Ron Hines DVM PhD
Read a more complete list of the causes of high and low blood pressure in dogs and cats here
In cats, the leading cause of high blood pressure is hyperthyroidism
Kidney Disease can be both the cause and the result of high blood pressure
Until recently, veterinarians would rarely measure your pet’s blood pressure during a check-up. That is because the standard arm cuffs used on humans just don’t work well on dogs or cats. But now, with easy access to specialized equipment designed specifically for cats and dogs, obtaining this important health 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 brewing until after some degree of damage has already occurred. Your dog or cat experiences no pain, no change in mood or appearance. Your pet’s appetite does not change. Physical exam and blood work results remain normal until the problem has been present for quite some time.
Any area of your pet’s body that is rich in small blood vessels (capillaries, arterioles, venules) has the potential to be damaged by hypertension. These tiny blood vessels were only designed to hold blood traveling at low pressure. When blood pressure becomes too high, they burst or leak causing damage to the tissues that surrounds them. Pets rarely if ever suffer the type of bleeding strokes humans do – the kinds that are brought on by high blood pressure in the brain. Instead, your pet’s kidneys and eyes are more likely to suffer damage. Occasionally, things reverse. Health issues that limit blood flow to your pet’s kidneys actually causes the hypertension. (ref) Whichever the case, it is quite common for dogs and cats with kidney problems also have some degree of elevated blood pressure.
Most vision loss in older dogs and cats is due to age-related cloudiness of the lenses of their eyes (“cataracts” actually, the correct term is lenticular sclerosis). But occasionally, high blood pressure causes blindness in dogs and cats by destroying cells in their retinas. Your veterinarian’s eye examination might detect unusually “snaky” arteries, retinal swelling or retinal detachments – all of which can be brought on by high blood pressure. Some veterinarians believe that in about half these cases in cats, the hypertension of hyperthyroidism is the underlying cause of these eye changes. Hyperthyroidism is a common problem in older, lean cats.
When you pet’s blood tests show an elevated blood urea nitrogen (BUN) or creatinine level – both possible signs of kidney damage – or urine that is too dilute – a blood pressure check is in order. Those problems often go hand in hand.
Dogs with overactive adrenal glands are also at a higher risk for high blood pressure. So are pets with diabetes. If routine health examinations of your pet repeatedly detect high blood pressure (not due to excitement), there is probably already an underlying health problem causing it. In contrast, it is common for us humans to develop high blood pressure with no detectable underlying health problem found responsible. It is only when high blood pressure in humans remains untreated that problems later develop.
Many veterinarians now screen all older (~7yr+) dogs and cats for high blood pressure during their yearly health examinations. In older cats, they may just suggest a thyroid hormone level assay and follow up with a blood pressure check when that level is abnormally high. It is also a good idea to have your pet’s blood pressure checked when abnormalities are detected in the retinas of your pet’s eyes. Any time your cat or dog appears to be unable to see clearly, ask your vet to examine the deep portions of its eyes and check its blood pressure. Some veterinarians believe that high blood pressure in pets also increases their risk of forming small blood clots.
How Will My Pet’s Blood Pressure Be Measured?
As I mentioned previously, the cuff and stethoscope method your doctor uses on you, does not work well on your pet. The cuff portion works satisfactorily on your pet’s lower front leg or tail, but veterinarians cannot hear the sounds of the passing blood adequately through the type of stethoscope your doctor and they use. Hair, variations in arm size, motion and different blood vessel anatomy all interfere with that. But it was found that a sensitive sound-sensing machine called a doppler will pick up the passage (motion) of rushing blood. It is accurate enough to pick up the first or the systolic pressure sound (the higher number) when evaluating your pet. Read about that device here and here. It will not detect the second or diastolic pressure sound accurately – so veterinarians in general practice rely on only the systolic reading. There are ways to obtain the second (lower) number or sound (diastolic pressure) but they are complicated and invasive. Even then, getting an reliable systolic reading in cats and dogs during an animal hospital visit can be tricky. It requires experienced technician assistance and the calculation of the average reading in a series of readings. Sometimes the hair below the instrument must be clipped. It tends to be most accurate when the pet’s owner is present to reassure their pet and keep it calm. At best, it delivers a “soft” number that may or may not be representative of the dog or cat’s true, at-home, blood pressure – any more than your pet’s pulse rate at the animal hospital is representative of its heart rate at home. Both are under control of the same nerves and hormones released during anxiety (the “white coat effect”) and exertion. (ref)
Many veterinarians believe that a dog or cat’s systolic blood pressure should not be higher than 170 mmHg. Others believe that the systolic blood pressure of a relaxed dog should not exceed 150mm or that in a cat, it should not exceed 160 mm. But the inaccuracies of the doppler technique and breed and temperament differences make precise “normal” blood pressure figures quite difficult for me to to give you. When diastolic pressure is accurately obtained (as it might be in a university veterinary facility) it has been reported that it should not exceed 83 or 100mmHg in dogs and cats respectively when they are normal. Most veterinarians believe that when sustained systolic pressure reaches 180, some degree of organ damage is likely to occur in your pet.
We can’t just give your pet a tranquilizer to calm it down. Tranquilizers in themselves have the ability to lower blood pressure readings. So most vets will discard your pet’s highest and the lowest reading they have obtained that day 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 That 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 a collection tube, dilated pupils, vision problems, an enlarged thyroid gland, lumpy kidneys, nose bleeds, and blood in the urine might be clues to your veterinarian that a blood pressure reading is in order. But they have many many other possible causes other than hypertension. In most cases, your veterinarian’s will suspect it because of your pet’s age, evidence of another disease known to cause hypertension or because it was picked up by chance on a routine blood pressure screening. If your pet is a cat, the diagnosis may have been hyperthyroidism based on a blood analysis (T4), its age and physical appearance (lean), vision problems, behavior or weight loss. If your pet is a dog, it may have been signs associated with diabetes or the pet’s 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 your vet can eliminate fear, anxiety and 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 probably enalapril . This drug belongs in a group of drugs called ACE-inhibitors. It has been used for years in humans and animals to lower blood pressure and ease the workload of the heart. Some veterinarians prefer benazepril, a similar drug. Enalapril was marketed as Vasotec® for humans and Enacard® for pets, but it is now off-patent and available in inexpensive generic forms.
When enalapril or benazepril is not sufficient, a second medication called amlodipine (Norvasc®) is often added. For some veterinarians, amlodipine is is their first choice in cats. This drug is in a group called calcium channel blockers . They are used quite commonly in human medicine to treat high blood pressure. It can be quite difficult or near impossible to get cats to swallow these small pills – and even if they do, pills and capsules can get stuck (become lodged in the esophagus) half way down to their stomach causing ulceration, scaring and damage. These medications are best crushed, mixed with a paste or a liquid and then given orally by syringe or compounded by a specialty pharmacy into a more peasant tasting liquid formula. These drugs have occasionally improved vision in cats with high blood pressure. When receiving channel blockers, the pet’s 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 the pet’s blood volume and, in so doing, lower blood pressure. Others suggest the blood vessel dilator (vasodilator), hydralazine (Apresoline®) for the same effect. I have no experience using that drug.
Some veterinarians also recommend a low salt diet for your pet. This might decrease water retention and blood volume and perhaps in that way lower blood pressure. But there is very little scientific evidence than salt-restricted diets have any effect on blood pressure in cats or dogs. There is certainly no harm in trying a moderately salt-restricted diet in your pet if you wish. Specialty diets designed for failing kidneys are suitable in that regard – if your pet will eat them and not loose healthy weight.
There is no one standard protocol or treatment for high blood pressure in dogs and cats. Your veterinarian will suggest the treatment plan that worked best in similar cases for her/him in the past. In pets with confirmed high blood pressure, I suggest you have its blood pressure rechecked three weeks after beginning any therapy or change in 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 require long term care:
Read in detail about this health problem through the link above. Studies have found that over 90 % of dogs and over 60% of cats with failing kidneys also have high blood pressure. Veterinarians often detect this disease when pets begin to drink water and urinate excessively. They confirm the diagnosis based on elevated blood urea nitrogen (BUN) and creatinine (CR) levels in your pet’s blood as well as the presence of large amounts of albumin protein in its urine. The newer SDMA test is valued by some. 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.
Read in detail about this health problem through the link above. Hyperthyroidism is most common in elderly cats. The majority of cats that develop this disease also develop high blood pressure (~87%). Medications or radioiodine treatments that decrease the amount of thyroid hormone in your cat’s blood should also help lower its blood pressure. I prefer, radioactive iodine treatment when it has been confirmed that high blood pressure has not already damaged your cat’s kidneys. That treatment can be prohibitively expensive for many cat owners if they do not already have pet health insurance.
Read in detail about this health problem through the link above. Cushing’s disease or hyperadrenalcorticism causes an excessive amount of cortisone hormone to be secreted by your pet’s adrenal glands. This is primarily a problem of middle-aged dogs. It is considerably less common in cats. Cortisone has many deleterious effects when its level in the body is persistently too high. Some veterinarians associate this disease with generalized endocrine gland dysfunction caused by neutering dogs and cats when they are too young or infants. (ref) You can also look for Dr Karen Becker’s videos about that on YouTube.
Read in detail about this health problem through the cat or dog link above. 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 (renin and angiotensin) which increase blood pressure in several ways. As I mentioned for over-active adrenal gland disease/Cushing’s, some veterinarians associate this disease with generalized endocrine gland dysfunction caused by neutering dogs and cats when they are too young or infants. (ref) Again, check out Dr. Becker’s videos as well.