Blood pressure is the force exerted by circulating blood against the walls of the body’s arteries. Learning to measure blood pressure manually using the auscultation method provides a highly accurate reading for monitoring cardiovascular health. The technique requires a sphygmomanometer, often called a blood pressure cuff, and a stethoscope to listen to the specific sounds produced by the blood flow. This traditional, hands-on approach remains the standard for validating readings taken by automated devices.
Necessary Tools and Preparation
The aneroid sphygmomanometer is the device used to apply and measure pressure. It consists of an inflatable cuff that wraps around the upper arm, containing a rubber bladder that compresses the artery when filled with air. Air is manually pumped into the bladder by squeezing the inflation bulb, and the rate of air release is controlled by an adjustable air release valve. The pressure inside the system is displayed on the circular dial gauge, known as the manometer, which registers the measurement in millimeters of mercury (mmHg).
A stethoscope is necessary to hear the sounds of blood flow within the artery once the cuff pressure is released. It has ear pieces connected by tubing to the chestpiece, which is placed directly over the artery. The chestpiece typically includes both a diaphragm and a bell, with the diaphragm being the part most often used for this procedure due to its ability to pick up higher-frequency sounds.
Obtaining an accurate reading requires proper patient preparation. The subject should be seated comfortably with their back supported and feet flat on the floor, ensuring their legs are not crossed. The arm being used must be bare, fully supported on a flat surface, and positioned so the midpoint of the upper arm is level with the heart. Before beginning the measurement, the subject should rest quietly for at least five minutes, as physical activity or anxiety can temporarily elevate blood pressure.
Performing the Manual Blood Pressure Measurement
The first step involves locating the brachial artery, the main blood vessel in the upper arm, typically found near the crease of the elbow on the inner side. Once the pulse is identified by palpation, the deflated cuff is wrapped snugly around the bare upper arm, approximately one inch above the elbow crease. A designated artery mark or arrow on the cuff should be centered directly over the located brachial artery to ensure proper pressure application.
To determine the maximum inflation level, the radial pulse should be palpated while the cuff is rapidly inflated until the pulse is no longer felt. This pressure point, called the pulse obliteration pressure, estimates the systolic pressure. The cuff should then be inflated an additional 20 to 30 mmHg above this number. Inflating quickly to this maximum pressure briefly stops blood flow and helps prevent underestimation of the reading due to the auscultatory gap.
After inflation, the stethoscope’s chestpiece is placed lightly over the brachial artery at the elbow crease. The air release valve is then opened slightly to begin the controlled deflation of the cuff, maintaining a steady rate of pressure decrease between 2 to 3 mmHg per second. Listening carefully through the stethoscope during this slow deflation is the core of the auscultatory method, as it allows for the precise detection of the specific sounds that indicate the blood pressure values.
Understanding Systolic and Diastolic Readings
The sounds heard through the stethoscope during the deflation process are known as Korotkoff sounds, caused by the turbulent blood flow as the artery opens and closes under the pressure of the cuff. The systolic pressure is determined by noting the reading on the manometer at the exact moment the first clear, repetitive tapping sound is heard. This initial sound corresponds to the first phase of Korotkoff sounds and represents the highest pressure in the arteries as the heart muscle contracts and pushes blood out.
As the cuff continues to deflate, the sounds change in quality, becoming swishing, then crisper, and finally muffled, representing the intermediate Korotkoff phases. The diastolic pressure is determined by observing the manometer reading when the sounds completely disappear. This point of silence corresponds to the fifth phase of Korotkoff sounds, indicating that the artery is fully open and blood flow has returned to a smooth state. This final number represents the minimum pressure exerted on the artery walls when the heart is relaxed between beats. To ensure the most accurate measurement, continue deflating the cuff for another 10 to 20 mmHg after the sounds have disappeared before fully releasing the remaining air.