Page 240 - Small Animal Internal Medicine, 6th Edition

212 PART I Cardiovascular System Disorders

BOX 11.1 peptides); blood volume regulation by the kidney; and
other factors.
VetBooks.ir Diseases Associated With Hypertension tions can lead to chronic elevation of arterial BP. For example,
Modulation of these systems by various disease condi-
Documented or Suspected Causes in Dogs and Cats
Renal disease (especially glomerular) hypertension can result from increased sympathetic activity
or responsiveness (e.g., with hyperthyroidism or hyperadre-
Hyperadrenocorticism nocorticism), increased catecholamine production (e.g.,
Hyperthyroidism with pheochromocytoma), or volume expansion caused by
Pheochromocytoma increased sodium retention (e.g., decreased glomerular fil-
Diabetes mellitus tration and reduced sodium excretion in renal failure, hyper-
Hyperaldosteronism
Intracranial lesions (↑ intracranial pressure) aldosteronism, or hyperadrenocorticism). RAAS activation,
High-salt diet (?) with subsequent salt and water retention and vasoconstric-
Obesity tion, can result from intrarenal disease (e.g., glomerulone-
phritis, chronic interstitial nephritis), enhanced production
Other Diseases Associated With Hypertension in People* of angiotensinogen (e.g., hyperadrenocorticism), or extrare-
Acromegaly nal diseases that increase sympathetic nervous activity or
Inappropriate antidiuretic hormone secretion interfere with renal perfusion (e.g., hyperthyroidism, renal
Hyperviscosity/erythrocytosis artery obstruction). Impaired production of vasodilator sub-
Renin-secreting tumors stances (e.g., prostaglandins, kallikreins) and effects related
Hypercalcemia to secondary hyperparathyroidism could be involved in
Hypothyroidism with atherosclerosis chronic renal failure.
Hyperestrogenism
Coarctation of the aorta High perfusion pressure can damage capillary beds. In
Pregnancy most tissues, capillary pressure is regulated by vasoconstric-
Central nervous system disease tion of arterioles that feed the capillaries, although this
control could be inadequate because of underlying organ
*Essential (idiopathic) hypertension is often associated with family disease. The continued arteriolar constriction secondary to
history, high salt intake, smoking, or obesity. chronic hypertension leads to hypertrophy and other vascu-
lar remodeling changes that can further increase vascular
mellitus also can be associated with higher BP in dogs. Other resistance. These structural changes and vascular spasm can
less common diseases associated with high prevalence of cause capillary hypoxia, tissue damage, hemorrhage, and
systemic hypertension include pheochromocytoma and infarction, which can lead to organ dysfunction (Box 11.2).
primary hyperaldosteronism (Conn’s syndrome). Because of Organs that are particularly vulnerable to damage from
the increased risk for hypertension in patients with such chronic hypertension are the eye, kidney, heart, and brain.
conditions, BP should be measured when the disease is diag- These structures often are referred to as target organs or end
nosed and periodically thereafter. Similarly, hypertension organs damaged by systemic hypertension. In the eye, hyper-
discovered during a routine examination could be an early tension often causes focal perivascular edema, hemorrhage,
marker of underlying diseases associated with hypertension, and ischemia, especially in the retina and choroid layers.
so additional testing is indicated. Certain drugs such as glu- Bullous or total retinal detachment is common. Hyphema,
cocorticoids, mineralocorticoids, nonsteroidal antiinflam- vitreal hemorrhage, and optic neuropathy also can occur.
matory agents, phenylpropanolamine, sodium chloride, and Renal glomerular hypertension occurs when afferent arterio-
even topical ocular phenylephrine can increase BP. Inherited lar autoregulation is disrupted. The resulting glomerular
idiopathic (essential) hypertension has been documented in hyperfiltration can lead to glomerulosclerosis, renal tubular
dogs and cats, although it is uncommon. Idiopathic hyper- degeneration, and fibrosis. These changes contribute to dete-
tension is considered a diagnosis of exclusion. Primary rioration of renal function and increases in vascular resis-
cardiac disease is not a recognized cause of systemic hyper- tance, thus chronic hypertension tends to perpetuate itself.
tension in dogs and cats. Proteinuria is an important manifestation of renal damage
and has been associated experimentally with severity of
Pathophysiology hypertension in cats and dogs. Reduction in proteinuria can
BP is the product of cardiac output and systemic vascular indicate that therapeutic benefit is being achieved, especially
resistance. BP is increased by conditions that raise cardiac in cats. BP is not directly correlated with serum creatinine
output (by increasing heart rate, stroke volume, and/or concentrations, and hypertension can develop before azote-
blood volume) or by those that increase peripheral vascu- mia, particularly in glomerular disease. Increased systemic
lar resistance. Arterial BP is normally maintained within arterial pressure and vascular resistance increase the after-
narrow bounds by the actions of the autonomic nervous load stress on the heart and stimulate left ventricular (LV)
system (e.g., via arterial baroreceptors); various hormonal hypertrophy and dilation of the ascending aorta. Increased
systems (e.g., the renin-angiotensin system [RAAS], aldos- cerebral vascular pressure can promote edema formation,
terone, vasopressin/antidiuretic hormone, and natriuretic raise intracranial pressure, and cause hemorrhage.