BP is the abbreviation for Blood Pressure, representing the force that circulating blood exerts against the walls of the body’s blood vessels, primarily the arteries. This pressure is generated by the heart as it pumps blood throughout the circulatory system to deliver oxygen and nutrients. A blood pressure measurement provides an informative view of a person’s cardiovascular health. Understanding this measurement involves two distinct numbers, reflecting different phases of the heart’s pumping cycle.
The Mechanics of Blood Pressure
Blood pressure is a measurement consisting of two values: systolic pressure and diastolic pressure. These two numbers correspond directly to the contraction and relaxation phases of the heart muscle. The higher number, systolic pressure, represents the maximum force on the artery walls when the heart contracts to push blood out.
The lower number, diastolic pressure, reflects the lowest pressure within the arteries when the heart is at rest between beats. During this resting phase, the heart chambers refill with blood. Both numbers provide a complete picture of the pressure dynamics within the circulatory system.
The heart’s action of ejecting blood during the systolic phase causes a rapid rise in arterial pressure. This surge creates the higher pressure reading. Conversely, the pressure naturally decreases during the diastolic phase as the heart relaxes and the blood vessels maintain a baseline resistance to flow.
How Blood Pressure is Measured
Blood pressure is measured using a device called a sphygmomanometer, which typically involves an inflatable cuff, a pump, and a pressure gauge. This equipment is designed to temporarily restrict and then gradually release blood flow in a major artery, usually the brachial artery in the upper arm.
The cuff is wrapped around the upper arm and inflated until it briefly stops blood flow. As air is slowly released, the healthcare professional listens for the return of blood flow sounds, known as Korotkoff sounds, using a stethoscope. The pressure reading when the first sound is heard is the systolic pressure.
The measurement continues as air is released, and the point at which the sounds disappear completely indicates the diastolic pressure. Readings are universally recorded in millimeters of mercury (mmHg), with the systolic value listed first (e.g., 120/80 mmHg). Automated digital devices use sensors to detect the subtle vibrations caused by the returning blood flow.
Understanding Blood Pressure Categories
Blood pressure readings are categorized to assess the level of risk to a person’s long-term cardiovascular health. A reading is considered Normal when the systolic pressure is less than 120 mmHg and the diastolic pressure is less than 80 mmHg. Maintaining blood pressure within this range is associated with better heart health outcomes.
The Elevated category is defined by a systolic pressure between 120 and 129 mmHg and a diastolic pressure still less than 80 mmHg. Although not yet considered high blood pressure, this range suggests a greater chance of developing hypertension in the future, prompting a recommendation for lifestyle adjustments.
Hypertension, or high blood pressure, is divided into two stages. Stage 1 Hypertension is when the systolic pressure is between 130 and 139 mmHg or the diastolic pressure is between 80 and 89 mmHg. Stage 2 Hypertension is a more severe condition, marked by a systolic pressure of 140 mmHg or higher or a diastolic pressure of 90 mmHg or higher.
Consistently high pressure forces the heart to work harder, damaging arteries and leading to serious health issues like stroke and heart attack. A reading higher than 180 mmHg systolic or 120 mmHg diastolic is considered a Hypertensive Crisis, requiring immediate medical attention.