Blood Pressure Control Flashcards
What is the equation for blood pressure?
Mean systemic arterial pressure =
cardiac output x total peripheral resistance
Why must blood pressure be closely auto-regulated?
To ensure there is a balance between organ perfusion and vascular damage
What is the equation for total peripheral resistance?
R = (8nL)/pi x r^4
R = resistance to blood flow L = length of the vessel n = viscosity of the blood r = radius of the vessel
What component has the largest effect on the value for total peripheral resistance?
radius of the blood vessel
This, therefore, also has a large effect on blood pressure
What else can the value for TPR be affected by?
Autonomic nervous system
What are the aims of the short- and long-term control mechanisms to regulate blood pressure?
To balance any changes in blood pressure to maintain a consistent organ perfusion pressure
What is the role of baroreceptors and where are they located?
In the carotid sinuses and aortic arch
They detect arterial pressure
How will decreased arterial pressure affect the baroreceptors?
Decreased firing of the baroreceptors
This increases sympathetic tone and decreases parasympathetic tone
How will increased arterial pressure affect the baroreceptors?
Increased firing of the baroreceptors
This increases parasympathetic tone and decreases sympathetic tone
On which organs does the sympathetic nervous system act on to achieve:
i. positive chronotropy
ii. positive dromotropy
iii. positive ionotropy
iv. positive lusitropy
i. sino-atrial node
ii. atrioventricular node
iii. ventricles and atria
iv. atria and ventricles
What is meant by ‘positive chronotropy’?
The action of the sympathetic nervous system will increase the heart rate
What is meant by ‘positive dromotropy’?
The sympathetic nervous system increases conduction velocity through the AV node
What is meant by ‘positive inotropy’?
The sympathetic nervous system increases the strength of muscular contraction
What is meant by positive ‘lusitropy’?
The sympathetic nervous system increases the rate of myocardial relaxation after contraction
What are the other 2 actions of the sympathetic nervous system after activation by baroreceptors?
- activation of the renin-angiotensin-aldosterone system
2. suprarenal stimulation leads to the release of catecholamines from the adrenal glands
What are the 2 types of natiuretic peptide?
What type of blood pressure control are they involved in?
Long-term blood pressure regulation
ANP - atrial natriuretic peptide
BNP - brain natriuretic peptide
What is the role of natriuretic peptides in blood pressure regulation?
They induce the excretion of Na+ in urine
They try to reduce the pressure in the system by increasing fluid loss through urine
When are natriuretic peptides released?
What condition is diagnosed by measuring levels of natriuretic peptides?
When myocytes are mechanically stretched by increasing plasma volume
Measuring levels of natriuretic peptides is used in diagnosing heart failure
What is hypertension defined by?
Having a systolic blood pressure greater than or equal to 140 mmHg
and/or a diastolic blood pressure greater than or equal to 90 mmHg
What is hypertension a result of?
Blood pressure control mechanisms are dysfunctional or unable to compensate for stressors on the body
What are the 2 types of hypertension?
- Primary (essential) (90% of cases)
2. Secondary (10% of cases)
What is significant about the cause of primary hypertension?
There is no cause of hypertension
It happens due to pathological maladaptation of the blood system
What is significant about the cause of secondary hypertension
There is something wrong with the body that is causing the blood pressure to be high
What are the most common contributing factors to primary (essential) hypertension?
- over-activation of physiological mechanisms
- age-related decrease in baroreceptor sensitivity
- age-related vascular calcification
What are the 5 most common causes of secondary hypertension?
- renal - renovascular disease, parenchymal disease
- endocrine - Conn’s or Cushing’s syndrome
- cardiovascular - coarctation of the aorta
- tumour - pheochromocytoma
- pregnancy - pre-eclampsia/eclampsia
What is pheochromocytoma?
A tumour of the adrenal glands caused by overactivation and catecholamine excess
What is significant about calcification of the blood vessels with increasing age?
Blood vessels are not as compliant
The total peripheral resistance cannot change as much
Why are at least three readings needed to diagnose hypertension?
“White coat syndrome” makes people anxious in a clinical setting
This causes their blood pressure to rise
What is often used to overcome the complications of “white-coat syndrome”?
Ambulatory/home blood pressure monitoring
How does hypertension lead to left ventricular hypertrophy?
What is this?
It involves thickening of the left ventricular wall
It occurs in response to the increase in pressure in the left ventricle
What happens to the cells in left ventricular hypertrophy and what is the result of this?
The cells do not become more numerous, they get bigger
The result of this is to try and force more blood out of the heart
What is diastolic dysfunction?
How is it a result of left ventricular hypertrophy?
Impaired filling of the left ventricle during diastole
Thickening of the LV wall means that the ventricle cannot relax properly to allow it to fill with blood
How diastolic dysfunction and LVH affect LV end diastolic pressure?
LVH leads to increased stiffness
Diastolic dysfunction leads to impaired relaxation
Both of these factors will increase LV end diastolic pressure
How can increased LV end diastolic pressure lead to systolic heart failure?
The increase in pressure is transmitted back into the LA and into the lungs
This leads to pulmonary congestion that leads to heart failure
How does prolonged hypertension affect the blood vessels?
It leads to vascular remodelling
Where does eutrophic remodelling occur?
What is the result of this?
Small arteries
Media-to-lumen ratio is increased but medial cross-sectional area decreased
This increases systemic vascular resistance and leads to an increase in diastolic blood pressure
Where does hypertrophic modelling occur and what is involved?
Large arteries
Media-to-lumen ratio and the medial cross-sectional area are increased
How does hypertrophic remodelling lead to an increase in systolic blood pressure?
Thickening of the smooth muscle layer leads to an increase in the stiffness of the wall
What is significant about remodelling of the arteries increasing blood pressure further?
remodelling reduces the compliance of the arteries
This further increases the blood pressure
What conditions are the blood vessels more prone to in hypertension?
- large vessel structural damage
2. atherosclerosis
Which parts of the body are affected by atherosclerotic disease?
All parts of the body are affected as all parts of the body contain blood
What can atherosclerosis in the coronary arteries, kidneys and neck lead to?
Coronary arteries - heart failure, arrhythmias, angina, myocardial infarction
Kidneys - renal failure
Neck - stroke
What are the 3 steps involved in hypertensive neuropathy?
- renal arteriole thickening leads to luminal narrowing
- the resulting ischaemia leads to tubular atrophy and interstitial fibrosis
- this leads to damage to the glomeruli, leading to haematoproteinuria
What is the outcome of hypertensive neuropathy?
Damage to the glomeruli leads to increased leakage
Things that are not meant to pass through the filter., such as proteins, pass through and are detected in urine
What is hypertensive retinopathy?
Popping of the small blood vessels in the eye due to high blood pressure
If untreated, a patient will eventually go blind
What are the 4 visible signs of hypertensive retinopathy?
- papilledema
- exudates
- flame haemorrhages
- cotton wool spots
What is papilledema?
Swelling of the optic disc
This is the point where the optic nerve enters the eye
What is an exudate?
Any fluid that filters from the circulatory system into lesions/areas of inflammation
What causes flame haemorrhages?
Accumulation of blood at the level of the nerve fibre
What are cotton wool spots and what causes them?
Fluffy white patches on the retina
Caused by damage to the nerve fibres due to swelling of the retinal nerve fibres
Why are hypertension investigations carried out?
- to look for a cause of secondary hypertension
- to assess end-organ damage
(signs of dysfunction in major organs which are affected by hypertension)
What is a full blood count used to look at in hypertension?
Haemoglobin levels
This gives an indication of blood viscosity
What is a urea and electrolyte test used to look at in hypertension?
It assesses kidney function
It looks for signs of renal impairment and hypernatremia
What is hypernatremia?
A rise in serum sodium concentration
Why are lipid and glucose levels measured when performing tests on hypertension?
To look for any other cardiovascular disease risk factors
e.g. glucose in urine indicates diabetes
What are urine samples checked for in hypertension?
Haematuria and proteinuria
presence of blood and/or protein in the urine
What is indicated by haematuria and/or proteinuria in hypertension?
If hypertension has affected the kidneys, blood and/or protein is present in urine
What would be seen on an ECG of someone with left ventricular hypertrophy and why?
QRS complex has a high amplitude
Hypertrophied muscle has a higher electrical amplitude
How could LVH be identified from an echocardiogram?
The thickness of the left ventricle wall can be measured to see if it is hypertrophied
Why might the diameter of the left atrium be measured on an echocardiogram?
To see whether left atrial dilatation is present
Why might left atrial dilatation be present?
What type of patients is this expected to be seen in?
High pressure in the ventricles due to LVH is transmitted back to the atria
This is present in patients who have had hypertension for a long time
How can coarctation of the aorta be identified on an echocardiogram?
What is this?
By using the Doppler effect
There is an abnormal narrowing in the aorta which leads to high blood pressure
What is fundoscopy?
Why is it used in patients with hypertension?
It involves looking at the retina in the back of the eyes
This is used to detect grade I - IV hypertensive retinopathy
In the case of pheochromocytoma, what test may be performed?
24-hour urinary catecholamines are collected
In the case of Conn’s syndrome, what test may be performed?
Plasma renin-aldosterone levels are measured
What are the 5 lifestyle modifications involved in the management of hypertension?
- increased exercise helps with blood pressure control
- weight loss
- changing diet
- smoking cessation
- education
Why does increasing exercise and weight loss help with management of hypertension?
Increased exercise helps with blood pressure control
Being overweight increases blood pressure and is associated with diabetes
What dietary changes help in management of hypertension?
Cutting down on salt and reducing the amount of alcohol consumed
What type of education may help people manage their hypertension?
Resources that allow people to make decisions for themselves
They do not like being told what to do directly
What is high blood pressure a risk factor for?
How does this affect smoking cessation?
Cardiovascular disease
If you have another risk factor for CVD, this should try to be cut out as well as lowering the blood pressure
If lifestyle changes do not work, what treatment is used for hypertension?
Why is this not the preferred method of treatment?
Pharmacological treatments
Medications have side effects so it is preferable that BP is lowered through lifestyle changes
What is the A(B)CD of pharmacological management of high blood pressure?
A - ACE inhibitors and ARBs
(B) - Beta blockers
C - Calcium channel blockers
D - diuretics
What is a commonly used ACE inhibitor and how does it work?
Ramipril
It inhibits angiotensin-converting enzyme (ACE)
angiotensin I cannot be converted to angiotensin II
What is a common angiotensin II receptor blocker (ARB)?
How does it work?
Candesartan
It blocks the effects of angiotensin II, even though it is still present in the blood stream
How do calcium channel blockers work?
They disrupt the movement of Ca2+ through calcium ion channels
What are the 2 types of calcium channel blockers and an example?
Dihydropyridine (e.g. amlodipine)
Non-dihydropyridine (e.g. diltiazem)
How do dihydropyridines lower blood pressure?
They cause vasodilation
How do non-dihydropyridines lower blood pressure?
They cause vasodilation
They are also negatively inotropic (decrease strength of muscular contraction)
And negatively chronotropic (decrease heart rate)
What is the result of blocking calcium channels on the heart and blood vessels?
It reduces total peripheral resistance
It also reduces cardiac output by decreasing the force and speed of contraction of the heart
What are diuretics and how do they reduce the blood pressure?
They induce diuresis which reduces the circulating volume of the blood
This reduces the preload, and the blood pressure
What are the 2 types of diuretics and examples?
Thiazide diuretics (e.g. Bendroflumethiazide)
Loop diuretics (e.g. furosemide)
What is the difference between loop and thiazide diuretics?
Loop diuretics act on the loop of Henle in the nephron
Thiazide diuretics act on the distal convoluted tubule
Why are beta blockers no longer used to treat hypertension?
They are not as effective as other treatments and have more side effects
How does Bisoprolol affect the heart and blood vessels?
It is a beta blocker that also reduces renin secretion
It blocks the effects of the sympathetic nervous system on the heart
There is no suprarenal stimulation or activation of the RAAS
What type of drug is doxazosin and how does it work?
It is an alpha-blocker which blocks the effects of adrenaline
Adrenaline causes blood vessels to narrow
How do moxonidine and spironolactone work?
moxonidine lowers sympathetic nervous system activity
spironolactone is an aldosterone antagonist
According to NICE guidelines, what are the 4 steps involved in a treatment plan for treating hypertension?
1 - Patients <55 start on A
Patients >55 or black start on C
2 - A + C
3 - A + C + D
4 - add another diuretic or a-blocker or b-blocker
According to NICE guidelines, how should treatment for hypertension begin?
Why?
Patients are started on a low dose to allow their body to get used to the medication
This allows for a gradual change rather than a steep decrease in BP
According to NICE guidelines, what happens if the initial dose of the first drug is not effective?
The dose can be increased over time until the blood pressure is significantly improved
According to NICE guidelines, what happens if the patient reaches the maximum dose of the first drug and it is not effective?
If they reach the maximum dose and their blood pressure is still high, a second medication is added
The same process is repeated
What should be done if a patient is on 3 different medications and their blood pressure has still not improved?
Ask the patient if they are taking their medication
Many patients stop taking medication as they do not like the side effects
Which hypertension drugs are preferred in left ventricular systolic dysfunction?
ACE inhibitors and A2RBs
Beta blockers
Which hypertension drugs are preferred in angina?
Beta blockers and calcium channel blockers
Which hypertension drugs are preferred in diabetes/proteinuria?
ACE inhibitors and A2RBs
When should ACE inhibitors and A2RBs not be used?
- pregnancy
- renal artery stenosis
- hyperkalaemia (high potassium levels)
Why should ACEi/A2RBs not be used in renal artery stenosis?
This can lead to pulmonary oedema and a massive fall in blood pressure
When should beta blockers not be used and why?
Asthma
Blue inhalers contain beta agonists
When should diuretics not be used?
- hypokalaemia (low potassium levels)
2. gout
