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




Tuesday, January 24, 2017

Body Parts - The Feline Spleen

Body Parts – The Spleen



Ask most people what their cat’s heart does, and they’ll tell you it pumps blood.  How about the lungs?  They breathe in oxygen and exhale carbon dioxide.  The kidneys? They filter toxins from the blood stream and put them in the urine.  The spleen?  That’s easy.  It… it… 

Admit it: you have no idea what the heck your cat’s spleen does.   Don’t be embarrassed.  You’re in good company.  The average person is clueless about all things splenic.   I think it’s time we shed a little light on this most puzzling of organs.


Here are the basics:  The spleen is a dark red organ that looks like a giant tongue.  It is longer than it is wide, and is covered by a thick fibrous capsule.  It is located near the stomach, on the left side of the body, however, the exact location of the spleen isn’t fixed.  Depending on its size and shape and the size of the surrounding organs, the spleen can migrate around the abdomen and visit the right side of the body.

The spleen performs a surprisingly large number of functions.  For the sake of clarity, I’ve narrowed down what I think are the four most important splenic duties:

·      Production of red blood cells.   Most people probably know that the bone marrow is the primary site of red blood cell production.  Well, the spleen is the next major site.
·      Storage of red blood cells.  The spleen holds a fair amount of blood.  If the body was suddenly in need of extra red blood cells in the circulation, the spleen has the ability to contract, releasing red blood cells into the bloodstream.
·      Filtration.  Think of the spleen as a giant filter that traps and removes old or abnormal blood cells from the circulation
·      Immunity. The spleen traps bacteria, foreign proteins, and other microbes and presents them to cells in the immune system, so that an immune response can be initiated. 

You’d think that with all of these important roles, the spleen would be essential for life.  Surprisingly, it’s not.  It can be surgically removed if necessary, and most animals will be fine.  However, it’s certainly better to have one than to not have one.

Disorders of the spleen are much more common in dogs than in cats.  Splenic disorders can be generally categorized as either primary or secondary.  A primary splenic disorder is one in which the spleen itself is the site of the illness.  The spleen can also be affected secondarily by a systemic disease that is occurring somewhere else in the body.

How do we know when something is amiss with the spleen?  When things go awry, spleen-wise, the spleen usually grows bigger.  Enlargement of the spleen is called splenomegaly.  This is not something a cat owner would be able to detect.  Splenomegaly is usually found during the physical examination, during the part of the exam where the veterinarian carefully presses on the abdomen to feel the internal organs.

Splenomegaly occurs in two forms: localized and generalized.  Localized splenomegaly is where one focal area of the spleen is enlarged.  We call the enlarged part a “splenic mass”.  Generalized splenomegaly is a diffuse enlargement of the entire spleen.  Localized splenomegaly is more common in dogs.  Generalized splenomegaly is more common in cats.

Once splenomegaly is discovered on examination, your veterinarian will recommend some diagnostic tests to help determine the cause.  Blood tests and x-rays may provide important information.  Abdominal ultrasound, however, is an excellent, non-invasive procedure to distinguish localized vs. generalized splenomegaly, and to further define the condition.  In most cases, however, a definitive diagnosis can only be achieved by obtaining a sample of cells from the spleen for analysis.  The sample is usually acquired via fine needle aspiration, a procedure in which a needle, attached to a syringe, is gently inserted into the spleen. Material is then aspirated into the hub of the needle and the contents sprayed onto a microscope slide.  The slide is evaluated by a clinical pathologist.  If this does not yield a diagnosis, abdominal exploratory surgery may be warranted. 

Sadly, infiltration of the spleen with cancer cells is the most common cause of splenomegaly in cats.  The most common cancer affecting the feline spleen is mast cell tumor.  Hemangiosarcoma (a very bad tumor; my cat Crispy died of this tumor) is the next most common, followed by lymphosarcoma. 

Fortunately, disorders of the spleen are much less common in cats, compared to dogs.   When they do occur, the prognosis will vary, depending on the cause.










Friday, January 13, 2017

Body Parts - the Feline Heart





Body Parts – the Feline Heart



            The heart is the main organ in the circulatory system.  Its job is to pump blood throughout the body, supplying oxygen and nutrients to the tissues.  Similar to the human heart, the feline heart has four chambers.  The two chambers on the top of the heart are the atria (plural for atrium).  The two chambers at the bottom of the heart are the ventricles.  The left atrium and left ventricle are separated from the right atrium and right ventricle by a dividing wall called the septum.



            Listening to your cat’s heart with the stethoscope is one of the most important parts of the veterinary exam.  The normal heart rate in a cat is 160 to 240, which is much faster than a human’s.  Cats are often nervous during the veterinary visit, so it’s not unusual to find heart rates in the 200’s.  The rhythm should be regular and the heartbeat should be easily heard.  Abnormalities in the heart rate and rhythm are fairly uncommon.  The most common abnormality heard with the stethoscope is a heart murmur.  A murmur is the sound of turbulent blood flow and may be an indicator that something is amiss.

            Coronary artery disease is the most common cause of death in humans in the U.S.  Fortunately, cats don’t get coronary artery disease. Nature, however, doesn’t play favorites when it comes to other heart diseases, and cats are indeed susceptible to disorders of this vital organ.  Therefore, the discovery of a heart murmur during your cat’s physical examination warrants further investigation.  It can be difficult for a veterinarian to know just by listening whether a feline heart murmur is merely a physiologic finding (i.e. there’s actually nothing wrong with the heart), or a pathologic finding (i.e. there is indeed something wrong with the heart). Physiologic murmurs are benign and can be caused by things such as stress, excitement, pain, or fever.  The only way to tell if a murmur is benign vs. pathologic is to perform echocardiography (sometimes also called a sonogram, or cardiac ultrasound).





            Echocardiography is best performed by a veterinary cardiologist. (Yes, there are veterinarians that specialize in cat and dog tickers only.) These cardiologists know exactly how thick or how thin the walls of each heart chamber is supposed to be, how fast the blood should be flowing as it travels out of the aorta and pulmonary artery, and how strongly the heart is supposed to be contracting.  By viewing the heart using ultrasound and taking a variety of measurements, the cardiologist can determine if heart disease is present.

            The most commonly diagnosed heart disease in cats is a condition called hypertrophic cardiomyopathy (HCM).  In cats suffering from HCM, the walls of the heart become progressively thicker, with one particular chamber, the left ventricle, usually becoming the most affected.  Think of the left ventricle as a coffee mug.  Now imagine the walls of the mug becoming thicker and thicker, growing inwardly.  The mug would hold less and less coffee.  In HCM, the ventricle holds less and less blood.  If the ventricle can now hold only half as much blood, the heart will try to compensate by pumping twice as hard to achieve the same effect.  Eventually, the muscle starts to give out, and congestive heart failure may develop.  Other complications, however, may arise before heart failure ever develops.  The most serious complication of HCM is a condition called aortic thromboembolism, abbreviated ATE.  In ATE, a blood clot develops in the left atrium.  A piece of the blood clot breaks free, travels down the aorta, and gets lodged at the very end, where the aorta branches to supply the legs with blood.  Cats become acutely paralyzed in the rear legs as a result.  This is a truly devastating complication that carries a very grave prognosis.  Sadly, as a feline practitioner, I have the terrible misfortune of seeing two or three cases of ATE a year, and every case ends disastrously. Sigh.  Cats diagnosed with HCM are usually prescribed a variety of medications aimed at slowing the progression of the disorder and reducing the risk of ATE, and many cats do well for many years after the diagnosis with no symptoms at all.

            HCM can strike any breed of cat, however, Maine Coons and Ragdolls are predisposed to the disorder.  Fortunately, the reason for their susceptibility was discovered several years ago: a mutation in the gene that codes for a specific protein in the heart.  A genetic test has been developed to screen cats for the disorder.  The test requires either a cheek swab or a blood sample. Responsible breeders can now test their cats for this mutation, and use selective breeding techniques to hopefully eliminate the gene from the population.

            Kittens will sometimes have a heart murmur that disappears as they mature.  A persistent murmur in a kitten, however, should be investigated, as congenital heart diseases occasionally do occur, and the sooner they are diagnosed and treated, the better the prognosis. 

           

           


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