14.5: Equipments Used To Measure Blood Pressure
Direct Method
This invasive approach involves cannulating a peripheral artery. During each cardiac contraction, pressure generates mechanical motion within the catheter, transmitted through rigid, fluid-filled tubing to a transducer. This transducer converts mechanical motion into electrical signals displayed as waveforms on a monitor. An automatic flushing system prevents blood backflow. Due to the potential risk of unexpected arterial blood loss, this method is primarily used in intensive care settings. Regularly calibrating and maintaining the transducer to ensure accurate readings is crucial.
Indirect Methods:
The indirect measurement methods are non-invasive and use devices such as sphygmomanometers, Doppler ultrasound devices, and a stethoscope.
Mercury Sphygmomanometer
This device consists of an inflatable cuff, a mercury manometer, a bulb, and a valve. The cuff is inflated to a pressure higher than the anticipated systolic pressure to measure blood pressure. Pressure is then slowly released while listening to Korotkoff sounds. Systolic pressure is identified at the first appearance of these sounds, and diastolic pressure is noted when the sounds disappear.
Manual Aneroid Sphygmomanometer
It comprises a cuff, bulb, valve, and manometer. This device requires correct cuff sizing for accurate readings. The cuff should be twenty percent wider than the upper arm diameter or forty percent of the arm’s circumference and should cover two-thirds of the arm’s length. It includes two tubes: one connected to the manometer and the other to the inflation bulb. The manometer, encased in glass, displays pressure in millimeters of mercury and should be calibrated to zero before use. Aneroid sphygmomanometers require biannual calibration checks and regular maintenance of the release valve.
Automated Blood Pressure Monitors
These monitors use oscillometric or auscultatory methods to measure blood pressure automatically without manual intervention. They detect arterial wall pressure, converting it into digital readouts. These devices facilitate regular blood pressure monitoring across various healthcare settings.
Doppler Ultrasound Device
This device emits high-frequency sound waves that reflect off circulating blood cells, producing an audible signal. It is particularly useful in conditions where pulse sounds are compromised, such as in patients with heart failure or coronary artery disease. The Doppler enhances and audibly represents these signals, aiding in accurate measurement under challenging conditions.
