Blood Pressure Measurement: Assessment of a Variable Quantity

Blood pressure (BP) is used to assess the cardiovascular system of a person. Assessment is however not possible based on a single measurement even if it is accurate. BP varies along the circulatory system, and at a given point fluctuates in time. Many internal and external factors influence the actual value of BP. Nevertheless, it is a common practice to characterize the BP of a person simply with two numeric values, one standing for the systolic and the other one for the diastolic pressure. This is meaningful only if the tested person is at rest, both systolic and diastolic pressures are constant, and pressure in the upper arm artery is measured by placing the cuff properly at the level of the heart so that the measurement does not alter the pressure to be measured. There are both short-term (even beat-to-beat) and long-term variations in BP, and therefore diagnosis must not rely on a single measurement. The paper shortly reviews the history of BP measurement, analyzes the accuracy and limits of reproducibility of indirect assessment in general and of the oscillometric method in particular. Examples are given, demonstrating how the most common errors distort the result of a non-invasive BP measurement. It is also advised how the best result can be achieved using the available BP meters.