Hypertension in cats is usually a secondary problem. Chronic renal failure is generally regarded as the most common cause of hypertension, with studies reporting anywhere from 20 to 61 percent of all cats with renal failure also suffering from hypertension. The second most common cause is hyperthyroidism. About 87 percent of all cats with hyperthyroidism also have hypertension.
The normal blood pressure for a cat is about 124 mm Hg. Older cats normally tend to run higher than this. Any cat with a reading over 150 should be checked carefully. (Since cats have such small arteries, most techniques simply involve taking a systolic reading. The 124 compares to the first number generally seen in blood pressure reports for humans.)
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Cats with hypertension may have damage to the eyes, kidneys, heart, and nervous system because these organs are not receiving the appropriate blood flow. Some cats will initially be diagnosed after retinal damage is found on an exam or a cat suddenly goes blind. Enlargement of the heart, with corresponding murmurs, may be noted.
Kidney failure and hypertension aggravate one another in a vicious cycle, leading to a faster progression of kidney failure. Neurological signs, such as ataxia or even seizures, may be secondary to hypertension.
Hypertension is diagnosed by using a small blood pressure cuff on either the forelimb or the base of the tail. An ultrasound probe may be used as an adjunct to detecting the pulse.
Treatment: Treatment involves the use of ACE inhibitors, such as enalapril and amlodipine, a calcium channel blocker-both medications are used in humans. Cats with acutely high blood pressure may need a single treatment with sodium nitroprusside, which rapidly lowers blood pressure. This must be closely monitored or the pressure can drop too low and leave the brain without adequate blood flow. Cats with hypertension should have regular rechecks to evaluate the success of their medications. Once hypertension is controlled, it is possible that some damage to the vision may correct itself.
WebMD Veterinary Reference from "Cat Owner's Home Veterinary Handbook"