title: Cerebral near infrared spectroscopy: emitter-detector separation must be increased.
abstract: We have compared the effect of increasing optode separation (range 0.7-5.5 cm) on the sensitivity of near infrared spectroscopy (NIRS) to discrete reductions in scalp and cerebral oxygenation in 10 healthy men (mean age 32, range 26-39 yr) using multichannel NIRS. During cerebral oligaemia (a mean reduction in middle cerebral artery flow velocity of 47%) induced by a mean reduction in end-tidal PCO2 of 2.4 kPa, the decrease in oxyhaemoglobin detected by NIRS became significantly greater with increasing optode separation (P < 0.0001). In response to scalp hyperaemia induced by inflation and release of a pneumatic scalp tourniquet, increases in oxyhaemoglobin became significantly smaller with increasing optode separation (P < 0.0002). These results are consistent with theoretical models of the behaviour of NIR light in the adult head and support the concept of using multi-detector NIRS to separate intra- and extracranial NIR signal changes. However, the emitter-detector separation used by currently available cerebral oximeters is not large enough to provide optimal spatial resolution.
authors.affiliation: Department of Neurosurgery, Frenchay Hospital, Bristol, UK.
authors.forename: T J
authors.initials: TJ
authors.lastname: Germon
authors.forename: P D
authors.initials: PD
authors.lastname: Evans
authors.forename: N J
authors.initials: NJ
authors.lastname: Barnett
authors.forename: P
authors.initials: P
authors.lastname: Wall
authors.forename: A R
authors.initials: AR
authors.lastname: Manara
authors.forename: R J
authors.initials: RJ
authors.lastname: Nelson
mesh_terms: D000328:Adult; D001921:Brain / Q000378:metabolism*; D002536:Cerebral Arteries; D002560:Cerebrovascular Circulation; D003576:Electron Transport Complex IV / Q000032:analysis; D006454:Hemoglobins / Q000032:analysis; D006801:Humans; D006940:Hyperemia / Q000378:metabolism*; D008297:Male; D010101:Oxygen Consumption; D010108:Oxyhemoglobins / Q000032:analysis; D012535:Scalp / Q000098:blood supply; D012680:Sensitivity and Specificity; D019265:Spectroscopy, Near-Infrared / Q000295:instrumentation / Q000379:methods*
chemical_list: D006454:Hemoglobins; D010108:Oxyhemoglobins; C100003:deoxyhemoglobin; D003576:Electron Transport Complex IV