Blood pressure is the force exerted by circulating blood against the walls of the arteries. This measurement is typically presented as two numbers separated by a slash, such as 120/80 mmHg. Monitoring blood pressure provides a simple yet powerful indication of how hard the heart is working to circulate blood and the resistance level within the arteries. An abnormal reading can signal an increased risk for serious health issues, including heart attack and stroke. Understanding these two distinct numbers is important for cardiovascular health.
Decoding Systolic and Diastolic Pressure
The two numbers in a blood pressure reading reflect the two different phases of the heart’s pumping cycle. The top number is the systolic pressure, and the bottom number is the diastolic pressure. Both values are measured in millimeters of mercury, abbreviated as mmHg.
Systolic pressure is the maximum pressure exerted against the artery walls when the heart contracts, actively pushing blood out to the rest of the body. This contraction phase is known as systole. Because it is the period of highest force, the systolic reading is always the larger number. This measurement is particularly relevant for assessing cardiovascular risk in people over the age of 50.
Diastolic pressure is the minimum pressure within the arteries when the heart is at rest, between beats. This resting phase is called diastole, when the heart chambers refill with blood. This lower pressure value indicates the constant resistance within the blood vessels, even without the heart’s forceful contraction.
The difference between the two measurements is called the pulse pressure, which reflects the stiffness of the arteries. While both numbers are important, a high systolic reading is often a stronger predictor of cardiovascular problems in older adults.
Interpreting Blood Pressure Categories
Medical professionals use standardized categories to interpret blood pressure readings, based on standards set by organizations like the American Heart Association. A reading is classified by whichever number—systolic or diastolic—falls into the higher category.
A reading is considered Normal when the systolic pressure is less than 120 mmHg and the diastolic pressure is less than 80 mmHg. Readings in the Elevated range have a systolic pressure between 120 and 129 mmHg and a diastolic pressure still less than 80 mmHg. This Elevated category indicates a person is likely to develop hypertension unless lifestyle changes are implemented.
Stage 1 Hypertension is diagnosed when the systolic reading is between 130 and 139 mmHg or the diastolic reading is between 80 and 89 mmHg. At this stage, lifestyle changes are routinely recommended, and medication may be considered for patients with other risk factors.
Readings of 140/90 mmHg or higher are classified as Stage 2 Hypertension, indicating a greater risk of heart disease and stroke. Patients with Stage 2 Hypertension are typically prescribed a combination of lifestyle changes and blood pressure medication.
A Hypertensive Crisis occurs when the systolic pressure is higher than 180 mmHg and/or the diastolic pressure is higher than 120 mmHg. This represents a severe, potentially life-threatening situation. If this high reading is accompanied by symptoms like chest pain or shortness of breath, it requires immediate medical attention.
Factors That Can Alter Your Reading
Blood pressure is not a static number, and various transient factors can cause temporary fluctuations, leading to inaccurate measurements. Recent physical activity, such as walking or exercising, can temporarily increase systolic pressure. It is generally recommended to rest for three to five minutes before taking a measurement to ensure an accurate baseline reading.
Stress and anxiety are common causes of temporary spikes in blood pressure, often termed “white coat syndrome” when occurring in a clinical setting. Emotional distress causes the body to release hormones like cortisol, which can temporarily elevate both systolic and diastolic pressure by 4 to 15 mmHg. Caffeine and tobacco consumption also act as temporary stimulants, often causing a rise in systolic pressure by 5 to 10 mmHg for a short period.
Improper measurement technique is another significant source of error that can artificially inflate a reading. Using a blood pressure cuff that is too small for the arm circumference can mistakenly increase the systolic reading by 10 to 40 mmHg. Taking the measurement over clothing or with an unsupported back, arm, or crossed legs can also result in a misleadingly higher number. These factors underscore the importance of proper preparation and technique for obtaining a reliable blood pressure reading.