Articles

Hypertension

September 18, 2019


Blood pressure is the pressure of
the blood on the arterial walls. When we talk about blood pressure it would
be shown in two numbers, (for example 120 mm Hg and 70 mm Hg.) The first number is expressed in terms of
the systolic blood pressure and the second number is the diastolic pressure. Since 2017, the American Heart Association
(AHA) considers optimal blood pressure to be lower than 120/80 mm Hg. Systolic blood pressure is the maximal pressure
in the arteries at the moment of pushing the blood into the aorta during the ventricular
contractions. Systolic blood pressure mainly depends on
the volume of blood ejected into the aorta, so-called stroke volume and it also depends
on heart rate. The heart rate is the number of heart beats
per minute. You can also define it as the speed at which
the heart beats. So, heart rate multiplied by stroke volume
is called cardiac output. The cardiac output is usually expressed in litres per minute. So in other words. The cardiac output is simply the amount of
blood pumped by the heart per minute. It is the product of the heart rate, which
is the number of beats per minute, and the stroke volume, which is amount pumped per
beat. The diastolic blood pressure is specifically
the minimum arterial pressure during relaxation of the ventricles when the ventricles fill
with blood. Diastolic blood pressure mainly depends on
total peripheral vascular resistance. The increased vascular resistance is mainly
attributable to small arteries and arterioles. Difference between systolic and diastolic
blood pressure is called pulse pressure. For example, if blood pressure is 120/80 mmHg,
then the pulse pressure is 40 mmHg. Pulse pressure depends on the interaction
of stroke volume and the ability of arteries to expand, also called compliance. Reduced arterial compliance causes the elevation
of the pulse pressure which often is found in elderly patients. Now, as we have talked about the physiology
of blood pressure, lets talk about hypertension, also known as high blood pressure. Hypertension is a long-term patient’s condition
which is characterized by persistent elevation of arterial blood pressure. Usually patient with hypertension complains
of headache, nausea and fatigue. Also, hypertension-associated complaints involve
blurred vision or loss of vision, chest pain, irregular heartbeat, mental disorders, ringing
in the ears. In 90% of patients, the cause of hypertension
is unknown. This is called primary (essential) hypertension
which is a multifactorial disease. The risk factors of primary hypertension include
obesity, high sodium intake, sympathetic activity, stress, old age and family history. But sometimes the causes of hypertension are
found, these are most often underlying, reversible causes; it is called secondary hypertension
The causes of secondary hypertension include: renal artery stenosis due to atherosclerosis
or fibromuscular dysplasia, vasculitis, kidney diseases, pheochromocytoma, hyperaldosteronism,
Cushing’s syndrome, hyperthyroidism, hypothyroidism, acromegaly, hyperparathyroidism, coarctation
of the aorta, obesity, excessive drinking of alcohol, obstructive sleep apnoea, pregnancy,
drugs such as oral contraceptive pill, immunosuppressive medications, stimulant drugs, nasal decongestants,
corticosteroids, caffeine High blood pressure in pregnancy is classified
into three types: pre-existing hypertension, gestational hypertension, pre-eclampsia. Gestational hypertension is defined as new-onset
hypertension during pregnancy without protein in the urine. Pre-eclampsia is defined when a pregnant woman
has high blood pressure and has protein in the urine. Pre-eclampsia can be complicated by a life-threatening
condition called eclampsia, which is a hypertensive emergency with seizures and proteinuria. There are differences in the definition of
hypertension between the European Society of Cardiology (ESC) and the American College
of Cardiology (ACC). According to ESC blood pressure is classified
as optimal, normal, high-normal, grade I hypertension, grade 2 hypertension, grade 3 hypertension
and isolated systolic hypertension. Optimal blood pressure means blood pressure
is less than 120/80 mm Hg. Normal blood pressure denotes systolic blood
pressure of 120-129 mm Hg and/or diastolic blood pressure of 80-84 mm Hg. High normal blood pressure means systolic
blood pressure of 130-139 mm Hg and/or diastolic blood pressure of 85-89 mm Hg. If blood pressure is 140/90 mm Hg and more
on two and more occasions, hypertension is diagnosed. Grade 1 hypertension means systolic blood
pressure of 140-159 mm Hg and diastolic pressure of 90-99 mm Hg. Grade 2 hypertension is diagnosed when systolic
blood pressure ranges from 160 to 179 mm Hg and/or diastolic pressure ranges from 100
to 109 mm Hg. If systolic blood pressure is 180 mm Hg and
more and/or diastolic hypertension is 110 mm Hg and more, grade 3 hypertension is diagnosed. An isolated systolic hypertension is diagnosed,
if systolic blood pressure is 140 mm Hg and more and diastolic blood pressure is less
than 90 mm Hg. The isolated systolic hypertension is graded
1, 2 or 3 according to systolic blood pressure. Also, Home blood pressure monitoring and Ambulatory
blood pressure monitoring can establish a diagnosis. According to ACC blood pressure is classified
as normal, elevated, stage 1 hypertension, stage 2 hypertension. Normal blood pressure means blood pressure
is less than 120/80 mm Hg. Elevated blood pressure denotes systolic blood
pressure of 120-129 mm Hg and/or diastolic blood pressure less than 80 mm Hg. Stage 1 hypertension is diagnosed when systolic
blood pressure ranges from 130 to 139 mm Hg and/or diastolic pressure ranges from 80 to
89 mm Hg. If systolic blood pressure is 140 mm Hg and
more and/or diastolic hypertension is 90 mm Hg and more, stage 2 hypertension is diagnosed. Currently, there is no single mechanism that
can explain pathology of the essential hypertension. Activation of the renin-angiotensin-aldosterone
system is considered to be major theory of essential hypertension. Juxtaglomerular cells release renin in response
to a decrease in afferent arteriole pressure, reduced sodium chloride delivery to macula
densa, increased sympathetic tone. Renin cleaves a decapeptide, angiotensin I,
from angiotensinogen. Angiotensin I is transformed in angiotensin
II by the angiotensin-converting enzyme also called ACE, which is synthesized mainly in
the lungs. Angiotensin II is the strongest vasoconstrictive
factor. Besides direct vasoconstrictive effect, it
causes aldosterone release in the adrenal cortex leading to the sodium and fluid retention
and potassium excretion, and impaired endothelial cell function. Also, angiotensin II causes the release of
vasopressin exhibiting reabsorption of water in the kidneys and it has vasoconstrictive
effects. Also, vasopressin enhances the sensation of
thirst. Angiotensin II stimulates sodium/hydrogen
exchangers increasing a sodium reabsorption. All these mechanisms lead to an increase in
both blood volume and vascular tone resulting in elevated blood pressure. Increased cardiac output and heart rate influence
on blood pressure much less than vascular resistance, but they can cause the “borderline
hypertension” in young people. Another mechanism of the blood pressure elevation
is based on abnormal cell membrane ion transport resulting in an increase in the intracellular
calcium, which increases vascular tone and stimulates hypertrophy. Endothelial dysfunction also plays an important
role in blood pressure elevation. The endothelial cell has impaired biosynthesis
or release of the nitric oxide and an increased vasoconstrictive response to endothelin. According to ESC, there are 3 stages of hypertension:
stage 1 – uncomplicated; stage 2 – an asymptomatic disease with hypertension-mediated organ damage; stage 3 – established cardiovascular or renal disease. Asymptomatic hypertension-mediated organ damage
involves following states: left ventricular hypertrophy, microalbuminuria or elevation
of albumin-creatinine ratio, chronic kidney disease, retinopathy, ankle-brachial index

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