title: Sex differences in the hemoglobin oxygenation state of the resting healthy human masseter muscle.
abstract: OBJECTIVE
  To determine whether sex differences exist in tissue oxygen saturation (StO2) and the hemoglobin (Hb) oxygenation state of the resting human masseter muscle.
  
  
  METHODS
  Near-infrared spectroscopy (NIRS) was used to measure StO2 and Hb oxygenation state in 20 healthy adult volunteers (10 women and 10 men). To determine the measurement range and reliability of the NIRS recording probe, the probe was set up on 12 layers of white acrylic resin plate, each 3 mm thick. Total hemoglobin levels were measured while a red vinyl resin plate, 1 mm thick, was inserted in turn between each of the 12 layers. Distances from the skin surface to the lateral surface (S-L) and to the medial surface (S-M) of the right masseter at the middle portion of the masseter were measured on T1-weighted magnetic resonance images (repetition time 500 ms, echo time 23 ms). Thickness of the masseter was calculated by subtraction [(S-M)--(S-L)]. For the study of Hb oxygenation state, the probe was positioned at the same position on the skin surface at the mandibular postural (rest) position.
  
  
  RESULTS
  The measurement range of the NIRS probe was from 9 to 21 mm under the skin, and the reliability of the probe was judged by intra- and inter-class correlation coefficients. There was no sex difference in S-L and the thickness of the masseter; the means of S-L and masseter thickness were 9.3 mm and 15.5 mm in men and 9.8 mm and 14.3 mm in women, respectively. Except for StO2 values, there were significant sex differences in the Hb oxygenation parameters, with the mean values in the men being approximately twice those in the women.
  
  
  CONCLUSIONS
  These results provide evidence that a sex difference in the Hb oxygenation state may exist in the masseter muscle of normal healthy subjects.
authors.affiliation: Department of Dentistry, Jikei University School of Medicine, 3-25-8 Nishi-shimbashi, Minato-ku, Tokyo, Japan 105-8461. sugisaki@jikei.ac.jp
authors.forename: M
authors.initials: M
authors.lastname: Sugisaki
authors.forename: A
authors.initials: A
authors.lastname: Misawa
authors.forename: A
authors.initials: A
authors.lastname: Ikai
authors.forename: K
authors.initials: K
authors.lastname: Young-Sung
authors.forename: H
authors.initials: H
authors.lastname: Tanabe
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D005260:Female; D006454:Hemoglobins / Q000378:metabolism*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008406:Masseter Muscle / Q000098:blood supply / Q000378:metabolism*; D015588:Observer Variation; D010100:Oxygen / Q000097:blood*; D010101:Oxygen Consumption / Q000502:physiology*; D011336:Probability; D012039:Regional Blood Flow / Q000502:physiology; D015203:Reproducibility of Results; D012727:Sex Characteristics; D019265:Spectroscopy, Near-Infrared; D013223:Statistics as Topic; D013382:Subtraction Technique; D014716:Vertical Dimension
chemical_list: D006454:Hemoglobins; D010100:Oxygen