title: Effects of hemoglobin concentration, skull thickness, and the area of the cerebrospinal fluid layer on near-infrared spectroscopy measurements.
abstract: BACKGROUND
  Previous studies documented that near-infrared spectroscopy values were affected by factors related to optical path length, such as hemoglobin concentration, the differential path length factor, skull thickness (t-skull), and the area of the cerebrospinal fluid layer (a-CSFL). Lately, the NIRO-100 (Hamamatsu Photonics, Hamamatsu, Japan) has provided a tissue oxygen index (TOI) that theoretically is not supposed to be affected by optical path length. Therefore, the authors hypothesized that TOI is not influenced by the above-described individual factors.
  
  
  METHODS
  Cardiac surgical or neurosurgical 103 patients (65 men and 39 women; aged 63 +/- 14 yr) were studied. TOI and regional cerebral oxygen saturation (rSO2) (INVOS 4100; Somanetics, Troy, MI) were measured sequentially on patients in a resting state. The t-skull and a-CSFL were calculated using computed tomographic image slices of the head corresponding with the position of near-infrared spectroscopy sensors. The effects of these two factors, hemoglobin concentration and mean arterial pressure, on TOI and rSO2 values were evaluated by linear regression analysis.
  
  
  RESULTS
  Simple linear regression analysis showed that mean arterial pressure (r = 0.27, P = 0.008), t-skull (r = 0.22, P = 0.034), a-CSFL (0.26, P = 0.012), and hemoglobin concentration (r = 0.42, P < 0.0001) were significant determinants of rSO2. Multiple linear regression analysis showed that hemoglobin concentration (r = 0.34, P < 0.001), a-CSFL (r = -0.252, P = 0.012), and t-skull (r = 0.22, P = 0.037) were significant determinants of rSO2. On the other hand, simple and multiple linear regression analysis showed that there was no significant determinant of TOI.
  
  
  CONCLUSIONS
  rSO2 values were affected by hemoglobin concentration, a-CSFL, and t-skull, but TOI values were not affected by individual factors.
authors.affiliation: Department of Anesthesiology, National Cardiovascular Center, Nara Medical University, Kashihara, Nara, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Yoshitani
authors.forename: Masahiko
authors.initials: M
authors.lastname: Kawaguchi
authors.forename: Norikazu
authors.initials: N
authors.lastname: Miura
authors.forename: Takashi
authors.initials: T
authors.lastname: Okuno
authors.forename: Tomoko
authors.initials: T
authors.lastname: Kanoda
authors.forename: Yoshihiko
authors.initials: Y
authors.lastname: Ohnishi
authors.forename: Masakazu
authors.initials: M
authors.lastname: Kuro
mesh_terms: D001794:Blood Pressure / Q000502:physiology*; D001837:Body Weights and Measures / Q000379:methods; D002555:Cerebrospinal Fluid / Q000000981:diagnostic imaging / Q000502:physiology*; D002560:Cerebrovascular Circulation; D005260:Female; D006454:Hemoglobins / Q000032:analysis*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010092:Oximetry / Q000379:methods; D012886:Skull / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D019265:Spectroscopy, Near-Infrared / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000379:methods
chemical_list: D006454:Hemoglobins