Hypertension

Hypertension = high blood pressure

Blood pressure (BP) = cardiac output (CO) x peripheral resistance (PR)

2 circulatory systems in which hypertension can occur:

• Systemic
• Pulmonary

25% of the UK population have hypertension.

Definition –

Sustained BP above a certain cut off level. Usually ≥140/80 mm Hg but this can vary with location.

Classification by cause–

• Primary (essential) – usually caused by lifestyle factors
• Secondary – caused by an underlying disease

1. Thyroid – hypo/hyperthyroidism
2. Parathyroids – hyperparathyroidism
3. Adrenal – Cushing’s syndrome, hyperaldosteronism, phaeochromocytoma

Many drugs result in secondary hypertension, below is a list of some of the most common offenders.

1. Oral contraceptive pill
2. Steroids
3. Alcohol
4. Amphetamines
5. Cocaine

Again there are lots of other physiological and pathological states which result in secondary hypertension.

It is important to think about what the most common cause may be and then to formulate a differential diagnosis list accordingly – don’t immediately jump straight to an obscure endocrine cause without excluding the more common causes first.

*this is a very brief overview of the RAAS system. For more detail please look at relevant information in Davidson’s or online. This will also be revisited in the Year 2 Renal/Urology module in more detail*

The renin-angiotensin-aldosterone system (RAAS) links the kidney, endocrine organs and cardiovascular system together.

It regulates BP & fluid balance through a variety of hormones.

It is shown briefly here in 3 simplified steps.

• Renal blood flow is reduced and is detected at the juxtaglomerular cells near the glomerulus
• This stimulates the kidneys to convert pre-renin into renin

• Angiotensinogen (secreted by the liver) is converted to angiotensin I by renin

  

• Angiotensin I is converted to angiotensin II by angiotensin-converting enzyme ACE secreted by lungs

  

• Angiotensin II has multiple sites of action across the body
• The overall effect of these changes is retention of water leading to an  increase in circulating blood volume and an increase in BP

End organ damage can be roughly classified into 2 pathological categories:

1. Benign hypertension results in slow changes to vessels with chronic end-organ dysfunction
2. Malignant hypertension leads to rapid changes in vessels with acute end-organ dysfunction. The patient’s BP is usually ≥ 180/110 mm Hg

• The left ventricle thickens in order to pump blood to the body against a high BP
• This abnormal thickening can lead to lots of problems like arrhythmias, ischaemic heart disease, heart failure & stroke
• This is shown in the picture below. Notice the thickened ventricle across the blue arrow

Benign hypertension can lead to –

• hyaline arteriosclerosis (hardening) of arterioles
• splitting of the elastic lamina resulting in damage to the arteriole wall
• Acceleration of underlying atherosclerosis

Malignant hypertension can lead to –

• Fibrinoid necrosis – a type of necrosis with proteinaceous material which resembles fibrin

In the next frame match the picture with the pathological process

Regarding the image below answer the following questions:

Answer the questions below related to the following 2 images.

• Longstanding hypertension can lead to the formation of saccular (berry) aneurysms along the Circle of Willis. These are different to the microaneurysms seen in the previous section as they are found within the subarachnoid space
• These can rupture resulting in sudden onset severe headache, nausea, photophobia & stiff neck

This is a middle cerebral artery cerebral infarct. Cerebral infarction is the most common cause of stroke and one of the main risk factors for it is hypertension.

It’s often preceded by narrowing (stenosis) of the internal carotid artery.

This picture outlines a severe stenosis indicated by arrow ‘A’. This narrowing can also lead to thrombus and embolus formation which can also to transient ischaemic attacks (TIAs) or cerebral infarction.

Below are 2 kidneys. Which one do you think looks normal? Compare and contrast the two and comment on the colour & surface of both.

• Hypertension affects the small arterioles of the retina resulting in hypertensive retinopathy
• This is usually asymptomatic, but can eventually lead to retinal haemorrhage and visual loss
• It is graded in 1-4 stages depending on clinical finding on fundoscopy
• Malignant hypertension can present with decreased vision +/- headache

A hypertensive crisis is a medical emergency.

Defined by an elevated BP (systolic >210mm Hg) with rapid decompensation of vital organ function

Effects all organs previously discussed:

–Hypertensive encephalopathy

–Hypertensive retinopathy

–Cardiac failure, pulmonary oedema, myocardial ischaemia

–Acute renal failure

It has lots of symptoms and signs due to its diffuse effect on the body. It is easier to break down signs and symptoms according to the body system

–Neuro – confusion, headache, fits, nausea & vomiting

–Ophthalmology – blurred vision

–Cardio – chest pain, SOB

–Renal – changes to urine output

Hypertension is an extremely important topic. I hope that by the end of this tutorial you get a better understanding of –

• The different classifications of hypertension
• The various causes of it
• The Renin-Angiotensin-Aldosterone-System
• End organ damage particularly in the heart, vascular system & brain