AVERAGER

Typical Number in Hospital: 5

Cost Bands: 4

References: 3,9

Although this has a common meaning, in medical equipment it normally refers to an electrical signal averager of the type used for averaging the response to a stimulus (light, sound, or the use of a short-acting drug). The response being monitored may be the heart rate, EEG, EMG, blood pressure, etc. and these may undergo fluctuations due to external interference or natural variations. If the response evoked by the stimulus is likely to be small compared with these other fluctuations, signal averaging may be employed to demonstrate the effect of the stimulus alone. The usual method is to repeat the test a number of times and add up all the responses so that natural fluctuations cancel out since they are not linked to the time of the stimulus. For evoked response averaging applied to an optical or auditory stimulus affecting the EEG the test may be repeated a large number of times in rapid succession so that a very small response may be detected in the presence of quite substantial noise. For a drug test, which may be carried out once only on each of a number of patients, the number of tests may be small.

Averagers are commonly found in the EEG, EMG and audiology clinics of hospitals and are usually microcomputers which hold the results in a computer memory so that each new result is added to the previous one in the computer memory. Tests performed using evoked response averagers include electric response audiometry (ERA), visual evoked response (VER), and electroretinogram (ERG).