OSCILLOTONOMETER

Typical Number in Hospital: 30

Cost Bands: 1

References: 2,6

Intermittent indirect blood pressure measurement can be conducted in the operating theatre by use of an oscillotonometer (sometimes called an oscillometer). This has two inflatable cuffs on the upper arm which connect via rubber tubes to a control unit, which looks like a large size aneroid pressure gauge but in fact contains two aneroid capsules which can be connected up to provide a differential pressure between the cuffs, or a single pressure (when the cuffs are connected together).

In operation, the cuffs are inflated together to above the systolic pressure using the usual bulb-type pump. The pressure is gradually released, and from time to time a switch is operated to change the internal connection between the two cuffs so that the lower cuff senses the pulsations due to arterial wall movement. These pulsations are a maximum when the upper cuff is at the systolic pressure. They fall gradually from this point and practically disappear at the diastolic pressure. The aneroid capsules are cleverly linked inside so that the gauge shows the pressure being applied to the upper cuff with the pulsations from the lower cuff superimposed.

Other equipment exists which utilizes double-cuff methods and electronic processing of the pressure and pulse signals. An example is described under Haemotonometer.