Asthma is an inflammatory respiratory disease that causes narrowing of the lung’s airways. More than 80 million cats currently live in American homes, and veterinary epidemiologists estimate that 800,000 or more of these animals – one percent or so of the nation’s domestic feline population – suffer from acute or chronic asthma. Although this condition – the most commonly diagnosed respiratory disorder in cats – is not curable, veterinary researchers are making progress in understanding its causes and devising methods for its effective treatment.
Asthma is a disease characterized by contraction of the small airways of the lungs. These airways can also become clogged or closed off by the accumulation of mucous. (Cats produce a particularly thick and sticky mucous in their lungs compared to dogs or humans.) Narrowed airways means less air, and thus oxygen, makes it into the lungs and on into the bloodstream.
The narrowing of the airways occurs when a cat’s immune system overreacts to the presence of an allergen and responds by releasing chemical messengers that cause inflammation and swelling of the sensitive lining of the bronchi, as well as contraction of the surrounding muscle.
An Asthma Attack in Detail:
· First, excess mucus forms. Then the airway walls swell with inflammation and can actually ulcerate. Finally, the airway muscles go into spasm, which leads to constriction.
· Airway constriction leads to inability to draw a deep breath, intolerance to exercise, coughing, and musical sighing sounds called wheezes. Not all these symptoms may be apparent at the same time. Sometimes a low-grade chronic cough is the only symptom.
· An acute asthmatic crisis can arise at any time and can be a life-threatening event. Asthmatic airway constriction can happen spontaneously or as a type of allergic reaction.
· When it comes to treatment, relieving and preventing airway constriction is essential.
Allergens may include tobacco smoke, dusty kitty litter, vapors from household cleaning solutions or sprays, pollen from trees, weeds or grass, mold and mildew, dust mites, smoke from fireplaces and candles, and even some foods. A study in Europe years ago revealed that 80% of respiratory disease in pets occurred in households with smokers.
The thick mucous that accumulates in an asthmatic cat’s lungs can trap bacteria. It also prevents the cilia, the tiny hairs that line the respiratory tract, from sending bacteria, debris and pollen back up and out, to be coughed up and swallowed like a normal airway can do. Bacterial infections of the airways (i.e. bronchopneumonia) are a common complication experienced by asthmatic cats.
A typical asthma attack occurs as follows: “The cat is at rest, not doing anything at all, or else it’s playing and suddenly stops. Its breathing becomes more rapid, and the cat starts trying to take in air with its mouth open. Its chest and abdomen move up and down abnormally, the breathing is shallow and rapid. And if you listen closely you may be able to detect a wheezing sound as the cat exhales.” Some cats will also cough.
Not sure whether your cat’s symptoms fit the description of asthma? Visit www.fritzthebrave.com, a website dedicated to cats with asthma. There are videos on the site of cats with asthma symptoms.
Dr. Goldstein classifies the severity of asthma attacks in the following four categories: (1) mild (the symptoms occur intermittently – but not daily – and they do not interfere with the cat’s lifestyle); (2) moderate (the symptoms do not occur daily, but when they do, they are more severe and debilitating, and they interfere with the cat’s activities); (3) severe (significantly debilitating symptoms occur daily); and (4) life-threatening (bronchial constriction results in potentially lethal oxygen deprivation, which causes normally pink tissues, such as the lips and nose, to turn blue).
At this point you have an emergency situation, and veterinary care is mandatory. In fact, he points out, veterinary counsel should be sought at the earliest stage. If the initial mild signs are ignored the condition can rapidly progress to the more severe stage. Then the cat may die unless emergency treatment is immediately obtained.
The first diagnostic step is a thorough physical exam, during which the veterinarian will initially use a stethoscope to locate the specific source of the wheezing while also attempting to rule out any heart or lung problems that may be causing the respiratory difficulties.
Next, the cat’s blood may be tested to look for a suspiciously high concentration of white cells called eosinophils, which are associated with an allergic response. Heartworm disease can also be a cause of asthma-like symptoms.
Lungworm is not a common parasite but can be an underlying cause of airway inflammation. Stool sample testing or deworming may be recommended for cats with wheezing or coughing.
Asthma can be difficult to diagnose when it’s mild or in the early stages. Chest x-rays (i.e. radiographs) are our best diagnostic tool but, unfortunately, some cats with asthma have normal radiographs. Radiographic signs will be more dramatic if the cat is having an asthma attack when the picture is taken or if symptoms are severe or chronic.
Classically, the chest radiograph will show what is called air-trapping. This means that the small airways have constricted to the extent that inhaled air cannot be exhaled. The lungs are larger in appearance than normal as they are over-inflated. The diaphragm may seem flattened due to this over-inflation.
Inflammation and mucus build up within airways, causing their walls to appear thickened in the radiograph. The terms used for such airway appearance are donuts, named for the appearance of the airways when viewed in cross-section. When viewing the airway from the side they look like double parallel lines, sometimes referred to as tramways. You may hear your veterinarian use these terms as they are classical findings in airway disease.
The right middle lung lobe is the first lobe to branch off ventrally (toward the breastbone) from the main bronchus. Airway contaminants such as pollen, along with mucous, tend to flow down to this lung lobe. Thus the right middle lobe is often the worst affected and may even collapse or shrink down into a non-functional part of the lung. On a lateral view, like the radiograph above, the right middle lung lobe is obscured by the heart Two x-ray views are usually needed in order to see all of the lung lobes. In a ventral-dorsal view with the cat laying on its back, the right middle lobe can easily be seen, as in the diagram below.