title: Influence of respiration and changes in expiratory pressure on cerebral haemoglobin concentration measured by near infrared spectroscopy.
abstract: Near infrared spectroscopy (NIRS) was used to measure the changes in concentration of cerebral oxy- and deoxygenated haemoglobin ([HbO2] and [Hb]) in six healthy adult volunteers spontaneously breathing against increased expiratory pressures (IEPs) between 0 and 20 cm H2O. During expiration, an increase in [HbO2] was recorded, accompanied by a smaller decrease in [Hb], producing a small increase in total cerebral haemoglobin concentration ([Hbsum]). The mean plus/minus SD change in [Hbsum] at the maximum 1EP of 20 cm H2O was 1.2 +/- 0.7 micromol L-1 (equivalent to 1.4%). Changes in [Hbsum] correlated with IEP level (r = 0.95) and changes in MABP (r = 0.96). The results suggest that homeostatic mechanism do not maintain cerebral blood volume or flow constant over the period of a single breath in normal adults.
authors.affiliation: Department of Medical Physics, University College London, England.
authors.forename: C E
authors.initials: CE
authors.lastname: Elwell
authors.forename: H
authors.initials: H
authors.lastname: Owen-Reece
authors.forename: J S
authors.initials: JS
authors.lastname: Wyatt
authors.forename: M
authors.initials: M
authors.lastname: Cope
authors.forename: E O
authors.initials: EO
authors.lastname: Reynolds
authors.forename: D T
authors.initials: DT
authors.lastname: Delpy
mesh_terms: D000328:Adult; D001794:Blood Pressure; D001921:Brain / Q000098:blood supply / Q000378:metabolism*; D006339:Heart Rate; D006454:Hemoglobins / Q000378:metabolism*; D006801:Humans; D011312:Pressure; D012119:Respiration / Q000502:physiology*; D013055:Spectrophotometry, Infrared
chemical_list: D006454:Hemoglobins