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High Blood Pressure in Your Dog or Cat
- Hypertension -

  Read a more complete list of the causes of high and low blood pressure in your pet here

Ron Hines DVM PhD

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Until rather recently, veterinarians would rarely measure your pet’s blood pressure. This is because the standard arm cuffs used on humans just didn't’t work well on dogs or cats. But with easier access to specialized equipment, obtaining this important measurement has become much more common.

What Does High Blood Pressure Do To My Pet?

High blood pressure or hypertension is a stealthy disease in all creatures. That is, there are few or no signs that there is a problem until after damage has occurred. Any area of the body that is rich in small blood vessels will be damaged by hypertension. The tiny arteries in these areas were only designed to hold a specific pressure. When blood pressure becomes too high, they burst or leak causing damage to the tissue that surrounds them. Pets do not seem to suffer the type of strokes humans do that are brought on by high blood pressure. Instead, your pet’s kidneys and eyes are more likely to be damaged. Occasionally, conditions that limit blood flow to the kidneys actually cause the hypertension. Whichever the case, the majority of dogs and cats with kidney problems also have some degree of elevated blood pressure.

Most vision loss in older pets is due to age-related clouding of the lenses of the eye (cataracts). But occasionally, high blood pressure causes blindness in pets by destroying cells in the retina. Your veterinarian’s eye exam might detect unusually “snaky” arteries, retinal swelling and retinal detachments – all of which can be signs of high blood pressure. In about half the cases in cats, the hypertension of hyperthyroidism is the underlying cause of these eye changes. This is often a problem in older cats.

When you pet’s blood tests show an elevated blood urea nitrogen (BUN) or creatinine level - both possible signs of kidney damage – a check of it’s blood pressure is also a good idea. The two problems often go hand in hand.

Dogs with over active adrenal glands are also subject to high blood pressure as are pets with diabetes. If a routine health examination of your pet detects high blood pressure (not due to excitement), there is probably already an underlying health problem causing it. In contrast, humans often develop high blood pressure with no initial underlying health problem. It is only when the problem in humans remains untreated that problems later develop.

Many veterinarians are now screening older (7yr+) pets for high blood pressure during their yearly health examinations. Other than because of advanced age, it is a good idea to have your pet’s blood pressure checked if abnormalities are detected in the retinas of your pet’s eyes. Any time your pet appears to be unable to see clearly, have the deep portions of its eyes examined. That is how retinal abnormalities are detected. We think that high blood pressure in pets also increases their risk of forming small blood clots. These are most serious when they form in the brain (strokes). Damage to the body due to high blood pressure is not limited to the kidneys, eyes and brain, the heart and liver are often also affected.
It is most noticeable in those organs, but it is unhealthy for all of your pet’s body and is a contributing factor in many common disease of dogs and cats.

How Is My Pet's Blood Pressure Measured?

The cuff and stethoscope method your doctor uses on you, will not work on your pet. The cuff portion works as well on your pet’s lower front leg or tail, but one can not hear the sounds of the passing blood adequately through a human stethoscope. Hair, variations in arm size, motion and different blood vessel anatomy all prevent this. But it was found that a sensitive sound- sensing machine called a Doppler is accurate enough to pick up the first or systolic sound in your pet. It will not detect the second or diastolic sound – so we usually rely on only the systolic reading. There are ways to obtain the second number (diastolic) but at the present time, this is quite complicated. Getting an accurate systolic reading can be tricky. It requires an experienced technician. Often the hair below the instrument must be clipped. I prefer that the owner be present to reassure the pet and keep it calm. We set up the apparatus in advance and try to keep noise in the waiting and exam rooms to a minimum.
Newer, less complicated non-doppler methods to measure both systolic and diastolic pressure are being developed (oscillometric meters). But so far, they do not work well in pets weighing less than 15 pounds.

Many veterinarians feel that a dog or cat’s systolic blood pressure should not be over 170 mm. If the pet is relaxed, dogs probably should not exceed 150mm and a cat’s systolic pressure should not exceed 160 mm. But the inaccuracies of the Doppler technique and breed and temperament differences make precise normal figures impossible to give at this time. If diastolic pressure is accurately obtained, it should not exceed 83 or 100 mm in dogs and cats respectively. We think that when systolic pressure reaches 180, some degree of organ damage will occur in your pet.

Your pet may become frightened at the animal hospital. This needs to be considered because it can falsely elevate blood pressure in normal animals. Some call this the “white coat effect”. With repeated measurements (up to 8) pets tend to become accustomed to the process and not fear it. But this is not always the case.

We can’t just give your pet a tranquilizer, because tranquilizers may lower the reading. So many vets discard the highest and the lowest reading they obtain and then make an average of the rest to come up with a value. Sight hounds (greyhounds, afghans, etc) overweight and older animals tend to have higher readings.

What Signs Might I See In My Pet To Indicate High Blood Pressure?

There is no pain associated with high blood pressure so the indications, if any, will be subtle or absent. A rapid heart rate, blood surging into the collection tube, dilated pupils, vision problems, an enlarged thyroid gland, lumpy kidneys, nose bleeds, and blood in the urine might be clues. But they all can have many causes not related to blood pressure. In most cases, your veterinarian detected signs of another disease known to cause hypertension or has picked up on it through routine blood pressure screening. If your pet is a cat, the diagnosis may have been hyperthyroidism based on a blood analysis, age, vision problems, behavior and weight loss. If your pet is a dog, it may be signs associated with diabetes, the kidneys or adrenal glands.

What Should I do If My Pet Has High Blood Pressure?

The first thing to do is to redo the test, preferably in a different setting, so that we can eliminate fear/stress as the cause. If it is still high on repeated tests, some other tests need to be run to identify the underlying cause of the hypertension.

The most common medication used to treat high blood pressure in pets is enalapril. This drug belongs in a group of drugs called ACE-inhibitors. It has been used for years to lower blood pressure and ease the work of the heart in humans as well. It was marketed as Vasotec for humans and Enacard for pets, but it is now off-patent and available in inexpensive generic forms. Similar medications in the same class are linisopril (Zestril,Prinivil), benazepril (Lotensin) and captopril (Capoten).

When enalapril is not sufficient, a second medication called Amlodipine (Norvasc) is often tried. Amlodipine is often the first choice in cats. This drug is in a group called calcium channel blockers and is a standard in human medicine. Another in this class is diltiazem (Cardizem, Dilacor, Tiazac) It can be quite difficult or impossible to get cats to swallow these small pills and even if they do, they may get stuck half way down to the stomach. But they can be crushed and mixed with a paste or a liquid given orally by syringe. These drugs have occasionally improved vision in cats with high blood pressure. When receiving channel blockers, kidney function should be monitored.

Another group of drugs that may help reduce blood pressure in cats and dogs are the beta-adrenergic blockers , propranolol (Inderal) and atenolol (Tenormin). They work by decreasing heart rate.

Diuretics such as furosemide (Lasix) and spironolactone (Aldactone,etc.) may also be employed to decrease blood volume and in so doing, lower blood pressure as may the vasodilator, hydralazine (Apresoline).

Some veterinarians also recommend a low salt diet for your pet. This may decrease water retention and blood volume and, through that, lower blood pressure. But there is less evidence than in humans that a low-sodium diet helps pets. There is certainly no harm in trying. Specialty diets designed for failing kidneys are also sometimes suitable.

Many veterinarians will begin your pet on amlodipine and enalapril and suggest you moderately restrict the amount of salt your pet receives. If your pet’s blood pressure returns to normal, these medications can be given indefinitely. If they are not sufficient, atenolol is added and if that is still insufficient, a diuretic is added. However, individual veterinarians suggest different regimens that worked best for them in the past.

I suggest you have your pet’s blood pressure rechecked three weeks after beginning any therapy or changing dose and then three or four times a year.

Most pets that have high blood pressure have one of the following underlying problems that will need care:

1) Chronic Kidney Disease
Studies have found that over 90 % of dogs and over 60% of cats with failing kidneys also have high blood pressure. We detect this disease when pets begin to drink excessively. We confirm the diagnosis based on elevated blood urea nitrogen and creatinine levels as well as the presence of large amounts of protein in the urine. It is unclear how many pets develop kidney damage because of high blood pressure and how many develop high blood pressure because of kidney damage. Both are known to occur. If high blood pressure is detected in your pet, its BUN and Creatinine levels need to be checked to evaluate the condition of its kidneys. Seriously damaged kidneys spill protein into the urine. In advanced cases, the protein can be detected in the urine. But in dogs and cats with high blood pressure, a second test that detects earlier damage should be performed. It is called an ERD test (early renal damage) test and it detects very small amounts of albumin (microalbuminuria) in your pet's urine - a sign of early kidney damage.

2) Over-active Thyroid Gland
Hyperthyroidism is most common in elderly cats. The majority of cats that develop this disease also develop high blood pressure (87%). Medications that decrease the amount of thyroid hormone in your cat’s blood should also help lower its blood pressure. But the ideal therapy, radioactive iodine treatment, can be prohibitively expensive if you do not have pet health insurance. A compounding problem is the large number of cats with hyperthyroidism and high blood pressure that have hidden kidney problems masked by the primary thyroid disease.

3) Over-active Adrenal Glands
Cushing’s disease or hyperadrenalcorticism causes an excessive amount of cortisone hormone to be secreted by the adrenal glands. This is primarily a problem in middle-aged dogs. Cortisone has many deleterious effects when its level in the body is too high.

4) Diabetes
When your pet’s pancreas can no longer produce insulin, a number of things happen in addition to high blood sugar. One effect of uncontrolled diabetes is damage to your pet’s kidneys. We do not fully understand why kidney damage leads to increased blood pressure in your pet. But it probably has to do with certain kidney hormones (rennin and angiotensin) which increase blood pressure in several ways.

Treatment for high blood pressure in pets is constantly being refined. As in people, high blood pressure needs to be attended to.