title: Effect of nitrous oxide on cerebral blood flow in normal humans.
abstract: We have studied the effect of nitrous oxide on cerebral haemodynamics in 24 healthy male volunteers. Hemispherical cerebral blood flow (CBF) was measured using the xenon-133 inhalation technique, blood flow velocities in the right middle cerebral artery were calculated using transcranial Doppler ultrasound and the pulsatility index (PI)--the inverse of which is theoretically proportional to flow in the vessel under investigation--was derived from analysis of the spectrally analysed velocity pulse wave form obtained from the middle cerebral artery. Each variable was measured with the subject inhaling 100% oxygen (1st baseline), 30% nitrous oxide in oxygen, 100% oxygen (2nd baseline) and 60% nitrous oxide in oxygen. CBF was significantly greater with 30% (0.01 > P > 0.001) and 60% nitrous oxide (P < 0.001) compared with baseline, although the difference between 30% and 60% nitrous oxide was not significant. Changes in 1/PI correlated closely with those in hemispherical CBF. Blood flow velocities increased significantly with 30% (P < 0.001) and 60% nitrous oxide (0.005 > P > 0.001), the difference between 30% and 60% nitrous oxide also being significant (0.005 > P > 0.001). We observed a plateau in the change in CBF caused by nitrous oxide and suggest that this may be explained by activation of intact autoregulative mechanisms in healthy human brain.
authors.affiliation: Department of Anaesthesia, Brook General Hospital, London.
authors.forename: L M
authors.initials: LM
authors.lastname: Field
authors.forename: D E
authors.initials: DE
authors.lastname: Dorrance
authors.forename: E K
authors.initials: EK
authors.lastname: Krzeminska
authors.forename: L Z
authors.initials: LZ
authors.lastname: Barsoum
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity / Q000187:drug effects; D001794:Blood Pressure / Q000187:drug effects; D002536:Cerebral Arteries / Q000000981:diagnostic imaging; D002560:Cerebrovascular Circulation / Q000187:drug effects*; D004325:Dreams / Q000502:physiology; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D008297:Male; D009609:Nitrous Oxide / Q000494:pharmacology*; D010100:Oxygen / Q000494:pharmacology; D011673:Pulsatile Flow; D014463:Ultrasonography
chemical_list: D009609:Nitrous Oxide; D010100:Oxygen