Visual analogue scales: how can we interpret them in experimental studies of irritation in the eyes, nose, throat and airways?

The aim of this study was to investigate if visual analogue scales (VAS) of objective symptoms could be validated against objective measurements in exposure studies of chemical vapours in humans. This validation comprises the results of symptom ratings of irritation and objective measurements of effects of the eye, nose and throat from studies of nine different chemicals. The objective measurements included blinking frequency as a measure of eye irritation, acoustic rhinometry of nose irritation and the lung function parameter FEV₁ of irritation in the throat and airways. The statistical analyses were performed with logistic quantile regression. The results show no overall clear correlation between symptom ratings of irritation and objective measurements, although some statistically significant association was found. The last rating of eye irritation during the exposure was significantly correlated at the 75th percentile to the change in blinking frequency during exposure compared with before (P = 0.013). There was also a significant association between ratings of discomfort in the nose and decrease of the minimal nasal cross-sectional area at the 75th percentile (P = 0.016). Further, a nonsignificant association between ratings of discomfort in the nose and decrease in nasal volume was found. No correlation between FEV₁ and ratings of discomfort in the throat or breathing difficulty was detected. There is a relationship between subjective symptoms and objective measures regarding eye and nose irritation at low chemical exposure levels. Thus, the results of this investigation support the use of VAS in chamber exposure studies and could consequently be expanded into field studies.