HYPERTENSION
Hypertension, or high blood pressure, is probably the
most common of all health problems in adults and is
the leading risk factor for cardiovascular disorders.
Hypertension commonly is divided into the categories
of primary and secondary hypertension. In primary,
or essential, hypertension, which accounts for 90% to
95% of all hypertension, the chronic elevation in
blood pressure occurs without evidence of other
disease. In secondary hypertension, the elevation of
blood pressure results from some other disorder, such
as kidney disease
Mechanisms of Blood Pressure Elevation
Several factors, including hemodynamic, neural,
humoral, and renal mechanisms, are thought to interact
in producing long-term elevations in blood pressure. As
with other disease conditions, it is probable that there is
not a single cause of essential hypertension or that the
condition is a single disease. Because arterial blood
pressure is the product of cardiac output and peripheral
vascular resistance, all forms of hypertension involve
hemodynamic mechanisms—an increase in either cardiac
output or peripheral vascular resistance, or a combination
of the two
.
Other factors, such as sympathetic nervous
system activity, kidney function in terms of salt
and water retention, the electrolyte composition
of the intracellular and extracellular fluids, and
humoral influences such as the renin-
angiotensin-aldosterone mechanism, play an
active or permissive role in regulating the
hemodynamic mechanisms that control blood
pressure.
Causes
Risk factors for primary hypertension include:
family history
advancing age
tobacco use
high intake of sodium
high intake of saturated fat
excessive alcohol consumption
sedentary lifestyle
stress
excess renin
diabetes mellitus.
Causes of secondary hypertension include
:
coarctation of the aorta
renal artery stenosis and parenchymal disease
brain tumor.
pheochromocytoma, Cushing's syndrome,
hyperaldosteronism, and thyroid,
pituitary, or parathyroid dysfunction
oral contraceptives, , estrogen replacement therapy,
and nonsteroidal anti-inflammatory drugs
pregnancy-induced hypertension
excessive alcohol consumption.
Target Organ Damage in
hypertension
Left ventricular hypertrophy
Angina/prior myocardial infarction
Heart failure
Stroke or transient ischemic attack
Nephropathy
Peripheral arterial disease
Retinopathy
Heart failure
A syndrome rather than a disease, heart failure
occurs when the heart can't pump
enough blood to meet the metabolic needs of the
body. Heart failure results in intravascular and
interstitial volume overload and poor tissue
perfusion. Although the most common cause of
heart failure is coronary artery disease, it also
occurs in infants, children, and adults with
congenital and acquired heart defects. Heart failure
may be classified according to the side of the heart
affected (left- or right-sided heart failure) or by the
cardiac cycle involved (systolic or diastolic
dysfunction).
Left-sided heart failure.
This type of heart failure
occurs as a result of ineffective left ventricular
contractile function. As the pumping ability of the
left ventricle fails, cardiac output falls. Blood is no
longer effectively pumped out into the body; it
backs up into the left atrium and then into the
lungs, causing pulmonary congestion, dyspnea, and
activity intolerance. If the condition persists,
pulmonary edema and right-sided heart failure may
result. Common causes include left ventricular
infarction, hypertension, and aortic and mitral
valve stenosis.
Right-sided heart failure
. Right-sided heart failure results
from ineffective right ventricular contractile function.
Consequently, blood is not pumped effectively through the right
ventricle to the lungs, causing blood to back up into the right
atrium and into the peripheral circulation. The patient gains
weight and develops peripheral edema and engorgement of the
kidney and other organs. It may be due to an acute right
ventricular infarction or a pulmonary embolus.
Systolic dysfunction.
Systolic dysfunction occurs when the left
ventricle can't pump enough blood out to the systemic
circulation during systole and the ejection fraction falls.
Diastolic dysfunction.
Diastolic dysfunction occurs when the
ability of the left ventricle to relax and fill during diastole is
reduced and the stroke volume falls.
CAUSES OF HEART FAILURE
1.Abnormal cardiac muscle function
Myocardial infarction.
Cardiomyopathy.
Myocarditis.
Valvular Heart Disease
Congenital Heart Defects
4.Increased Pressure Work
Systemic hypertension
Pulmonary hypertension
Coarctation of the aorta
5.Increased Perfusion Work
Thyrotoxicosis
Anemia
6.Constrictive Pericarditis
7.Increased Volume Work
Arteriovenous shunt
Excessive administration of intravenous fluids
Pathophysiology
The pathophysiology of heart failure involves an interaction
between two factors: (1) a decrease in cardiac output
(2) the recruitment of compensatory mechanisms designed to
maintain tissue perfusion.
All causes of heart failure eventually lead to reduced cardiac
output, which triggers
compensatory mechanisms such as Frank Starling mechanism,
increased sympathetic activity, activation of the renin-
angiotensin-aldosterone system, ventricular dilation, and
hypertrophy. These compensatory mechanisms are used to
maintain the cardiac output. This state is called compensated
heart failure. Unfortunately, these mechanisms were not
intended for long-term use. In severe and prolonged heart failure,
the compensatory mechanisms are no longer effective and may
themselves worsen the failure, causing what is termed
decompensated failure.
In heart failure, counterregulatory substances such as
prostaglandins and atrial natriuretic factor are produced in an
attempt to reduce the negative effects of volume overload and
vasoconstriction caused by the compensatory mechanisms. Atrial
natriuretic factor works to counteract the negative effects of
sympathetic nervous system stimulation and the renin-
angiotensin-aldosterone system by producing vasodilation and
diuresis. Eventually,the muscle becomes stretched beyond
optimum limits and contractility declines.