Factors affecting pain intensity in a pain model based upon tonic intranasal stimulation in humans

Objective: The present publication describes an inflammatory pain model bas ed on an air-stream introduced in the nasal cavity. The aim of the present study was to investigate the influence of how, humidity and temperature of the airstream on the intensity of the evoked pain sensations. Methods: Six healthy volunteers participated in the study. Pain was produce d by a stream of air introduced to the nasal cavity at different flow rates (5, 6 and 8 l/min), humidity (20 and 80% relative humidity) and temperatur e (16, 24, and 32 degrees C). The evoked pain was quantified by means of vi sual analogue scales. Results: The air-stream induced a dull and burning painful sensation. The i ntensity of pain was found to be related to the air-stream's humidity and t emperature. Specifically, a dry airstream (20% relative humidity) evoked si gnificantly stronger pain than a humidified air-stream (80% relative humidi ty). Pain was significantly greater at a temperature of 32 degrees C than a t 24 degrees and 16 degrees C, while the temperatures of 16 and 24 degrees C did not differ with respect to pain intensity. In contrast, a tendency to wards stronger pain produced by a flow of 81 compared to that with 51 could not be statistically justified within the present study. Conclusions: The non-invasive pain stimulus was found to be easily applicab le and the evoked pain sensation could be modified by variation of humidity and temperature of the airstream.