Sphygmomanometer Health Article

Definition

A sphygmomanometer is a device for monitoring blood pressure.

Purpose

The sphygmomanometer is designed to monitor the blood pressure by measuring the force of the blood in the heart where the pressure is greatest, during the contraction of the ventricles as blood is pumped from the heart to the rest of the body (systolic pressure), and during the period when the heart is relaxed between beats and pressure is lowest (diastolic pressure).

The device is used to establish a baseline at a health-care encounter and on admission to the hospital. Checking blood pressure is also performed to monitor the effectiveness of medication and other methods to control hypertension, and as a diagnostic aid to detect various diseases and abnormalities.

Description

The sphygmomanometer consists of a hand bulb pump, a unit that displays the blood pressure reading, and an inflatable cuff that is wrapped around the patient's upper arm. Care should be taken to ensure the cuff is the correct size to give an accurate reading. Children and adults with smaller or larger than average-sized arms require special sized cuffs appropriate for their needs. A stethoscope is also used in conjunction with the sphygmomanometer to hear the blood pressure sounds. Some devices have the stethoscope already built in.

The sphygmomanometer can be used in a variety of settings:

• home
• hospital
• primary care, clinic, or clinician's office
• ambulance
• dental office

There are three types of equipment for monitoring blood pressure.

The mercury-based unit has a manually inflatable cuff attached by tubing to the unit that is calibrated in millimeters of mercury. During blood pressure measurement, the unit must be kept upright on a flat surface and the gauge read at eye level. Breakage of the unit may cause dangerous mercury contamination and would require specialist removal for disposal.

The aneroid unit is mercury free and consists of a cuff that can be applied with one hand for self-testing, a stethoscope that is built in or attached, and a valve that inflates and deflates automatically with the data displayed on an easy-to-read gauge that will function in any position. The unit is sensitive and if dropped, may require recalibration.

The automatic unit is also mercury free and is battery operated. It has a cuff that can be applied with one hand for self-testing, and a valve that inflates and deflates automatically. (Units with manual inflation are also available.) The reading is displayed digitally and a stethoscope is not required, therefore, the unit is useful for someone who is hearing impaired. A wrist monitor is also available for home testing. Some more expensive models also remember and print out recordings. The automatic units may be more portable than the bulkier mercury devices.

Blood pressure can be measured with any of the units, although mercury units are becoming less common due to the hazards of mercury.

Operation

The flow, resistance, quality, and quantity of blood circulating through the heart and the condition of the arterial walls are all factors that influence the blood pressure. If blood flow in the arteries is restricted, the reading will be higher.

Blood pressure should be routinely checked every one to two years. It can be checked at any time but is best performed when the patient has been resting for at least five minutes, so that exertion prior to the test will not unduly influence the outcome of the reading.

To record blood pressure, the patient should be seated with his left arm bent slightly, and the arm bare or with the sleeve loosely rolled up. With an aneroid or automatic unit, the cuff is placed level with the heart and wrapped around the upper arm, one inch above the elbow. Following the manufacturer's guidelines, the cuff is inflated and then deflated and the nurse records the reading.

If the blood pressure is monitored manually, a cuff is placed level with the heart and wrapped firmly but not tightly around the arm one inch above the elbow over the brachial artery, with creases in the cuff smoothed out. With a stethoscope over the brachial artery in front of the elbow with one hand and listening through the earpiece, the cuff is inflated well above normal levels (to about 200mm Hg), or until no sound is heard. The cuff is then inflated a further 10mm Hg above the last sound heard. The valve in the pump is slowly opened no faster than 5mm Hg per second to deflate the pressure in the cuff to the point where a tapping sound is heard over the brachial artery. This point is noted as the systolic pressure. The sounds continue as the pressure in the cuff is released and the artery is no longer occluded. At this point, the noises are no longer heard and this is noted as the diastolic pressure.

With children, the tapping noise changes to a soft muffled sound. That point is noted as the diastolic pressure, since sounds continue to be heard as the cuff deflates to zero.

Blood pressure results are recorded with the systolic pressure first, then the diastolic pressure (e.g. 120/70).