What is the difference between systolic (blood pressure when the heart beats) and diastolic (blood pressure when the heart rests) pressure?

Difference Between Systolic and Diastolic Blood Pressure

Systolic blood pressure represents the pressure in arteries during heart contraction (systole), while diastolic blood pressure represents the pressure when the heart is relaxing between beats (diastole). 1

Physiological Basis

Systolic Blood Pressure

• Measured when the first Korotkoff sounds are heard during blood pressure measurement 1
• Represents the maximum arterial pulsatile pressure that occurs during ventricular contraction 1
• Typically increases progressively with age due to stiffening of large arteries 1
• Normal range is <120 mmHg, with values 120-139 mmHg considered prehypertensive 1

Diastolic Blood Pressure

• Measured at the disappearance of Korotkoff sounds (fifth sound) 1
• Represents the minimum arterial pulsatile pressure during ventricular relaxation 1
• More closely reflects peripheral vascular resistance 2
• Normal range is <80 mmHg, with values 80-89 mmHg considered prehypertensive 1

Clinical Significance

Cardiovascular Risk

• Both systolic and diastolic blood pressures independently predict cardiovascular events 3
• In younger individuals (<55 years), both components are similarly predictive of stroke and coronary mortality 1
• In middle-aged and elderly patients, systolic blood pressure becomes more important 1
• There is a continuum of cardiovascular risk associated with blood pressure levels - the higher the pressure, the higher the risk 1

Pulse Pressure

• Defined as the difference between systolic and diastolic blood pressure 1
• Increases with age as arteries become less elastic 2
• Serves as a marker of arterial stiffness, especially in elderly patients 1
• High pulse pressure (particularly in older adults) indicates advanced organ damage and increased cardiovascular risk 1

Measurement Considerations

Proper Technique

• Blood pressure should be measured after 5 minutes of rest in a seated position 1
• Arm should be supported at heart level with appropriate cuff size 1
• Multiple readings should be taken (at least two) on different occasions 1
• Both systolic and diastolic values should be recorded 1

Classification

According to current guidelines, blood pressure categories include:

• Optimal: <120/80 mmHg
• Normal: 120-129/80-84 mmHg
• High normal: 130-139/85-89 mmHg
• Grade 1 hypertension: 140-159/90-99 mmHg
• Grade 2 hypertension: 160-179/100-109 mmHg
• Grade 3 hypertension: ≥180/≥110 mmHg 1

Clinical Implications

Treatment Considerations

• Both systolic and diastolic values should guide treatment decisions 1
• In older adults with isolated systolic hypertension (elevated systolic with normal diastolic), treatment should focus on reducing systolic pressure while avoiding excessive lowering of diastolic pressure 4
• Excessively low diastolic pressure (<60-70 mmHg) may compromise coronary perfusion, especially in patients with coronary artery disease 4

Special Populations

• In elderly patients, systolic hypertension is more common due to arterial stiffening 5
• In younger adults, isolated diastolic hypertension may occur but is less common 1
• The relationship between blood pressure components and outcomes may vary with age and comorbidities 3

Common Pitfalls

• Focusing only on diastolic pressure while ignoring elevated systolic values
• Using inappropriate cuff size, which can artificially elevate or reduce blood pressure readings 1
• Failing to consider pulse pressure as an additional risk marker in older adults 1
• Not accounting for white coat hypertension or masked hypertension, which require out-of-office measurements 1

Both systolic and diastolic blood pressure values are important clinical parameters that provide complementary information about cardiovascular health and should be considered together when assessing cardiovascular risk and making treatment decisions.