An objective olfactory sensory test, using CNV (contingent negative variation) as an index has been developed, and its clinical usefulness was tested on patients.
1) The principle of this method is the measurement of the voltage change recorded from the scalp electrodes. The olfactory stimulation was given as the first stimulus (S
1), and acoustic or photic stimulation as the second stimulus (S
2). When the subject notices both S
1 and S
2 stimuli, a monophasic negative change is produced at the interval between S
1 and S
2. 0This negative wave of about 10μV, known as the CNV, can be a good indicator for objective olfactometry.
2) A triggering device using photo-sensors was developed and applied in this test. The socalled T&T olfactometer could be used by this device.
3) The fundamental factors affecting this response was studied, as such on respiration, number of samples, S
1-S
2 intervals, nature of S
2, recording system and reinforcement.
4) In normal subject, the positive response was obtained in approximately 67% in the "no pre-warning" method, and approximately 77% in the "pre-warning" method, for odourous substances of A5, B4 and D5. In the cases applied for three odourous substances, the positive response at least to one of them was observed in 85% for the former, and in 100% for the latter. The response threshold agreed with the subjective threshold in 75% of cases and the remainder of 25% showed better threshold by 1-2 levels.
5) Test for patients showed that there was a good agreement between the subjective and objective threshold in the cases with acute sinusitis at stages of pre- and post-treatment. However, in cases with psychogenic olfactory disorders, and with malingering after head trauma or by occupational disorders, the difference was observed between subjective and objective threshold, that is, complete loss of olfactory sensitivity in subjective test despite positive CNV response.
6) Olfactory sensory disorders due to psychogenic or malingering can be verified by this method, and it is possible to obtain the objective recordings of olfactory sense.
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