Fig. 4. Middle cerebral artery flow velocity, expressed as percentage change from the baseline value, in healthy volunteers (n = 8) during hypocania and inhalation of 30% nitrous oxide while maintaining hypocapnia. The changes have been normalized for 1 kPa decrease in end-tidal carbon dioxide. MCA FV = middle cerebral artery blood flow velocity; N2O = Nitrous oxide; EtCO2= end tidal carbon dioxide; kPa = kilopascal.