MB

Sodium and Hypertension Review

Lecture Overview

  • Topic: Sodium and hypertension

  • Course: KHPM324 Chronic Diseases of Modern Society

  • Instructor: Hannah Oh, ScD

Review Quiz Instructions

  • To participate in the review quiz, go to:

    • Website: www.socrative.com

  • Log in as a student

  • Enter your name for participation points

  • Room Number: 2

Blood Pressure Fundamentals

Definition of Blood Pressure

  • Blood Pressure (BP): A measure of the force exerted by circulating blood on the walls of blood vessels.

  • Formula:
    \text{Blood Pressure} = \text{Cardiac Output} \times \text{Vascular Resistance}

Measurement

  • Blood pressure is often measured in the brachial artery.

  • Units of measurement are expressed in millimeters of mercury (mmHg).

Timing of Measurements

  • Blood pressure is measured at various times throughout the day, reflecting changes in body activity and state.

Systolic vs. Diastolic Blood Pressure

Systolic Blood Pressure

  • Occurs during contraction of the heart (squeezing phase) when blood is pumped out of the heart.

Diastolic Blood Pressure

  • Occurs during relaxation of the heart (refilling phase) when blood returns to the heart.

Understanding Hypertension

Definitions

  • Hypertension: A condition defined typically as a blood pressure reading of 140/90 mmHg or higher.

  • Increased Risk Indicators for Hypertension:

    • 115/75 mmHg is associated with an increased risk of:

    • Stroke

    • Myocardial infarction (heart attack)

    • Heart failure

    • Renal failure

    • Cognitive impairment

Prevalence of Hypertension

Age-related Statistics

  • Hypertension prevalence among individuals aged 30 years and older is alarming.

    • Definition: Systolic BP ≥ 140 mmHg or Diastolic BP ≥ 90 mmHg, or currently using antihypertensive medication.

    • Prehypertension: Individuals not hypertensive but have readings of systolic BP 120-139 mmHg or diastolic BP 80-89 mmHg.

    • Contributing factors include:

    • Obesity

    • Excess sodium intake

    • Alcohol consumption

    • Lack of physical activity

    • Smoking

Long-term Risks of Untreated Hypertension

  • Chronic hypertension significantly increases the risk of cardiovascular diseases and mortality.

  • The transition from prehypertension to hypertension requires proactive management.

Mechanisms Linking Sodium and Hypertension

Vascular Aging

  • Age-related increases in blood pressure are closely connected to:

    • Increased stiffness of large arteries, which reduces compliance.

    • Reduced compliance leads to a rise in systolic blood pressure.

Pathophysiological Mechanisms

  • Key elements contributing to hypertension:

    • Increased arterial stiffness

    • Proliferation of smooth muscle cells in arteries

    • Endothelial dysfunction (impaired functioning of blood vessel linings)

    • Enhanced vasoconstriction, leading to higher vascular resistance

    • Elevated angiotensin II activity, which affects sodium and water reabsorption.

Renin-Angiotensin-Aldosterone System

  • Components and functioning:

    1. Renin: Enzyme secreted by kidneys in response to low blood pressure

    2. Angiotensinogen: Protein converted to angiotensin I

    3. Angiotensin I: Transformed into angiotensin II by angiotensin-converting enzyme (ACE)

    4. Angiotensin II: Triggers vasoconstriction and aldosterone release which increases sodium and water retention

Dietary Sodium Intake and Hypertension

Physiological Effects of Sodium

  • High dietary sodium initiates a sequence that leads to:

    • Increased intravascular fluid volume

    • Higher cardiac output

    • Higher vascular resistance

    • Elevated blood pressure

  • In hypertensive individuals, sodium excretion (pressure-natriuresis) is compromised.

Pressure-natriuresis

  • Definition: An autoregulatory response of the kidneys to increased arterial pressure, leading to enhanced sodium and water excretion to stabilize blood pressure.

Local Renin-Angiotensin-Aldosterone Systems

  • Local systems can become damaged by sustained activation, leading to fibrosis and further sodium retention.

Characteristics of Populations with Low Blood Pressure

Diet and Lifestyle Traits

  • Populations with lower prevalence of high blood pressure tend to have:

    • Very low salt intake (10-50 mmol/day)

    • Diets rich in vegetables

    • Low intake of meats

    • Minimal obesity prevalence

Healthful Dietary Patterns

Impact on Blood Pressure

  • Certain dietary patterns have been shown to effectively lower blood pressure and include:

    • DASH Diet: Dietary Approaches to Stop Hypertension

    • Mediterranean Diet

  • Healthful diets help to:

    • Reset the pressure-natriuresis curve

    • Reduce blood volume

    • Alleviate aortic stiffness

    • Enhance vasodilation in smaller resistance vessels

Dietary Sodium Reduction Analysis

  • Studies indicate that reducing sodium to lower levels leads to significant drops in systolic blood pressure.

Dietary Interventions and Models

Three Primary Dietary Strategies

  • Diets to lower blood pressure include:

    1. Healthful dietary patterns (e.g., Vegetarian, Mediterranean, DASH)

    2. Reduced sodium intake

    3. Management of overweight and obesity

DASH Diet Specifications

  • The DASH diet is composed of:

    • High in fruits, vegetables, whole grains, fish, poultry, beans, nuts, and low-fat dairy

    • Limited red meat, sweets, and sugar-containing beverages

  • Benefits:

    • Encourages intake of nutrient-rich foods known to support blood pressure management (e.g., potassium, magnesium, calcium, fiber).

Study Results on Systolic Blood Pressure

  • Comparison among various diets showed significant differences in systolic blood pressure reductions.

  • For example, mean systolic BP values via DASH diet indicated reduced pressures compared to control diets.

Pressure-Natriuresis Effect of DASH Diet

  • The DASH diet promotes renal sodium excretion effectively, allowing for normalization of blood pressure under varying conditions.

Randomized Trials Outcomes

  • Evidence indicates additive benefits of DASH dietary approach combined with weight loss.

  • Example findings:

    • With weight loss: SBP reduction of 13 mmHg

    • Without weight loss: SBP reduction of 8 mmHg

Conclusions

  • Aging arteries can be rejuvenated through dietary interventions like the DASH diet.

  • A comprehensive dietary approach supports the restoration of blood vessel compliance and endothelial function.

  • Ongoing emphasis on low sodium intake and maintaining a healthy weight are essential for effective hypertension management and prevention.