Understanding Blood Pressure

Understanding Blood Pressure

What Is Blood Pressure? 

The heart is constantly beating to supply oxygen-rich blood to all the organs and tissues in the body.1 The blood vessels in the body transport this oxygen-rich blood and experiences pressure with each heartbeat. This pressure can be measured with a blood pressure meter, which measures the pressure within the large arteries.

What Is Systolic and Diastolic Blood Pressure?

Blood pressure is measured in two different numbers: systolic blood pressure, or the “top number”, and diastolic blood pressure, or the “bottom number”.2 This pressure is measured in units of millimeters of mercury (mm Hg).1 Systolic blood pressure measures the maximum blood pressure, referring to the pressure within the large arteries when the heart contracts to pump blood throughout the human body. Diastolic blood pressure measures the lowest blood pressure, referring to the pressure within the large arteries when the heart relaxes between pumps.2

For instance, if someone’s blood pressure reading shows 120/82 mm Hg, it is read as “120 over 82” and refers to a systolic blood pressure of 120 mm Hg and a diastolic blood pressure of 82 mm Hg.

What Are Healthy and Unhealthy Blood Pressure Numbers?

Blood pressure is an important indicator of health.2 It is essential for the body to maintain healthy blood pressure, sustaining enough pressure to supply the body with sufficient oxygen-rich blood but preventing blood pressure from becoming too high that it causes damage to the body. Hypertension, or high blood pressure, is one of the major risk factors for cardiovascular diseases (ie, heart and blood vessel-related diseases).3 

The American Heart Association and the American College of Cardiology provide a helpful guideline with blood pressure categories for adults.

Blood Pressure Categories in Adults

Blood Pressure Category

Systolic Blood Pressure (mm Hg)


Diastolic Blood Pressure (mm Hg)









Stage 1 Hypertension




Stage 2 Hypertension





1. What Is Blood Pressure and How Is It Measured? In: InformedHealth.Org [Internet]. Institute for Quality and Efficiency in Health Care (IQWiG); 2019. Accessed July 17, 2023. https://www.ncbi.nlm.nih.gov/books/NBK279251/
2. Shahoud JS, Sanvictores T, Aeddula NR. Physiology, Arterial Pressure Regulation. In: StatPearls. StatPearls Publishing; 2023. Accessed July 17, 2023. http://www.ncbi.nlm.nih.gov/books/NBK538509/
3. Whelton PK, Carey RM, Aronow WS, et al. 2017 ACC/AHA/AAPA/ABC/ACPM/AGS/APhA/ASH/ASPC/NMA/PCNA Guideline for the Prevention, Detection, Evaluation, and Management of High Blood Pressure in Adults: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines. Hypertension. 2018;71(6):e13-e115. doi:10.1161/HYP.0000000000000065



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