MERCURY MANOMETER

Typical Number in Hospital: 300

Cost Bands: 1

References: 2

Blood pressure measurement by sphygmomanometer is normally performed using a mercury manometer. This can consist of a U- tube half-filled with mercury, but more commonly it is a single tube, held vertical in use, which sits in a small reservoir of mercury. The reservoir is connected by a rubber tube to the source of air pressure to be measured. As pressure is applied mercury is forced up the column and the pressure can be read from a scale behind. The actual pressure is indicated by the difference in the level of the mercury in the column and the reservoir. Thus, the relative areas of the surfaces of the two sections of the device must be such that the reservoir level does not descend much due to the volume of mercury forced up the column during measurement.

This type of manometer is slow acting and cumbersome but has the advantage that it cannot give incorrect readings and, due to the high specific gravity of mercury (13.6), only a short tube is required to indicate the full range of possible blood pressures. Normally it provides for measurement up to 300 mmHg.