White coat effect

It is fairly common for people to be more tense than usual in a clinical setting, resulting in higher blood pressure readings in the clinic or hospital than at home (systolic pressure on average 10 mmHg higher and diastolic pressure about 5 mmHg higher). Arriving early to an appointment to have some time to relax and using the average mode of the monitor may help reduce this effect. Patients presenting a high blood pressure may be asked to measure their blood pressure at home or at a pharmacy to rule out the white coat effect.

A mercury-based sphygmomanometer indicates blood pressure with a column of mercury. It consists of a manually inflatable cuff, air bladder, tubing, mercury gauge and a rubber bulb. When measuring blood pressure, it must be kept upright on a flat surface and the gauge must be read at eye level. No recalibration is necessary. The systolic and diastolic pressure readings are based on the sounds produced by the blood flowing inside the arteries (Korotkoff sounds). Auscultation with a mercury sphygmomanometer has been performed worldwide for more than a century and is still regarded as the most accurate and the gold standard method (especially for individuals with pulse irregularities), despite being phased out in some countries and clinical settings due to the health and environmental risks associated with mercury leakage and technological advances. 

An aneroid sphygmomanometer does not contain mercury. It consists of a cuff, an in-built or attached stethoscope, a valve that inflates and deflates automatically and a gauge that can be read in any position. Like the mercury sphygmomanometer, readings must be based on Korotkoff sounds. Recalibration checks may be necessary due to the mechanism being sensitive to strain and shocks. Studies on non-shockproof aneroid sphygmomanometers have shown that only devices undergoing a regular (half-) yearly technical inspection (including recalibration) ensured a reliable measurement accuracy. When such procedure was lacking, up to 60% of devices demonstrated technical defects (especially portable instruments) or unacceptable measurement inaccuracy. A sphygmomanometer with the patented shock-proof® technology from Riester on the other hand is designed to sustain a fall of 120 cm (4ft) and still remain properly calibrated – an industry-leading performance that in turn translates into lower lifetime costs and an increased confidence that a high level of accuracy can be maintained over a longer period of time than traditional sphygmomanometers. 

An automatic digital sphygmomanometer is powered by batteries or AC adapter. It is also mercury-free and employs oscillometric measurements, a microprocessor, electronic pressure sensors and calculations rather than auscultation. Like the two other types of sphygmomanometers, it includes an inflatable cuff. However it differs in its use of pressure sensors to evaluate and measure the oscillations of the arteries. Inflation can be manual or generated by a valve that automatically inflates and deflates. The reading is displayed digitally and a stethoscope is not required.

This type of blood pressure monitor is the most commonly found outside the clinical environment as it is simple to use and reasonably priced. The British Heart Foundation recommends using an upper cuff rather than a wrist or a finger cuff; using the right cuff size (there should be just enough space to slide two fingertips underneath the upper arm cuff); buying a BIHS-validated monitor; and making sure it is either serviced and calibrated or replaced every two years.

When purchasing a digital sphygmomanometer, it is important to verify that it has been clinically validated for relevant conditions as their calculations may otherwise not be correct in cases of arrhythmia, preeclampsia or arteriosclerosis, among others. Riester’s RBP-100 for example allows arrhythmia detection and is clinically validated for patients with special conditions: hypertension, hypotension, diabetes, pregnancy, pre-eclampsia, arteriosclerosis, end-stage renal disease and obesity.