Hypertension Flashcards
Describe the epidemiology of hypertension
Hypertension affects approximately 1 billion people worldwide and is the leading global cause of death
Describe the distribution of BP and hypertension
BP distribution is unimodal and any distinction between normal and abnormal is arbitrary.
this leads to the definition of hypertension:
o The level of BP above which investigation and treatment will do more good than harm.
The BP accepted as normal has decreased over time.
Why is the cut-off arbitrary
The numbers are fluid- they change all the time.
The criteria are arbitrary as blood pressure varies with age and levels are variable within the population.
Current British guidelines define hypertension as a sustained resting blood pressure above 140mmHg and/or 90mmHg.
What does the risk of CVD increase with
Increasing BP, even within the normal range.
Describe ambulatory blood pressure
blood pressure automatically recorded at regular interval and averaged to show true mean - 5-10mmHg lower than recorded in surgeries
Push towards this- cheap and reliable- patients take responsibility for their own health.
What is current practice encouraging BP targets of
Current practice is tending to lower target systolic BP to 120 mmHg but NOT always well tolerated- people who lower their BP dramatically may feel ill- treat patients not numbers.
Describe the relationship between BP and age
Mean BP rises with age
Pulse pressure rises with age (as DBP does not rise much)
The majority of people >60y would be expected to be hypertensive by current definitions, almost everyone hypertensive by >80y
In almost all societies (low salt communities are an exception) mean BP rises with age, pulse pressure also rises after mid-life. This means that the number of people diagnosed as hypertensive increases with age, recent data from the Framingham longitudinal study indicates that if you live long enough you will almost certainly become hypertensive by current definitions.
Is there are reliable threshold for BP and stroke mortality risk
ThThis slide plots a population distribution of systolic BP and the relationship between systolic BP and risk of stroke. The relationship between BP and risk is exponential (log linear) and there is no threshold for risk. Every 20mmHg increase in BP results in a doubling in risk of stroke (or CHD – not shown). Similar relationships have been shown for BP and coronary heart disease and other cardiovascular disease.
ere is no reliable threshold for BP risk
What is the consequence of a lack of a threshold
- As there is no threshold, a large burden of disease is on people with a ‘normal’ BP.
o 50% of attributable burden falls on people with a BP < 141mmHg.
Describe primary hypertension
Unidentifiable cause – primary or essential
(85-95% of cases)
they are idiopathic
Describe secondary hypertension
secondary 5-15%% e.g.
Renal disease, including renal artery stenosis- decreases renal perfusion- stimulating the RAAS
Tumours secreting aldosterone (Conn’s syndrome) - salt and water retention, increasing blood volume, preload and therefore CO- increasing BP
Tumours secreting catecholamines (phaeochromocytoma)
Oral contraceptive pill
Pre-eclampsia/pregnancy associated hypertension
Rare genetic causes (e.g. Liddle’s syndrome
Coarctaction of the aorta- resistance to flow through the aorta- thus increasing TPR and BP
Hypertension from a disease of which hypertension is a symptom.
Describe the genetic aetiology of hypertension
- Monogenic (single genes causing hypertension) – VERY RARE.
o Liddle’s Syndrome.
o Apparent mineralocorticoid excess. - Complex polygenic (multiple genes causing hypertension) – COMMON.
Estimates suggest that the heritability of high blood pressure is around 30-50%.
Describe the environmental aetiology of hypertension
Dietary salt (sodium) Obesity / overweight, lack of exercise Alcohol Pre-natal environment (~birthweight) Pregnancy (pre-eclampsia) Other dietary factors and environmental exposures?
Describe the genetics behind hypertension
Most genes involved in the regulation of Na+ in the Kidney.
Twin and other studies suggest 30-50% of variation in blood pressure is attributable to genetic variation but to date identified SNPs only account for <4% of this variance1.
Monogenic disease causes <1% of hypertension
Liddle’s syndrome
Mutation in amiloride-sensitive tubular epithelial Na channel
Apparent mineralocorticoid excess
Mutation in 11b-hydroxysteroid dehydrogenase
Complex polygenic causes
Multiple genes with small effects (positive and negative)
Interactions with sex, other genes, environment
Describe the importance of dietary salt on BP
- Dietary salt – PRINCIPAL CAUSE in terms of environmental factor
o With low sodium intake throughout life, there is no rise in BP with age.
Increased salt excretion= increased DBP- linear relationship.
What is hypertension associated with
Increased TPR (major cause) Decreased arterial compliance Normal cardiac output Normal blood volume / ECV Central shift in volume Secondary to reduced venous compliance
Describe the importance of TPR
The relationship between BP, cardiac output and peripheral resistance is key to understanding the haemodynamics of high BP. Numerous studies have shown that in established primary (essential) hypertension the increased blood pressure is due to elevated peripheral resistance.
What factors increase the TPR
Structural narrowing of the arteries- remodelling- walls get thicker- lumen gets smaller- may be adaptive (not necessarily caused by hypertension)
Active narrowing of the arteries- vasoconstriction- probably short term.
Capillary loss- Rarefaction (reduction in density) (Adaptive? Damage?
What is meant by isolates systolic hypertension
Systolic BP ≥ 140 mmHg, diastolic BP ≤ 90 mmHg
Condition of people over age 60
There are no specific treatments for ISH as against “standard” hypertension
What are the causes of isolates systolic hypertension
Due to increasing stiffness of medium/large arteries
Pulse wave reflected and is greater by the time it reaches brachial artery
Does NOT mean that TPR increases
Stiffer arteries reflect the pulse wave and effectively amplify it when they are supposed to cushion it.
Describe the role of the kidney in the development of primary hypertension
play a key role in salt regulation and so BP regulation (PRINCIPAL CAUSE)
Describe the role of the endocrine system in the development of primary hypertension
Endocrine/paracrine factors
Inconsistent evidence
Describe the role of the SNS in the development of primary hypertension
Sympathetic nervous system
Evidence linking high sympathetic activity to the development of hypertension
Describe the mechanisms by which the Kidney plays a role in hypertension
The kidney exerts a major influence on BP through regulation of sodium/water/extracellular fluid volume1
Impaired renal function or blood flow is the commonest 2º cause of hypertension (e.g. renal parenchymal disease, renal artery stenosis)
Almost all monogenic causes of hypertension affect renal Na+ excretion
Salt intake is strongly linked with blood pressures of human populations. Populations with low salt have low population blood pressures and no rise in BP with age.
Animals with reduced renal Na+ handling (genetic or experimental) develop hypertension. Excess salt intake in many animals results in elevated blood pressure
