Htn according to spm

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Hypertension - Park's Textbook of Preventive and Social Medicine (SPM)

Definition

Hypertension is a chronic condition of major public health concern due to its role in causing coronary heart disease (CHD), stroke, and other vascular complications. It is the commonest cardiovascular disorder, accounting for 20-50% of all cardiovascular deaths.

Defining hypertension is inherently difficult and "by necessity arbitrary." Sir George Pickering first formulated the concept that blood pressure in a population is distributed as a continuous bell-shaped curve, with no real separation between normotension and hypertension. The dividing line between normal and high blood pressure can therefore be defined only in an operational way.

Classification (WHO/JNC)

Classification is based on the average of two or more readings on two or more occasions after initial screening, in adults ≥18 years not taking anti-hypertensives:

Category	Systolic (mm Hg)	Diastolic (mm Hg)
Optimal	< 120	and < 80
Normal	120-129	and/or 80-84
High Normal	130-139	and/or 85-89
Grade 1 (Mild) HTN	140-159	and/or 90-99
Grade 2 (Moderate) HTN	160-179	and/or 100-109
Grade 3 (Severe) HTN	≥ 180	and/or ≥ 110
Isolated Systolic HTN	≥ 140	and < 90

Isolated systolic hypertension: SBP ≥140 mmHg with DBP < 90 mmHg.

Types / Classification

Primary (Essential) Hypertension: Cause unknown - accounts for 90% of all cases.
Secondary Hypertension: Due to an identifiable cause - accounts for ~10% of cases.
- Causes: chronic glomerulonephritis, chronic pyelonephritis, adrenal gland tumours, congenital coarctation of the aorta, toxaemias of pregnancy, oral contraceptives (the commonest present cause of secondary HTN, due to the oestrogen component).

Epidemiology

Global prevalence: Estimated 1.13 billion people in 2015.
Overall prevalence in adults: ~30-40%; age-standardized prevalence is 24% in men and 20% in women.
60% prevalence in persons aged >60 years.
Estimated 10 million deaths and >200 million DALYs attributed to elevated BP in 2015.
DALYs due to HTN have increased by 40% since 1990.
Leading causes of SBP-related death: IHD (4.9 million/year), haemorrhagic stroke (2 million), ischaemic stroke (1.5 million).

Prevalence in India (NFHS-4, 2015-16)

Women (15-49 yrs): 11% hypertensive; ~30% prehypertensive.
Men (15-49 yrs): 15% hypertensive; ~43% prehypertensive.
Prevalence higher in Sikhs (24% men, 16% women), Jains (19% men, 16% women).
North-eastern states have higher prevalence.
Strong association with obesity - 38% of obese men and 29% of obese women were hypertensive.

"Rule of Halves" (Iceberg Disease)

Hypertension is an iceberg disease. In the 1970s it became evident that:

Only 1/2 of all hypertensives in the population were aware of their condition.
Only 1/2 of those aware were being treated.
Only 1/2 of those treated were adequately controlled.

This "rule of halves" is even worse in developing countries where medical services are limited.

"Tracking" of Blood Pressure

If blood pressure of individuals is followed from early childhood into adult life, those with initially higher pressures continue to track higher as they age - low pressure tends to remain low, high tends to become higher. This is called "tracking" and can identify children "at risk" of developing hypertension in the future.

Risk Factors

1. Non-Modifiable Risk Factors

Factor	Detail
Age	BP rises with age in both sexes; greater rise in those with initially higher BP
Sex	Men show higher average BP at adolescence; post-menopause, women may catch up
Genetic factors	Polygenic inheritance; monozygotic twins more concordant; children of two hypertensive parents have 45% risk vs. 3% if both parents normotensive
Ethnicity	Black communities consistently show higher BP; difference up to 20 mmHg by 6th decade

2. Modifiable Risk Factors

Factor	Detail
Obesity	Greater weight gain = greater risk; central obesity (waist:hip ratio) particularly important
Salt intake	High salt (7-8 g/day) increases BP proportionately; Japan (>400 mmol Na/day) has high HTN; primitive societies (<60 mmol Na/day) have virtually none
Potassium	Antagonizes sodium; supplements lower BP in mild-moderate HTN
Saturated fat	Raises both BP and serum cholesterol
Dietary fibre	Inversely related to risk of CHD and HTN
Alcohol	High intake raises BP, especially systolic; reversible with abstinence
Heart rate	Hypertensives have invariably higher resting heart rate (sympathetic overactivity)
Physical inactivity	Inactivity promotes obesity and indirectly raises BP
Environmental stress	Psychosocial stress raises catecholamines (noradrenaline higher in hypertensives)
Oral contraceptives	Commonest cause of secondary HTN (oestrogen component)

Organ Damage

Organ damage does not always correlate precisely with BP level:

Markedly high BP can occur without organ damage.
Organ damage can be present with only moderate BP elevation.
Presence of organ damage increases cardiovascular risk at any level of BP.
Blood pressure and organ impairment must be evaluated separately.

Blood Pressure Measurement

Three sources of error:

Observer errors: Hearing acuity, interpretation of Korotkoff sounds.
Instrumental errors: Leaking valve, cuff too small (gives falsely high readings).
Subject errors: Position, anxiety, fear.

Key points:

WHO recommends sitting position for recording BP.
Use either right or left arm consistently.
Phase I Korotkoff = systolic pressure; Phase V (disappearance) = diastolic pressure (most studies use Phase V).
Record at least three times over ≥3 minutes; record the lowest reading.

Prevention of Hypertension

WHO has recommended two broad approaches:

1. Primary Prevention

a. Population Strategy Directed at the whole population regardless of individual risk. Even a small reduction in average BP produces large reductions in cardiovascular complications.

Interventions include:

Nutrition: Reduce salt to ≤5 g/day; moderate fat; avoid high alcohol; restrict energy intake.
Weight reduction: Achieve BMI 18.5-24.9.
Exercise promotion: Regular physical activity lowers weight, blood lipids, and BP.
Behavioural changes: Stress reduction, smoking cessation, yoga, meditation.
Health education: Community mobilization, awareness of preventive measures.
Self-care: Teach patients to measure their own BP and keep log-books.

b. High-Risk Strategy

Aims to prevent individuals from reaching BP levels requiring treatment.
Appropriate when risk factors have low prevalence in the community.
Uses family history of HTN and "tracking" from childhood to identify high-risk individuals.

2. Secondary Prevention

Goal: Detect and control high BP in affected individuals.

(i) Early Case Detection: HTN is largely asymptomatic until organ damage occurs - population screening is the only effective diagnostic method. Screening must be linked to follow-up and sustained care.

(ii) Lifestyle Modifications (Table 2):

Modification	Recommendation	Approximate SBP Reduction
Weight reduction	Maintain BMI 18.5-24.9	5-20 mmHg per 10 kg loss
DASH diet	Fruits, vegetables, low-fat dairy; reduced saturated fat	8-14 mmHg
Dietary sodium reduction	≤100 mEq/day (2.4 g Na or 6 g NaCl)	2-8 mmHg
Physical activity	Brisk walking ≥30 min/day, most days	4-9 mmHg
Alcohol moderation	≤2 drinks/day (men); ≤1 drink/day (women)	2-4 mmHg

Note: Stop smoking for overall cardiovascular risk reduction.

(iii) Antihypertensive drug therapy: Modern drug therapy can effectively reduce BP and the excess risk of morbidity/mortality from coronary, cerebrovascular, and kidney disease.

Source: Park's Textbook of Preventive and Social Medicine, pp. 423-427

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