Friday, February 17, 2017

Body Parts - The Lungs

Body Parts – The Lungs


In this post, I’m going to shout about the kitty lungs, because there’s a lot to shout about.  Feline lungs are remarkably similar to your own lungs.  For example, the lungs occupy most of the space in the chest cavity, lying on both sides of the heart, just like they do in humans. 

In my mind, I think of the lungs as being divided into two portions – the airways, and the lung tissue. An easy way to understand it is to imagine a tree in full bloom.   The trunk of the tree is like the trachea (windpipe).  Imagine the trunk goes up a bit, and then divides into two big branches.  Those are the main bronchi.  Those big branches give rise to smaller branches. Those are the bronchioles.  Those branches divide into smaller and smaller branches, which is exactly what happens to the bronchioles in the lungs.  Finally, think of the leaves that grow on all of the small branches as the lung tissue that surrounds the little bronchioles. Get the picture? The trunk, branches and twigs are the airways; the leaves are the lung tissue. 




You can break down the function of the lung into two main jobs:  ventilation and perfusion.  Ventilation is breathing – the movement of air in and out of the lungs.  Perfusion is the process by which the lung absorbs oxygen from the air into the blood stream and exchanges it for carbon dioxide, which is exhaled into the environment.  Most of the time, ventilation and perfusion are both happening correctly and simultaneously, allowing the blood to receive the proper amount of oxygen for delivery to the vital organs.

When something goes wrong with the lungs there could be an airway problem, which can affect ventilation, or a problem with the lung tissue itself, which can affect perfusion.  For example, a common lung disorder in cats is bronchitis.  Infectious bronchitis is due to an infection (usually bacterial) of the airways.  The infection causes impaired flow of air through the airways. This affects ventilation.  Asthma is a type of bronchitis caused by an allergy to something in the environment.  When a cat breathes in an allergen, it causes the airways to constrict.  It becomes harder for air to pass through these narrowed airways.  The cells lining the airways become irritated by the allergen, and they will produce mucus, which may plug the already narrowed airways.  Clearly, asthma affects ventilation.  Infectious bronchitis is treated with antibiotics.  Asthma is treated with anti-inflammatory drugs and drugs that dilate the airways, making it easier to breathe.  Of course, the best treatment for asthma would be to remove the offending allergen from the environment (cigarette smokers, take the hint), although identifying the allergen can be difficult.
 
An example of a problem with the lung tissue itself would be a bacterial infection of the lungs.  This is called pneumonia.  When the lung tissues get infected and the lung fills with pus, it prevents oxygen from being absorbed into the bloodstream and carbon dioxide from being removed.  Another condition affecting the lung tissue is pulmonary edema.  In this disorder, the lung fills with fluid, which impairs perfusion similar to the way pneumonia does.  Pulmonary edema usually occurs as a result of heart failure.  Pneumonia is treated with antibiotics.  Pulmonary edema is treated with diuretics – drugs designed to remove the fluid from the lungs.  If heart disease is the cause, medications to treat the heart are administered as well. 

How do we know that a cat is experiencing a lung problem?  A primary clinical sign of a lung problem is coughing.  Hey, wanna drive a veterinarian crazy?  Tell him that your cat is trying to “cough up a hairball”.  Hairballs come from the stomach.  Cats vomit up hairballs; they do not “cough” them up.  If your cat hunkers down, extends his neck, and makes several raspy throat-clearing sounds, he is coughing, and it is not a hairball.  It is likely asthma or bronchitis.  Another sign of lung disease is labored breathing.  The medical term for this is dyspnea (DISP-nee-uh).  If your cat is lying around relaxing, but his chest is moving as if he’s just done a few laps around the jogging track, there’s probably a lung issue going on.  He needs veterinary attention immediately.  Like, now. 

Here’s another way to drive your veterinarian batty: tell him your cat has been “wheezing”.   Wheezing is the sound of air trying to flow through narrowed airways in the lungs.  It’s something you hear when you put a stethoscope up to a cat’s chest.  When I’m told a cat is wheezing, I instinctively think “lung problem”.   When a cat owner says “wheezing”, they probably mean stertor, which is noisy breathing that occurs during inhalation.  It’s a low-pitched sound. In other words, your cat is snoring.  This is not a lung problem.  Another possibility that the cat has a blockage of the nasal passages (simply put, a stuffy nose), resulting in high pitched, noisy breathing.  This is called stridor.  Because wheezing usually means lung disease and lung disease is sometimes an emergency, don’t say your cat is wheezing.  It freaks us out.  Say your cat is congested or has noisy breathing instead.  I (and thousands of veterinarians) thank you.



Sunday, February 5, 2017

Body Parts - The Feline Bladder

Body Parts – The Bladder


In a past blog post, I described the important role the kidneys play in a cat’s overall health.  In addition to making hormones and regulating the blood pressure, the kidneys filter toxins from the bloodstream, creating urine in the process.  So where does that urine go after it is manufactured by the kidneys? Anyone who’s waited in line for the bathroom at a baseball game knows, it’s the bladder!

The bladder is a muscular organ found in the pelvic region of the abdomen.  Unlike the multitalented kidney, the bladder has one task, and one task only:  to store urine.   Once the bladder reaches a certain degree of distention, nerves in the bladder send a signal to the brain that it’s time to urinate, and the cat trots off to (hopefully) the litter box.

Inflammation of the bladder – cystitis – is one of the most commonly diagnosed feline disorders.   There are several characteristic signs of bladder inflammation in cats:  frequent trips to the litter box (pollakiuria); straining to urinate (stranguria); urinating in inappropriate places (periuria); and presence of blood in the urine (hematuria).  Cats with cystitis may show any or all of the signs described above.



 
There are many potential causes of cystitis.  Bacterial urinary tract infections (UTIs) are a common cause.  Female cats, longhaired cats, diabetic cats, and cats with kidney disease are at increased risk for acquiring UTIs.  The formation of crystals in the urine (crystalluria) may lead to cystitis.  The crystals can irritate the delicate bladder lining, resulting in inflammation.  Bladder stones (cystic calculi) are another common cause of cystitis.  Crystals in the urine may coalesce to form a small stone (or multiple stones). The stones usually cause severe irritation to the bladder, and cats often show all of the symptoms described earlier, most notably blood in the urine.  Tumors of the bladder do occur, but thankfully, they are an exceedingly rare cause of cystitis in cats.

Diagnosing the cause of a cat’s cystitis requires a few specific diagnostic tests.  The most basic of these are a urinalysis, urine culture, and an x-ray.  Ideally, the urine should be obtained in a sterile fashion so that a urine culture can be performed at the same time.  Urinalysis allows us to assess the urine for the presence of red blood cells, white blood cells, and crystals.  Sometimes, bacteria are seen microscopically in the urine, confirming a diagnosis of a UTI.  However, if bacteria aren’t identified on a urinalysis, it does not mean that a UTI isn’t present.  Culturing the urine is the gold standard for confirming the presence of a UTI.  Even if bacteria are seen on a urinalysis, a culture should be performed.  A urine culture identifies exactly which bacterial species is causing the infection and which antibiotics would be most effective against it.   An x-ray should be taken to see whether a bladder stone is the cause of the cystitis.  Most bladder stones are radio-opaque, meaning that they will be visible on an x-ray.   

Sometimes, when evaluating a cat with symptoms of cystitis, the x-ray shows no stones, the culture shows no infection, and the urinalysis shows no crystals.  All the urinalysis reveals is the presence of blood.  We call this condition “idiopathic cystitis”, which is a fancy medical way of saying that there is no known cause for the bladder inflammation.  In fact, this is the most common cause of cystitis in cats. 

In the past few years, it has been recognized that idiopathic cystitis in cats closely resembles a type of cystitis commonly seen in women, called interstitial cystitis.  The term “feline interstitial cystitis (FIC)” is now thought to be a more appropriate term than idiopathic cystitis.

The treatment of cystitis is dependent on the cause.  Urinary tract infections are treated with antibiotics.  Crystals in the urine can be controlled or eliminated by feeding prescription diets designed for this purpose.  These diets are restricted in the minerals that comprise the crystals, and they are formulated in a way that results in the urine having a pH between 6.2 and 6.6, which is ideal for preventing crystal formation.  Bladder stones may have to be removed surgically, however, depending on the mineral composition of the stone, it may be possible to dissolve the stone by feeding a severely mineral restricted, highly acidifying prescription diet for a few weeks.

Feline interstitial cystitis is the most common cause of cystitis in cats, and often the most challenging to treat, because no specific cause has been identified.  Over the past decade, however, research at The Ohio State University has revealed that environmental stress often plays a substantial role in the development of FIC in cats.  Indoor cats frequently find themselves without acceptable outlets for their natural instinctive behaviors such as hunting for food, hiding from predators, and scratching.  The stress of this lifestyle can manifest in several ways, such as development of FIC.  The Ohio State University has developed The Indoor Pet Initiative, a program designed to advise pet owners on how to modify and enrich the environment for indoor cats, alleviating many of the stresses that can lead to illnesses like FIC.  As a feline practitioner, I strongly support the sensible suggestions offered.  With stress-related illnesses, preventing the problem from occurring is a much wiser approach then trying to remedy the problem after it becomes established.  For more information on environmental enrichment for indoor cats, visit the Indoor Pet Initiative website at https://indoorpet.osu.edu/home




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