sneezing, as handlers rush to cover the dog’s nose to stop it. There is an abundance of research and articles on respiratory distress in brachycephalic breeds, but the syndrome has a wider circle of affliction than previously thought, and it does not only affect short-nosed dogs. My breed is Norwich terriers, a mesocephalic breed sadly affected in large numbers by respiratory troubles.

            

             Cephalic index refers to the size and shape of the skull.  All dogs are classified into three groups based on that index: dolichocephalic (long headed), mesocephalic (moderate headed), or brachycephalic (short headed). A brachycephalic skull is relatively broad and short, typically with the breadth of at least 80% of the length. Dog breeds such as Pugs and Bulldogs belong in this group, where the muzzle practically disappears, and are sometimes characterized as extremely brachycephalic.  A mesocephalic (also referred to as mesaticephalic) skull is of intermediate length and width, and my breed, Norwich terriers, belong in that category. A dolichocephalic skull is a relatively long skull, typically with the breadth less than 80% of the length. Think of a Whippet or a Borzoi.

Veterinary internists specializing in BAOS are seeing increasing numbers of mesocephalic dogs with respiratory problems.  Breeds like Cavalier King Charles Spaniel, suffering from airway obstructions in statistically significant numbers, may be classified by some as a brachycephalic breed, a contested classification, but there is no question that Norwich terriers, Labrador retrievers, and Bull terriers do not belong to the brachycephalic group. Yet, these breeds are affected by the syndrome too. Anecdotal knowledge of breathing problems in some of the non-brachycephalic breeds has been circulating for a while.  Finally, in the last few years, some new studies gave us solid scientific evidence supporting that fact. BAOS can affect a mesocephalic breed in large numbers as well.  A case in point is my breed - the Norwich terrier.

 

The ABCs of Respiratory Problems

 

             Before I present those studies, let me offer a quick summary of what Brachycephalic Airway Obstruction Syndrome means in anatomic terms. As the name indicates, there is a chronic airway obstruction in some place, or typically, more than one place, and 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. They run together. BAOS is not a static problem, but rather a condition that can worsen in time, as one anatomic abnormality causes deformation of another.  Air can meet obstruction anywhere in its journey towards lungs, and once it does, it creates air friction further down on its way to the lungs, causing more damage.

 

             Dog’s lungs expand and suck the air in.  Like all mammals, dogs breathe though 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 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 thoracic (chest) cavity to equalize the pressure between the lungs and the outside air. As air rushes through the nose, at high pressure, it might already meet some resistance.  The nostrils might be pinched, and therefore afford less passage than needed. That, in turn, would create higher air pressure going down the respiratory tract.  That air friction would cause other problems.  If nostrils are not pinched, the posterior nasal passages might be too narrow.  Any place within nasal passages that is too narrow, being it pinched nostrils, or narrow posterior passages (further down the nose), or both, are referred to as stenotic nares.

 

             Within the mouth, there could be deformities as well.  The most common one 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 is a part of the mammal anatomy 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 is, the more obstruction.  Interestingly, a too short soft palate is not a good thing either.  That too may cause air turbulence. 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.  It is the epiglottis. That little flap may be malformed too, but epiglottis malformation is much less common than an elongated soft palate.

            

             Elongated soft palate, or stenotic nares, or both, cause an ongoing stress on the walls of the larynx, in effect sucking them inward.  The first part of the larynx that would take the brunt of the chronic high air turbulence, and sucking of the laryngeal walls, are 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 resonance of the vocal cords.  In other words, they are the acoustical concert hall for our dogs’ barking and whining. Chronic airway obstruction everts (pulls inward) 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, but also aggravate the problem.  Further damage, which higher turbulent air pressure can 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 pulling of air, can be pulled much further inward.  That process is called a laryngeal collapse, as the walls collapse inward towards the air passage. Increased vibrations in the airway result in swelling and irritation of the laryngeal membranes, further worsening the situation.

 

             Another sad possibility within BAOS is tracheal collapse. The trachea (windpipe) is a tube composed of tracheal membrane connecting a number of cartilage rings.  Contrary to a common misconception, the 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 brachycephalic dogs may be hypoplastic (underdeveloped) and may present still another obstacle in breathing. Needless to say, a narrow trachea would only contribute to overall respiratory resistance and the problems already mentioned.  Unfortunately, the dog may be born with a normal trachea and have it collapse as a result of chronic air turbulence stemming from upper airway abnormalities.  Such tracheal collapse is referred to as acquired tracheal collapse, to distinguish it from a congenital condition (present at birth).

 

             Dogs suffering from any number of BAOS problems show noisy respiratory effort (especially during exercise or stress) and heat intolerance.  They may snort, snore, or gag while eating or drinking, pant noisily, wheeze, reverse-sneeze. These are only symptoms, but the real danger lies in the possibility of hypoxia (shortage of oxygen) and even death from suffocation.

 

BAOS Getting a New Name- Research Showing Respiratory Obstruction Syndrome in Non-Brachycephalic Dogs

 

             In 2004 European breeders of Norwich terriers initiated a study into breathing problems in their dogs. The most extensive study, conducted at the University of Berne, has not been published yet.  Some initial results were shocking, and understandably were met with disbelief.  Since the study has not been published yet, I cannot quote the statistics, but let me sum it up as a high incidence of anatomic abnormalities in respiratory tract in the breed. It is important to note that the dogs were assigned randomly to this research and still showed a high number of afflictions.  Soon after the conclusion of the study at the University of Berne, another Norwich-specific study was done at the University of Zurich, published in 2005, comparing Norwich terriers’ respiratory functions to those of brachycephalic breeds.  The methods used by Dr. Marisa Rosaspina’s team were more extensive than in the Berne study.  In addition to laryngoscopy, the dogs underwent rhinomanometry (which I will explain further down), measurements of the nostrils, as well as radiographs of the skull and the thorax. The subjects of the study were 23 Norwich terriers and 8 Beagles representing the mesocephalic breed, and 8 brachycephalic dogs.

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Digging and Popping since 2000

             The illustration on the right pertains to rhinomanometry, another diagnostic procedure used in the Zurich study by Dr. Rosaspina.  Rhinomanometry (“rhino” means “nose” in Greek and “manometry” refers to taking measurements) is a relatively new method of taking measurement of the air flow and pressure within the nose during respiration. Nasal resistance or obstruction can be calculated from the figures obtained. It is a highly accurate method of measuring the air flow, and therefore indicating constrictions in the dog’s nasal passages. Please note the metal hook in the drawing.  It separates the nasal passages from the rest of the respiratory tract.  The anesthetized dog has the metal hook inserted into its mouth and wears a mask connected to a rhinomenometer.  To create a seal between the mask and the dog’s palate, ordinary pizza dough was used where the drawing shows the bell shaped mask. The devise is pumping air into nasal cavities and measuring the return of the air flow, as the air is redirected back by the metal hook which prevents it from traveling further down the airways.  Meanwhile, the dog is breathing through a tube inserted into his mouth and throat. 

Zurich Study At A Glance

Norwich statistics out of 23 dogs:

19 had elongated soft palate

20 had enlarged tonsils

 17 had everted laryngeal saccules

6 had constricted glottis

1 had laryngeal collapse

2 had narrowed tracheas

8 Brachycephalic dogs exhibited similar problems

Control group of 8 Beagles had NONE of the above issues

 

 

The object of the study was a comparison between the Norwich breed and brachycephalic dogs in reference to respiratory problems.  The diagnostic procedure described above showed that brachycephalic syndrome affects the Norwich breed, although Norwich terriers belong to the mesocephalic group. To complete the comparison, skulls of all three groups were compared (the Norwich terriers/ Beagles/ brachycephalic dogs) through x-rays and skull measurements.  The authors of the study concluded that Norwich terriers are clearly not a brachycephalic breed, and so they found no correlation between skull size and respiratory problems.

The ultimate conclusion of the study was a suggestion to rename brachycephalic syndrome, as it does not affect only brachycephalic breeds. It clearly affects Norwich terrier breed as well. In all recent articles and written exchanges about breathing problems in our breed we refer to it as Upper Airway Syndrome.  It is becoming a common term for Norwich fanciers.

The Zurich study comparing Norwich terriers to brachycephalic breeds initiated another study which is still in progress.  This new study, under Dr. Daniel Koch, is further exploring Dr. Marisa Rosaspina’s broad conclusion that the skull size is not related to respiratory problems.  The initial results of the study indicate that, indeed, Norwich terriers do not have skulls similar to brachycephalic breeds but within the Norwich terriers examined there is a clear pattern of more dogs with shorter muzzles and wider skulls being affected with Upper Airway Syndrome. This new study will conclude in December 2008.

Originally published in Dog News

The researchers visually examined the dogs’ soft palates for their size, thickness and presence of any deformities. The drawing on the left illustrates an example of an elongated soft palate, the most common abnormality of the palate found in Norwich terriers. Out of 23 Norwich terriers in the study, 19 were diagnosed with this condition.

Similarly to the study conducted in Berne, all the dogs in the Zurich study underwent laryngoscopy, where a flexible tube of an endoscope equipped with a camera traveled down the dog’s respiratory tract.  Laryngoscopy requires anesthesia.  The most common abnormality found in the examined Norwich terriers was the occurrence of enlarged tonsils and everted laryngeal saccules.  Out of the 23 Norwich terriers examined, 20 exhibited enlarged tonsils, and 17 had everted laryngeal saccules. Other conditions included narrowed tracheas in 2 Norwich terriers, and one dog was observed with a laryngeal collapse.  The brachycephalic group exhibited a similar rate of incidence of the respiratory tract malfunctions, while all Beagles in the study tested clear.

Based on a rhinomanometry test, the Norwich in the study showed resistance in the air flow indicating stenotic nares (constricted nasal passages). Their occurrence in brachycephalic dogs in the study was higher, and Beagles again showed no restriction in nasal passages. Upon visual observation and taking measurements, only the brachecyphalic dogs showed pinched nostrils. None of the Norwich terriers and Beagles exhibited that condition.  It is important to note that even as their nostrils were of proper size, the Norwiches did exhibit restricted air flow through their nasal cavity as measured by rhinomanometry.

 

Cellular Oxygenation Study at the University of Zurich, Switzerland – Possibly There Is a Biological Marker

While perusing a wonderful online library of research papers at the University of Zurich, I came upon another fascinating study by Dr. Daniel Koch.  The aim of his research was to estimate the tissue oxygen saturation of brachycephalic dogs.  That instantly perked my interest.  Dr. Koch was showing that with the measurement of blood serum VEGF and EPO, an objective grading system can be established for a brachycephalic syndrome. Imagine!  A blood test that would finally show us a degree of oxygen deprivation on a cellular level!  I love numbers.  You cannot skew them with interpretation too easily. Numbers indicating VEGF levels offer a more objective grading system than an interpretational test, like a visual examination, not to mention being a much less invasive and costly alternative to laryngoscopy.

VEGF (interestingly pronounced “veg-F”) stands for “vascular endothelial growth factor”, a signaling protein that I like to call “a messenger of bad news”. In human medicine VEGF has been implicated with poor prognosis in breast cancer. In rheumatoid arthritis it indicates swelling, and also stimulates angiogenesis (the formation of capillaries). In diabetic retinopathy, VEGF is heralding changes which may threaten the sight.  Whenever VEGF levels rise, it’s always bad news. EPO stands for erythropoietin, a hormone regulating red blood cell production. EPO is “the good guy”.

The authors of the study took a few assumptions, namely that hypoxia (shortage of oxygen in the body) induces the release of VEGF, and lowers the production of EPO.  The methods used in the study were serum VEGF and EPO levels measured before physical exercise, and then 4 hours after it.  Subjects of the study were 8 brachycephalic dogs and 8 mesocephalic dogs.

Findings:

 In the brachycephalic group there was a significant increase from the initial level of VEGF to the 4 hours-mark level, and from the control group at 0 hour.

Initial EPO values were lower in the brachycephalic group than in the mesocephalic group, but the level changes were not as significant as in VEGF tests.

The measurement of the VEGF values before and 4 hours after a short physical exercise, offers an instrument to estimate the oxygen saturation. Similarly, dogs that underwent corrective surgeries can be evaluated by measuring VEGF levels post- exercise to determine the success of the surgery.

Interestingly, the paper specifically lists a number of mesocephalic breeds that can benefit from this test, among them Norwich terriers.

VEGF as an indicator of hypoxia is a brand new concept, but it is being picked up by more and more research teams.  I have found numerous researches on human hypoxia and VEGF levels, for example: the paper by researchers from Veterinary Biomedical Sciences at the University of Saskatchewan, in Canada, dealing with barn disease, and a number of other studies on hypoxia at high altitudes. What it means to us, dog fanciers, is that there is a real possibility on the horizon of bringing a noisy breather for a simple blood test, which would show the level of VEGF (a biological marker for Upper Airway Syndrome).  For now, we have to rely on more traditional, and more invasive diagnostic methods: endoscopy of the respiratory tract, rhinomanometry,  and radiographs of the thoracic area for the evaluation of trachea.

One thing we have to unfortunately resign to is the fact that Upper Airway Syndrome is a disease affecting many more breeds than initially thought.  It is not a “Bulldog thing”. I vividly remember conversations years ago between breeders of Norwich terriers sharing amusing stories of “Norwich noises”.  Sadly, what we took for endearing quirks of our breed, the snorting, the “piggy noises”, snoring during sleep, were all the telltale signs of the trouble brewing in the breed.  While Norwich fanciers struggle to come up with a coherent grading system for Upper Airway Syndrome to establish sound breeding practices, may other breed fanciers learn from our experience and take the funny “piggy noises” seriously, even if their breeds are not brachycephalic.

 

 

Magda Omansky