Systolic Blood Pressure, or SBP, is often referred to as the “top number” in a typical blood pressure reading. SBP is a direct indicator of the force exerted by the heart as it pumps blood throughout the circulatory system. As a standard vital sign, SBP is continuously monitored to help detect issues before they cause lasting damage.
Defining Systolic Pressure and Blood Pressure Measurement
Systolic pressure measures the maximum force blood exerts against the walls of the arteries during a single heartbeat. This pressure peak occurs during ventricular systole, the phase when the heart’s ventricles contract. This powerful contraction propels a volume of blood, called the stroke volume, out of the heart and into the aorta and pulmonary artery.
Blood pressure measurement is typically achieved using a device called a sphygmomanometer. The cuff is inflated around the upper arm until the pressure temporarily stops blood flow through the brachial artery. As the pressure is slowly released, the first sound heard through a stethoscope, known as a Korotkoff sound, marks the return of blood flow and registers the SBP.
Diastolic Blood Pressure (DBP), the “bottom number,” reflects the lowest pressure in the arteries. DBP occurs during ventricular diastole, the phase when the heart muscle relaxes and refills with blood between beats. Both SBP and DBP are measured in millimeters of mercury (mmHg) and are reported with the systolic value first, such as 120/80 mmHg.
Understanding SBP Reference Ranges
Normal and Elevated Ranges
Clinical guidelines categorize SBP readings to determine cardiovascular risk and the need for intervention. A reading is considered Normal when SBP is less than 120 mmHg and DBP is less than 80 mmHg. Maintaining SBP below this threshold is associated with the lowest risk of heart disease and stroke.
Elevated blood pressure is defined by an SBP ranging from 120 to 129 mmHg, with the DBP remaining below 80 mmHg. Individuals in this range are at increased risk of developing hypertension and are generally advised to implement lifestyle modifications.
Hypertension Stages
Hypertension is clinically divided into two stages based on SBP and DBP values. Stage 1 Hypertension is diagnosed when SBP is between 130 and 139 mmHg or DBP is between 80 and 89 mmHg. Stage 2 Hypertension is a more serious condition, defined by an SBP of 140 mmHg or higher, or a DBP of 90 mmHg or higher.
Hypertensive Crisis
A Hypertensive Crisis is an immediate medical concern, characterized by an SBP exceeding 180 mmHg and/or a DBP over 120 mmHg. This extreme elevation can be life-threatening and requires emergency medical attention, especially if accompanied by symptoms like chest pain, severe headache, or shortness of breath. A general treatment goal is often set below 130/80 mmHg for most adults.
The Health Implications of Elevated SBP
Sustained high SBP, or hypertension, is the most prevalent modifiable risk factor for cardiovascular disease. The constant, excessive force against the arterial walls causes gradual damage to the vascular system over time. This chronic stress accelerates arterial stiffness, where blood vessels lose their natural flexibility and elasticity.
Arterial stiffening forces the heart to work harder to push blood through resistant vessels, leading to the thickening and weakening of the heart muscle and eventually causing heart failure. Uncontrolled high SBP contributes significantly to the buildup of plaque within the arteries, increasing the likelihood of a blockage.
Elevated SBP increases the risk of stroke and damages blood vessels in the kidneys, impairing their ability to filter waste and leading to chronic kidney disease. A strong link has been established between high SBP and an increased risk of cognitive decline and dementia. The risk of major cardiovascular events, including myocardial infarction (heart attack), increases progressively for every 20 mmHg rise in systolic pressure above the normal range.
Recognizing and Addressing Low SBP
Low SBP occurs when the reading is less than 90 mmHg, often paired with a DBP below 60 mmHg. While some healthy individuals naturally have lower blood pressure, a sudden or symptomatic drop in SBP can signal an underlying health issue.
Symptoms of low SBP include lightheadedness, dizziness, unsteadiness, blurred vision, weakness, fatigue, and nausea, which can lead to fainting or syncope. These symptoms occur because the brain and other organs are not receiving sufficient blood flow and oxygen to function correctly.
Common causes for a drop in SBP include significant dehydration, internal blood loss, and side effects from certain medications used to treat high blood pressure or depression. Serious underlying issues include severe infections like sepsis, heart problems, or a severe allergic reaction known as anaphylaxis. Extreme hypotension can progress to a state of shock, a life-threatening condition due to severely limited blood flow.