6 / Blood Pressure

Circulation

The continuous, orderly movement of blood through the body's network of vessels, driven by the heart's rhythmic activity, making blood flow pulsating and its speed rhythmically changeable

Unit of Measurement

Blood pressure is measured in millimeters of mercury (Hgmm)

Systole (SBP)

The maximum pressure value occurring during the contraction of the ventricles, with a normal range of 90-120 Hgmm

Diastole (DBP)

The minimum or baseline value measured during the relaxation of the ventricles, with a normal range of 60-89 Hgmm

Mitral Valve

This valve closes at the start of systole

Aortic Valve

This valve opens to allow blood ejection during systole

Ventricular Volume Changes

Volume starts at approximately 130mL and drops to a minimum of 50mL during systole

Pressure Variability

A normal person's blood pressure can vary by as much as 30 Hgmm during a single 1-minute continuous recording

Mean Arterial Pressure (MAP) Definition

Represents the theoretical continuous pressure that would produce an equivalent blood flow (liters/min), used to understand if organs receive enough blood

Mean Arterial Pressure (MAP) Formula

MAP = (SBP + 2 x DBP) / 3

Pulse Pressure

The numerical difference between the Systolic Blood Pressure (SBP) and the Diastolic Blood Pressure (DBP)

Hypotension (Low Pressure)

Category where SBP is <90 and DBP is <60, meaning the MAP is too weak

Normal Blood Pressure

Category where SBP is 90-120 and DBP is 80-89; all organs receive adequate blood ?

Prehypertension

Category where SBP is 120-139 and DBP is 80-89; the heart starts to work harder than it should

Stage 1 Hypertension

Category where SBP is 140-159 and DBP is 90-99; chronic stress causes high pressure that damages vessel walls, requiring medication or lifestyle changes ?

Stage 2 Hypertension

Category where SBP is 160-179 and DBP is 100-109; high risk stage that increases the significance of a stroke or heart attack

Traditional Measurement Method

Uses a sphygmomanometer and a stethoscope, typically applied to the left upper arm

Measurement Step 1

The cuff is inflated higher than the SBP to completely close the artery

1st Korotkoff Sound

Heard as the cuff deflates and reaches SBP; marks the restart of blood flow with turbulence and signifies Systolic Pressure

2nd Korotkoff Sound

Heard as pressure drops and the artery fully reopens; turbulence stops and the sound muffles or disappears, marking Diastolic Pressure

Wrist Devices

Convenient but less reliable automated method; often provide higher values due to inappropriate use

Oscillometric Measurement

Technique used by automated monitors where a sensor detects tiny vibrations (oscillations) in the artery during cuff deflation to calculate readings

Smart Watches

Use pulse plethysmography; the least reliable method which requires periodic recalibration with a traditional cuff

White Coat Hypertension

A slight increase in blood pressure specifically evoked by a medical or laboratory context

Cardiovascular Reactivity

Individual differences in the magnitude of cardiovascular response (HR, BP) to a novel or stressful situation; high reactivity is a major risk factor for disease

Subjective Perception

Humans cannot accurately sense actual BP and often rely on inaccurate external cues or assumed associations with emotional states

Treatment Risks

Patients may fail to take medication regularly because they cannot feel elevated BP or they incorrectly adjust doses based on subjective mood

BP vs. ECG in Psychophysiology

BP is used less frequently because the measurement process catches the subject's attention and creates "artefacts" (psychophysiological changes)