Hypertension, Feline - contd.
Blood pressure is determined by cardiac output and the total resistance to blood flow in blood vessels throughout the body. Cardiac output itself is related to the heart rate and to the amount of blood pumped by the heart with each beat. Regulation of blood pressure encompasses a very complex interplay between receptors in the brain, the peripheral blood vessels, and the kidneys, endocrine, and cardiovascular systems. When blood pressure is high, complications can occur due to release of fluid, plasma, or bleeding into the tissues. Spasm of blood vessels may result in lack of oxygen in cells in target organs such as the eyes, kidneys, heart, and brain. Changes, including heart muscle thickening, may occur secondary to hypertension.
Hypertensive cats usually are taken to the veterinarian because of signs secondary to the underlying cause of their high blood pressure, or because of damage to the eyes, kidneys, cardiovascular system, or central nervous system. On physical examination, findings such as retinal hemorrhage or detachment may be seen. Other changes like blood in the eye or blood vessel abnormalities in the retina may be detected. Reduced kidney size may occur in cats with long-standing kidney disease. Heart murmurs are often heard, but lung changes secondary to heart disease are not usually due to hypertension alone. Additional heart changes, such as an abnormally rapid heart rate or the presence of an extra heart sound called a gallop rhythm, are also common. Cats with hyperthyroidism may be agitated or pant during their exams, and usually have an enlarged thyroid gland that can be palpated in the neck.
Hypertension is diagnosed most commonly through indirect blood pressure measurement. Bloodwork, x-rays, and ultrasound examination are performed to look for underlying causes of hypertension as well as changes secondary to it. Treatment focuses on the use of oral medications to control blood pressure, although in crisis situations there are drugs that can be used intravenously if deemed appropriate. There are many different classes on anti-hypertensive drugs. The calcium channel blocker amlodipine, marketed as Norvasc, is one of the most commonly prescribed anti-hypertensive drugs for cats.
