PATHOPHYSIOLOGY OF HYPERTENSION
LEARNING OUTCOMES
DEFINE HYPERTENSION
UNDERSTAND THE PATHOPHYSIOLOGY OF HYPERTENSION
DISCUSS CURRENT PERPECTIVES IN THE TREATMENT OF HYPERTENSION
HYPERTENSION
Hypertension is an important public health concern globally
- Affects around a billion individuals worldwide
- About 1 in 4 adults
- Accounts for more than 10 million deaths each year
DEFINE IT AS: A rise in arterial blood pressure, sufficient to raise the incidence of stroke, myocardial
infarction, heart failure and renal failure
- Simplistically we can define it as a chronic and usually progressive raised arterial blood pressure
of a 140 systolic over 90 millimetres mercury diastolic (140/90 mmHg)
- Chronically elevated systemic blood pressure
To get accurate diagnosis, guidelines from the British hypertension society, blood pressure should be
measured on three to four occasions while the patient is sitting over several weeks before the decision is
made.
Blood pressure is monitored yearly if it is between the ranges of 135-139 systolic/ 85-89 diastolic
Often the clinic ambulatory blood pressure monitoring is carried out by the clinical physiologist when the
individuals are borderline.
Classification- in the majority of cases there’s no obvious predisposing organic cause
- Essential hypertension (95% of cases)- termed essential because it was thought the rise in blood
pressure was essential to maintain tissue perfusion
- Secondary hypertension- found in only about 5-10% of cases. Has an identifiable pathological cause
(e.g. renal disease; Pre-eclamptic toxaemia
- occurs in the third trimester and about 2-6% of pregnancies)
- Defined as a Brachial artery blood pressure of more than 140/90
with the proteinuria of greater than 0.3g per day
- this normally resolves postpartum
Essential Hypertension can follow one or two courses
- Benign essential hypertension: usually symptom-less and diagnosed after a routine check-up. The
most common form of the disease. There are a number of predisposing factors which include:
o obesity; excessive alcohol consumption; high dietary salt intake; stress; lack of exercise
which results in serious consequence later in life such as stroke
- Malignant hypertension: rare- presents by a Rapid increase in BP.
o This leads to heart failure, peripheral oedema, hypertensive retinopathy
, WHY DOES THE ARTERIAL BLOOD PRESSURE RISE?
Pathophysiological alterations in the walls of blood vessels
The primary pathology is the small arterial narrowing which leads to increased peripheral resistance. And
this is raised in every organ including the kidneys
- Small resistance-size arteries
- Small arterial narrowing raises peripheral resistance and mean arterial blood pressure [MAP]
Rarefaction is also seen in some organs and this is where there is a reduction in the number of vessels per
unit tissue volume
- Seen in skin, retina and intestines
The increase in peripheral resistance leads to an increase in mean arterial pressure. According to:
MAP = CO x Peripheral Resistance
Mean arterial pressure = cardiac output x the peripheral resistance
Large arterial changes include:
- Large elastic arteries
- Large arterial stiffening exacerbates systolic hypertension
- Elastin fragmentation
- Increased wall stiffness, increased pulse wave velocity
And therefore reduced compliance- which also increases pulse wave velocity
The large vessel changes are usually secondary, and they cause a rise in systolic and pulse pressure
FEATURES OF HYPERTENSION
So the small vessel narrowing is initially due to the
increased vascular tone/reactivity
- usually reversible by vasodilator drugs
o so when the patients are given vasodilators
then the blood pressure normalises.
o But over time, the vessel wall structure
starts to change. And this is known as
remodelling – usually associated with
increased media thickness
In mild hypertension
- vascular myocytes rearrange and there is increased
extracellular matrix and it leads to narrowing by
about 10%
EUTROPHIC MODELLING: The process of changing the vessel wall without changes in the amount or
characteristics of the material
- This is the typical form of remodelling and hypertension
- Ratio of wall thickness to internal radium is increased by ~30%
- Smaller diameter
In severe hypertension there is also
- hypertrophy of the vascular myocytes which increases vascular wall area, and this is
HYPERTROPHIC REMODELLING- changes in vessel wall with increased amount of material
o And this change may be triggered by angiotensin II, which is a vasoconstrictor, but it is also a
growth factor, so it stimulates the hypertrophy and the hyperplasia of the vessel wall.
Other important pathophysiological feature of hypertension is endothelial dysfunction – early hallmark of
the disease
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