Blood Pressure Disorders

Introduction

Blood pressure disorders encompass a range of conditions affecting the regulation and maintenance of arterial pressure. Understanding the measurement techniques, diagnostic criteria, and pathophysiology is essential for recognizing and managing these disorders in clinical practice.

Measuring Blood Pressure

Auscultatory Method

The auscultatory method is the standard clinical technique for measuring blood pressure, typically using a sphygmomanometer and stethoscope.

• Sphygmomanometer: Device with an inflatable cuff to occlude the brachial artery.

• Stethoscope: Used to listen for Korotkoff sounds over the artery.

• Procedure:

  1. Patient should be at rest, with arm supported.

  2. Apply appropriately sized cuff to the upper arm and inflate to occlude the brachial artery.

  3. Release cuff pressure slowly (about 2 mm Hg per second).

  4. The first Korotkoff sound heard indicates systolic blood pressure (SBP).

  5. The disappearance of Korotkoff sounds marks diastolic blood pressure (DBP).

• Korotkoff Sounds: Series of sounds heard as the cuff pressure is released, corresponding to changes in blood flow through the artery.

Example: If the first sound is heard at 120 mm Hg and the last at 80 mm Hg, the BP is recorded as 120/80 mm Hg.

Other Methods for Blood Pressure Measurement

• Automated/Semiautomated Devices: Measure pulsatile oscillations and convert them to BP readings. Less accurate than auscultatory method but useful for home monitoring.

• Intra-arterial Measurement: Direct measurement via intravenous catheter placed in a peripheral artery or vein. Reserved for hospitalized or ICU patients due to invasiveness.

Blood Pressure Definitions

Classification of Blood Pressure

Blood pressure is classified based on systolic and diastolic values. Accurate diagnosis requires multiple measurements on separate occasions.

Note: Diagnosis should not be made based on a single reading or visit; average readings from at least three measurements on two to three separate occasions are recommended.

Hypertension

Types of Hypertension

• Primary (Essential) Hypertension: Hypertension of unknown etiology (idiopathic). Accounts for the majority of cases.

• Secondary Hypertension: Hypertension resulting from a distinct underlying disorder or condition.

Pathophysiology of Primary Hypertension

Primary hypertension involves complex vascular and humoral changes leading to increased arterial pressure.

• Vascular Remodeling: Cellular changes such as fibrosis, hypertrophy, and atherosclerosis decrease the lumen size of small arteries and arterioles.

• Chronic Vascular Inflammation: Cytokine-mediated changes in the vascular intima reduce lumen size and increase arterial stiffness.

• Decreased Compliance: Reduced elasticity of arteries increases systolic blood pressure.

• Altered Vascular Tone: Diminished nitric oxide (NO) production leads to reduced vasodilation, while increased endothelin promotes vasoconstriction.

• Sympathetic Outflow: Increased adrenergic activity raises vascular resistance.

• Volume Expansion: Excessive salt and water intake, renal insufficiency, and impaired natriuretic peptide response contribute to increased intravascular volume.

Equation: Blood pressure is determined by cardiac output (CO) and systemic vascular resistance (SVR):

Pathophysiology of Secondary Hypertension

Secondary hypertension is directly attributable to another disease or condition and may be curable with appropriate treatment.

• Renovascular Hypertension: Atherosclerosis or thrombosis of the renal artery reduces perfusion, stimulating the renin-angiotensin-aldosterone system (RAAS).

• Adrenocortical Disorders: Conditions such as primary hyperaldosteronism or Cushing syndrome cause sodium and water retention independent of RAAS.

• Pheochromocytoma: Tumor of the adrenal medulla leads to excessive catecholamine secretion, causing episodic or sustained hypertension.

• Drug-Induced Hypertension: Medications such as oral contraceptives, erythropoietin, cyclosporin, stimulants (cocaine, amphetamines), NSAIDs, and corticosteroids can elevate blood pressure.

Clinical Manifestations of Hypertension

Organ Damage and Symptoms

Hypertension is often asymptomatic until it causes long-term organ damage.

• Cardiovascular: Atherosclerosis increases risk of stroke, heart failure, coronary artery disease, and peripheral vascular disease. Left ventricular hypertrophy develops due to increased afterload.

• Renal: Nephrosclerosis and glomerular dysfunction lead to chronic kidney disease, proteinuria, and elevated serum creatinine.

• Cerebral: Dementia and subcortical white matter demyelination result from hypoperfusion.

• Ophthalmic: Retinopathy due to vascular changes, including wall hyperplasia and thickening.

Treatment of Primary Hypertension

Lifestyle Modifications

• Regular exercise and weight loss

• Dietary changes, including reduced sodium intake (<2.4 g/day)

• Tobacco cessation and limiting alcohol consumption

Antihypertensive Medications

Disorders of Low Blood Pressure

Orthostatic Hypotension

Orthostatic hypotension is an abnormal decrease in blood pressure upon standing from a supine position.

• Definition: Decrease of ≥20 mm Hg in SBP or ≥10 mm Hg in DBP upon standing.

• Symptoms: Presyncope, blurred vision, angina, and muscle weakness, especially in the morning or post-prandially.

• Causes: Decreased intravascular volume (dehydration, diuretics, blood loss), medications, neurodegenerative disorders (Parkinson's, diabetes), and impaired autonomic nervous system function.

Normal BP Homeostasis: Supine to Upright

• Upon standing, venous return to the heart decreases, triggering compensatory mechanisms (baroreflex, sympathetic activation, RAAS) to maintain blood pressure.

Treatment of Orthostatic Hypotension

• Prevent dehydration and ensure access to fluids.

• Manage diuretic medications and avoid excessive alcohol.

• Educate patients to rise slowly and move legs before standing.

• Pharmacologic agents: Fludrocortisone (promotes sodium/water retention), midodrine, phenylephrine, droxidopa (norepinephrine pro-drug).

Shock Syndromes

Definition and Types

Shock is defined as sustained hypotension and hypoperfusion insufficient to meet the metabolic needs of the body, resulting in cellular hypoxia and organ failure.

• Cardiogenic Shock: Impaired cardiac contractility reduces cardiac output.

• Hypovolemic Shock: Insufficient stroke volume due to decreased blood volume.

• Distributive Shock: Includes septic, anaphylactic, and neurogenic shock, characterized by vasodilation and reduced systemic vascular resistance.

Equation: Shock is associated with a critical drop in mean arterial pressure (MAP):

Example: Septic shock involves proinflammatory cytokine-induced vasodilation, while anaphylactic shock is mediated by histamine-induced vasodilation.

Additional info: Pregnancy-related blood pressure disorders are not covered in these notes.