Hypertension can be difficult to diagnose in cats. The stethoscope (listening) method used to diagnose hypertension in people cannot be used in cats. A Doppler device is needed to detect blood flow or a special instrument that measures oscillations in the blood vessels must be used. Excitement can artificially raise blood pressure, just as it does in people (white coat effect). Cerebral or brainstem vascular injury can cause swelling (edema) or the bleeding into the brain that is also called a stroke. Clinical symptoms include abnormal behavior, depression, neurological deficits, head tilt, seizures and coma.
The diagnosis of hypertension requires close attention to the technical aspects of blood pressure measurement such as selection of the appropriate cuff size and assuring uniform compression of the artery.
When there are associative clinical signs or diseases related to hypertension, a high blood pressure measurement is of great significance. In the otherwise healthy cat, diagnosis should be approached cautiously so as not to label a healthy, but perhaps excited, pet as hypertensive.
The underlying cause of hypertension must be addressed. Known causes include: chronic kidney diseases, hyperadrenocorticism (Cushing's disease), hyperthyroidism, tumors of the adrenal gland (pheochromocytoma/adrenocortical tumor), drugs such as those used to treat urinary incontinence in cats and central nervous system disorders.
Hypertension can also develop from diseases of the endocrine organs. Diseases of the adrenal gland are particularly common in cats and have been associated with hypertension. One example is Cushing's disease, which may be controlled by medication.
Some cases of hypertension are idiopathic or essential, which means they have no known cause.
Hypertension can cause serious injury to target organs including the brain, eyes, heart, kidneys and blood vessels in these and other organs. These changes can include:
Retinal edema (swelling) or hemorrhage and retinal detachments (separation of the layers) can lead to sudden blindness. Sudden blindness may also develop consequent to bleeding into the eye, known as intraocular hemorrhage or hyphema.
Elevated blood pressure increases the work of the heart. Frequently, a murmur or extra heart sound, an atrial gallop, will be heard with the stethoscope in cats with hypertensive heart disease. Left ventricular thickening (hypertrophy) and heart enlargement (cardiomegaly) are indications of chronic hypertension. These changes can be identified by an echocardiogram (most sensitive), electrocardiogram or thoracic radiograph (least sensitive). Coronary arteries also are injured from high arterial pressures. Heart failure stemming from hypertensive heart disease is exceedingly rare. In cats with chronic valvular heart disease, hypertension increases the risk for development of congestive heart failure.
Kidney disease is one of the most common reasons for high blood pressure. Glomerular disease is especially associated with hypertension. High blood pressure continues to injure the kidneys creating a vicious cycle.
Injury to blood vessels or direct transmission of pressure across the microscopic blood vessels and capillaries is responsible for many of the clinical signs of hypertension.