Symptoms of low blood pressure in a cat. High and low blood pressure in cats: causes of deviation and their consequences. Important information for patients

Authors): A.V. Girshov, veterinarian, S.A. Luzhetsky, veterinarian
Organization(s):"Clinic of Neurology, Traumatology and Intensive Care of Dr. V.V. Sotnikov", St. Petersburg
Magazine: №5-6 - 2013

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Feline systemic arterial hypertension as a systemic circulatory pathology is often reported in older cats (over 14 years of age). It has been established that this pathology is often associated with chronic renal failure and hyperthyroidism. At the same time, the possibility of the development of idiopathic genesis of increased peripheral vascular resistance and developing endothelial dysfunction cannot be excluded.

The clinical picture of systemic arterial hypertension is usually caused by damage to the blood vessels of target organs (brain, heart, kidneys, eyes) with the development of serious neurological, ophthalmological, cardiological and nephrological disorders in the uncontrolled course.

Specific antihypertensive medications can significantly improve end-organ function and long-term prognosis in these cats. The main goal of treatment is to prevent further damage to the microvasculature of target organs. The range of possible antihypertensive drugs is quite diverse and includes a large number of drugs from different pharmacological groups. Today, ACE inhibitors and calcium channel blockers from the dihydropyridine group (amlodipine) are considered the drugs of choice in the treatment of arterial hypertension in cats. The use of combined antihypertensive therapy with the inclusion of ACE inhibitors and amlodipine also seems highly effective, which achieves maximum angioprotection for target organs.

Feline systemic hypertension is systemic circulatory pathology, which is often recorded in older cats (over 14 years). This pathology is often associated with chronic renal failure and hyperthyroidism. But there is also the possibility of the development of idiopathic increasing of peripheral vascular resistance and developing endothelial dysfunction. Clinical manifestation of systemic arterial hypertension is usually caused by vascular lesions of target organs (brain, heart, kidneys and eyes). These lesions lead to the serious uncontrolled neurological, ophthalmological, cardiac and nephrology problems. Specific antihypertensive drugs can significantly improve a vital function of the target organs and the long-term prognosis for these cats. The main aim of the treatment is to prevent further damage of the microvasculature of the target organ. There is a great range of possible antihypertensive drugs from different pharmacological groups. Today the main drugs to the treatment of feline hypertension are considered ACE inhibitors and calcium channel blockers from the dihydropyridine group (amlodipine). Use of combination antihypertensive therapy with ACE inhibitors and amlodipine is also very effective for the maximum angioprotection of the target organs.

Systemic hypertension (an abnormal increase in systemic blood pressure) as a circulatory pathology is often reported in older cats. A high incidence of systemic hypertension is observed in cats with chronic renal failure (61%) and hyperthyroidism (87%) (Kobayashi et al, 1990). But at the same time, hypertension occurs in cats even in the absence of renal failure and euthyroidism (normal thyroid status). Because untreated hypertension in cats can lead to serious neurological, ophthalmological, cardiac and nephrological disorders, treatment of these patients is strongly recommended. In addition, specific antihypertensive drugs can significantly influence end-organ function and long-term prognosis.

Systemic hypertension (SH) usually presents as a complication of another systemic pathology and is therefore classified as secondary hypertension. However, in certain cases, when the cause of HS is not established during a full examination, they speak of primary or idiopathic hypertension.

Epidemiology

Hypertension is more common in older cats, with an average age of 15 years and a range of 5 to 20 years ( Littman, 1994, Steele et al, 2002). It is not clear enough whether an increase in blood pressure with age may be normal in healthy older cats or whether it should be regarded as an early subclinical stage of the development of a pathological process. No breed or gender predisposition to hypertension has been identified in cats.

Pathophysiology

Although systemic hypertension is frequently identified in cats with chronic kidney dysfunction, the relationship between increased blood pressure and kidney damage as an underlying cause is not clear. Vascular and parenchymal renal diseases in humans are proven causes of hyperreninemic hypertension. Moreover, an increase in the volume of extracellular fluid is one of the mechanisms for the development of hypertension in patients in the late stages of kidney disease ( Pastan & Mitch, 1998). There is evidence that in cats with naturally occurring hypertension and renal failure, there is no increase in the level and activity of plasma renin and an increase in plasma volume ( Hogan et al, 1999; Henik et al, 1996). This suggests that some cats have primary (essential) hypertension and that the kidney damage is secondary and a consequence of chronic glomerular hypertension and hyperfiltration.

Likewise, the relationship between hyperthyroidism and hypertension in cats is not well defined, even though the incidence of hypertension is high in cats with thyrotoxicosis. Hyperthyroidism leads to an increase in the number and sensitivity of myocardial b-adrenergic receptors and, as a consequence, increased sensitivity to catecholamines. In addition, L-thyroxine has a direct positive inotropic effect. Consequently, hyperthyroidism leads to an increase in heart rate, stroke volume and cardiac output and, as a result, an increase in arterial blood pressure. However, in cats, no significant relationship was found between serum thyroxine concentrations and arterial blood pressure ( Bodey & Sansom, 1998). In addition, in some cats, with proper and effective treatment of hyperthyroid status, arterial hypertension may persist. Thus, it is assumed that in a proportion of cats with hyperthyroidism, hypertension is independent of hyperthyroid status. Other unlikely causes of hypertension in cats include hyperadrenocorticism, primary aldosteronism, pheochromocytoma, and anemia.

The fact that hypertension in cats can be observed in the absence of kidney or thyroid disease suggests that in some cases, as in humans, systemic hypertension in cats can be considered a primary idiopathic process, including increased peripheral vascular resistance and endothelial dysfunction.

Clinical signs

Clinical signs are usually a derivative of target organ damage (brain, heart, kidneys, eyes). As blood pressure rises, autoregulatory vasoconstriction of arterioles occurs to protect the capillary beds of these highly vascularized organs from high pressure. Severe and prolonged vasoconstriction can ultimately lead to ischemia, infarction, and loss of capillary endothelial integrity with edema or hemorrhage. Cats with hypertension may exhibit symptoms such as blindness, polyuria/polydipsia, neurological signs including seizures, ataxia, nystagmus, hind limb paresis or paralysis, dyspnea, epistaxis ( Littman, 1994). Rarer possible signs include “fixed gaze”, vocalization ( Stewart, 1998). Many cats do not show clinical signs and hypertension is diagnosed after murmurs, gallop rhythms, electrocardiographic and echocardiographic abnormalities are identified. In cats, systemic hypertension is often associated with left ventricular hypertrophy. Usually this is moderate hypertrophy and asymmetric septal hypertrophy of the left ventricle. Dilatation of the ascending aorta is detected radiographically or echocardiographically, but it is not clear whether this finding is due to hypertension or a normal age-related change. Cats suffering from systemic hypertension often have left ventricular diastolic dysfunction due to decreased relaxation of the left ventricular wall.

Wide variability in electrocardiographic changes includes ventricular and supraventricular arrhythmias, atrial or ventricular complex dilatation, and conduction disturbances. Tachyarrhythmias are resolved with proper hypertension treatment.

Acute blindness is a common clinical manifestation of systemic hypertension in cats. Blindness usually occurs due to bilateral retinal detachment and/or hemorrhage. In one study, 80% of hypertensive cats had hypertensive retinopathy with retinal, vitreous, or anterior chamber hemorrhages, retinal detachment and atrophy, retinal edema, perivasculitis, retinal artery tortuosity, and/or glaucoma ( Stiles et al, 1994). Retinal lesions usually regress with antihypertensive therapy, and vision returns. Retinal detachment is a common cause of blindness in older cats and, much less commonly, dogs.

The cause of retinal detachment, in this case, is high blood pressure. Increased pressure changes the walls of the capillaries of the uvea and increases their permeability over time.

Clinical signs of retinal detachment are: dilated pupil, pupils of different sizes, impaired pupillary-motor reactions, impaired chromatic pupillary-motor reactions, intraocular hemorrhage, visual impairment. Retinal detachment is confirmed using ophthalmoscopy. If the transparency of light-conducting media is impaired, ultrasound of the eyeball can be used. Both of these methods allow you to examine the retina simply and painlessly.

The stages of the disease depend on changes in the fundus picture. The assessment takes into account the condition of the optic nerve head, the presence of foci of retinal detachment, the condition of the retinal vessels, the presence of areas with signs of hemorrhages, and the presence of hyperreflective areas.

Often, changes in the fundus are the first signs of a systemic disease. An animal may look healthy and have no problems with orientation in space, but at this time early changes are already occurring in the fundus of the eye, which can be detected by ophthalmoscopy. Detection of early changes in the fundus allows for a timely diagnosis and avoidance of complications such as retinal detachment.

The central nervous system is predisposed to damage as a result of hypertension because it is replete with small vessels. In cats, these injuries can cause convulsions, head tilt, depression, paresis and paralysis, and vocalization.

Chronic hypertension may cause kidney damage as a result of changes in afferent arterioles. Focal and diffuse glomerular proliferation and glomerular sclerosis may also develop. (Kashgarian, 1990). Following renal dysfunction, chronic systemic hypertension causes a sustained increase in glomerular filtration pressure, which plays a key role in the progression of renal function deterioration. (Anderson & Brenner, 1987; Bidani et al, 1987). Proteinuria and hyposthenuria are not common in cats with arterial hypertension, but microalbuminuria is observed (Mathur et al, 2002).

Diagnosis of hypertension

Suspicion of the presence of arterial hypertension in a cat can be based on the presence of characteristic retinal lesions. However, other causes of retinal detachment and/or hemorrhages cannot be excluded. Arterial hypertension must certainly be confirmed by measuring blood pressure. Blood pressure measurements should be performed to confirm or refute the presence of hypertension in cats with left ventricular hypertrophy, renal dysfunction or hyperthyroidism, and in cats over 7 years of age with murmurs or a galloping rhythm. In addition, blood pressure measurements should be performed in cats with the above-described signs of brain damage.

Hypertension in cats was defined as an indirect systolic pressure greater than 160 mmHg. (Littman, 1994; Stiles et al., 1994) or 170 mm Hg. Art. (Morgan, 1986) and diastolic blood pressure more than 100 mm Hg. Art. (Littman, 1994; Stiles et al., 1994). However, blood pressure will increase with age in cats and can exceed 180 mmHg. systolic and 120 mm Hg. diastolic pressure in practically healthy cats over 14 years of age. (Bodey and Sansom, 1998). Thus, a diagnosis of hypertension can be made in a cat of any age whose systolic blood pressure is >190 mmHg. rt. Art. and diastolic pressure > 120 mm. rt. Art. Cats with a clinical picture of appropriate arterial hypertension and a systolic pressure of 160 to 190 mmHg. rt. Art. should also be considered to have hypertension, especially if they are under 14 years of age. In the absence of clinical signs of hypertension and systolic blood pressure from 160 to 190 mm Hg. Art. and diastolic pressure between 100 and 120 mm Hg. Art., repeated measurements are necessary several times during the day or possibly several days.

Therapeutic strategy

Early diagnosis and treatment of cats with systemic arterial hypertension is important. Although not all cats exhibit clinical signs, failure to promptly diagnose and treat them can lead to extremely undesirable consequences. Drawing an analogy with arterial hypertension in humans, we can borrow the term “silent killer”.

The main goal of treatment is to prevent further damage to the eyes, kidneys, heart and brain. This is achieved not only by lowering blood pressure, but also by improving blood circulation in target organs.

Numerous pharmacological agents are available as antihypertensive agents, including diuretics, β-blockers, angiotensin-converting enzyme inhibitors (ACEIs), angiotensin II receptor blockers, calcium channel antagonists, direct-acting arterial vasodilators, centrally acting α2-agonists, and α1-blockers.

Cats with hypertension tend to become refractory to the antihypertensive effects of adrenergic blockers such as prazosin, as well as direct-acting arterial vasodilators such as hydralazine. In addition, long-term use of direct-acting drugs often leads to undesirable stimulation of compensatory neurohumoral mechanisms. Diuretics, β-blockers, or a combination of both will effectively lower blood pressure in most hypertensive cats but do not reduce end-organ damage (Houston, 1992).

According to Poiseuille's law, blood pressure is determined by the product of systemic vascular resistance and cardiac output, and therefore the decrease in blood pressure resulting from the use of diuretics and beta-blockers results from a decrease in cardiac output. These drugs lower blood pressure through a mechanism that reduces flow to target organs, thereby compromising myocardial, renal, and brain perfusion. At the same time, calcium channel antagonists, ACE inhibitors, and angiotensin II receptor blockers reduce blood pressure by reducing vascular resistance. This mechanism is more effective in improving end organ perfusion. Calcium channel antagonists, in particular, lack myocardiodepressive effects, and ACE inhibitors have shown beneficial effects on renal function, coronary perfusion, and cerebral perfusion in people with hypertension (Houston, 1992; Anderson et al, 1986) Centrally acting α-adrenergic agonists lower blood pressure by reducing vascular resistance and have also been shown to maintain target organ function. Diuretics and beta-blockers reduce cardiac output, stroke volume, coronary and renal blood flow, increasing renal vascular resistance. In addition, these drugs do not reduce left ventricular hypertrophy. On the other hand, calcium channel blockers, ACE inhibitors, angiotensin II receptor blockers, and centrally acting drugs have the opposite effect.

Amlodipine is a long-acting antihypertensive drug belonging to the calcium channel blockers. This drug relaxes the smooth muscles of blood vessels, blocking the influx of calcium. Its main vasodilating effect is a systemic decrease in vascular resistance. In addition, this effect extends to the coronary arteries. This drug is safe and effective even in cats with renal dysfunction when used orally at a dose of 0.2 mg/kg once daily. When taken daily, amlodipine reduces blood pressure within 24 hours (Snyder, 1998). In addition, cats do not develop refractoriness to amlodipine and have a persistent therapeutic effect with long-term therapy.

ACE inhibitors such as enalapril, ramipril and benazepril are also good choices for the treatment of hypertension in cats. However, these drugs are often ineffective as monotherapy in cats. ACE inhibitors may be best used in combination with amlodipine.

In cats resistant to amlodipine or ACE inhibitors, only a combination of these drugs can safely provide adequate blood pressure control. When ACE inhibitors (enalapril or benazepril) are added to amlodipine therapy, doses of 1.25 to 2.5 mg/cat/day are used). Also, some cats receiving this combination of drugs have improved kidney function. Experimental data show that the combination of these two classes of antihypertensive drugs not only increases the effectiveness of lowering blood pressure, but also maximizes target organ protection (Raij & Hayakawa, 1999). The angiotensin receptor blocker irbesartan in combination with amlodipine has been shown to be effective in some cats refractory to ACE inhibitors.

Cats with neurological disorders due to brain damage require aggressive treatment to quickly lower blood pressure. Amlodipine and ACE inhibitors have a relatively slow hypotensive effect and require 2-3 days to reach the peak of the hypotensive effect. In such clinical situations, intravenous administration of sodium nitroprusside (Natrium nitroprussid) will be more effective for rapid relief of a hypertensive crisis. However, safe use of this drug requires careful dose titration using an infusion pump (1.5-5 mg/kg/min) and continuous blood pressure monitoring. Hydralazine may be used as an alternative to sodium nitroprusside when rapid blood pressure reduction is not required. This drug is usually given orally every twelve hours, starting at a dose of 0.5 mg/kg and increasing as needed to 2.0 mg/kg every 12 hours. Caution is advised when using fast-acting, potent antihypertensive drugs to treat hypertensive crises. A rapid and severe drop in blood pressure can lead to acute cerebral ischemia and thereby worsen neurological deficits.

Target organs for hypertension

Organ/System

More often the effect occurs when

Cats don't smoke, don't eat excessive amounts of salt, and their lives are generally calm and stress-free, so why should we worry about their blood pressure? For a long time, most veterinarians did not know or even imagine that cats could have high blood pressure or hypertension, and they did not know how to measure this pressure. Subtle, barely noticeable signs that indicate high blood pressure in a cat are more frequent and loud meowing during the day and a “woozy”, sleepy state of your pet, as if she is under the influence of alcohol.

Veterinarians now know from extensive testing that high blood pressure is quite common in older cats and, fortunately, is highly treatable. Measuring a cat's blood pressure and obtaining accurate and reliable data is quite difficult, because very few animals remain completely calm and relaxed when visiting a veterinarian. There are several types of instruments used to measure blood pressure, but they all have a cuff placed on the patient's leg and a mechanism to determine when blood may be flowing through partially compressed blood vessels. It is necessary to take 3-5 measurements to accurately estimate the value of systolic blood pressure. When systolic pressure is above 180, there is a high risk of damage to organs and tissues.

High blood pressure causes problems with the heart and with blood circulation throughout the body. In cats, one of the main organs affected by high blood pressure is the eyes. Tiny blood vessels in the eye can burst when there is too much pressure on them. When this happens, retinal detachments and hemorrhages begin, and blindness can occur. If an owner immediately notices sudden blindness in a cat and the cat is diagnosed with high blood pressure, immediate treatment may result in the restoration of vision. If high blood pressure is not treated within a few days, the chances of the retina healing and vision being restored are extremely low.

Most people develop hypertension without a specific medical problem. In cats, high blood pressure is always a secondary condition to chronic kidney disease. hyperthyroidism (hyperthyroidism) or diabetes. If you have a cat suffering from these diseases, you should check its blood pressure at least 1-2 times a year. If your cat is diagnosed with arterial hypertension, it is important to do all the necessary tests and undergo an examination to find possible causes and the underlying disease.

The initial drug used to treat high blood pressure in cats is amlodipine. It is produced in tablet form for humans and is very difficult to cut into smaller doses, so it is recommended to purchase a special tablet cutter for more accurate dosing. Amlodipine is a calcium channel blocker. Cats usually need to take it orally (by mouth) once or twice a day. If amlodipine does not help lower blood pressure, other drugs are added.

Unfortunately, studies have not shown a significant effect of diet on a cat's blood pressure, but diets for older cats, like those for cats with kidney disease, tend to be lower in sodium and are also recommended for hypertension. Blood pressure usually stabilizes within 1-2 weeks of treatment, but cats almost always require ongoing treatment for the rest of their lives. The exception is high blood pressure caused by hyperthyroidism; if this disease is eliminated, the pressure will normalize.

It is helpful for owners to know how cats develop hypertension. Blood pressure testing should be an integral part of regular veterinary visits for older cats and for young cats with suspicious clinical signs (symptoms).

Hypertension in cats.

Based on materials from the website www.icatcare.org

Hypertension(hypertension) is the medical term used for high blood pressure. This disease is quite common in older cats.

Feline hypertension usually develops as a result of other medical problems (called 'secondary hypertension'), although primary hypertension (hypertension without other "underlying" medical conditions) can also occur in cats. Unlike humans, who are more likely to have primary hypertension (also known as 'essential hypertension'), cats are more likely to have secondary hypertension. In most cases, secondary hypertension in cats is caused by chronic kidney disease, but other diseases can also lead to its development. A connection has also been established between hypertension and hyperthyroidism (overactive thyroid gland) in cats.

Hypertension is dangerous for the cat’s entire body. The following organs are most vulnerable:

Eyes. There may be bleeding in the eye and abnormalities in the retina, such as swelling and detachment. As a result of these disorders, the cat's vision can be affected and even blindness, often irreversible, can develop. In some cases, hemorrhages in the anterior chamber of the eye may be visible without the use of special equipment.

Brain and nervous system. Neurological signs may cause bleeding in these areas of the cat's body. such as strange behavior, staggering or drunken gait, seizures, dementia and coma.

Heart. Gradually, the muscles in one of the main chambers of the heart (the left ventricle) thicken as the heart has a harder time performing its pumping tasks when pumping high-pressure blood. In very severe cases, this can lead to the development of chronic heart failure. The cat may experience shortness of breath and lethargy.

Kidneys. Over time, high blood pressure increases your risk of developing kidney problems. In cats with kidney problems, hypertension can significantly complicate the disease over time.

Diagnosis of hypertension in cats.

Because hypertension is often the result of other diseases, cats may exhibit symptoms of an underlying disease. For example, in hyperthyroidism in cats with high blood pressure, the main clinical signs may be weight loss (despite an excellent appetite) and hyperactivity.

Many cats may not show any specific signs of hypertension until the disease reaches a stage where the eyes begin to bleed or the retina detaches - these cats are often brought to the vet for sudden blindness. Therefore, early detection of hypertension is very important to alleviate the disease and reduce the danger to the eyes and other organs of the cat's body.

Some cats suffering from hypertension appear depressed, lethargic, and withdrawn, even if there are no signs of damage to other organs. Many owners note the restoration of their cat's normal behavior after starting treatment for hypertension. It appears that with severe hypertension, cats, like humans, may suffer from headaches.

To detect hypertension early, it is recommended to regularly measure blood pressure in cats over 7 years of age, as hypertension is more common in older cats. Initially, this can be done once a year, but as the cat gets older, the pressure should be monitored at least twice a year, in addition, pressure monitoring should be carried out at any visit to the veterinarian.

Constant monitoring of blood pressure should be carried out in cats suffering from kidney disease, hyperthyroidism, heart disease, sudden blindness, as well as in cats with other visual impairments and neurological disorders, in order to prevent the development of hypertension in time.

Many clinics have the appropriate equipment to measure blood pressure in cats. Often these devices are similar to those used by humans, with an inflatable cuff placed over the cat's paw or tail. The process of measuring pressure takes a couple of minutes, does not cause pain and is easily tolerated by most cats.

A detailed eye examination is also important to diagnose hypertension in cats. In the initial stage of the disease, small changes in the blood vessels of the fundus and retina can be detected. In more severe cases, changes can be significant, including retinal detachment and bleeding in the eye. Typically, abnormalities are observed in both eyes of a cat, but (less commonly) may be found in only one.

In the absence of devices for measuring blood pressure, it is possible to diagnose hypertension during an eye examination, especially taking into account the dynamics of changes after the start of treatment. However, with the help of special devices for measuring blood pressure in cats, diagnosis and monitoring of the results of therapy is much more effective.

Treatment of hypertension in cats.

After confirmation of hypertension, treatment of cats is carried out in two directions:

The first is treatment aimed at lowering blood pressure using antihypertensive drugs. Many medications are now available, usually based on amlodipine and benazepril.

The second is identifying and treating the underlying disease, such as kidney disease that causes hypertension. In some cases (for example, with hyperthyroidism), treatment of the underlying disease can also solve the problem of high blood pressure. Urine and blood tests are usually done to identify the underlying disease.

It is also important to assess what complications of hypertension are present in the cat (for example, eye diseases) in order to properly control them during therapy. Cats exhibit very wide variability in response to antihypertensive drugs, and blood pressure stabilization may take varying periods of time. It may be necessary to change medications, change the dose and/or frequency of administration, or use more than one drug.

Response to therapy is best monitored by regular blood pressure measurements and eye examinations. In cats with kidney disease, it is important to continually monitor kidney function during treatment.

Prognosis for the treatment of hypertension in cats.

Cats with primary hypertension (without an underlying medical condition causing the high blood pressure) can usually control the disease and prevent complications, such as those that threaten vision.

In the case of secondary hypertension, the long-term prognosis directly depends on the nature and severity of the disease causing the increase in pressure. In all cases, it is important to monitor your blood pressure carefully and regularly to avoid complications.

Diagnosis and treatment of hypertension in cats

Doctors call hypertension a “silent killer” because most people are asymptomatic, but statistics show that this pathology significantly increases the risk of diseases of the blood vessels of the brain, myocardial infarction and kidney failure. Unfortunately, in veterinary medicine the situation is completely different. In most animals, hypertension is diagnosed due to the appearance of symptoms of severe KO lesions. This is largely due to the fact that veterinarians neglect to measure blood pressure (BP) in their patients during routine diagnostic examinations: currently, BP is determined mainly in cases where clinical manifestations of systemic hypertension appear in animals.

BASIC POINTS

> Hypertension Typically diagnosed in cats when signs of end organ disease (EA) develop. The eyes are most often affected, which is accompanied by loss of vision in animals.

> Hypertension most often develops in aging cats; The highest risk group includes animals with chronic renal failure.

>Cats are easy to measure blood pressure (BP) non-invasive methods, but this may cause difficulties in animals that hypertension develops from fear .

> Amlodipine, a calcium channel blocker, is currently the drug of choice for the treatment of hypertension in cats.

Clinical signs of hypertension

Clinical signs associated with hypertension that prompt cat owners to contact veterinarians are most often eye lesions, but there are cases when increased blood pressure is accompanied by severe dysfunction of the brain, heart and kidneys, sometimes there is bleeding in the nasal cavity (epistaxis).

Visual impairment due to hypertension

Unfortunately, owners of cats suffering from hypertension most often begin to pay attention to the health of their pets when they unexpectedly go blind. Other visual disturbances that owners notice in cats with elevated blood pressure include hemorrhage in the anterior chamber of the eye (hyphema) and dilated pupils (mydriasis). Ophthalmological examination of cats blinded due to hypertension reveals hemorrhages in the anterior chamber of the eyes, vitreous body, retina and underlying tissues, as well as serous retinal detachment. In typical cases, the lesions are bilateral, although the pathological changes in one eye may be stronger than the other. Examples of such violations are presented in Fig. 1.

Figure 1. Lesions in the eyes of blind cats characteristic of hypertension

A. Intense papery retinal detachment.

b. Retinal detachment and numerous small hemorrhages in the retina,

V. Hyphema.

Secondary changes that sometimes develop against the background of hypertension are glaucoma and retinal atrophy.

Mild changes are detected in cats only when examining the fundus before the cat loses vision. In this case, lesions such as small hemorrhages in the retina, focal detachment and edema are detected. In addition, small, dark areas of focal degeneration may be visible in the retina. Such lesions are often found in the tapetum part of the fundus, near the optic nerve head. Examples of these changes are shown in Fig. 2.

Figure 2. Eye changes that can develop in cats with hypertension that have retained their vision. Photos are published with the kind permission of Rebecca Elks.

A. Foci of hemorrhage in the retina.

b. Small areas of bullous retinal detachment.

V. Small areas of bullous detachment and areas of retinal degeneration.

Although visual changes in hypertensive cats are commonly described as “hypertensive retinopathy,” this pathological process actually affects the vascular layer to the greatest extent. For example, retinal detachment occurs when aqueous humor is released from the terminal arterioles and capillaries of the iris and accumulates in the subretinal space. Degeneration of the retinal pigment epithelium occurs due to severe ischemia of the choroid. Optic nerve lesions are rarely reported in cats, possibly because such changes are masked by concurrent swelling and hemorrhage. In addition, it is quite difficult to detect swelling of the unmyelinated optic nerve, located in the recessed part of the eyeball, in cats. The clinical signs and pathophysiology of hypertension-associated pathological changes in the feline retina, iris and optic nerve are described in detail in a recently published review.

Neurological manifestations of hypertension

The following neurological signs are observed in cats with hypertension: weakness, ataxia, loss of ability to navigate the environment. Signs of dysfunction of the vestibular apparatus, neck flexion, paraparesis, stupor, convulsions and death. In cats with hypertension, neurological symptoms develop less often than visual impairment: nevertheless, this is noted in at least a third of all cases. Meanwhile, it is very likely that neurological disorders often remain unrecognized for a number of reasons. Due to the variability of symptoms manifested in cats with hypertension, hypertension cannot be diagnosed based on the neurological nature of the pathology. Many cats in this situation are euthanized before a definitive diagnosis can be made. Additionally, in cats with severe eye damage, some of the neurological impairment (eg, depression) may be directly related to their blindness. The presence of mild neurological changes in hypertension may explain why many cat owners report improvement in their pet's clinical condition after starting treatment with antihypertensive drugs, even if vision is not restored.

Cardiovascular manifestations of hypertension

Cardiac systolic murmurs and a gallop rhythm are often heard on auscultation in hypertensive cats. Other abnormalities of the cardiovascular system, less frequently recorded in this pathology, include diastolic heart murmurs and tachycardia. arrhythmias and shortness of breath.

Meanwhile, heart murmurs and other mentioned disorders are more often detected in aging cats, even those with normal blood pressure. The latter circumstance does not allow us to assume hypertension based on the presence of such symptoms: in other words, to make such a diagnosis it is necessary to measure blood pressure.

Cats with hypertension rarely show signs of congestive heart failure. This occurs when hypertension aggravates another existing cardiovascular disease in the animal, but it is unlikely that it itself is responsible for the heart failure. However, suspicion that a cat has cardiovascular disease does not eliminate the need to measure the animal's blood pressure.

X-ray examination of cats with hypertension reveals an enlarged heart, especially the left ventricle, and the presence of undulation of the thoracic aorta.

The echocardiographic changes most commonly seen in cats with hypertension include mild hypertrophy of the left ventricular wall and interventricular septum. However, it is noteworthy that the heart size of many cats with systemic hypertension remains within the normal range. Differences in systemic echocardiographic parameters between healthy and hypertensive cats of the same age are virtually minimal.

Diagnosis of hypertension

CD is determined by direct and indirect methods. Direct methods serve as the gold standard. They are based on arterial puncture or insertion of a catheter into the artery. Meanwhile, direct methods are unacceptable for routine measurement of blood pressure in sick animals, which is due to the difficulties of puncturing their arteries, an increase in blood pressure as a result of the pain reaction and stress in the animal during the procedure, and the risk of complications such as infection, vascular thrombosis and hemorrhage. A method for measuring blood pressure using transponder sensors inserted into vessels for a long time is described, but so far it has found application only in experimental studies.

Indirect methods are more convenient for measuring blood pressure in sick animals. Of these, the Doppler method and oscillometric methods are most often used when working with cats. The Korotkoff auscultatory method, widely used in medicine, cannot be used to determine blood pressure in cats due to the low amplitude of arterial murmurs. Choosing an indirect method for measuring blood in cats is not easy - each method has its own advantages and disadvantages.

Oscillometric method

Oscilloscope equipment detects changes in blood pressure in the air-filled cuff surrounding the peripheral artery. The amplitude of the oscillation varies depending on the arterial pressure and cuff pressure. The advantage of the method is the ability to determine both systolic and diastolic blood pressure.

However, the CD values. corresponding to high amplitude oscillations are usually more reliable than systolic and diastolic blood pressure values. Studies conducted on cats under general anesthesia have shown that the oscillometric method gives underestimated blood pressure (especially systolic) values, while it is increased. Quite a high incidence of failure to determine CD has been reported in cats; These data confirm the results of studies on conscious cats, in which the average duration of this procedure was found to be excessively long.

More importantly, there are reports of this. that the results of oscillometric measurements of blood pressure do not correlate well with the readings of direct methods for determining blood pressure in conscious cats and do not make it possible to diagnose cases of hypertopic eye damage. A number of factors can negatively influence blood pressure measurements in conscious animals, including locomotor activity and heart rate, which are higher than in cats under general anesthesia.

This method is based on measuring an ultrasonic signal reflected by moving blood cells with a sensor.

The CD value is determined using a sigmomanometer, the cuff of which covers the animal’s limb proximal to the sensor. One publication comparing direct and indirect methods for determining blood pressure in animals under general anesthesia reported that: Although the Doppler method is more accurate than the oscillometric method, opposite results were obtained in another experiment.

However, adherents of the Doppler method prefer this method because it is more reliable for measuring blood pressure in conscious cats and allows identifying animals with hypertensive eye damage. The use of this method is limited by the inability to determine diastolic blood pressure.

However, the fluctuations in its successively obtained readings are much smaller than those of other indirect methods for determining blood pressure; these differences are most clearly manifested in the hypotensive state of animals.

Hypertension from fear

Whatever non-invasive method the veterinarian uses to measure BP, he must always take into account the existing phenomenon of fear hypertension and take all possible measures to avoid this short-term increase in BP that occurs in animals during a visit to the veterinary clinic. The described phenomenon also occurs in people who have blood pressure measured, not only during an outpatient visit, but also during the provision of medical care. This can lead to misdiagnosis of hypertension and subsequent treatment that is not necessary. The possibility of developing the phenomenon of hypertension from fright in cats has been proven under experimental conditions. To measure blood pressure and heart rate, cats were implanted with radiotelemetry sensors. Readings were taken in quiet conditions and then during a visit to the veterinarian. It was found that the average systolic blood pressure in the latter case increased by 18 mm Hg compared to the previous level, which was determined in a quiet environment for 24 hours. Art. The nature and intensity of the manifestation of the phenomenon of hypertension from fright in different cats were different, and fluctuations in blood pressure during the period of short-term hypertension associated with it reached 75 mm Hg. Art. How pronounced the phenomenon of hypertension from fear would become could not be judged by changes in heart rate. The results of this and other studies clearly show the importance of allowing cats to acclimate to the environment in which their CD measurements are to be performed.

Conditions for carrying out CD measurements

KD can be measured on the front or hind limbs, as well as on the tail. However, to obtain comparable results, this should always be done in the same place, since the results of determining blood pressure in different parts of the cat’s body can vary significantly. The width of the cuff should be approximately 40% of the circumference of the animal's limb. The use of too wide a cuff leads to underestimated readings, and too narrow cuffs lead to overestimated readings; however, the differences between the two are usually quite small.

What are the criteria for hypertension?

There is no consensus as to what level of blood pressure should be considered sufficient to diagnose hypertension in cats. Very few studies have been conducted to establish normal values ​​for this indicator. Although those CD values. which were determined in healthy cats by different authors varied significantly, however, the value of CD determined in different experiments in young healthy animals using surgically implanted radiotelemetric sensors turned out to be the same. This indicates that disagreements among different authors regarding the normal value of blood pressure in cats are due to the unequal accuracy of the methods they used for indirect determination of blood pressure or the phenomenon of hypertension from fear. The determined radiotelemetric level of CD in humans, cats and many other mammals turned out to be the same. Apparently, it corresponds to the blood pressure value at which optimal blood supply to the brain and internal organs is achieved.

Mass examinations of people have shown that systolic and diastolic blood pressure has a pronounced long-term and etiological effect on the consequences of concomitant diseases. Therefore, knowledge of the value of “normal” and “hypertensive” blood pressure is unnecessary - it is only important to maintain blood pressure at an optimal level, which prevents undesirable consequences (for example, cardiovascular diseases). The optimal blood pressure for many people is significantly lower than what is considered “normal.” For example, according to statistics, 25% of adults in developing countries of the world have blood pressure exceeding the permissible norm, which dictates the need for their treatment with antihypertensive drugs. The situation is further complicated by this. What. as studies have shown, the optimal blood pressure is not some stable value, but depends on the clinical condition of the patient. For example, in people with kidney disease, the desired “optimal” BP should be significantly lower than for the general world population (16). In cats, the only clinical complication of hypertension is ocular damage, as evidenced by numerous retrospective observations made under uncontrolled conditions. We diagnose systemic hypertension in this species when the systolic blood pressure exceeds 175 mmHg. Art. and there are eye lesions. If no changes in the organs of vision are detected, then such a diagnosis can only be made by re-establishing an increased systolic blood pressure in the animal during its re-examination at the next visit to the veterinary clinic. Once the diagnosis is made, treatment begins. By using the diagnostic criteria mentioned above, cats with hypertension can be prevented from developing ocular lesions. However, it is unknown whether treating cats with lower KD will have any further benefit. For example. 160-Р5 mm Hg. Art.

Which cats are at increased risk for developing systemic hypertension?

In order to diagnose hypertension before the development of associated irreversible KO lesions and associated symptoms, it is useful to have an idea. Which cats are at the highest risk of systemic hypertension. In such patients, blood pressure should be measured regularly for preventive purposes. Cats usually do not have primary hypertension - an increase in blood pressure, as a rule, occurs against the background of other diseases (causing the development of hypertension or concomitant ones), most often chronic renal failure and hyperthyroidism. These questions are discussed in detail below. In addition, there are a number of less commonly diagnosed diseases in cats that can cause systemic hypertension.

Chronic renal failure is the syndrome most often accompanied by severe hypertension in cats. During a mass examination of cats with hypertension accompanied by eye damage, an increased concentration of creatinine in the blood was detected in 44 of 69 (64%) animals.

HarrietM. Sim

It would seem that problems with blood pressure are unique to humans, but this is not so. Our pets can also suffer from this type of pathology, even if it happens much less frequently. A good example is hypertension in cats.

Nowadays, veterinarians officially recognize that high blood pressure in cats is an unpleasant reality. If this pathology is not dealt with in any way, it can even lead to the death of the animal. Hypertension almost never occurs as an independent disease: more often it is caused by acute or chronic renal failure and/or. Statistics show that blood pressure problems affect 60% of cats with kidney failure and approximately 90% of cats with hyperthyroidism. Thus, the causes of hypertension in cats in most cases are serious functional disorders in the endocrine system and urinary organs.

Less commonly, pathology develops with inflammation of the adrenal glands, as well as with their tumors. There are also cases of idiopathic arterial hypertension, the causes of which remain a mystery. We must not forget that increased blood pressure can be a logical response to severe stress. For example, after a veterinarian’s visit, it is useless to measure a cat’s blood pressure, as it will be greatly increased.

Arterial hypertension severely injures four main systems: the kidneys, eyes, central nervous system and cardiovascular system. In some cases, the pressure is so great that small capillaries begin to burst en masse. The lungs are especially susceptible (“pulmonary” hypertension in cats). The result may be retinal detachment, pulmonary fibrosis, hemothorax, or stroke. Since hypertension hits the kidneys hard, in case of renal failure a vicious circle is formed when one pathology contributes to the development of the second. In most cases, this disease is diagnosed in older animals.

Symptoms of arterial hypertension

Unfortunately, the symptoms of hypertension in cats are very vague and uncharacteristic. Since this pathology is almost always secondary to diseases of the thyroid gland and kidneys, the clinical picture will largely correspond to the primary disease. The main features are:

• Loss of appetite.
• Increased thirst and urination (polydipsia and).
• Weight loss (can be rapid if the cat has severe weight loss).

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Sometimes blood pressure problems are indicated by heart murmurs or serious eye problems. These signs help to understand that the animal has serious functional disorders in the body. This is one of the reasons why it is extremely important to regularly take your pet for a complete preventative veterinary examination.

In the case when the pressure rises suddenly and sharply, a very characteristic symptom will be sudden blindness and disorientation in space. The blood vessels in the eye will rupture and the retina will detach. In this case, vision is lost partially or completely. The cat's pupils dilate greatly. Cats panic, cannot move, and often bump into furniture, doors and corners when trying to run.

Less commonly, chronic hypertension can cause cerebral hemorrhage. When walking, the cat leans heavily, falls to the side, it is disoriented, there may be sudden attacks that strongly resemble epilepsy. But much more often the animal simply falls into a coma and quickly dies.

Diagnostics

The most reliable method for detecting hypertension is... a regular tonometer, the cuff of which is placed on the paw or base of the tail. The procedure itself is absolutely painless, and in balanced animals reliable results can be obtained already from the second or third time. But such “prudent” cats are very rare. Much more often you can observe real hysteria, accompanied by attempts to scratch and bite both the veterinarian and his own owner.

If so, you will have to try to calm your pocket tiger. Sit with the cat and pet him. Some foreign forums even advise using aromatic oils and other homeopathy. These medications do not reduce blood pressure, but may help calm the cat. As a rule, pressure must be measured several times to obtain reliable results.

How to treat this disease?

So how is hypertension treated in cats? It all depends on the primary disease that caused the increase in pressure. The sooner it is detected and the sooner effective treatment is prescribed, the greater the chance that hypertension will not develop at all.

Perhaps the most commonly discussed disease among the older generation is high blood pressure. And this is far from accidental, since it is this pathology that doctors call the “silent killer.” Hypertension in cats also occurs, and also leads to very unpleasant consequences.

Is the medical term used to refer to high blood pressure. Several years ago, everyone confidently believed that this problem was characteristic exclusively of humans, but now information has appeared that fully confirms the existence of this pathology among our smaller brothers. Cats also suffer from high blood pressure.

This disease is divided into two types: primary and secondary. In cats, it is secondary pathology that is common, that is, a pathology that develops under the influence of some other diseases. Primary arterial hypertension in animals is extremely rare, but its possibility cannot be ruled out. Scientists and veterinarians suggest that in this case we can talk about a genetically determined defect.

Very often, problems with blood pressure occur when an animal has diseased kidneys. Chronic renal failure is most often to blame. If a cat has hyperthyroidism, he will certainly suffer from high blood pressure.

Symptoms

What are the symptoms of hypertension in cats? There are no particularly specific signs, but high blood pressure hits various organs hard. Seeing certain changes, an experienced veterinarian will certainly be able to make the correct diagnosis. This pathology is most dangerous for the eyes. Bleeding, retinal detachment, glaucoma - these are not all the consequences. In most cases, they lead to complete or partial blindness of the animal and disorientation in space. Any owner can notice all these manifestations.

Read also: Heart disease in cats: types, causes, symptoms, treatment

Of course, problems with blood vessels also have a serious impact on the state of the nervous system. The cat may behave very strangely or inappropriately, walk unsteadily or “drunk”, and with a severe course of the disease, everything can end in a coma.

How does the heart react to increased blood pressure? Very hard. If the pathology develops chronically, hypertrophy of the heart muscle first develops. But over time, the body’s strength is no longer enough for this. Gradually, the heart weakens, and dystrophic and degenerative effects develop in its tissues. In very severe cases, they lead to the development of congestive heart failure. This is expressed in shortness of breath, swelling, shallow and very rapid breathing.

Considering the critical filtration function of the kidneys, one should not be surprised at their pronounced response to increased blood pressure. It severely damages the renal glomeruli and tubules, and therefore significantly increases the risk of developing renal failure. If the cat already had some problems with this organ, then in this case everything will become much worse.

Diagnostic measures

Many cats simply do not have any noticeable symptoms, so they only learn about problems with blood pressure indirectly. In cases where his vision suddenly disappears or severely deteriorates. Early detection of arterial hypertension is precisely why it is so important: only in this case there is a chance to keep your pet’s eyes healthy.

Some cats with hypertension appear depressed, lethargic, and withdrawn. After starting treatment, many breeders are surprised to notice that their pets again become cheerful, playful and nimble. It is likely that cats may also experience severe headaches, but there is no official confirmation of this yet.

Read also: Pneumonia in a kitten: types and methods of treatment

Blood and urine tests are required! This is due to the fact that this is the only way to detect hormonal problems in a timely manner.

Experienced veterinarians say that in cats over seven years of age, blood pressure is measured for preventive purposes at least once a year, and upon reaching the age of ten, this operation is performed at least once every six months. As a rule, a separate card is created for each old cat, in which the results of measuring blood pressure are listed in a separate column.

How, in fact, is it measured? Surprisingly, for this it is quite possible to use any “human” tonometer purchased at the nearest pharmacy. The cuff is either attached to the paw or wrapped around the base of the tail.

Important! In this case, animals can become very nervous, and therefore the results of a single measurement will be completely unreliable. Therefore, they try to carry out measurements in a calm, homely atmosphere, measuring the pressure at least five times.

However, modern veterinary clinics also have special devices for this purpose. They are smaller in size and their use does not cause as much fear in cats. We repeat once again that the results of measurements taken during “hysterical attacks” cannot be considered reliable!

Treatment

Thus, the treatment of hypertension in cats has two main goals:

• Firstly, high blood pressure is reduced with the help of special medications. Many remedies are available today, but commonly used amlodipine And benazepril.

• The primary disease is urgently identified. If it is completely eliminated, then in most cases the pressure readings immediately return to normal.