PPS Epidemiology of Hypertension

Question 1

Epidemiology of Hypertension

Answer 1

PPS

Question 2

What factors can systematically affect BP measurements?

Answer 2

Subject:
anxiety -> high BP

Observer:
technique -> high/low
personality -> high/low

Instrument:
characteristics -> high/low

Cuff size:
small cuff -> high/low
large cuff -> high/low

Environment:
noisy, cold -> high

No. of readings:
more readings -> lower (esp if BP high initially)

Question 3

An initial high blood pressure is often followed by lower readings- why?

Answer 3

Accomodation’

1 -Accommodation – sympathetic response to initial blood pressure readings falls, blood pressure falls

2 -Statistical phenomenon `regression to mean’ – when the initial BP measure is high, repeat measures tend to be lower

Question 4

Why is high blood pressure globally important?

Answer 4

Looking at global burden of disease causes, the top item on that is actually high blood pressure.
It’s the most important single cause of ill health and death in a global context.

Question 5

Why is high blood pressure a problem?

Answer 5

Higher blood pressure levels cause markedly higher risks of cardiovascular disease (CVD), especially coronary heart disease (CHD) and stroke

High blood pressure levels high enough to increase CVD risk are very common in the general population

Question 6

What does High BP increase the risks of?

Answer 6

Coronary (ischaemic) heart disease
Stroke (all types)
Ischaemic stroke
Haemorrhagic stroke
Subarachnoid haemorrhage
Heart failure
Hypertensive heart disease
Sudden death
Renal (kidney) failure
All-cause mortality

Question 7

What is a cohort (longitudinal) study?

Answer 7

An observational study, just observing associations not attmepting to change BP (eg Framingham study)

Take BP measurement (ideally based on repeated measurements providing ‘usual blood pressure’)
-> follow up after 5-10 years
Risk of developing cardiovascular disease or dying from it

Question 8

What is the Framingham study?

Answer 8

The study began in 1948 by recruiting an Original Cohort of 5,209 men and women between the ages of 30 and 62 from the town of Framingham, Massachusetts, who had not yet developed overt symptoms of cardiovascular disease or suffered a heart attack or stroke. Since that time the study has added an Offspring Cohort in 1971 and more

Monitoring of the Framingham Study population has led to the identification of major CVD risk factors, as well as valuable information on the effects of these factors such as blood pressure, blood triglyceride and cholesterol levels, age, gender, and psychosocial issues. Risk factors for other physiological conditions such as dementia have been and continue to be investigated.

Question 9

What are the two ways of describing the effect of high BP on risk?

Answer 9

Ratio of risks (high/normal, eg 6/2)

Difference of risks (high minus normal, 6-2)

Question 10

How do we measure overall strength of association between BP and CVD?

Answer 10

USE OF RELATIVE RISK

Relative risk provides a good summary of the influence which high blood pressure has on cardiovascular risk across the population

Described as ratio:
= Risk of disease outcome in people with a cause/Risk of disease outcome in people without a cause

= Cardiovascular risk in people with high BP/Cardiovascular risk in people without high BP

= Cardiovascular risk in people with a higher BP/Cardiovascular risk in people with a lower BP

Question 11

How strong are the relative risks of high blood pressure (70-79 years)?

Answer 11

Systolic: risk of stroke and CHD with high reading is around double, but ~0.5 with lower
Diastolic: risk of stroke and CHD with high reading is around double, but ~0.5 with lower

These proportional risks apply across all BP levels above SBP 115 mmHg, DBP 75 mmHg

RRs are slightly higher in younger people, slightly lower in olderpeople

Question 12

How do measure strength of association between BP and CVD?

Answer 12

USE OF RELATIVE RISK
= Cardiovascular risk in people witha higher BP/Cardiovascular risk in people with a lower BP

Relative risk: Interpretation
= 1.0 Exposure has no effect on risk
= 2.0 Exposure associated with doubling of risk (twice as likely’) = 0.5 Exposure associated with halving of risk (half as likely’) (`protective’)

In practice, relative risk estimates always have associated error, which needs to be considered in interpretation

Question 13

How does complications of hypertension affect risk?

Answer 13

Complications of high blood pressure:
left ventricular hypertrophy
proteinuria or renal impairment
hypertensive retinopathy

….then the relative risks of CVD in people with high blood pressure are even higher….Emphasizes the need to control blood pressure before this happens

Question 14

Which is more strongly related to risk, systolic or diastolic pressure?

Answer 14

Both are important, systolic slightly more so

In older people, high’ systolic BP can occur with normal’ diastolic pressure (isolated systolic hypertension), is associated with increased CV risk

So blood pressure is strongly related to CV risk, and making it more problematic is that high BP is widespread

Question 15

How prevalent is high BP in England?

Answer 15

41% male, 33% female overall have high BP (1988)

Even average BP level in population associated with increased CHD risk (Average SBP is 150)

Question 16

What is the problem with the ‘old’ view of high BP and normal BP?

Answer 16

Used to think by looking at distribution of people with normal BP we could deperate it out from people with high blood pressure who would be at the top end of the distribution, but this is incorrect.

Blood pressure is a single distribution. Impossible to pick out a seperation, though it may be skewed to the right

BLOOD PRESSURE IS CONTINUOUSLY DISTRIBUTED IN THE POPULATION: THERE IS NO CLEAR SEPARATION BETWEEN NORMAL’ AND HIGH’

THERE IS NO OBVIOUS CUT POINT IN THE ASSOCIATION BETWEEN BLOOD PRESSURE AND CVD RISK

Question 17

How do we define high BP?

Answer 17

DEFINING HIGH BLOOD PRESSURE ON THE BASIS OF THE BP LEVEL ABOVE WHICH LOWERING BP IS BENEFICIAL
This is the definition generally used

Question 18

Why do some people within a population have higher BP than others?

Answer 18

A small proportion of individuals with high blood pressure have a specific medical cause (secondary hypertension)<1% in general population, <5% in medical clinics

Most have no specific medical cause – this is referred to as primary’ or essential’ hypertension – we still do not entirely understand the cause

Question 19

What are medical causes of secondary hypertension?

Answer 19

Coarctation of aorta
Renal and renal vascular disease
Adrenal disease:
-cortex: Primary hyperaldosteronism, Cushing’s syndrome
-medulla: phaeochromocytoma

Pregnancy
Drugs especially Oral Contraceptive Pill, Hormone Replacement Therapy

Question 20

What are key factors contributing to higher BP in general population?

Answer 20

Biggest to lowest impact

High body fatness (high BMI)
High alcohol intake
High salt intake
Low potassium intake
Low fibre/high fat diet
Physical inactivity
Stress (uncertain how much)

Question 21

Why does BP rise with age in adult life in Western populations but not in all populations?

Answer 21

In populations where BP does NOT rise with age:
rural communities in less developed settings
hunter gatherer, subsistence diet (low fat, low salt, less alcohol)
low BMI
high physical activity
low stress

Western population very different lifestyle

Question 22

Do the low blood pressure levels have an environmental or genetic explanation?

Answer 22

Studies of migration and BP

Most robust studies have been in people moving from low blood pressure (origin) to higher blood pressure (adoption) populations

Generally show that blood pressure patterns change (increase) to match those of the adopted population

Change generally occurs within 6 months of migration

Strong evidence for mainly ADULT ENVIRONMENTAL influence on population BP

Question 23

Risk factors for high BP

Answer 23

A risk factor is something which is associated with a high risk of a condition, but is not necessarily a cause of it. For high BP important risk factors are:
Age
Ethnicity
Family history
BMI
Alcohol intake
(gender not a strong risk factor for high BP)

Question 24

What are the benefits for lowering BP?

Answer 24

Substantial evidence from randomized trials of blood pressure reduction and their effect on CVD risk

Sustained reduction in blood pressure over about 5 years (particularly using BP lowering medications) effectively reverses the risks of previously higher blood pressure on CVD risk shown in cohort studies

The more blood pressure level is lowered, the greater the reduction in cardiovascular risk

No obvious target for BP reduction above SBP of 120 mmHg, DBP 70 mHg

Question 25

How to lower BP with drugs

Answer 25

ABCD

ACE inhibitors
Beta blockers
Calcium channel blockers
Diuretic (thiazide)

ARBs (angiotensin 2 receptor antagonists)
Alpha blockers
Centrally acting (Imidazoline I1-receptors agonist)

Question 26

What are the effects of BP lowering treatments (evidenced from trials)?

Answer 26

All medications have similar BP lowering effect

All reduce risk of both CHD and stroke but Beta-B less (11% reduction in CHD compared to 14, 15, 17 from the rest)

Some special benefits (C and D in stroke prevention

Special benefit of low dose combinations

Big differences in treatment costs

Question 27

Non-pharmacological ways of lowering BP?

Answer 27

Aim to remove key underlying causes

Weight loss
Reduce alcohol intake
Reduce salt intake
Increase fresh fruit and vegetable intake
Regular aerobic exercise
Reduce saturated fat intake

Question 28

Who should have their BP lowered?

Answer 28

The traditional view
The reason for lowering blood pressure is that it is high….The people who need their blood pressure lowered are those who have a high blood pressure

The newer view
The reason why we lower blood pressure is to reduce cardiovascular disease (CVD) risk (mainly coronary heart disease and stroke). The people who need their blood pressure lowered are the people who are at high cardiovascular (CVD) risk (almost irrespective of blood pressure level)

Middle view
Take account of both blood pressure and cardiovascular risk

Question 29

What determines cardiovascular risk?

Answer 29

Older age
Male
High BP
High blood cholesterol 
Smoking
Diabetes
Previous heart disease/stroke

Number of factors present – each doubling CVD risk

Question 30

What is attribute risk?

Answer 30

Effects of key causal factors (high blood pressure, cholesterol and smoking) multiply together to determine cardiovascular risk

What this means is that the impact of blood pressure on cardiovascular risk depends on the other elements of the cardiovascular risk profile

We can show this most simply using attributable risk, which shows how much high BP affects CVD risk in particular patients

Question 31

How do we measure the impact of high BP on risk in individuals?

Answer 31

USE OF ATTRIBUTABLE RISK

*Attributable risk =
Cardiovascular risk in people witha high BP MINUS Cardiovascular risk in people with a normal BP

This provides a measure of the impact of high blood pressure on the absolute risk of disease

This measure of risk varies between individuals

• Also known as excess risk’, risk difference’(can also consider `attributable benefit’ of treatment)

Question 32

How does baseline risk change overall risk?

Answer 32

A patient could have higher baseline CVD risk, and attribute risk higher due to high BP as well and their total risk is much higher than someone with a lower baseline.

Impact of high BP much greater in patient with high baseline CVD risk

Question 33

What happens to attributable benefit of patient with higher attribute risk?

Answer 33

IN A SIMILAR WAY, THE ATTRIBUTABLE BENEFIT OF BP REDUCTION MUCH GREATER IN A PATIENT WITH A HIGH CVD BEFORE TREATMENT

Impact of high BP lowering much greater in patient at high CVD risk, attributal benefit much bigger for them vs someeone who didn’t have their attribute risk.

Question 34

Effect of high BP on CVD risk in patients with already high CVD risk?

Answer 34

For a given increase in blood pressure the proportional effects on CVD risk will be similar in all patients.

However, the effect of high blood pressure on CVD risk in individual patients will be much larger if the patient is already at high CVD risk irrespective of their blood pressure (e.g older patient, with CVD already, several key risk factors etc)

Similarly, the benefits of blood pressure treatment will be much greater in a patient who is already at high CVD risk

Greatest benefits in patients who have a large BP reduction on treatment and had a high risk of cardiovascular disease

Question 35

What are the grade approaches to blood pressure diagnosis and management?

Answer 35

Grade 1 -start non-pharmacological measures, use BP lowering drug treatment if CV risk is high

Grade 2 -BP lowering drug treatment indicated

Grade 3 -aggressive BP lowering drug treatment

Question 36

First line treatment for hypertension

Answer 36

ACE inhibitor for under 55 yrs
CC blocker or Thiazide diuretic for over 55 + ethnic minority

BP target: SBP less than 140, DBP less than 90

Question 37

What is involved In the newer approach to BP diagnosis and management?

Answer 37

Measure blood pressure and assess overall cardiovascular risk (including age, medical history, BP, lipids, smoking, diabetes etc, ideally in a `risk score’)

If considered to be at high CVD risk, then consider a range of measures to lower blood pressure – and other elements of CVD risk

• BP lowering treatment (small doses of multiple Rx)
• Cholesterol lowering treatment
• `Heart healthy’ diet
• Smoking cessation

Question 38

DALY

Answer 38

disability adjusted life year