Hypertension
Hypertension is the single largest modifiable cause of death on the planet. It rarely announces itself — most people with dangerously high blood pressure feel completely well — and yet, silently, year after year, it batters the arteries, thickens the heart, scars the kidneys, and primes the brain for stroke. That gap between how harmless it feels and how much harm it does is exactly why it earned the nickname "the silent killer," and why understanding it well is one of the highest-yield things a clinician can learn.
The remarkable part of the story is that we now know hypertension is not only measurable but treatable — and that treating it prevents strokes, heart failure, and kidney failure. That knowledge is surprisingly recent. For the first half of the twentieth century, respectable physicians believed high blood pressure was a necessary compensation that should be left alone. Unlearning that mistake, largely thanks to the Framingham Heart Study, is one of the great victories of modern medicine.
Learning Objectives
- Explain how blood pressure is generated and regulated moment-to-moment and over the long term (cardiac output, systemic vascular resistance, the RAAS, baroreflex, and the kidney's pressure-natriuresis).
- Distinguish primary (essential) from secondary hypertension and list the secondary causes worth screening for.
- Define the current diagnostic thresholds and explain why out-of-office measurement matters.
- Describe the mechanisms and clinical signs of target-organ damage in the heart, brain, kidney, eye, and vasculature.
- Build a rational stepwise management plan using lifestyle change and the major drug classes, and recognise hypertensive emergencies.
Quick Answer
Hypertension is persistently elevated arterial blood pressure, defined by most guidelines as an office reading at or above 130/80 mmHg (ACC/AHA) or 140/90 mmHg (ESC/WHO), confirmed with out-of-office measurement. Around 90–95% of cases are primary (essential) — no single identifiable cause, driven by genetics, ageing arteries, salt, weight, and neurohormonal dysregulation — while 5–10% are secondary to a specific and often correctable problem such as renal artery stenosis, primary aldosteronism, or obstructive sleep apnoea. Untreated, it damages target organs: left ventricular hypertrophy and heart failure, stroke, chronic kidney disease, retinopathy, and accelerated atherosclerosis. Management combines lifestyle change (weight, salt, exercise, alcohol) with drug therapy — typically an ACE inhibitor or ARB, a calcium channel blocker, and a thiazide-like diuretic, escalated to combinations as needed. The benefit of treatment is large and proven: every 10 mmHg drop in systolic pressure meaningfully cuts stroke and cardiovascular death.
Where It Came From
For most of medical history, blood pressure could not even be measured non-invasively. Stephen Hales famously cannulated a horse's artery in 1733 and watched blood rise nearly nine feet up a glass tube — the first blood pressure measurement — but a practical clinical tool waited almost two centuries. Scipione Riva-Rocci introduced the inflatable arm cuff in 1896, and in 1905 the Russian surgeon Nikolai Korotkoff described the tapping sounds heard through a stethoscope as the cuff deflates, giving us the systolic and diastolic values still read today.
Having a number, however, did not mean doctors knew what to do with it. Through the 1930s and 1940s the dominant view — held by giants of medicine — was that elevated pressure was essential hypertension: the very word "essential" implied the body needed that pressure to force blood through stiffened arteries into vital organs. Lowering it was thought dangerous. The most cited illustration is that President Franklin D. Roosevelt's blood pressure was allowed to climb into the range of 180–230/120 mmHg during his final years; the prevailing wisdom offered little beyond rest and reassurance, and he died of a massive cerebral haemorrhage in 1945.
The turning point was epidemiology. In 1948 the U.S. Public Health Service began the Framingham Heart Study, following thousands of residents of Framingham, Massachusetts, over decades. By the 1960s its data had shown, unambiguously and for the first time, that higher blood pressure predicted a steeply higher risk of stroke, heart attack, and heart failure — and that the risk was continuous, with no safe "normal high." It was Framingham that popularised the very idea of a cardiovascular risk factor. The proof that treating pressure helped came from the landmark VA Cooperative Studies (Veterans Administration, 1967–1970), which were stopped early because the untreated group suffered so many strokes and deaths that continuing was unethical. Within a generation, hypertension went from an untouchable compensation to one of medicine's most treatable conditions.
How Blood Pressure Is Generated and Regulated
Arterial pressure is, at its simplest, the product of two things:
Blood pressure ≈ Cardiac output × Systemic vascular resistance
Cardiac output is how much blood the heart pumps per minute (heart rate × stroke volume); systemic vascular resistance is how tightly the small arteries (arterioles) are constricted. Anything that raises either raises pressure. Acute stress raises output and constricts vessels; chronic hypertension is usually a problem of raised resistance in stiffened, remodelled arterioles.
The body defends pressure with layered controllers operating over different timescales:
- Seconds (the baroreflex): Stretch receptors in the carotid sinus and aortic arch sense pressure. A sudden rise triggers the brainstem to slow the heart and relax vessels; a fall does the opposite. This is why you don't faint every time you stand up. Crucially, the baroreflex resets to defend whatever pressure has become chronic — one reason established hypertension is self-perpetuating.
- Minutes to hours (the RAAS): When renal perfusion falls, the juxtaglomerular cells release renin, which converts angiotensinogen to angiotensin I; ACE (mostly in the lung) converts that to angiotensin II, a potent vasoconstrictor that also stimulates aldosterone, causing the kidney to retain sodium and water. This renin–angiotensin–aldosterone system is the single most important pharmacological target in hypertension.
- Days (the kidney and pressure-natriuresis): Guyton's key insight was that the kidney sets long-term pressure. When pressure rises, a healthy kidney excretes more salt and water, lowering volume and pressure back toward normal. In hypertension this curve is shifted: the kidney only excretes the sodium load at a higher set-point, so pressure stays elevated. This is why salt and renal function are central to the disease.
Primary versus Secondary Hypertension
Primary (essential) hypertension accounts for roughly 90–95% of cases. There is no single cause; instead multiple small pushes accumulate — polygenic susceptibility, arterial stiffening with age, excess dietary sodium, obesity and insulin resistance, sympathetic overactivity, and impaired renal sodium handling. It typically appears from middle age onward and clusters with other cardiometabolic risk factors.
Secondary hypertension (5–10%) has an identifiable, often correctable cause. Suspect it when hypertension is severe, resistant to three or more drugs, appears very young (under 30) or abruptly, or is accompanied by tell-tale features. The high-yield causes:
| Cause | Clue | Key test |
|---|---|---|
| Obstructive sleep apnoea | Snoring, daytime somnolence, obesity | Sleep study |
| Primary aldosteronism (Conn's) | Hypertension with low or low-normal potassium | Aldosterone-to-renin ratio |
| Renal artery stenosis | Abdominal bruit, rise in creatinine after ACE inhibitor, flash pulmonary oedema | Doppler ultrasound, CT/MR angiography |
| Chronic kidney disease | Abnormal creatinine, proteinuria | eGFR, urinalysis |
| Phaeochromocytoma | Episodic headache, palpitations, sweating | Plasma/urine metanephrines |
| Cushing's syndrome | Central obesity, striae, easy bruising | Dexamethasone suppression test |
| Coarctation of the aorta | Young patient, arm-leg BP difference, radio-femoral delay | Echo/CT |
| Drugs | NSAIDs, oral contraceptives, decongestants, steroids, liquorice | History |
Worked clinical vignette: A 34-year-old man has blood pressure of 172/104 mmHg despite three drugs, and his serum potassium is 3.1 mmol/L without diuretic use. That combination — young, resistant, hypokalaemic — should immediately prompt an aldosterone-to-renin ratio. A high ratio points to primary aldosteronism, potentially curable by adrenal surgery or well controlled with spironolactone. Missing this labels a curable disease as "essential" and condemns the patient to lifelong polypharmacy.
Diagnosis and Staging
A single high reading is not hypertension. Pressure varies with anxiety, pain, caffeine, and the "white-coat" effect of being in a clinic. Diagnosis should be confirmed with repeated measurements and, ideally, out-of-office readings — either home monitoring or 24-hour ambulatory blood pressure monitoring (ABPM). ABPM also reveals masked hypertension (normal in clinic, high at home — genuinely dangerous) and the loss of the normal nocturnal "dip," itself a risk marker.
Thresholds differ between guidelines, which confuses students; know both:
| Category | ACC/AHA 2017 (mmHg) | ESC/ESH & WHO (mmHg) |
|---|---|---|
| Normal | less than 120/80 | less than 130/85 |
| Elevated / High-normal | 120–129 systolic and less than 80 diastolic | 130–139 / 85–89 |
| Stage 1 / Grade 1 | 130–139 or 80–89 | 140–159 / 90–99 |
| Stage 2 / Grade 2 | at or above 140 or 90 | 160–179 / 100–109 |
| Grade 3 / severe | — | at or above 180 / 110 |
Proper technique matters more than the exact cut-off: patient seated and rested for five minutes, back supported, arm at heart level, correct cuff size, and an average of two or more readings.
Target-Organ Damage
The reason we treat is to prevent damage to the organs that high pressure relentlessly injures:
- Heart: The left ventricle pumps against high resistance and hypertrophies (LVH). A thickened, stiff ventricle relaxes poorly, causing heart failure with preserved ejection fraction; eventually it may dilate and fail. Hypertension also accelerates coronary atherosclerosis and predisposes to atrial fibrillation.
- Brain: Hypertension is the leading modifiable cause of both ischaemic and haemorrhagic stroke. Small deep vessels develop lipohyalinosis, causing lacunar strokes and, over time, vascular cognitive impairment. Sudden severe rises cause hypertensive encephalopathy.
- Kidney: Pressure damages the glomeruli (hypertensive nephrosclerosis), producing proteinuria and progressive decline in eGFR — hypertension is both a cause and a consequence of chronic kidney disease, a vicious cycle.
- Eye: The retina offers a direct window on small vessels. Hypertensive retinopathy progresses from arteriolar narrowing and arteriovenous nipping to flame haemorrhages, cotton-wool spots, and finally papilloedema (a sign of malignant hypertension).
- Large arteries: Accelerated atherosclerosis and increased risk of aortic aneurysm and dissection.
Assessing target-organ damage — ECG or echo for LVH, urinalysis and eGFR for the kidney, fundoscopy for the eye — both confirms severity and sharpens the urgency of treatment.
Management
Lifestyle change is the foundation and can lower systolic pressure substantially:
- Weight loss: roughly 1 mmHg per kilogram lost.
- DASH-style diet: rich in fruit, vegetables, and low-fat dairy — up to 11 mmHg.
- Sodium restriction: to under about 2 g sodium (5 g salt) per day — 5–6 mmHg.
- Physical activity: 150 minutes/week of aerobic exercise — 5–8 mmHg.
- Alcohol moderation and smoking cessation (smoking mainly compounds cardiovascular risk).
Drug therapy. The first-line classes are the ABCD framework:
- A — ACE inhibitors / ARBs (e.g. ramipril, losartan): block the RAAS; preferred in younger patients, diabetes, and those with proteinuria or heart failure. Never combine an ACE inhibitor with an ARB.
- B — Beta-blockers (e.g. bisoprolol): no longer first-line for uncomplicated hypertension but valuable with coexisting angina, prior MI, or heart failure.
- C — Calcium channel blockers (e.g. amlodipine): preferred in older patients and Black patients of African/Caribbean ancestry.
- D — Thiazide-like diuretics (e.g. indapamide, chlortalidone): reduce volume and vascular resistance.
A practical modern algorithm: start one agent (A for younger/diabetic; C or D for older or Black patients). If a single drug is insufficient — as it usually is — combine A+C, then A+C+D. Resistant hypertension (uncontrolled on three drugs including a diuretic) warrants adding spironolactone and re-screening for secondary causes.
Hypertensive emergency is severely elevated pressure (often above 180/120 mmHg) with acute target-organ damage — encephalopathy, acute heart failure, aortic dissection, acute kidney injury, or eclampsia. This needs controlled intravenous lowering (labetalol, nicardipine, or nitroprusside) in a monitored setting. The critical teaching point: lower pressure gradually (by about 20–25% in the first hour, except in dissection), because dropping it too fast can cause cerebral, renal, or myocardial ischaemia. Severely high pressure without acute organ damage is hypertensive urgency, managed with oral therapy over days — not an excuse for aggressive IV treatment.
Real-World Applications
- Population screening: Because hypertension is symptomless, opportunistic measurement at every clinical contact — and community/pharmacy screening — is how most cases are caught.
- Chronic disease clinics: Titrating drugs, reinforcing adherence (a major real-world failure point), and monitoring renal function and potassium after starting RAAS blockers or diuretics.
- Perioperative and pregnancy care: Blood pressure control changes anaesthetic risk; pregnancy hypertension (pre-eclampsia) is a distinct, urgent entity where labetalol, nifedipine, and methyldopa are used and ACE inhibitors are contraindicated.
- Everyday self-management: Validated home monitors let patients track their own pressure, which improves control and detects white-coat and masked patterns.
Common Mistakes
- "My blood pressure feels fine, so it must be normal." Hypertension is almost always asymptomatic until it causes a stroke or heart attack. Symptoms are a poor guide; only measurement reveals it. Correction: rely on numbers, not feelings, and screen even the well.
- Diagnosing hypertension from one clinic reading. A single elevated value may be anxiety or white-coat effect. Correction: confirm with repeated and out-of-office readings before committing someone to lifelong therapy.
- Assuming all hypertension is essential. Missing secondary causes — especially primary aldosteronism, which is far more common than once thought — condemns curable patients to lifelong drugs. Correction: screen when young, severe, resistant, or accompanied by clues like hypokalaemia.
- Dropping pressure too fast in an emergency. Slamming a very high pressure down to "normal" can starve the brain and kidneys of blood, causing infarction. Correction: lower gradually (about 20–25% in the first hour) except in aortic dissection.
- Stopping treatment once the pressure "normalises." Patients often quit medication feeling cured. Correction: explain that treatment controls, not cures — the pressure will climb back if drugs stop.
Comparison and Connections
| Feature | Primary (essential) | Secondary |
|---|---|---|
| Frequency | 90–95% | 5–10% |
| Cause | Polygenic, multifactorial | Single identifiable lesion |
| Typical onset | Middle age onward | Very young or abrupt |
| Curable? | No — controllable | Often yes |
| Clues | None specific | Hypokalaemia, bruit, episodic symptoms |
Hypertensive emergency vs urgency: both have very high numbers, but only the emergency has acute target-organ damage and needs IV treatment; urgency is managed orally. Do not treat a scary number in isolation — treat the organs.
Hypertension vs atherosclerosis: related but distinct. Hypertension is a haemodynamic problem (excess pressure) that accelerates atherosclerosis (a lipid-driven arterial wall disease); they compound each other's risk.
Practice Questions
Recall
Q: What two variables determine mean arterial pressure, and which one is chiefly raised in established essential hypertension? A: Cardiac output and systemic vascular resistance. In established essential hypertension, the systemic vascular resistance is chiefly elevated due to stiffened, remodelled arterioles.
Understanding
Q: Why does the kidney's pressure-natriuresis relationship explain persistent hypertension? A: Normally, a rise in pressure makes the kidney excrete more sodium and water, lowering volume and returning pressure to baseline. In hypertension this curve is shifted rightward, so the kidney only excretes the needed sodium at a higher pressure set-point — meaning pressure remains chronically elevated rather than self-correcting.
Application
Q: A 68-year-old woman of European ancestry has a confirmed BP of 158/94 with no other conditions. What is a reasonable first-line drug, and why? A: A calcium channel blocker such as amlodipine (or a thiazide-like diuretic). In older patients, whose hypertension is more volume/vessel-stiffness driven and often lower-renin, C or D agents are preferred over A (ACE inhibitor/ARB) as monotherapy.
Analysis
Q: A 29-year-old man has BP of 168/106 on three drugs and a potassium of 3.0 mmol/L. What is your reasoning and next step? A: Young age, drug resistance, and spontaneous hypokalaemia strongly suggest secondary hypertension, most likely primary aldosteronism. The next step is an aldosterone-to-renin ratio; a high ratio warrants confirmatory testing and adrenal imaging, because the condition may be surgically curable or well controlled with spironolactone.
FAQ
Is 130/80 really "high"? My grandparent was told 140/90 was the line. Both are defended thresholds. The 2017 ACC/AHA guidelines lowered the diagnostic line to 130/80 based on trials showing benefit from earlier intervention, while European and WHO guidelines keep 140/90 for diagnosis. The disagreement is mostly about labelling; everyone agrees risk rises continuously and that lifestyle change matters well before drugs.
Do I have to take blood pressure pills for life? Usually yes for essential hypertension — the drugs control the pressure but don't cure the underlying tendency, so it returns if they stop. However, significant weight loss and lifestyle change can sometimes let a patient reduce or occasionally stop medication under supervision. Secondary hypertension, if the cause is corrected, may resolve.
Can I just eat less salt instead of taking medication? Salt restriction genuinely lowers pressure (around 5–6 mmHg) and is worthwhile for everyone, but for most people with established hypertension it is not enough on its own. It is a foundation, not a full substitute, for drug therapy in moderate-to-severe cases.
Why do I get side effects like a dry cough or ankle swelling? A dry cough is classic for ACE inhibitors (from bradykinin build-up) and is easily solved by switching to an ARB. Ankle swelling is common with calcium channel blockers like amlodipine. Report side effects rather than silently stopping — there is almost always an alternative.
What's the difference between the two numbers? The top (systolic) is the peak pressure when the heart contracts; the bottom (diastolic) is the resting pressure between beats. In people under about 50, diastolic matters more; after that, systolic pressure and pulse pressure (the gap between them) become the stronger predictors of cardiovascular risk because arteries stiffen with age.
Quick Revision
- BP ≈ cardiac output × systemic vascular resistance; long-term pressure is set by the kidney (pressure-natriuresis).
- Regulation: baroreflex (seconds), RAAS (minutes-hours), renal sodium handling (days).
- 90–95% primary; screen for secondary if young, severe, resistant, or with clues (hypokalaemia → aldosteronism).
- Confirm diagnosis with repeated and out-of-office readings; know both 130/80 (ACC/AHA) and 140/90 (ESC/WHO) thresholds.
- Target-organ damage: LVH/heart failure, stroke, nephrosclerosis, retinopathy, atherosclerosis/dissection.
- Lifestyle first (weight, DASH, salt, exercise, alcohol); drugs by ABCD, usually A+C then A+C+D; add spironolactone for resistance.
- Emergency = severe BP + acute organ damage → controlled IV lowering (about 20–25%/first hour). Urgency = high BP, no acute damage → oral.
- Framingham proved BP is a continuous risk factor; VA trials proved treatment saves lives.
Related Topics
Prerequisites
- Cardiovascular physiology and blood pressure regulation: Physiology
- Renal function and the RAAS: Nephrology
Related Topics
- Antihypertensive drug classes: Pharmacology
- Endocrine causes of secondary hypertension: Endocrinology
Next Topics
- Coronary artery disease and its risk factors
- Heart failure, including HFpEF driven by hypertension
- Stroke and cerebrovascular disease: Neurology