Psychophysical examination of pain induced by defined CO2 pulses applied to the nasal mucosa.

In 12 volunteer subjects, noxious chemical stimulation was performed by applying precisely controlled CO2 pulses to the nasal mucosa. Each subject participated in 2 identical psychophysical sessions including: (1) determination of the pain threshold, (2) determination of stimulus response functions to different durations of CO2 pulses with fixed concentration and (3) determination of stimulus response functions to different concentrations of CO2. In this test we also examined the relative sensitivity of the visual analogue scale (VAS) and the magnitude estimation (ME) procedure. The reliability of the psychophysical data was tested by comparing the results obtained in both sessions. The intra-individual variability of the pain threshold was rather low. All the CO2 pulse widths used induced phasic pain sensations which when averaged encoded stimulus durations of up to 1 sec. Longer application periods did not further increase the pain sensations. The stimulus response functions to different concentrations of CO2 could be described well with Stevens' power functions. In our hands the VAS and ME procedures proved to be equally sensitive. The obtained psychophysical data appeared to be rather reliable since no significant differences in the ratings obtained in both sessions could be observed.