Epidemiology of blood pressure and hypertension

Question 1

What are the main factors that can affect BP measurements?

Answer 1

• anxiety of patients
• technique of practitioner
• personality of practitioner
• calibration of instrument/machine
• Cuff size
• Environment (cold, noisy, rushed)
• number of BP readings on which it is based

Question 2

What is accommodation in BP measures?

Answer 2

= reduction of sympathetic arousal with more readings

Question 3

Why is BP an important problem?

Answer 3

• higher BP strongly associated with high CVD and stroke risks
• Risk associated with high BP is very common in general population

Question 4

What is RISK?

Answer 4

= probability of an event

number of cases compared to the general population at risk in a specified period of time

Question 5

How can we measure strength of association between BP and CVD? (As an e.g.)

Answer 5

relative risk

Question 6

What is relative risk?

Answer 6

risk in ‘exposed group’ / risk in ‘unexposed’ group

if no effect of exposure on outcome, RR=1

Question 7

How are clinical signs defined as being abnormal? e.g. when is BP referred to as hypertension

Answer 7

the level at which Rx provides benefit

or conversely the lower level (hypo-) would be the level at which deficiency presents as Sx

Question 8

What are the 2 main types of hypertension?

Answer 8

PRIMARY: aka essential: no specific medical cause

SECONDARY: caused by a specific medical condition (small number of individuals)

Question 9

What are eg of causes of secondary hypertension?

Answer 9

• coarctation of aorta
• renal/vascular disease
• adrenal disease (cushing’s, phaeochromocytoma)
• pregnancy
• Drugs: combined pill and HRT

Question 10

What are the main risk factors for essential hypertension?

Answer 10

• high BMI
• high EtOH
• high Na+/K+
• low fibre
• physical inactivity
• stress ?

Question 11

What are the characteristics of populations in which BP does not rise with age?

Answer 11

• rural communities in less developed settings
• hunter gatherer, subsistence diet
• low mean BMI
• high physical activity
• low stress

Question 12

What do migration studies tell us about BO?

Answer 12

• most people move from low to high BP -population
• BP patterns change to match those of the host population
• this change occurs within 1st 6 month of moving
• stromg evidence for mostly ENVIRONMENTAL influence on population BP

Question 13

What is a risk factor?

Answer 13

factor which is associated with high risk of a condition, but is not necessarily a cause
NB gender is not a strong risk factor for high BP

Question 14

What are the main risk factors for hypertension?

Answer 14

• older age
• Afro-Caribbean
• FHx
• high BMI
• High EtOH

Question 15

What is used to assess the impact of high BP (for e.g.) on the individual patient?

Answer 15

attributable risk

Question 16

What is attributable risk?

Answer 16

= excess risk

exposed group risk MINUS unexposed group risk

Question 17

What are the 2 types of risk?

Answer 17

relative risk: ratio of exposed to unexposed

attributable risk: difference between exposed and unexposed risk

Question 18

What causes elevations in the baseline BP? And subsequent risk of CVD?

Answer 18

• existing CVD
• older afe
• DM
• high blood cholesterol
• smoking
• high BP
  risks from several factors tend to MULTIPLY together

Question 19

What is the ‘rule of halves’ in relation to BP?

Answer 19

old school thinking 
of those with high BP:
- half had it measured
- half have received treatment
- half had good BP control

Question 20

What is the rule of two thirds for BP?

Answer 20

more recent thinking

- 30% well controlled BP

Question 21

How would treating BP need to be done to help overall CVD risk?

Answer 21

would need for this to occur at population level for there to be an impact
rather than on a case-to-case basis

Question 22

What is population strategy?

Answer 22

introduction of public policy
to impact the entire BP distribution at population level
causing a total shift/reduction in BP/CVD risk

Question 23

What is DALY and QALY?

Answer 23

disability adjusted life years = DALY

quality adjusted life years = QALY

Question 24

What are the main parameters that underly epidemiological approaches to treatment?

Answer 24

• distribution of disease (e.g hypertension global prevalence and location)
• risk factors such as age, ethnicity and sex on disease distribution
• impact of available Rx and interventions on this distribution
• burden of disease on society and economy (severity vs. prevalence)
• targeting of Rx based on other or associated risk factors e.g. use of beta blockers in post-MI and calcium channel blockers