A manual blood pressure cuff, technically known as an aneroid sphygmomanometer, is a non-electronic device used to measure the pressure exerted by circulating blood on the walls of arteries. Unlike automated digital monitors, the manual method requires a trained operator to listen for specific sounds, a technique called auscultation. This technique remains the gold standard in many clinical settings because it allows for the detection of subtle variations in blood flow and irregular heart rhythms that a machine might miss. When performed correctly, the direct measurement process provides a high degree of accuracy and reliability.
Essential Components of the Manual Cuff
The manual blood pressure system consists of several integrated parts that work together to temporarily restrict and monitor blood flow. The cuff contains an inflatable rubber bladder that applies external pressure to the arm’s artery. This cuff is connected by tubing to the aneroid manometer, a circular dial gauge that displays the pressure in millimeters of mercury (mmHg).
Inflation of the bladder is achieved by repeatedly squeezing the rubber inflation bulb. Air pressure is controlled by a small, adjustable air release valve usually located near the bulb. The stethoscope is a mandatory component used to listen over the artery, allowing the user to detect the distinct sounds of turbulent blood flow necessary to determine the pressure values.
Preparation for an Accurate Reading
Achieving a reliable blood pressure measurement begins with careful preparation, as patient factors can easily distort the reading. The subject should rest quietly in a chair for at least five minutes, with their back supported and feet flat on the floor, avoiding talking or using a phone. It is important to refrain from consuming caffeine, exercising, or smoking for at least 30 minutes before the measurement.
Proper positioning of the arm is essential, requiring the upper arm to be bare and supported at the level of the heart. The correct cuff size must be selected; the inflatable bladder’s width should cover approximately 40% of the arm’s circumference. Using a cuff that is too small can lead to a falsely elevated reading, while a cuff that is too large may result in a falsely low reading. Before application, check the aneroid gauge to ensure the needle rests precisely on the zero mark, confirming calibration.
The Step-by-Step Measurement Procedure
Once the patient is prepared, wrap the appropriately sized cuff snugly around the upper arm, about one inch above the crease of the elbow. First, palpate the brachial artery, located on the inner side of the arm near the elbow, and position the stethoscope’s bell directly over this pulse point. Next, rapidly inflate the cuff to a pressure approximately 30 mmHg higher than the person’s usual systolic pressure, or to 160–180 mmHg if the typical value is unknown.
This high pressure temporarily occludes the brachial artery, stopping blood flow and silencing any sounds heard through the stethoscope. Open the air release valve slightly to allow the pressure to drop at a controlled rate of about 2 to 3 mmHg per second. This slow, steady deflation is necessary to accurately detect the first audible sound, known as Korotkoff Phase I.
The pressure reading on the gauge at the exact moment the first faint, repetitive tapping sound is heard represents the systolic blood pressure. As the pressure continues to decrease, the sounds will become louder and then eventually fade and disappear. The point where the sounds disappear completely, known as Korotkoff Phase V, is recorded as the diastolic blood pressure. After noting the diastolic value, deflate the cuff quickly and completely to relieve pressure on the arm.
Interpreting and Recording Blood Pressure Values
The measurement yields two distinct values, expressed as a fraction: systolic pressure over diastolic pressure, measured in millimeters of mercury. The systolic pressure (the top number) reflects the maximum pressure within the arteries when the heart contracts. The diastolic pressure (the bottom number) represents the minimum pressure in the arteries when the heart is relaxed and refilling with blood between beats.
A reading below 120/80 mmHg is considered normal, while 120–129 systolic and less than 80 diastolic is classified as elevated. Stage 1 hypertension is diagnosed when the systolic pressure is between 130 and 139 mmHg or the diastolic pressure is between 80 and 89 mmHg. All readings must be immediately recorded, noting the specific arm used and the exact time of the reading. Taking two separate readings, separated by a one-minute rest period, and averaging them provides a more accurate representation.