Hypertension is a medical term that means high blood pressure. The most common clinical presentation of feline hypertension is sudden blindness. This occurs because high pressure in the blood vessels of the retina causes the retina to detach. Affected cats have widely dilated pupils that do not constrict when exposed to bright light.
Most cats with hypertension have an underlying illness responsible for its development – kidney disease, heart disease and hyperthyroidism are the three most common diseases associated with high blood pressure. In rare circumstances, primary hypertension, high blood pressure without an associated or underlying cause, can occur. The diagnosis is made by measuring the blood pressure and treatment is usually initiated if the elevation is severe or if symptoms due to the high blood pressure are present.
Because hypertension is commonly associated with an underlying cause, the clinical signs seen in an individual cat are often due to the disease that causes the elevated blood pressure. Examples of possible symptoms associated with the underlying disease of renal (kidney) failure include lethargy, anorexia, weight loss, polydipsia (excess thirst), polyuria (excess urination) and vomiting. Clinical signs of hyperthyroidism, another disease associated with high blood pressure, include weight loss, vomiting, polydipsia and polyuria. Signs due to hypertension itself vary and may range from no clinical signs to ocular abnormalities, neurological abnormalities, such as seizures, collapse and abnormal behaviour secondary to complications from haemorrhage may also occur.
The diagnosis is made by documenting elevated readings during blood pressure measurement. Once the diagnosis is established, other pieces of information are important in assessing feline hypertension. A complete blood count, chemistry profile, urinalysis and thyroid hormone level will detect evidence of kidney failure, hyperthyroidism and other complicating disorders. Heart murmurs are often heard and additional heart changes, such as an abnormally rapid heart rate or the presence of an extra heart sound are also common.
Many different types of drugs can be used to treat hypertension. Diuretics decrease blood volume, which in turn can decrease cardiac output. A class of drugs called beta-blockers can be used to decrease blood pressure. These drugs help lower heart rate and, in turn, lower cardiac output. Finally, calcium channel blocking drugs may be used to decrease cardiac output and blood vessel resistance, thereby lowering blood pressure.
Once treatment is started, blood pressure should be re-evaluated to see if it is improving. In addition, it is important to ensure that the blood pressure has not dropped too low. Other follow-up procedures depend on the presence of additional diseases.
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