Blood pressure is determined by two factors: the amount of blood circulating in the vessels and the force of pressure it exerts on the walls of the arteries. Blood pressure measurement devices may be manual or automatic and depend on the setting in which the measurement is obtained. A typical measurement is obtained at the brachial artery located in the upper arm and reads the systolic pressure, the highest pressure in the artery when the heart is contracting, as well as the diastolic pressure, the lowest pressure in the artery when the heart is relaxing. Blood pressure is recorded as 120/80, for example, with the systolic measurement on top.
Clinical Setting
The standard manual way to measure blood pressure is by using a device called a sphygmomanometer. The blood pressure reading appears on a numbered dial or via a column of mercury to allow the health care professional to record the two numbers associated with diastolic and systolic pressures, according to the National Heart Lung and Blood Institute. A cuff is placed around the upper arm which attaches to a small pump by a tube. The pump inflates the cuff to increase pressure around the arm to momentarily stop the arterial blood flow. Then a valve located on the end of the pump is turned to release the cuff pressure slowly and restart the blood flow. The health provider will place a stethoscope, a medical listening device, on the arm right below the cuff area to listen to the blood flow as it restarts. The first thumping sound determines the systolic measurement, while the last thumping sound before all sounds cease determines the diastolic measurement.
An automated non-invasive blood pressure measurement device may be used routinely in a clinical setting to obtain blood pressure readings. A cuff is placed around the arm, which then automatically inflates and gradually deflates. According to Dr. Humbly as stated in "Update in Anesthesia", the device works by measuring oscillations on the pressured cuff caused by the pulse. On the other hand, an invasive blood pressure is obtained by placing a small cannula directly in an artery for more precise measurements that are displayed on a screen. This option is used primarily for critically ill patients.
Home Setting
For measuring blood pressure in a home setting, a digital monitor can provide more ease of use than using a manual device such as a sphygmomanometer, according to the American Academy of Family Physicians (AAFP). The automatic device consists of a small unit with a screen that displays the blood pressure measurement. A cuff attached to the device should be placed around the upper arm and a button on the device automatically inflates the cuff. Depending on the model, semiautomatic devices require self-inflation of the cuff using a pump. The cuff will then automatically deflate as the device measures blood pressure. At the end of the process, the screen will display systolic and diastolic pressure measurements. According to the AAFP, digital monitors are sensitive to body movements or irregular heart rate and can provide inaccurate results in those cases. Also, the device requires batteries and may be expensive ranging from $30 to $100, states AAFP.
Similar digital monitor devices can measure blood pressure from the wrist or finger. Wrist monitors may be appropriate for people with larger upper arms that do not accommodate the cuff size or those with discomfort using the arm cuff. The wrist should be held at the heart level to retrieve an accurate reading. The Mayo Clinic does not recommend devices measuring blood pressure from the finger and states arm devices provide the most accurate measurements.
Public Setting
Blood pressure measuring devices available at some pharmacies and retails stores operate on the same principle as a home digital monitor device. The arm is placed in the cuff area which then inflates at the push of a button and gradually releases the cuff pressure to provide measurement figures on a screen. Accuracy may be an issue with using these devices as the machine uses a standard "one size fits all" cuff. Correct cuff size is crucial in obtaining a correct measurement. According to the Mayo Clinic, public machines may not be maintained properly and should not be relied on for regular blood pressure measurement tracking.
References
- National Heart Lung and Blood Institute: How is Blood Pressure Tested?
- FamilyDoctor.org: Blood Pressure Monitoring at Home
- Mayo Clinic: Get the Most Out of Home Blood Pressure Monitoring
- "Update in Anesthesia"; Measuring the Blood Pressure; Dr. Peter Humbly; Issue 11 2000
