THE EFFECTS OF INHALED NITROUS-OXIDE ON SOME MEASURES OF ATTENTION

This study compared the sensitivity of various measures of attention t o the effects of CNS depression, using a randomised single-blind two-p eriod cross-over study. Nineteen healthy volunteers, 10 males and nine females, aged 20-49 took part in a single session in which they inhal ed 15% nitrous oxide in oxygen or 100% oxygen (placebo) through a face -mask for 45 min, followed by a 10-min interval after which they recei ved the other treatment in counterbalanced order. They performed a bat tery of five attention tasks and completed visual analogue scales star ting 10 min after the beginning of each inhalation period. The most se nsitive measures of the effects of this dose of nitrous oxide were let ter cancellation, which had three target letters to cancel, and an aud itory attention task with different stimuli to the two ears. Measures of concentrated attention without distracters (continuous attention ta sk and continuous performance task) were less sensitive, though clear effects were seen at these doses. Tests of differing complexities may involve distinct functions which could be differentially affected by d ifferent classes of drug. Thus both simple and more complex tasks shou ld be represented in studies assessing attentional function in detail.